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    15 June 2021, Volume 32 Issue 6
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    Opinion of the EditorinChief
    A coordinated three-dimensional network for observing large-scale terrestrial ecosystem status changes and the consequences on resources and environment
    YU Gui-rui, ZHANG Lei-ming, ZHANG Yang-jian, YANG Meng
    2021, 32(6):  1903-1918.  doi:10.13287/j.1001-9332.202106.040
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    Co-driven by environmental change and human activity, global ecosystem has been experiencing rapid changes, with cascading effects on resources and environment. The changes of ecosystem status and its spatiotemporal evolution drivers, and the related resource and environmental effects have been recognized as the long standing topics of large-scale terrestrial ecosystem science. The coordinated observation networks distributed across different continents and the globe provide the valuable tools for observing and evaluating ecosystem state change, for revealing and elaborating mechanisms underlying ecosystem response, for cognizing and understanding ecosystem evolution, and for predicting and early-warning of ecosystem change. Committing to serving the continental-scale ecosystem science and supporting regional ecological environmental governance, this review first comprehensively analyzed the current status of ecological environment observation research networks, then proposed their development directions. This review advocated to develop a collaborative observation system with characteristics of multi-element, multi-interface, multi-medium, multi-process, multi-scale and multi-method, and to establish the new generation of continental ecosystem observation-experiment research network composed of high technology integration, regional distribution network, network management intellectualization, long-term observation & experiment, multi-functional model simulations, and remote data integration and resource sharing. We elaborated on the function orientation, design philosophy, design scheme, construction objectives and technical system of the research network. We hoped provide references for the development of terrestrial ecosystem observation network in China.
    Special Features of Stable Isotope Ecology
    Vertical distribution of natural abundance of stable carbon and nitrogen isotopes along the soil profile and the underlying mechanisms
    CHEN Miao, LIU Shun, XU Ge-xi, SHI Zuo-min
    2021, 32(6):  1919-1927.  doi:10.13287/j.1001-9332.202106.028
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    Understanding the changes of natural abundance of stable carbon and nitrogen isotopes (δ13C and δ15N) along soil profile is of great importance in revealing the mechanisms of soil carbon and nitrogen cycling in terrestrial ecosystems. Based on a comprehensive review on the distribution of δ13C and δ15N along soil profile, the mechanisms underlying their vertical distribution were mainly introduced here. There were three mechanisms driving the δ13C vertical distribution in soil profile: 1) historical changes of vegetation δ13C value, 2) changes of C3-C4 species dominance in plant communities, 3) accumulation of 13C-enriched microbial-derived carbon during decomposition. The effects of 13C Suess effect on the vertical distribution of δ13C in soil profile were also discussed. There were four mechanisms underlying the vertical distribution of δ15N in soil profile: 1) 15N-depletion gas loss during denitrification, 2) accumulation of 15N-enriched microbial-derived nitrogen during decomposition, 3) accumulation of 15N-encriched mycorrhizal fungi residues in deep soil as a result of transferring 15N-depleted nitrogen compounds to plants by mycorrhizae, 4) intera-ction between soil organic matter and mineral substance. We proposed important concerning points for the future study on vertical distribution of natural abundance of stable carbon and nitrogen isotopes in soil profile.
    Distribution of hydrogen and oxygen stable isotope of water in soil-plant-atmosphere continuum (SPAC)system of a typical forest area
    LI Yu-qian, MENG Yu-chuan, SONG Hong-wei, DU Cheng-hong, XIANG Qi-yun
    2021, 32(6):  1928-1934.  doi:10.13287/j.1001-9332.202106.020
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    Water cycle in the soil-plant-atmosphere continuum (SPAC) is an important research topic in hydrology and ecology. The differences in the composition of hydrogen and oxygen stable isotopes in different water bodies can indicate water cycle process. Based on the measurements of isotopic compositions in precipitation, soil water, and plant water, we analyzed water isotope evolution in a SPAC system located in a subtropical evergreen broad-leaved forest in Chengdu Plain. The different interface processes of regional water cycle was revealed. The results showed that the local meteoric water line (LMWL) equation was δD=7.13 δ18O+2.35 (R2=0.99), and the soil evaporation line (SEL) equation was δD=6.98δ18O-0.32 (R2=0.92). In the water transportation process of precipitation-soil water-plant water, hydrogen and oxygen isotopes were gradually enriched. The δ18O in water of the surface soil layer (0-35 cm) was sensitive to precipitation input, as it was directly affected by precipitation. In contrast, the δ18O in water of the middle and deep layers (35-100 cm) was relatively stable. The isotopes of plant xylem water were slightly more enriched than those of soil water, indicating the possibility of slight evaporation or transpiration through phloem or bark in plant water transportation. The estimation of plant water intake from different soil layers was performed by direct correlation method. Cinnamomum camphora mainly used water from the middle layer, Broussonetia papyrifera mainly used that from the surface layer, and Parathelypteris glanduligera tended to use surface soil water and precipitation intercepted by plants because of the shallow root system. Compared with P. glanduligera, C. camphora and B. papyrifera experienced stronger water evaporation and the isotopes were influenced by more intense dynamic fractionation.
    Effects of precipitation on water use characteristics of Caragana intermedia plantations with different stand ages in alpine sandy land
    GAO Ya, HE Ling-xian-zi, JIA Zhi-qing, LI Qing-xue, DAI Jie
    2021, 32(6):  1935-1942.  doi:10.13287/j.1001-9332.202106.008
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    To clarify the changes of water sources for Caragana intermedia plantations at different ages (4, 9, 17 and 31 years) in response to rainfall in the Gonghe Basin of Qinghai Province, China, we used the stable isotope technique to identify δ2H and δ18O compositions of soil water, xylem water, groundwater, and rain water before and after rainfalls. The proportions of different water sources were calculated by the Iso-Source model. The results showed that the δ2H and δ18O compositions of the shallow soil layer (0-40 cm) of all plantations responded significantly to the precipitation. The isotopic values of plant xylem water, soil water, and groundwater of each plantation were spotted on the lower right of the local meteoric water line (LMWL) either before or after rainfall, with lower intercepts and slopes than LMWL and the global meteoric water line (GMWL). The isotopic compositions of xylem water and soil water of C. intermedia plantations were closer to LMWL after rainfall. The 4- and 9-year-old C. intermedia plantations mainly used shallow soil water, the 17-year-old plantation mainly used middle layer soil water (40-90 cm), and the 31-year-old plantation primarily use deep soil water before rainfall. After rainfall, the shallow soil layer became sources of water absorption for all plantations. The utilization proportions of groundwater for all plantations were only 1.8%-11.9%. In general, water sources of different aged C. intermedia plantations showed similar responses to rainfall, by primarily absorbing the shallow soil water supplied by rainfall and reducing the use of groundwater.
    Long-term water use characteristics and patterns of typical tree species in seasonal drought regions
    WANG Xin, JIA Guo-dong, DENG Wen-ping, LIU Zi-qiang, LIU Zi-he, QIU Gui-fu, LI Wen-li
    2021, 32(6):  1943-1950.  doi:10.13287/j.1001-9332.202106.022
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    In the areas with seasonal drought, water is the key factor affecting plant growth and development. Based on long-term continuous observation data, it is of great significance to explore plant water use patterns for vegetation construction in areas with seasonal drought. Taking Platycladus orientalis in Beijing mountainous area as the research object, stable hydrogen and oxygen isotope technique was applied to measure the isotopic composition of water from the soil, plant branches, and precipitation from 2012 to 2017. The relative contribution of soil water from different soil layers to P. orientalis was quantified by the MixSIAR model. The results showed that soil water in the deep layer (40-100 cm) was more stable than that in the shallow layer (0-40 cm). The variation of soil water content and water isotope values in the shallow layer were more obvious due to the effects of evaporation and precipitation. P. orientalis mainly absorbed stable deep soil water, with a relative contribution rate of 55.7%. In the dry season, with the decreases of soil water content, the absorption depth of plants to soil water gradually shifted to the shallow layer. Under conditions of moist, natural condition, mild drought and moderate drought, the relative contribution rates of deep soil water were 59.8%, 57.9%, 54.6%, 52.7%, respectively. To maintain higher transpiration in the wet season, P. orientalis relied more on deep soil water under mild and moderate drought conditions than in the dry season. Under the conditions of moist, natural condition, mild drought and moderate drought, the relative contribution rates of deep soil water were 58.9%, 57.6%, 56.4%, and 57.1%, respectively. The adaptive characteristic of P. orientalis, which adjusts the depth of root water absorption according to soil moisture condition, is of great significance for tree species selection in ecological afforestation and long-term management planning in areas with seasonal drought.
    Spatial and temporal variations of hydrogen and oxygen isotopes and sources of water vapour indicated from satellite precipitation products along the transection of 38°north latitude in North China
    TAN Kang-da, WANG Shi-qin, ZHENG Wen-bo
    2021, 32(6):  1951-1962.  doi:10.13287/j.1001-9332.202106.026
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    The variations of hydrogen and oxygen isotopes in rainfall are critical for understanding the sources of rainfall and the influence of local evaporation. Satellite precipitation products with high time resolution (for instance 1 h) could be helpful for testifying the accuracy of water sources, as it can clearly illustrate the route of cloud movement. In this study, we analyzed the composition of hydrogen and oxygen isotopes in different rainfall events in three stations from 2015 to 2018 along the transection of 38° N latitude from Taihang Mountains to the coastal region in North China, Taihang Mountain Station (mountainous area), Luancheng Station (pre-mountain plain) and Nanpi Station (coastal low plain). By selecting typical rainfall events, water vapor sources and its influence rainfall on hydrogen and oxygen isotopes were analyzed with hourly available CMORPH satellite precipitation products. Results showed that the hydrogen and oxygen isotopes of precipitation were cha-racterized by enrichment in the rainy season and depletion in the dry season. The hydrogen and oxygen isotopes in the rainy season showed a tendency of depletion with the increases of precipitation. The slope and intercept of the fitted relationship of hydrogen and oxygen isotopes in the piedmont region of the mountains were the lowest, indicating that precipitation in the piedmont plain was significantly affected by secondary evaporation fractionation. The effect of evaporation resulted in the largest variations of isotope ratio in the dry year. In the mountainous station, due to the heavy rainfall, large isotopic variation was found in rich precipitation year. Based on the route analysis of sate-llite precipitation products, dominant water vapor in the region was inland and northwest-oriented water vapor, while water vapor in the rainy season was from southwest and from the Pacific Ocean. There was a significant difference in the hydrogen and oxygen isotopes of precipitation in the mountainous and plain stations in 2016, owing to water vapor sources and effects of rainfall for the mountainous and evaporation for plain. The results from HYSPLIT model showed that during the rainstorm on 19th July in 2016, water vapor at the mountainous station was mainly from the southwest, while that in the coastal plain was a mixture of southwest and southeast sources. Overall, our results showed that spatial and temporal variations of hydrogen and oxygen isotopes were controlled by both water sources and evaporation processes along the transection of 38° north latitude in North China.
    Influence of ball milling with PTFE plastic tube on carbon isotope ratio measurement of C4 plants.
    LI Lei, WANG Xu-ming, Rudi Schäufele, CAI Bing-gui, GONG Xiao-ying
    2021, 32(6):  1963-1970.  doi:10.13287/j.1001-9332.202106.019
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    Before the measurement of stable carbon isotope signatures (δ13C), plant samples should be well homogenized. Using a ball-mill fitted with poly tetra fluoroethylene (PTFE) plastic tubes is one of the most efficient and convenient methods. However, sample-tube plastic might contaminate plant samples during milling. In this study, a two-factor experiment was carried out using four growth chambers, with different relative humidity of the air (50% and 80%) and δ13C of the air (13C depleted and enriched). Leaf samples of Cleistogenes squarrosa (C4) were milled and homogenized using a ball-mill fitted with PTFE tubes and measured for δ13C, and the results were compared with that of leaf samples milled using metal tubes. Due to plastic contamination, 13C discrimination (Δ13C) of the two groups of plants, which were grown in CO2 with different δ13C and could be assumed as replicates, were significantly different (with an offset of 4.8‰ on average). The contamination led to errors in δ13C of individual leaves up to 8‰. Given the lower Δ13C value of C4 plants (normally about 1‰-8‰) compared with that of C3 plants, such an error caused by plastic contamination far exceeded the acceptable error range. By using a two-member mixing model that was similar to the ‘Keeling plot', such errors could be effectively eliminated, and the δ13C of plant samples and pollutants were accurately estimated. Our results showed that the widely applied method of using PTFE tubes for ball-mill homogenization is not suitable for examining Δ13C of C4 plants, as it might lead to large errors. For studies with high precision requirements, samples should be milled in stainless-steel tubes.
    Quantitative separation of evapotranspiration components of Platycladus orientalis ecosystem based on multiple isotope models
    WU Yu-xin, ZHANG Yong-e, JIA Guo-dong, WANG Yu-song, YU Xin-xiao
    2021, 32(6):  1971-1979.  doi:10.13287/j.1001-9332.202106.023
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    To fully understand the changes in the evapotranspiration components in forest ecosystem and their contribution to evapotranspiration at daily scale, we used the hypothesis theory of isotopic steady state and non-steady state combined with the water isotope analyzer system to quantitatively split and compare the evapotranspiration components of Platycladus orientalis ecosystem during the growing season. Results showed that the 18O of water from different sources during the four mea-surement days (August 5, 8, 10, 11, 2016) all showed surface soil water and oxygen isotope composition (δS) > branch water and oxygen isotope composition (δX) > atmospheric water vapor oxygen isotopes composition (δV), with obvious differences due to the isotope fractionation. Oxygen isotopes composition of soil evaporated water vapor (δE) was between -26.89‰～-59.68‰ at the daily scale, showing a pattern of first rising and then decreasing. The oxygen isotopic composition of evapotranspiration water vapor in forest ecosystem (δET) was between -15.99‰～-10.04‰. The oxygen isotopic composition of transpired water vapor under steady state(δT-ISS) was between -12.10‰～-9.51‰. The oxygen isotopic composition of transpired water vapor under non-steady state (δT-NSS) was between -13.02‰～-7.23‰. δET and δT-NSS had the same changing trend throughout the day at the daily scale, while the trend of δET, δT-ISS and δT-NSS was approximately the same during 11:00-17:00. In general, the contribution rate of plant transpiration to total evapotranspiration showed that FT-ISS was between 79.1%-98.7%, and FT-NSS was between 88.7%-93.7%. Our results suggested that water consumption through soil evaporation was far less than that of vegetation transpiration in the study area, and that vegetation transpiration dominated forest evapotranspiration.
    Water use characteristics of artificial sand-fixing vegetation on the southern edge of Hunshandake Sandy Land, Inner Mongolia, China
    SU Wen-xu, JIA De-bin, GAO Rui-zhong, LU Jun-ping, LU Fang-yuan, ZHAO Hang, WANG Fang
    2021, 32(6):  1980-1988.  doi:10.13287/j.1001-9332.202106.024
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    We examined the characteristics of water use in typical tree species of arbor and shrub in Hunshandake Sandy Land, Populus cathayana and Salix gordejevii, in the different seasons, with the aim to provide theoretical basis for the structural optimization of the artificial shelterbelt. Samples of precipitation, soil water, groundwater and stem water of the two vegetation were collected, and their distribution characteristics of δD-δ18O were analyzed by hydrogen and oxygen stable isotope technology. The contribution rate of these potential water source to the arbor and shrub species were calculated using multi-source linear mixing model. The precipitation equation line in the study area was δD=7.84δ18O+9.12, while soil moisture lines in the dry and wet season were δD=3.56δ18O-41.28 and δD=4.30δ18O-42.02, respectively. The δD-δ18O of soil water and stem water in the two seasons were lower than the precipitation δD-δ18O, indicating that both of them were strongly affected by the evaporation. Soil water contents in the shallow layer were strongly affected by rainfall and evaporation, with substantial fluctuation. With the increases of soil depth, soil water content tended to be stable, and the hydrogen and oxygen isotope in each soil layer showed significant differences. In the dry season, P. cathayana mainly utilized soil water in 0-40 cm and 120-200 cm layers, with contribution rates of 50.2% and 31.5%, respectively. S. gordejevii mainly absorbed soil water in 20-40 cm and 60-100 cm layers, and the contribution rates were 53.2% and 22.9%, respectively. In the wet season, the greatest contribution of soil water to P. cathayana was mainly in the 0-40 cm soil layer, accounting for 72.8%. S. gordejevii was mainly in the 0-20 cm soil water, evenly utilized the deeper soil water and groundwater. Due to the differences in root depth and distribution of the arbor and shrub, their water use strategies differed in different seasons, which was conducive to the stability of the shelterbelt community and tree species coexistence in Hunshandake Sandy Land. We proposed that the mixed planting species with different root depth should be considered in the future planting of artificial shelterbelt, which would help rationally utilize water resources and maintain the stability of sandy land ecosystem.
    Effects of soil moisture on microbial processes of soil nitrogen gases production under anaerobic conditions
    LI Jin, KANG Rong-hua, YU Hao-ming, WANG Ying-ying, YAO Meng, FANG Yun-ting
    2021, 32(6):  1989-1997.  doi:10.13287/j.1001-9332.202106.010
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    Gaseous nitrogen (N) emission [nitric oxide (NO), nitrous oxide (N2O), and nitrogen (N2)] is an important pathway of soil N loss. Nitrification and denitrification are the main processes of gaseous N production in soil. However, the contribution of heterotrophic nitrification, co-denitrification, and anammox to gaseous N production remains uncertain. In a laboratory soil incubation experiment, we used the 15N labelling and pairing technique, combining the nitrification inhibitor dicyandiamide (DCD), to quantify the contribution of different microbial processes to soil NO, N2O and N2 production under anaerobic conditions. The results showed that after 24 h anaerobic incubation, the highest total 15N recovery of three gases occurred at 65% water filled pore space (WFPS), accounting for 20.0% of total added 15N. Denitrification contributed 49.9%-94.1%, 29.0%-84.7%, and 58.2%-85.8% to the production of NO, N2O and N2 respectively, suggesting that denitrification was the predominant process of those three N gases emission. Heterotrophic nitrification was an important pathway of NO and N2O production, particularly at conditions with low soil water content (10% WFPS), with its contribution to those two N gases production being 50.1% and 42.8%, respectively. Co-denitrification contributed 10.6%-30.7% of N2O production. For N2 production, the total contribution of co-denitrification and anammox was 14.2%-41.8%. The role of co-denitrification can not be ignored for N2O and N2 production. Our results demonstrated that the 15N labelling and pairing technique is a promising tool to quantify the contribution of different microbial processes to gaseous N loss.
    Tracing the sources of sedimentary organic matter in Nanyue small watershed based on 13C, 15N and C/N
    CHEN Xuan, LI Yu-e, WAN Yun-fan, GAO Qing-zhu, WANG Bin, QIN Xiao-bo
    2021, 32(6):  1998-2006.  doi:10.13287/j.1001-9332.202106.030
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    Losses of organic matter in agricultural watersheds result in eutrophication and land degra-dation, which not only threaten water quality and food security, but also lead to environmental problems such as the greenhouse gases emission. We used 13C, 15N and C/N as fingerprint markers to trace the sources of sedimentary organic matter at the outlet in the Nanyue small watershed. We analyzed the spatial distribution in watershed sedimentary organic matter and soils of typical land use types, including forest, paddy field, and vegetable fields. The Bayesian stable isotope mixing model was used to quantitatively estimate the contribution of different sources. The results showed that there was significant spatial variation of δ13C. The δ13C of sediment organic matter (-22.6‰±0.53‰) and forest soil (-23.13‰±1.71‰) was significantly higher than that of paddy soil (-25.24‰±1.4‰). The differences of δ15N among the sources were not significant, with sediment having the maximum (4.37±0.83)‰ and forest soil having the minimum (2.38±1.97)‰. Forest soil had the highest C/N of 16.66±7.18, while paddy soil had the lowest C/N of 11.95±0.92. The results of the Bayesian stable isotope mixture model showed that the contribution rates of forest land, paddy fields and vegetable fields to the organic matter deposited at the outlet in the watershed were 19.6%, 15.7%, and 64.7%, respectively. Paddy filed and vegetable field had a combined contribution rate of 80.4%. It was concluded that, soils of agricultural land were the main sources of organic matter deposited in the Nanyue small watershed, and that nutrient loss in the watershed would be effectively controlled by optimizing farmland management.
    Effects of zinc levels on synthesis and translocation of 13C-photoassimilates in leaves to fruit of apple during fruit expanding stage
    YU Bo, QIN Si-jun, LYU De-guo
    2021, 32(6):  2007-2013.  doi:10.13287/j.1001-9332.202106.021
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    To explore the effects of zinc levels on the synthesis and translocation of photosynthetic products from leaves to fruits, and to lay a theoretical foundation for improving fruit quality through zinc supplementation during the critical period of apple fruit development, a field experiment was carried out with a eight-year old ‘Hanfu'/GM256/Malus baccata Borkh apple. We used the 13C tracer method to examine the effects of different zinc levels (ZnSO4·H2O 0, 0.1%, 0.2%, 0.3%, 0.4%, expressed by CK, Zn1, Zn2, Zn3, Zn4, respectively) on translocation of photosynthate to fruit during the stage of fruit expanding. The results showed that, with increasing zinc concentration, Rubisco enzyme activity, net photosynthetic rate, sorbitol and sucrose content, sorbitol 6-phosphate dehydrogenase, and sucrose phosphate synthase enzyme activities of leaves first increased and then decreased, with the highest values being observed in Zn3 treatment. Zn3 treatment significantly increased the 13C assimilation capability of leaves. Compared with other treatments, the 13C of self-retention (labeled leaves and labeled branches) was lowest in Zn3 treatment (61.2%) and the output of 13C photoassimilates was highest in Zn3 treatment (38.8%). 13C absorption of apple fruit showed a trend of Zn3 ＞ Zn2 ＞ Zn4 ＞ Zn1 ＞ CK. In summary, foliar zinc application under appropriate concentration (0.3% ZnSO4·H2O) enhanced photosynthesis, increased the assimilation capability of leaves, and promoted the directional transportation of photosynthate to fruit.
    Trophic niche partitioning of four pelagic shark species in the tropical Atlantic based on multi-tissue stable isotopes ratios
    CHEN Zi-ang, WU Feng, DAI Xiao-jie, LI Yun-kai
    2021, 32(6):  2014-2020.  doi:10.13287/j.1001-9332.202106.027
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    Stable carbon and nitrogen isotope ratios (δ13C and δ15N, respectively) of multiple tissues with different turnover rates can provide trophic information at different timescales, and thus play an important role in tracing the changes of feeding, habitat utilization and trophic niche of consumers. The δ13C and δ15N contents of muscle, liver and blood of blue sharks (Prionace glauca), longfin mako sharks (Isurus paucus), crocodile sharks (Pseudocarcharias kamoharai) and shortfin mako sharks (I. oxyrinchus) from tropical Atlantic were measured, and the trophic niche was evalua-ted. The results showed that I. oxyrinchus, P. kamoharai, and P. glauca had similar δ15N values, higher than that of I. paucus. Feeding segregation was found between P. glauca and other species, showing unique trophic niche. The largest trophic niche width was observed in I. oxyrinchus, indicating the high diversity of prey and (or) feeding habitats. High trophic niche overlap was found in P. kamoharai and I. oxyrinchus, implying their potential competition for resources. There was no correlation between the differences among tissues in the δ13C or δ15N values and the body size of I. oxyrinchus, P. kamoharai and P. glauca, indicating no recent diet shifts for those species. I. paucus showed significant correlation between δ15N differences in liver, blood and muscle with the shark fork length, indicating its short-term diet shift. The similarity of δ13C and δ15N values and the higher metabolic rates of liver and blood were found in all four shark species, implying the similar incorporation rates of both tissues, which were considered as the short-term indicator of diet.
    Stable isotope ratio characteristics and origin tracing of Portunus trituberculatus
    PENG Kai-xiu, CUI Yan-mei, JIANG Fang, LI Fan, XU Bing-qing, ZHANG Hua-wei, TIAN Xiu-hui, XU Ying-jiang
    2021, 32(6):  2021-2027.  doi:10.13287/j.1001-9332.202106.025
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    A method for geographical discrimination of Portunus trituberculatus was explored to provide technical support for the protection of geographical indication products and for tracing the origin of seafood. P. trituberculatus were collected from three major production areas, including the Yellow Sea, the Bohai Sea, and the East China Sea. The variations of carbon and nitrogen stable isotope values of origins and the correlation of stable isotope ratios in different tissues were analyzed. The results showed that there were significant differences in carbon and nitrogen stable isotope ratio among different origins. Significant isotope fractionation effects were observed among different tissues. The discriminant model was developed and the origin discriminant analysis was performed by the stable isotope ratios of different tissues in P. trituberculatus. The correct rate of origin diffe-rentiationf using carbon and nitrogen stable isotopes in muscle and gills (>95%) was significantly higher than that of hepatopancreas and gonad, indicating that stable isotope ratios of muscle and gills could effectively differentiate P. trituberculatus in different sea areas. This study filled the gap of stable isotope tracing technology for P. trituberculatus.
    Food web in jellyfish-shrimp-shellfish polyculture pond
    WANG Bai, TIAN Jia-shen, ZHOU Zun-chun
    2021, 32(6):  2028-2034.  doi:10.13287/j.1001-9332.202106.009
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    To analyze the feeding habits and trophic level of jellyfish (Rhopilema esculentum), Chinese shrimp (Fenneropenaeus chinesis), grass shrimp (Penaeus monodon), and clam (Ruditapes philippinarum), and the food web structure in marine aquaculture pond, we measured the δ13C and δ15N values of the four species and different feed from May to September in 2017. The average proportional contribution of different feed to the four species were analyzed using the IsoSource linear mixture model. The results showed that zooplankton was the main food source to jellyfish, Engraulis japonicus was the main food source to the two shrimp species, and the phytoplankton, benthic diatoms and dejecta of the two shrimp species were the main food source to the clam. The trophic level of the clam ranged from 2.64 to 2.95, with a mean value of 2.84. The trophic level of jellyfish ranged from 2.78 to 3.27, with a mean value of 3.06. the grass shrimp ranged from 3.03 to 3.54, with a mean value of 3.25. The trophic level of Chinese shrimp ranged from 3.76 to 4.40, with a mean value of 3.95. Results of comprehensive analysis showed that the clam was the primary consumer, jellyfish was the secondary consumer, and shrimps were the predators. Jellyfish filtered the dejecta of the two kinds of prawns and improved water quality of the polyculture pond to a certain extent.
    Feeding ecology of Engraulis japonicus based on stomach contents and stable isotope
    WANG Jing, JIANG Ri-jin, HU Cui-lin, LI Zhe, XIAO Yi, XU Yong-jiu, HE Zhou-ting, XU Han-xiang
    2021, 32(6):  2035-2044.  doi:10.13287/j.1001-9332.202106.029
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    Engraulis japonicus, an important fishery resource, is a key species in ecosystem trophodynamics studies. In this study, we examined stomach content of E. japonicusby stable isotope analyses, with samples collected from the East China Sea in 2008-2009 and 2020. The aim of this study was to demonstrate their diet composition, diel and ontogenetic changes in feeding habits and trophic level. Results of the stomach content analysis showed that E. japonicus mainly fed on planktonic crustaceans and small fish. The main prey species were Euphausia pacifica [index of relative importance (IRI)=87.6%; frequency(F)=57.6%], Paracalanus parvus (IRI=3.2%, F=15.3%), and Themisto gracilipes (IRI=2.1%, F=13.1%). Results of the stable isotope analysis showed that Copepoda were the main food source of E. japonicus, followed by Euphausiacea, and the contribution rate of Amphipoda was the least, which was less than 1%. There was significant diel change in diet composition. Feeding intensity was higher in the daytime than at night, with the highest in the dusk and the lowest at midnight. Ontogenetic change in feeding habit occurred when fork length reached 90 mm, over which the fish fed both zooplankton and small fishes. The δ13C of E. japonicus was between -21.66‰ and -18.14‰, with an average of (-19.92±0.86)‰. The δ15N of E. japonicus ranged from 4.07‰ to 10.78‰, with an average of (8.14±2.48)‰. Both δ13C and δ15N values were positively correlated with fork length. Trophic level of the fish was 3.4 with stomach content analysis and 2.7 with stable isotope analysis. The results would provide important reference for understanding nutritional status of pelagic small fish, and offer some basic data to establish ecopath model.
    Original Articles
    Effects of experimental warming on soil nitrogen transformation in alpine scrubland of eastern Qinghai-Tibet Plateau, China
    LIU Mei, MA Zhi-liang
    2021, 32(6):  2045-2052.  doi:10.13287/j.1001-9332.202106.007
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    We investigated the effects of warming on soil nitrogen cycling process in alpine scrub ecosystem, with an in-situ simulated warming experiment at Sibiraea angustata alpine scrubland on the eastern Qinghai-Tibet Plateau, China. We examined the responses of soil nitrogen transformation rate to warming in three critical periods (the early, late, and non-growing seasons). The results showed that warming increased soil temperature by 1.2 ℃, but decreased soil moisture by 2.5%. The soil net nitrogen mineralization rates (i.e., ammonification and nitrification) in the growing season were significantly higher than those in the non-growing season. The rates of soil net nitrogen fixation in the non-growing season were significantly higher than that in the growing season. Soil nitrification was the major process of soil nitrogen transformation in the early growing season, while soil ammonification was the major one in the late growing season and non-growing season. The effects of experimental warming on soil nitrogen transformation differed among those three periods. Experimental warming significantly increased soil net ammonification, nitrification, nitrogen mine-ralization and fixation in the early growing season, and enhanced soil net nitrification and nitrogen mineralization in the non-growing season. However, warming significantly decreased soil net nitrification, nitrogen mineralization and fixation in the late growing season and soil net ammonification in the non-growing season. Moreover, warming did not affect soil net nitrogen fixation rates in the non-growing season and soil net nitrification rates in the late growing season. Future climate warming would significantly change soil nitrogen transformation by accelerating soil nitrogen cycling in the alpine scrub ecosystem on the eastern Qinghai-Tibet Plateau.
    Spatial pattern and interspecific association of tree species in coniferous and deciduous broad-leaved mixed forest under different disturbance intensities
    CUI Yu-hua, HAN You-zhi, ZHANG Meng-tao, YANG Xiu-qing, ZHAO Zhan-he
    2021, 32(6):  2053-2060.  doi:10.13287/j.1001-9332.202106.003
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    We explored the effects of disturbance densities on the spatial pattern and the association of tree species in the coniferous broadleaved mixed forest in Pangquangou Nature Reserve of Guandi Mountain. Using three factors including canopy density, stand density and number of stumps, we classified the disturbance intensities of different forest stands into three levels, non-disturbance, moderate disturbance, and severe disturbance. The spatial distribution pattern and the association of different tree species were analyzed by spatial point pattern K2 function. The results showed that the diameter distribution of trees in undisturbed plots was inverted ‘J' type, while that of moderate disturbance and serious disturbance plots was under bimodal curve distribution. The stand distribution pattern showed a small-scale aggregated distribution under undisturbed and moderately distur-bance, and a random distribution under heavy disturbance. At the small scale, the coniferous and broadleaved species showed no correlation in undisturbed stands, were positively correlated in moderately disturbed stands, and negatively correlated in seriously disturbed stands. At large scale, they were no correlated in both moderately and seriously disturbed stands. The results suggested that abundance of trees with small diameter in the forests was negatively with disturbance intensity, which led to the lower degree of intraspecific aggregation at small scale. Meanwhile, appropriate levels of disturbance would benefit the collaborative use of environmental resources for trees. Our results revealed the impacts of disturbance density on forest community structure and could provide theoretical basis for forest management.
    Effect of canopy condition on Machilus nanmu seedling configuration and biomass allocation
    LIAO Rui-yan, WU Xiao-qi, JIN Cheng, HUANG Li, QIAN Shen-hua, YANG Yong-chuan
    2021, 32(6):  2061-2069.  doi:10.13287/j.1001-9332.202106.004
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    The adaptation strategy of seedlings plays a decisive role in population regeneration. Machilus nanmu is a tree species belonging to Lauraceae, which is national class Ⅱ protected species and one of the dominant species in the evergreen broadleaved forest in Jinyun Mountain, Chongqing. Therefore, it is of great significance to understand the adaptation strategies of M. nanmu seedlings to maintain population regeneration and protect the biodiversity of evergreen broadleaved forest. We studied the temporal dynamics of early adaptation strategy of M. nanmu in Jinyun Mountain in Chongqing and its response to heterogeneous habitats from the perspective of morphology and biomass allocation. The seedlings of M. nanmu were classified into different age stages (stage 1: 1-3 a; stage 2: 4-6 a; stage 3: 7-9 a) under different canopy environments (gap/understory). Stem configurations (except branch angle) and leaf inclination angle of M. nanmu seedlings in the gap were significantly greater than understory at stages 2 and 3. Root configurations (except root diameter) and leaf area were significantly greater than that in the understory at stages 1 and 2. Specific leaf area in the gap was significantly smaller than understory at all three stages. Across all the conditions, biomass distribution was dominated by leaves. From the stage 2, stem biomass distribution of M. nanmu seedlings in the gap was increased, while root biomass distribution was decreased. There was no significant variation in root biomass of M. nanmu seedlings in the understory. The coordination among different organs of M. nanmu seedlings would help their adaptation to different habitats. Root and leaf of M. nanmu seedlings in the gap were significantly correlated, with the correlation changing from positive to negative as the age increased. While in the understory, there was significant positive correlation between root and stem, but no correlation between root and leaf. The slope of SMA equation of branch weight and branch length had significant difference under different canopy environments only at stage 3, while the slope of SMA equation of leaf and root biomass and configuration had no significant difference. Most of the SMA equation intercepts between biomass and configuration differed significantly at stage 2.
    Altitudinal phenotypic plasticity of leaf characteristics of Polygonum viviparum
    WANG Yu-ping, GAO Hui-hui, ZHANG Feng, CHEN Li-xiang, SUN Wen-bin
    2021, 32(6):  2070-2078.  doi:10.13287/j.1001-9332.202106.001
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    We investigated leaf tissue structure, leaf epidermis characteristics and chloroplast ultrastructure of Polygonum viviparum at different altitudes (2300, 3200 and 3900 m) on the Qilian Mountain, using paraffin section, scanning electron microscopy and transmission electron microscopy methods. The results showed that plant leaves were typical bifacial. With increasing altitude, the number of leaf epidermal hair reduced but the diameter of hair increased, with more compact of the cuticular wax layer on leaf lower epidermis. Leaf thickness reached a maximum at 3200 m and was increased by 39.6% and 50.5%, respectively, compared with that from 2300 m and 3900 m. From 2300 m to 3200 m, the cell layers of palisade tissue increased from two to three, while intercellular space decreased. The cell layer of spongy tissue did not change, whereas intercellular space increased with increasing altitude. At 3900 m, the number of cell layer of palisade tissue reduced to two, epidermal cell volume and the intercellular space of palisade tissue increased while the intercellular space of spongy tissue decreased. The thickness of epidermal cell increased. There was no significant difference among three altitudes in the number of cell layers. The accumulation of surface appurtenances and the substomatal appendages, and stomata density of lower epidermis increased with altitude. Meanwhile, the position of stomata changed from arched epidermis to invagination. From 2300 m to 3200 m, the grana lamella increased from 6-9 to 8-12 and then reduced to 2-3 at 3900 m. The number of grana decreased, the lamellae became dense, the arrangement direction of grana was irregular at 3900 m. The chloroplasts swelling and the envelope partially degradation could be observed. The correlations among the anatomical characteristics of leaves indicated an apparent co-evolution between parts of anatomical indices in the leaves. In particular, indices such as spongy tissue thickness exhibited high plasticity across altitudes. Our results suggested that diffe-rences in anatomical structure and ultrastructure characteristics of P. viviparum along altitude were adaptation strategies for the complicated alpine heterogeneous habitats.
    Growth and reproduction dynamics of different-aged artificial Caragana korshinskii in sandy-hilly region of northwest Shanxi Province, China
    WANG Guo-hua, SONG Bing, XI Lu-lu, GOU Qian-qian
    2021, 32(6):  2079-2088.  doi:10.13287/j.1001-9332.202106.005
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    The sandy-hilly region of northwest Shanxi is a typical fragile agro-pastoral ecotone in north China. With the artificial Caragana korshinskii at 0 (the uncultivated land), 6, 12, 18, 40 and 50 years-old in the typical sandy-hilly region of northwest Shanxi as the subjects, we investigated soil moisture, aboveground and belowground biomass, individual morphological characteristics, growth, reproduction, and photosynthetic physiological characteristics of different-aged C. korshinskii, with the aim to evaluate the long-term growth and reproductive dynamic characteristics of artificial C. korshinskii. The results showed that soil moisture was significantly affected by stand ages. Soil moisture was low under the 6-year-old C. korshinskii plantation. During 6-18 years-old, soil moisture increased due to the increased crown width and reduced the near-surface wind speed, solar radiation, and soil water evaporation. During 18-50 years-old, soil moisture decreased sharply due to higher biomass and plant transpiration of C. korshinskii, and soil moisture was reduced to the lowest level of 11.1%. C. korshinskii mainly developed underground root system during 6-18 years-old, and changed to the aboveground biomass accumulation in 18-40 years-old. At the 40-year-old stand, biomass reached to the highest level with the greatest crown width and plant height. During 40-50 years-old, crown width and plant height decreased significantly, while the growth began to degrade. Photosynthetic capacity (chlorophyll a, b, carotenoid and total chlorophyll content) gra-dually decreased with the increases of planting ages, especially after 18 years-old. The quantity and quality of C. korshinskii seeds increased from 6 to 40 years-old, reached the maximum at 40 years-old stand, and began to decrease after 50 years-old. In the later growth period (30-40 years-old), more seeds with small individual weight were produced compared with early period (6-12 years-old). The germination test showed that small seeds had higher germination rate than the large ones under the same stand age, suggesting a shift of reproduction strategy. After 50 years-old, both of the growth and reproduction of C. korshinskii degenerated, and the plantation began to degrade.
    Sensitivity of spring phenology to elevation in Qinling Mountains, China
    LI Jian-hao, TAO Jian-bin, CHENG Bo, WU Qi-fan, PENG Hong-jie
    2021, 32(6):  2089-2097.  doi:10.13287/j.1001-9332.202106.016
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    Vegetation phenology, a regular and periodic phenomenon in nature, is an important indicator for natural environment, especially climate change. The study of spatiotemporal variations of vegetation phenology is of great significance for monitoring the changes of terrestrial vegetation. In this study, the Savitzky-Golay (S-G) filtering method was used to reconstruct time-series MODIS enhanced vegetation index (EVI) data in the Qinling Mountains from 2001 to 2018. The dynamic threshold method was used to extract the spring phenological parameter (start of growth season, SOS). The correlation between multi-year mean SOS and interannual variation with altitude and slope was analyzed. The results showed that SOS was delayed by 1.82 d with every 100 m increase in altitude in the Qinling Mountains. The interannual change trends of SOS mainly concentrated in 0-5 d·(10 a)-1. The pixels with delaying trend were mainly distributed in low-altitude regions, with the delaying degree being gradually decreased with the elevation. The interannual change trend of SOS in high-altitude regions was more complex than that in lower-altitude regions. The multi-year average SOS in the northern slope was approximately 2.9 d earlier than that of the southern slope, whereas the southern slope had a more significant advancing trend. The interannual change trends of SOS in both north and south slopes showed a delaying trend in low-altitude, with little difference between north and south slopes. The advancing trend in middle and high altitude was significantly different.
    Dynamics of desertification in the lower reaches of Shiyang River Basin, Northwest China during 1995-2018
    WEI Wei, YU Xiao, ZHANG Meng-zhen, ZHANG Juan, YUAN Tao, LIU Chun-fang
    2021, 32(6):  2098-2106.  doi:10.13287/j.1001-9332.202106.012
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    We collected remote sensing images of lower reaches of the Shiyang River Basin in 1995, 2000, 2005, 2010, 2015, and 2018. We analyzed the dynamics of desertification in Minqin County by constructing desertification difference index, using RS and GIS theories and methods. We established the Albedo-NDVI feature space based on the normalized vegetation index (NDVI) and surface albedo (Albedo). The results showed that the desertification area in the lower reaches of Shi-yang River Basin accounted for more than 90% of the total area of the Minqin. Oasis scattered in large areas of desertified land. Moderate desertification accounted for more than 70% of the total area of the county. The area of desertification in Minqin showed an decreasing trend from 1995 to 2018, with an average annual reduction area of 22.06 km2 and an average annual reduction rate of 0.1%. During the study period, various types of desertification area contracted and expanded simultaneously, and the relative changes of severe, moderate, mild, and slight desertification areas were -1.5%, 0.2%, -0.9%, and 3.8% respectively. Those results indicated that the severity of desertification was reduced. The desertification area was generally at a stable state. There was no large-scale desertification process and no obvious trends of desertification. Desertification control had achieved phased results. In the study area, the area where the desertification decreased in a fluctuation way accounted for 15.2%, while the area with increased desertification only accounted for 3.9%. The areas with irregular fluctuations of desertification were mainly distributed in the transitional area of desert oasis and the edge area of oasis, with an area of 17.7% of the total land area. The desertification change was more active in the ecotone of oasis and desert area, which was the key control and repair region in the future.
    Soil-epikarst structures and their hydrological characteristics on dolomite slopes in karst region of southwest China
    ZHANG Jun, FU Zhi-yong, CHEN Hong-song, LIAN Jin-jiao, QIN Chang
    2021, 32(6):  2107-2118.  doi:10.13287/j.1001-9332.202106.013
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    Epikarst is the core area of karst critical zone, with important hydrologic regulation and storage function. However, the effects of karst development degree on hydrologic characteristics of epikasrt is still unclear. We used geophysical exploration and hydrogeological techniques, combined with the dynamic monitoring of moisture and water levels, to quantify the karst development degrees and their hydrologic characteristics on slope lands. We analyzed the responses of soil-epikarst systems to rainfall. Results showed that geophysical exploration technology could be well applied to the detection of surface-subsurface structures in the karst areas. The average thickness of soil and surface karst zone on the slope was less than 0.63 m and 2.60 m, respectively. The slopes of strong-karstification characterized by high apparent resistivity, well-developed joint fractures, and strong permeability (0.73 m·d-1). Such a result indicated that epikarst could regulate precipitation. The responses of soil moisture had a larger rainfall threshold (>20.50 mm·d-1) and the water level was determined by rainfall amount. In contrast, the slope with weak-karstification had low apparent resistivity and weak permeability (0.07 m·d-1). Moisture and water level were sensitive to rainfall. Karst channels were developed locally at 240-300 cm with a permeability coefficient of up to 432 mm·d-1. Obvious preferential flow was observed in extreme rainfall events on this slope, which could induce flood disaster in the adjacent depression. Our results would provide scientific basis for further research on water resources regulation, management, and eco-hydrology in karst areas of southwest China.
    Integration of evapotranspiration remote sensing products based on Bayesian model averaging: An example from Three-River-Source National Park
    WANG Jun-bang, ZHAO Xuan-lan, YE Hui, ZHANG Zhi-jun, HE Hong-lin
    2021, 32(6):  2119-2128.  doi:10.13287/j.1001-9332.202106.017
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    Evapotranspiration (ET) is a fundamental flux in land surface hydrothermal process. Because of the differences in basic concepts, assumptions, application scales, different models have induced varying uncertainties to the estimation and simulation of evapotranspiration. With the Three-River-Source National Park as an example, we used the Bayesian model averaging (BMA) method to integrate the ET estimations from five models of PT-JPL, ARTS-GIMMS3, ARTS-MODIS, MODIS global evapotranspiration product (MOD16), and SSEBop, and tried to improve the estimating accuracy of evapotranspiration. The results showed that the five models could well capture the seasonal variations in evapotranspiration at Haibei Flux Station, with an explanation range of 64%-86% variability in the observed ET, and a root means square deviation (RMSD) ranged from 0.47 mm·(8 d)-1 to 0.76 mm·(8 d)-1. BMA-based ET greatly improved its explanation to 89% and decreased the RMSD to 0.43 mm·(8 d)-1. The Three-River-Source National Park experienced an overall insignificant increasing trend in its inter-annual ET from 2003 to 2015. At the regional scale, the effects of temperature and precipitation on evapotranspiration were not significant, but were significant in the Yangtze River Source Park. Temperature and precipitation had positive impacts on evapotranspiration. The evapotranspiration showed different trends due to the geographi-cal differences between parks. This study provided a method reference for other multi-source data integration analysis. The integrated evapotranspiration data could effectively reduce the uncertainty of the original models and provide a more accurate data basis for the study of regional water heat change, which is of great significance to better understand water cycle under climate changes.
    Vegetation cover change and its response to climate change on the Loess Plateau, Northwest China based on ICEEMDAN method
    SUN Qian-qian, LIU Chao, ZHENG Bei-jun
    2021, 32(6):  2129-2137.  doi:10.13287/j.1001-9332.202106.011
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    The long-term series of geographic data and remote sensing data contain noise and perio-dic fluctuation. We used the improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) to decompose the data of the normalized difference vegetation index (NDVI), precipitation, and temperature from 1982 to 2015 on per-pixels in the Loess Pla-teau to obtain residuals. Using the residual with less noise and periodic fluctuations, we examined the changes of NDVI and the relationship between NDVI and climatic factors. The results showed that the spatial change trend of NDVI was mainly increasing from 1982 to 2015 in the Loess Plateau. The significance of the change trend of residual NDVI (95.9%) was greater than the original NDVI (72.3%), with spatial variations. Temperature and precipitation could largely explain the changes in vegetation coverage. The proportions of areas with extremely significant positive and negative correlations between temperature and NDVI on the Loess Plateau were 83.7% and 13.9%, respectively, while that between precipitation and NDVI were 54.4% and 37.2%, respectively. There were obvious spatial variations in the responses of vegetation to climate change on the Loess Plateau. Different climatic factors had different effects on different types of vegetation. In general, temperature had stronger correlation with different vegetation than precipitation. Therefore, temperature was the main driving factor for the changes of vegetation cover in the Loess Plateau.
    Plant species diversity of Carex peat mire in Changbai Mountains, China
    WANG Ming, LI Xing-li, DONG Yan-min, WANG Sheng-zhong, LIU Bo, JIANG Ming, WANG Guo-dong
    2021, 32(6):  2138-2146.  doi:10.13287/j.1001-9332.202106.002
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    We investigated the plant species richness both in cespitose Carex mires (C. schmidtii, C. meyeriana) and non-cespitose Carex mire (C. lasiocarpa) in Changbai Mountain. A total of 83 species (36 families, 59 genuses) was recorded in three sites. Among which, 71 species occurred in the C. meyeriana site, 61 species in the C. schmidtii site, and 26 species in the C. lasiocarpa site. The total species number and species richness in the two cespitose Carex mires were much higher than that in the non-cespitose Carex mire, while those on tussocks were much higher than between tussocks in the two cespitose Carex mires. Plant species richness on tussocks was positively related to the height, basal circumference and surface area of the tussocks, suggesting that tussocks were important for plant species diversity in Carex mires. Results of the canonical correspondence analysis indicated that the differences in soil water content, nutrient (soil organic carbon, total N, total P and C/N), and litter layer depth were the main factors influencing the differences of plant community composition on tussocks and between-tussocks. In the cespitose Carex mires, the hummock-hollow microtopography could foster high diversity by increasing surface area and creating multiple micro-habitats. Given its function in maintaining high species diversity, cespitose Carex could be a preferred species for vegetation restoration in degraded peat mires.
    Soil bacterial community composition and functional potentials along the vertical vegetation transect on Mount Segrila, Tibet, China
    AN Qian-dong, XU Meng, ZHANG Xu-bo, JIAO Ke, ZHANG Chong-yu
    2021, 32(6):  2147-2157.  doi:10.13287/j.1001-9332.202106.035
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    Information on the spatial distribution of soil microbial communities on the Tibetan Pla-teau is critical for in-depth understanding the important roles of microbes in typical alpine ecosystems. In this study, 16S rDNA Illumina Miseq sequencing was used to analyze the variations in bacterial community composition and functional potentials in soils sampled from four elevations on Mount Segrila, Tibet, and the driving environmental factors. Results showed that richness and Shannon diversity index of soil bacteria significantly decreased with increasing altitude. The relative abundances of Acidobacteria, Chloroflexi, Gemmatimonadetes, and Nitrospirae significantly increased, whereas that of Proteobacteria, Actinobacteria and Bacteroidetes significantly decreased with increasing altitude. In KEGG pathway (level Ⅱ), the relative abundance of genes related to membrane transport and the metabolism of amino acids, lipids, terpenoids and polyketones was significantly lower at high elevations. In contrast, genes related to carbohydrates metabolism, signal transduction, replication and repair and enzyme family were more abundant at high altitudes. Soil bacterial community composition and predicted functions were significantly affected by vegetation types and soil properties, with soil pH being the key driver. There were significant correlations between the abundances of predicted functions and bacterial taxa, such as Acitnobacteria, Bacteroidetes, and Fibrobacteres. The dissimilarity in the composition of KEGG pathway genes along the elevational gradient (β-diversity) showed a significantly positive correlation with the dissimilarity in bacterial community structure, indicating that there was a strong relationship between microbial community composition and potential functionality.
    Spatial variation and optimization of ecological carrying capacity in Jiangsu coastal area, China
    ZHANG Shan-shan, ZHANG Lei, CHEN Ting, DONG Ya-wen, ZHU Xiao-dong, QI Ling-yan
    2021, 32(6):  2158-2168.  doi:10.13287/j.1001-9332.202106.015
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    The research on spatial pattern and optimization of regional ecological carrying capacity is especially necessary to promote the overall development of economic transformation, upgrading and ecological protection and restoration. This study chose the natural, social and economic complex ecosystem of Jiangsu coastal area as subject. The concept model of pressure-state-potential (PSP) of ecological carrying capacity was established. A total of 15 indices were used to represent the interaction of three level states. With the support of GIS and other space technologies, the magnitude, spatial variation of regional ecological carrying capacity were examined through comprehensive evaluation of multiple indices and analysis of single index. Results showed that the spatial pattern of the suitability of single factor ecological carrying capacity in Jiangsu coastal area showed a variety of trends. There were significant differences in the area, proportion and layout of the same index across different cities and counties. The spatial differentiation of pressure and state superposition index showed that low pressure suitable bearing, low pressure generally suitable bearing, low pressure unsuitable bearing, high pressure suitable bearing, high pressure generally suitable bearing, bearing high pressure unsuitable bearing area was 3971.42, 6885.21, 3705.23, 4597.03, 6853.26, and 6403.97 km2, accounting for 12.3%, 21.2%, 11.4%, 14.2%, 21.1% and 19.8% of the total area, respectively. The results of spatial differentiation of superposition index of state and potential showed that the area integral of low potential suitable bearing, low potential general sui-table bearing, low potential unsuitable bearing, high potential suitable bearing, high potential general sui-table bearing and high potential unsuitable bearing was 3030.79, 6545.30, 5874.31, 3253.31, 7614.38, and 6097.83 km2, accounting for 9.4%, 20.2%, 18.1%, 10.0%, 23.5% and 18.8% of the total area, respectively. Most areas showed distribution characteristics of low pressure bearing area corresponding to high potential bearing area and high pressure bearing area corresponding to low potential bearing area in spatial pattern. There was an interaction of mutual influence, mutual promotion and collaborative promotion between pressure and state superposition index and state and potential superposition index.
    Simulation of Lanzhou urban land expansion based on multi-agent model
    WANG Zi-yang, SHI Pei-ji, ZHANG Xue-bin, WANG Ying-shu, XIE Xiao-yi
    2021, 32(6):  2169-2179.  doi:10.13287/j.1001-9332.202106.014
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    Using the four periods of land use data and socio-economic statistics of Lanzhou City in 1995, 2005, 2015 and 2018, we examined the evolution characteristics and driving forces of urban land use in Lanzhou, with expansion intensity index, Logistic regression, and principal component analysis method. Based on the multi-agent model, the expansion of urban land use in Lanzhou under multiple scenarios in 2025 was simulated using Netlogo software. The results showed that the intensity and scale of urban land expansion in Lanzhou City from 1995 to 2018 showed an increasing trend, with a total of 307 km2 of cultivated land and water area. The expansion of urban land in Lanzhou City was significantly related to regional GDP, social fixed asset investment, population density, population, policy, and terrain. The multi-agent model on the Netlogo software could simulate the expansion trend of urban land in Lanzhou, which provided a reliable simulation method for the expansion of valley-type cities. From 2020 to 2025, urban land use under the comprehensive development scenario, natural expansion development scenario, ecological and farmland protection development scenario all showed an increasing trend. The scale of expansion would range between 42.6-134.3 km2. The expansion mode would mainly be infilled expansion. Our results could provide decision support for the land space planning and ecological environment layout optimization for Lanzhou City.
    Spatial-temporal variations and influencing factors of eco-environment vulnerability in the karst region of Southeast Yunnan, China
    WANG Qian, ZHAO Xiao-qing, PU Jun-wei, YUE Qi-fa, CHEN Xing-yu, SHI Xiao-qian
    2021, 32(6):  2180-2190.  doi:10.13287/j.1001-9332.202106.018
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    Due to its vulnerability and anthropogenic disturbance, ecological problems in karst areas are prominent, such as vegetation destruction, soil erosion, and rocky desertification. Comprehensive analysis of ecological vulnerability and influencing factors in karst areas can provide scientific support for regional ecological restoration and environmental governance. With Guangnan County, a typical karst region in southeastern Yunnan, as an example, we constructed a karst regional eco-environmental vulnerability assessment index system from the perspective of natural and factitious factors. We used SPCA to assess the ecological vulnerability in 2000, 2010 and 2018. We further analyzed the temporal and spatial variations and explored its influencing factors by using geographic detectors. From 2000 to 2018, the changes of overall fragility were small, but the degree of fragility had been intensifying. The grade of ecological vulnerability was mainly slight fragile. The area with mild, moderate and severe fragility was increasing, while the area of extremely fragile showed no change. Guangnan County had a higher ecological vulnerability in the south of “Zhetu-Liancheng-Yangliujing-Banbang”, and lower in the north. The spatial agglomeration effect of vulnerability was strong in this county. The north part of Guangnan was vulnerable low-low agglomeration areas, while the southwest and southeast parts were in high-fragility-high agglomeration areas. The implementation of ecological engineering was conducive to the improvement of regional ecological fragility, while the disturbance of human activities further deteriorated ecological fragility. The area proportion of rocky desertification and stratum lithology had stronger influence on ecological fragility of the karst area. The most important influencing factor of the karst ecological fragility was the development of karst carbonate rocks.
    Control effect of blue light on Bemisia tabaci
    HAN Du-bin, CHEN Xiang-rong, ZHOU Fu-cai, CHEN Xue-hao, WU Xiao-xia, ZHAO Ming
    2021, 32(6):  2191-2198.  doi:10.13287/j.1001-9332.202106.038
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    Light is a important way in controlling vegetable pests. In this work, we examined the effects of blue light on Bemisia tabaci on cucumbers, as well as on nutrients, secondary metabolites, and resistance-related enzymes in cucumbers. Results of the direct repellent test showed that blue light had a strong repellent effect on B. tabaci, which increased with light intensity and exposure time. The repellent effect of direct light was stronger than that of transmitted light under the same light intensity and time. The population decline rate of B. tabaci was 77.7% after direct exposure to 1200 lx blue light for 5 min, being 17.4% higher than that of transmitted light. After 2 min exposure to 1750 lx blue light, the population decline rate was 41.2%, which was 10.6% higher than that of transmitted light. Under the condition of pot culture, blue light also had a good repellent effect on B. tabaci on leaves. The corrected population decline rate of B. tabaci reached 88.5% after 5 h exposure to 100 lx blue light. Blue light affected the development of B. tabaci. In addition, blue light significantly increased the contents of soluble sugar, free protein, total phenols and flavonoids in cucumber leaves, decreased the content of proline. The contents of trans-β-farnesene, trans-2-hexenal, cis-4-heptanal, trans-β-ocilene, D-carvone, longifolene and 3-carene, and the activities of peroxidase, catalase, superoxide dismutase, ascorbate peroxidase were significantly increased. The results suggested that blue light could drive off B. tabaci and influence the resistance of cucumber. 100 lx blue light had a good control effect on B. tabaci.
    Effects of plant community and soil properties on soil bacterial community in Bitahai Wetland, Southwest China
    ZHANG Zhong-fu, YU Qing-guo, WANG Hang, LIU Hui-hui, ZHAO Ya-chuan, XIE Xue-yang, ZHANG Meng, GENG Wei
    2021, 32(6):  2199-2208.  doi:10.13287/j.1001-9332.202106.039
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    Soil microorganism was the engine of the migration and transformation of biological elements in the soil-plant system of wetland ecosystems. Exploring the relationship between plant community, soil properties, and spatial structure with soil microorganisms is the key to maintain the health and stability of wetlands. In order to examine the effects of plant community, soil properties, and spatial structure on the bacterial community in wetlands, we used two-way indicator species analysis (TWINSPAN) to classify plant communities from 35 samples collected in Bitahai Wetland. We measured microbial community composition at the surface soil of the samples using high-throughput sequencing technology, and analyzed the relationship among plant community, soil pro-perties and spatial structure with bacterial community. The results showed that plant communities could classified into three different types by TWINSPAN. The physiognomy and structure of plant communities in same community type were relatively consistent. We found that quantitative classification had good applicability in vegetation classification of plateau wetland ecosystem. Acidobacteriota (21.0%), Chloroflexi (15.5%), Proteobacteria (15.3%) and Bacteroidetes (10.1%) had higher population densities (≥10%) in Bitahai Wetland. Analysis of similarities (ANOSIM) showed that different plant community types differed significantly in bacterial community composition, suggesting that plant communities could affect bacterial community. Cano-nical correspondence analysis (CCA) results showed that plant diversity, soil water content (SWC), pH, iron (Fe) and spatial structure were the dominated factors that significantly affecting bacterial community. The variance partitioning analysis (VPA) results showed that bacterial community was affected by single environment factors and their interactions. Our results highlighted that bacterial community is shaped by plant community, soil properties and spatial structure, with their effects being indivisible.
    Long-term effects of imbalanced fertilization with lime and gypsum additions on denitrifying functional genes of an Ultisol at Yingtan, Jiangxi, China
    DUAN Chun-jian, WAN Song, YE Gui-ping, FAN Jian-bo, WANG Quan-cheng, HE Ji-zheng, LIN Yong-xin
    2021, 32(6):  2209-2216.  doi:10.13287/j.1001-9332.202106.033
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    The abundance of denitrifying functional genes plays a key role in driving the soil nitrous oxide (N2O) emission potential. Nitrite reductase genes (nirK and nirS) and nitrous oxide reductase genes (nosZ I and nosZ II) are the dominant denitrifying funtional genes. In this study, real-time quantitative PCR was conducted to evaluate the effects of 32-year imbalanced fertilization and lime and gypsum additions on the abundances of nirK, nirS, nosZ I and nosZ II genes in an Ultisol at Yingtan, Jiangxi Province. We further explored the underlying driving factors. The results showed that, compared with the balanced fertilization treatment, fertilization without phosphorus (P) signifi-cantly decreased the abundances of nirK, nirS, nosZ I and nosZ II genes. Fertilization without nitrogen (N) significantly reduced the abundances of nirK, nosZ I and nosZ II, but did not affect the abundance of nirS. Fertilization without potassium (K) did not affect the abundances of all denitri-fying functional genes. Results of stepwise regression analysis and random forest analysis showed that soil pH was a key environmental factor affecting the abundances of nosZ I and nosZ II. The application of lime or lime + gypsum significantly increased soil pH, which subsequently increased the abundances of nosZ II and nosZ II/nosZ I by 150%-231% and 127%-155%, respectively. Our results suggested that application of lime or lime + gypsum favored nosZ II more than nosZ I in upland Ultisols, which might enhance the relative importance of nosZ II in N2O reduction. Overall, fertilization without P would reduce denitrifying gene abundances, while the application of lime or lime + gypsum enriched nosZ II and increased ratio of nosZ II/nosZ I, which might be beneficial for reducing N2O emission potential in the Ultisols.
    Effects of biomass conditioner on soil nutrient and microbial community characteristics of alpine desertified grassland in northwest Sichuan, China
    SONG Jia-shen, ZHANG Xiao-li, KONG Fan-lei, LIU-Xiao-lin, AN Wen-jing, LI Yu-yi
    2021, 32(6):  2217-2226.  doi:10.13287/j.1001-9332.202106.036
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    Biomass conditioner made from agricultural and animal husbandry waste for resource disposal could be used to improve desertified soil, which is one of the effective ways of ecological management on desertified grasslands in northwest Sichuan. To clarify the effects of different raw material conditioners on alpine desertified grassland in northwest Sichuan, we analyzed the effects of three conditioners on soil nutrients and microbial community characteristics. With no conditioner as the control (CK), three different biomass conditioners were set up with an application rate of 12 t·hm-2, including mushroom dregs (JZ), straw (JG) and biochar (SWT). The results showed that all biomass conditioners could significantly increase soil available nutrients and active organic carbon by 23.0%-521.6%. Among the three conditioners, JG had the best effect, with an improvement range for soil nutrient and organic carbon of 65.1%-521.6%. Because biomass conditioner was only applied in the first year, soil available nutrients and active organic carbon in the second year decreased by 4.5%-92.3% compared with that of the first year, while soil organic carbon and microbial biomass carbon content of the second year increased by 5.6%-458.0%. The biomass conditioners changed the relative abundance of the dominant bacteria in the microbial community. JG significantly affected bacterial flora, while JG and JZ affected fungal flora. Compared with CK, JG significantly reduced the diversity of soil bacteria and fungi. The Shannon index was decreased by 2.9% and 31.8%, while the Simpson index was increased by 175.0% and 320.9%, respectively. Results of the redundancy analysis showed that the contents of soil available nutrients and active organic carbon were important factors affecting microbial community composition. The contents of soil nitrate and microbial biomass carbon had greater impacts on bacterial community composition, explaining 65.9% of community variations. The contents of soil available potassium and microbial biomass carbon had a greater impact on fungal community composition, explaining 83.2% of community variation. According to the comprehensive comparison, straw conditioner could significantly increase soil available nutrients and active organic carbon, and benefit the growth of beneficial bacteria and fungi, which could be used as a promotion measure to improve soil quality of alpine desertified grassland in northwest Sichuan.
    Seasonal variation of phytoplankton community structure in the Tianhe Reservoir of the Daluoshan Mountain in southern Zhejiang Province, China and its indication to water quality
    WANG Guo-tao, CHEN Bin-bin, WANG Min, QIN Wen-li , QIN Zhi-xia, ZHANG Tian-tian, LI Ren-hui, MA Zeng-ling
    2021, 32(6):  2227-2240.  doi:10.13287/j.1001-9332.202106.032
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    To explore the association between phytoplankton community structure and water quality of the Tianhe Reservoir in Wenzhou, Zhejiang, we examined the phytoplankton and physico-chemical factors in the Tianhe Reservoir from February 2019 to January 2020. A total of 89 phytoplankton species belonging to 60 genera and 7 phyla were identified. The annual average abundance and biomass of phytoplankton were 2.02×105 cells·L-1 and 0.26 mg·L-1 respectively. Bacillariophyta was dominant in the whole year. Chlorophyta was dominant in spring and autumn. Cyanophyta was dominant in summer. Both Euglenophyta and Pyrrophyta appeared in the whole year. Cryptophyta appeared in autumn and winter. However, none of them was dominant due to their low abundance. The dominant species throughout the year were Melosira granulata, Synedra acus, Navicula cryptocephala, Asterionella formosa, Pseudoanabaena, Closterlum venus, Pediastrum duplex, Peridinium bipes, Dinobryon cylindricum and Cryptomonas ovata. Results of redundancy analysis (RDA) showed that water temperature, total nitrogen, CODMn and pH value were the main factors driving phytoplankton community structure in the whole year. According to the evaluation based on diversity indices, including Shannon index, Pielou evenness index, Margalef richness index and comprehensive trophic status index (TLI), water quality of Tianhe Reservoir is between oligotrophication and mesotrophication.
    Application of environmental DNA technology in natural reproduction of the four major Chinese carps in Yichang section of Yangtzi River, China
    LI Sha, LIU Xue-qing, JIANG Wei, XIAO Kan, HUANG An-yang, ZHANG Qi
    2021, 32(6):  2241-2248.  doi:10.13287/j.1001-9332.202106.037
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    We explored the sample collection and DNA extraction method of environmental DNA (eDNA) technique. Droplet digital PCR (ddPCR) was used to detect the eDNA concentration of the four major Chinese carps in different water layers and different cross-sections of Yichang section of Yangtze River trunk stream. We analyzed the relationship between eDNA concentration and density of egg and fry, and explored the feasibility of using eDNA technique to monitor the natural reproduction of the four major Chinese carps. Compared with the results from traditional survey methods, the eDNA concentration of the four major Chinese carps was extremely significantly correlated with egg and fry density. The maximum concentration was consistent with the peak occurrence time of egg and fry, suggesting that eDNA technique could predict the fishcrowd behavior for spawning. The investigation of cross-section eDNA concentration during two consecutive years suggested that the range of fish spawning ground was 4.5 km upstream to 1 km downstream of Yuyangxi. The predicted spawning ground was located within the range estimated by traditional methods from the lower part of Carmine Dam to Honghua Tuo. Our results indicate that eDNA technique, as a new ecological investigation method, could more accurately determine the distribution of fish with a certain population size, and thus with a good application prospect.
    Reviews
    Soil heterogeneity and its interaction with plants in karst areas
    HE Jie, YAN You-jin, YI Xing-song, WANG Yong, DAI Quan-hou
    2021, 32(6):  2249-2258.  doi:10.13287/j.1001-9332.202106.006
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    Soil heterogeneity is at a high level in the karst areas, which resulted from the complex habitat. On the one hand, plants have some adaptive strategies to such special habitats by forming certain morphological and physiological characteristics, which result in higher diversity of functional traits. One the other hand, plants improve the physical and chemical properties of soil through a series of life activities. The interactions between plants and soil drive ecosystem structure and function and its responses to global climate change. Here, we summarized the characteristics of soil hete-rogeneity in the karst areas, and reviewed the response of plant functional traits to soil and the feedback of plants to soil. It revealed the coupling mechanism between plants and soil in karst eco-system. We provided a future outlook, including future research contents and directions based on the current research status in this field, which aimed to provide theoretical reference for maintaining the structural and functional stability of fragile karst ecosystems.
    Ecological remediation of earthworms on soil-plant system: A review
    WANG Bing-lei, WANG Chong, LIU Meng-li
    2021, 32(6):  2259-2266.  doi:10.13287/j.1001-9332.202106.034
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    Soil-plant system is the basic structural unit of the biosphere, with close mutual feedback between soil and plants. The degradation of soil exerts various abiotic stresses to plants, disturbs the physiological metabolism of plants, and inhibits nutrient acquisition. Earthworms are known as “ecosystem engineers”, which can regulate soil physical-chemical-biological characteristics, improve the quality of the degraded soil (saline soil, heavy metals and organic pollutants contaminated soil), alleviate plants under stress, increase soil nutrient availability, promote plant growth. Furthermore, through the secretion of signal substances, earthworms could improve the resistance of plants. The ecological remediation effects of earthworms on soil-plant system are of great significance for improving environment of plant growth and maintaining the health and stability of soil.
    Soil phage and their mediation on the horizontal transfer of antibiotic resistance genes: A review
    CHEN Mo-lian, AN Xin-li, YANG Kai, ZHU Yong-guan
    2021, 32(6):  2267-2274.  doi:10.13287/j.1001-9332.202106.031
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    The spread of antibiotic resistance in soil is a global threat to public health and food safety, challenging the prevention and treatment of human infectious disease. The horizontal transfer of ARGs mediated by bacteriophages (phages) is an important pathway for the spread of antibiotic resistance genes (ARGs). However, the knowledge on the contribution of phages to ARGs transmission in soil is elusive. Here, we reviewed the distribution characteristics of phages in soil and its driving factors. We summarized the main methods for purification and enrichment of soil phage, reviewed recent achievements in the mechanism of phage-mediated horizontal transfer of ARGs in soil and proposed some outstanding questions. This review would contribute to understanding the important ecological role of phages in driving the horizontal transfer of ARGs, and provide a basis for developing management strategies to mitigate ARGs pollution.