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    15 June 2020, Volume 31 Issue 6
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    Special Features of Stable Isotope Ecology
    Source and spatio-temporal variation characteristics of dissolved inorganic carbon in Wanfenghu Reservoir, China
    ZHAO Zong-quan, SUO Hui-ying, JIAO Shu-lin
    2020, 31(6):  1783-1790.  doi:10.13287/j.1001-9332.202006.028
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    The flux and form of dissolved inorganic carbon (DIC), an important part of carbon budget, play a key role in the biogeochemistry of aquatic ecosystem. By analyzing physicochemical parameters and water DIC and δ13CDIC characteristics in Wanfenghu Reservoir, we examined the behavior and source of DIC. In the epilimnion, water pH in the entire reservoir was conservative, being weakly alkaline. Nitrate (NO3--N) had the maximum coefficient of variation and a high spatio-temporal variation. Due to the dilution effect, the lowest values of electrical conductivity (EC), partial pressure of carbon dioxide (pCO2) and DIC appeared during the summer high flow phase. On the water column in summer, redox potential (Eh) and NO3--N did not change with water depth, while other indicators changed significantly, with greatest variation in the thermocline. Water temperature (T), pH and Eh all decreased with increasing water depth in both seasons, while pCO2 showed an opposite trend. Water EC, total alkalinity (TA), and DIC decreased with increa-sing water depth in summer, but with a smaller gradient of change in winter. The DIC in water was negatively correlated with water pH and Eh, while positively correlated with EC and pCO2 in both seasons. 2) The concentration of DIC was 2.66-4.9 mmol·L-1 in summer and 3.38-4.52 mmol·L-1 in winter. During the period of thermal stratification, the variation gradients of DIC and δ13CDIC in the thermocline were most significant. DIC was positively correlated with δ13CDIC of epilimnion in summer. DIC was negatively correlated with δ13CDIC in epilimnion in winter and on water column in both summer and winter. However, the variation of DIC and δ13CDIC with water depth was not obvious in winter. 3) In summer, δ13CDIC was -7.71‰- -1.38‰, indicating that the dissolution of carbonate minerals was dominant. In winter, δ13CDIC was -16.93‰- -9.44‰, signifi-cantly lower than that in summer but with a wider range, indicating biological input of CO2 and mineralization of organic matter were the main sources. The δ13CDIC varied significantly in different seasons and water depths because of differences in carbon sources and changes in the relative contribution proportion of carbon sources.
    Effects of water vapor source and local environmental factors on the hydrogen and oxygen isotopic compositions of precipitation in Huitong, Hunan Province, China
    SUI Ming-zhen, ZHANG Ying, XU Qing, GAO De-qiang, WANG Ting, WANG Si-long
    2020, 31(6):  1791-1799.  doi:10.13287/j.1001-9332.202006.020
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    Deuterium (D) and oxygen-18 (18O) are common environmental tracers in water. Understanding the isotopic compositions of precipitation is necessary for further studies on local and global water cycling processes. To reveal the mechanism of isotopic compositions of precipitation in subtropical monsoon region in response to environmental changes, we collected 49 precipitation samples and recorded related environmental factors from May 2017 to August 2019 in Huitong field station of Chinese Academy of Sciences in Hunan Province. We analyzed the temporal variations in D and 18O values in precipitation and analyzed the influence of water vapor source and local environmental factor on stable isotopic compositions of precipitation. The local meteoric water line was established as δD=(7.45±0.17)δ18O+(10.10±1.25) (R2=0.93, P<0.01), the slope of which was slightly lower than China’s meteoric water line and the global meteoric line. The D and 18O values of precipitation samples were closely coupled with local meteorological conditions and dominant moisture sources. The 18O and D contents were depleted during summer monsoon season but enriched during winter monsoon season. During the summer monsoon and post-monsoon seasons, precipitation in this area came mainly from the Bay of Bengal, the South China Sea, and the West Pacific at three different types of air pressure, which lead to the similarity of the D-excess value of the precipitation to global average. The lower intercept of meteoric water line and the higher D-excess value for precipitation during the winter monsoon season resulted from moisture from remote westerly air masses, degenerated tropical marine air masses from the Bay of Bengal, and inland moisture in the pre-monsoon period, which were also affected by local environmental factors.
    Effects of soil water stress and atmospheric CO2 concentration on photosynthetic and post-photosynthetic fractionation
    DING Bing-bing, ZHANG Yong-e, YU Xin-xiao, JIA Guo-dong, WANG Yu-song, ZHENG Peng-fei, JIANG Tao, XIA Juan-juan
    2020, 31(6):  1800-1806.  doi:10.13287/j.1001-9332.202006.024
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    Analysis of plant photosynthesis and post-photosynthetic fractionation can improve our understanding of plant physiology and water management. By measuring δ13C in the atmosphere, and δ13C of soluble compounds in leaves and branch phloem of Platycladus orientalis, we examined discrimination pattern, including atmosphere-leaf discrimination during photosynthesis (ΔCa-leaf) and leaf-twig discrimination during post-photosynthesis (ΔCleaf-phlo), in response to changes of soil water content (SWC) and atmospheric CO2 concentration (Ca). The results showed that ΔCa-leaf reached a maximum of 13.06‰ at 95%-100% field water-holding capacity (FC) and Ca 400 μmol·mol-1, and a minimum of 8.63‰ at 35%-45% FC and Ca 800 μmol·mol-1. Both stomatal conductance and mesophyll cell conductance showed a significant linear positive correlation with ΔCa-leaf, with a correlation coefficient of 0.43 and 0.44, respectively. ΔCleaf-phlo was not affected by SWC and Ca. Our results provide mechanism of carbon isotopes fractionation and a theoretical basis for plant survival strategies in response to future climate change.
    Assessing water sources for Populus simonii with different degrees of degradation based on stable isotopes
    ZI Er-die·BA He-ti, JIA Guo-dong, YU Xin-xiao, SHI Jia-mei, JIANG Tao
    2020, 31(6):  1807-1816.  doi:10.13287/j.1001-9332.202006.023
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    Water availability is the key factor limiting plant growth in arid regions. Populus simonii is a typical shelterbelt tree species in Zhangbei County, Hebei Province, with an important role in constructing ecological barrier. With stable isotope technique, graphical method, and multiple linear mixing model, we analyzed water sources and water use strategies of P. simonii in different growth periods with four different degrees of degradation (non-degraded, slightly degraded, modera-tely degraded and severely degraded) in Zhangbei County. Results would help improve our understanding on the cause and mechanism of the large-scale degradation of P. simonii in this area. The results showed that water sources of P. simonii in the early growth stage (May-June) from all four degradation degrees were relatively simple. P. simonii mainly used soil water in 0-40 cm, with the utilization rates being 34.2%, 50.1%, 41.6%, and 55.7% for the four degradation degrees, respectively. At the middle growth stage (July-August), non-degraded P. simonii utilized soil water from layers of 200-280 cm and 280-400 cm, with utilization rates of 20.2% and 30.9%, respectively. Soil water at 200-280 cm and 280-400 cm layers was utilized by slightly degraded poplar, with the contribution rates of each layer being 33.2% and 27.9%, respectively. Moderately degraded P. simonii utilized soil water from the depths of 0-40 cm and 40-120 cm, with the rates of 30% and 26.9%, respectively. Water utilization rate of severely degraded P. simonii to 0-40 cm depth was 55.4%. At the late growth stage (September-October), water sources of non-degraded P. simonii transferred to the upper-middle soil layers, with the utilization rate of 0-40 cm, 40-80 cm, and 80-120 cm being 23.3%, 17.2%, and 16.5%, respectively. The utilization rate of the slightly degraded P. simonii was 35.7% at 0-40 cm and 20.6% at 80-200 cm. The moderately and severely degraded P. simonii mainly utilized soil water at 0-40 cm layer, with the contribution rates of soil water being 43.7% and 51.8%, respectively. With the exacerbation of degradation, the main water source of P. simonii gradually transferred from deep to surface soil water.
    Characteristics and processes of reverse sap flow of Platycladus orientalis based on stable isotope technique and heat ratio method
    LIU Zi-qi, WANG Yu-song, ZHANG Huan, JIA Guo-dong
    2020, 31(6):  1817-1826.  doi:10.13287/j.1001-9332.202006.013
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    Plants could maintain growth by foliar water uptake and reverse sap flow under certain conditions, particularly in regions with seasonal drought. This physiological activity is often overlooked, however, leaving a gap in quantitatively understanding the processes and mechanisms underlying water utilization of forest vegetation under drought stress. In this study, with both field comparison experiments and pot experiments, we used heat ratio method with stable isotope technique to monitor a typical plantation tree species, Platycladus orientalis, in the Beijing mountainous area. We aimed to analyze the patterns and the influencing factors of the reverse sap flow occurrence in P. orientalis, to quantify the amount and the replenishment rate of reverse sap flow, and to examine the characteristics and processes of reverse sap flow at different parts of plants. In the field comparison experiment, reverse sap flow was detected at the breast height of stem and in the root in the controlled plot (drought plot) after rainfall. The reverse sap flow of root system was detected later than that in the stem. By contrast, no reverse sap flow was observed in the natural plot. In the pot experiments, the recharge rate of all the groups reached the peak value two hours after the rainfall treatment. Except for the groups of severe and moderate drought, recovery of δD to the original level was observed eight hours after rainfall, and the reverse sap flow on plants generally lasted no more than 24 h. The amount of foliar water uptake and the reverse sap flow to the branches and rhizosphere soil had a negative relationship with the initial soil moisture. The maximum recharge rates for leaves, branches, and rhizosphere soil were (9.5±0.1)%, (5.9±0.3)% and (5.7%±0.6)%, respectively. Different rates and timing of the reverse sap flow were observed at different parts of P. orientalis. Under complex and variable conditions of water supply, it is of great significance to examine the process and mechanism of reverse water movement of plants to better understand its survival and competitive strategies.
    Simulation of δ18O in Platycladus orientalis leaf water with different kinetic fractionation coefficients
    SHI Jia-mei, YU Xin-xiao, JIA Guo-dong, ZHANG Qiu-fen, WANG Dan-dan, WANG Ya-peng
    2020, 31(6):  1827-1834.  doi:10.13287/j.1001-9332.202006.021
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    Clarifying 18O isotope composition of leaf water (δL,b) would provide theoretical refe-rence for the study of leaf physiology and forest hydrology. We continuously monitored the concentration of atmospheric water vapor (Wa) and 18O isotope composition of atmospheric water vapor (δv) at the canopy of Platycladus lateralis plantation in the mountain area of Beijing. We analyzed the effects of kinetic fractionation coefficients εk1(32%) and εk2(28%) on the prediction of δL,b by combining the measured leaf water 18O isotope (δx) and δL,b of P. lateralis. The results showed that the diurnal variation of Wa was irregular. Atmospheric relative humidity (RH) showed a “V” shape of diurnal variation, and stomatal conductance (gs) increased first and then decreased at the diurnal scale. Wa, RH, and gs showed a significant negative correlation with δL,b when isotopes approached a steady-state equilibrium around noon. The kinetic fractionation coefficient εk1 and εk2 were applied to the Craig-Gordon model to predict δL,b under the isotopic quasi-steady-state condition. The results showed that the predicted values of εk2 approached the observed values of δL,b. This result indicated that the application of εk2 to the model was more consistent with the change of water isotope concentration in the leaves of P. lateralis in the mountain area of Beijing. These results would improve our understanding of water isotope enrichment model and evapotranspiration resolution model in leaves.
    Water sources of riparian plants based on stable hydrogen and oxygen isotopes in Lanzhou section of the Yellow River, China
    SU Peng-yan, ZHANG Ming-jun, WANG Sheng-jie, QIU Xue, WANG Jia-xin, DU Qin-qin, GUO Rong, CHE Cun-wei
    2020, 31(6):  1835-1843.  doi:10.13287/j.1001-9332.202006.022
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    As plant species for riparian ecological restoration in northern China, Tamarix ramosissima and Salix matsudana play an important role in river protection, flood control, regional climate regulation, and landscape construction of riparian vegetation. Two sampling sites were selected in the riparian zones along the Lanzhou section of Yellow River, where plant xylems and potential water sources were collected. The direct comparison method, Bayesian mixture model MixSIAR and the proportional similarity index (PS index) were used to determine the proportions of water utilization for each potential water source and the relationship of two species in water utilization. The results showed that shallow soil (0-30 cm) was the main water source during growing season, with utilization ratio being 28.3% for T. ramosissima and 24.4% for S. matsudana. For T. ramosissima, river water had the lowest contribution (16.6%), and for S. matsudana, groundwater contributed the least (17.9%). In the months with low soil moisture, plants increased the utilization ratios of river water and groundwater. The PS index at the sampling site S1 and S2 was 91.0% and 87.7%, respectively. On a monthly basis, the index in May was the highest, indicating an inter-month divergence in water use relationship. At the floodplain, there were even utilization ratios for each potential water source, which is an optimal strategy to obtain water from each potential source to the maximum extent. Our results provided theoretical basis for riparian tourism development along the Lanzhou section of the Yellow River and plant water management in environment protection in the Yellow River Basin.
    Partitioning ecosystem respiration of a Platycladus orientalis forest in the west mountainous area of Beijing, China using stable carbon isotope
    XU Xiao-wu, LI Han-zhi, YU Xin-xiao, JIA Gong-dong
    2020, 31(6):  1844-1850.  doi:10.13287/j.1001-9332.202006.025
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    Based on stable carbon isotope, we quantitatively partitioned ecosystem respiration in a Platycladus orientalis forest in the west mountainous area of Beijing. Results from this study could lay the foundation for carbon exchange research in forest ecosystems of this region. The spectroscopy technique was used to continuously measure CO2 concentrations and δ13C values at different height of the forest. Soil and branch chambers were used for measuring nighttime δ13C values in underground and aboveground respiration, and then the proportions of respiration components were calculated. Combined with soil respiration efflux measurement, ecosystem respiration was then quantitatively partitioned. The results showed that δ13C values of respiratory components fluctuated, which ranged from -31.74‰ to -23.33‰ in aboveground respiration of plants and from -32.11‰ to -27.74‰ in soil respiration. The δ13C values of ecosystem respiration was at the middle of those ranges. Soil respiration averaged 1.70 μmol·m-2·s-1 at night, accounting for 47%-91% of ecosystem respiration. Aboveground respiration averaged 0.72 μmol·m-2·s-1, contributing less to ecosystem respiration. Daytime respiration based on isotope mixing model calculation had greater variability than that based on temperature response model, with a mean value of 2.31 μmol·m-2·s-1 and 2.28 μmol·m-2·s-1, respectively.
    Effects of inhibitors and pig manure on the transformation of urea nitrogen in paddy soil
    YU Chun-xiao, ZHANG Li-li, YANG Li-jie, LI Wen-tao, WU Kai-kuo, XIE Xue-shi, LI Dong-po, WU Zhi-jie
    2020, 31(6):  1851-1858.  doi:10.13287/j.1001-9332.202006.026
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    With the aim to understand the response of different nitrogen forms in paddy soil under the conditions of urea combined with inhibitors and pig manure, and to explore the nitrogen retention and supply capacity of paddy soil under different management strategy, we conducted a pot experiment with 15N labeled urea. There were six treatments: no nitrogen fertilizer (CK), pig manure (M), urea (N), urea+pig manure (NM), urea+inhibitor (NI), urea+inhibitor+pig manure (NIM). Urease inhibitor (PPD+NBPT) and nitrification inhibitor (DMPP) were used as the inhibitor combination. Soil nitrogen pools, conservation of 15N labeled urea, and rice N adsorption were measured in rice seedling, tillering, and mature stages. Results showed that pig manure significantly increased soil ammonium concentration, soil microbial biomass nitrogen and fixed ammonium, as well as the storage of urea nitrogen in various pools at tillering stage, and significantly increased rice yield. Addition of the inhibitors increased NH4+ fixation by clay minerals and nitrogen immobilization by microorganisms compared with treatment N, and increased urea-derived NH4+ fixation by clay minerals compared with treatment NM. Pathway analysis showed that pig manure increased urea-N assimilation and yield of rice. The urea-derived ammonium fixed by clay minerals was temporarily stored after inhibitors application. NIM treatment stored more N in microbial biomass, and the released ammonium coupled the turnover and mineralization of microbial provided more available nitrogen for the later growth of rice. Both NM and NIM treatments are recommended in paddy fields of north China.
    Effects of potassium levels on translocation of 13C-photoassimilates to fruit in ‘Fuji’ apple during fruit expanding period
    SHA Jian-chuan, CHEN Qian, WANG Fen, XU Xin-xiang, ZHU Zhan-ling, GE Shun-feng, JIANG Yuan-mao
    2020, 31(6):  1859-1866.  doi:10.13287/j.1001-9332.202006.027
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    A field experiment was carried out in a six-year old ‘Fuji’3/M26/Malus hupehensis Rehd. apple with the 13C tracer method to examine the changes of chlorophyll fluorescence parameters, photosynthetic characteristics of leaf, sugar transporter gene expression, 13C assimilation capability and the characteristics of translocation and distribution of 13C-photoassimilates to fruit under different levels of potassium addition (K2O 0, 0.5%, 1.0%, 1.5%, 2.0%, expressed by CK, K1, K2, K3, K4, respectively). Potassium aqueous solution smear the leaves within 20 cm around the fruit at fruit enlargement stage. Compared with other treatments, K3 treatment significantly increased Rubisco enzyme activity, net photosynthetic rate, maximal photochemical efficiency of PSII, actual photochemical efficiency of PSII, coefficient of photochemical quenching, sorbitol and sucrose content, sorbitol 6-phosphate dehydrogenase (S6PDH) and sucrose phosphate synthase (SPS) enzyme activities and 13C assimilation capability of leaves. Furthermore, K3 treatment increased gene expression of sorbitol transporter MdSOT1 and MdSOT2 and sucrose transporter MdSUT4, and promoted the unloading of sugar in fruit. The 13C of self retention (self leaves and self branches) was the highest in CK (82.6%) and the lowest in K3 treatment (60.5%). With increasing potassium concentration, the 13C absorption of fruit first increased and then decreased, which was the highest in K3 treatment (1.31 mg·g-1) and the lowest in CK (0.57 mg·g-1). Our results indicated that foliage application of potassium solution improved PSII photochemical efficiency, activities of key enzymes related with carbon assimilation, synthesis ability, and outward transport ability of photosynthates in leaves, and consequently promoted the directional transportation of sugar to fruit. The amount of photoassimilates transported to fruit was the most under 1.5% K2O treatment (K3).
    Effects of different integration of water and fertilizer modes on the absorption and utilization of nitrogen fertilizer and fruit yield and quality of apple trees
    TIAN Ge, LI Hui-feng, TIAN Meng, LIU Xiao-xia, CHEN Qian, ZHU Zhan-ling, JIANG Yuan-mao, GE Shun-feng
    2020, 31(6):  1867-1874.  doi:10.13287/j.1001-9332.202006.030
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    We examined nitrogen use efficiency of 15N-urea of 15-year-old ‘Gala’ apple trees by broadcast fertilization (T1), nitrogen fertilization with drip irrigation (T2) and nitrogen fertilization with subsurface irrigation (T3), to further improve the water and fertilizer integration technology for apple orchard and to improve nitrogen utilization efficiency. The results showed that leaf area, chlorophyll, and leaf nitrogen content of leaves were significantly higher in T3 treatment than those in T1 and T2 treatments. Soil mineral nitrogen content (20-40 cm) in each period followed the order of T3>T2>T1, while that in 0-20 cm followed an order of T2>T3>T1. The Ndff value at organ level (the contribution rate of the 15N amount absorbed by various organs of the tree to the total nitrogen content of the organ) was the highest in T3 treatment in each period, followed by T2 and T1 treatments. The utilization rate of 15N in the fruit ripening period followed an order of T3>T2>T1. The 15N utilization rate of T3 reached 24.2%, being 1.19 and 1.65 times of T2 and T1, respectively. The 15N distribution rate in the fruits during the fruit maturity stage was the highest in T1 treatment, while that in the storage organs was the highest in T2 treatment and that in the reproduction organs was the highest in T3 treatment. The single fruit weight, yield, soluble solids, hardness, soluble sugar and sugar-acid ratio were the highest in T3 treatment, followed by T2 and T1 treatments. In summary, nitrogen application by percolation irrigation (subsurface application) significantly promoted leaf growth and nitrogen utilization of apple tree, and improved fruit yield and quality.
    Nitrogen uptake, distribution, and utilization in young bearing Huangguan pear trees under 15N-urea application in spring
    SUN Ming-de, WU Yang, LIANG Zhen-xu, TIAN Hai-qing, ZHAO Yan-yan, DU Rui-rui, LIU Jun, LIU Song-zhong
    2020, 31(6):  1875-1881.  doi:10.13287/j.1001-9332.202006.029
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    We investigated the characteristics of nitrogen uptake, distribution, and utilization in the three-year-old bearing Huangguan pear trees following 15N-urea application in early spring. The results showed that the growth of pear trees was mainly depended on vegetative organs such as shoots and leaves at the stage from budbreak to shoot growth arrest, but mainly on storage organs (roots) and supplemented by the formation of fruit yield and quality at the stage from shoot growth arrest stage to fruit harvest. Meanwhile, tree biomass, especially that storage organs, substantially increased. All organs, especially newly developed shoots and leaves, acquired more N in shoot growth arrest stage due to vigorous growth, with relatively higher N derived from fertilizer (Ndff). Ndff of each organ except for root was lower at fruit maturity stage than that at shoot growth stage. Most of the labeled nitrogen was distributed in the newly developed organs (shoots and leaves) from budbreak to shoot growth arrest stage, but in the storage organs during shoot growth arrest stage to fruit maturity stage. Labeled fertilizer nitrogen was mainly distributed in the storage organs, followed by the vegetative organs. Reproductive organs had the lowest allocation in the experimental stage. For the three-years-old pear trees, the ratio of absorbed N from fertilizer was responsible for 31.1% and 21.0% of total absorbed nitrogen from budbreak to shoot growth arrest stage and from shoot growth arrest stage to fruit maturity stage, respectively, with the remaining N (68.9% and 79.0% of total) being absorbed from soil N.
    Mesophyll conductance to CO2: Methods and current knowledge
    GONG Xiao-ying, MA Wei-ting, YU Yong-zhi, LI Lei
    2020, 31(6):  1882-1888.  doi:10.13287/j.1001-9332.202006.010
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    Mesophyll conductance (gm), the total conductance of CO2 diffusion from substomatal cavity to the site of carboxylation within chloroplast, is a major limiting factor for photosynthesis and a key parameter for improving photosynthetic resource use efficiency of crops. Online 13C discrimination method is an important method for plant eco-physiological studies and a well-established method for measuring gm of C3 plants, although it has not been widely used due to challenges in methodology and high demands on experimental facilities. In this review, we summarized the characteristics of commonly used methods for gm, introduced the basic theory of the online 13C discrimination method, namely Farquhar’s photosynthetic 13C discrimination model; systematically introduced the practical measurements, equations and the components of facilities; and reviewed the drivers for variation in gm of C3 plants. At the last part, we discussed the outlook of the development of methodology, new experimental protocols, and applications in measurement scenarios.
    Original Articles
    Altitudinal differentiation in the radial growth of Betula platyphylla and its response to climate in cold temperate forest: A case of Oakley Mountain, Northeast China
    LYU Zhao-yang, YUN Rui-xin, WU Tao, MA Yan-jun, CHEN Zhen-ju, JIN Yu-ting, LI Jun-xia
    2020, 31(6):  1889-1897.  doi:10.13287/j.1001-9332.202006.011
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    Climate change has profound impacts on the structure and function of forest ecosystem. Under the background of climate warming, the growth patterns and climate responses of different species in different environments determine the development and stability of ecosystems. Using the method of tree chronology with ring width data of Betula platyphylla in Oakley Mountain of Daxing’an Mountains, we examined the relationship between the growth climate response of the pioneer B. platyphylla in larch forest and temperature rise and altitudinal changes. The results showed that climate warming resulted in the differentiation on B. platyphylla in different altitude. The radial growth of B. platyphylla increased significantly at the low altitude area (1050 m), while there were little changes at the relatively high altitude area (1250 m). Before the time of rapid warming (1980), the radial growth of B. platyphylla on two altitude areas were significantly stressed by low temperature in winter (October to February). During the period of rapid warming (1981-2010), low temperature stress in winter did not affect tree growth, with the growing season (May to July) temperature becoming the main limiting factors to the radial growth of B. platyphylla at the relatively high altitude areas. The growth of B. platyphylla increased in the low altitude stands with favorable water and heat conditions. The distribution of B. platyphylla may generally spread to high altitude sites in the study area under climate warming.
    Variation in the vegetation fade stage and its relationships with climate and vegetation productivity in Inner Mongolia, China
    SA Ri-gai, BAO Gang, BAO Yu-hai, HU Ri-cha, JIANG Kang
    2020, 31(6):  1898-1908.  doi:10.13287/j.1001-9332.202006.019
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    Based on the MODIS NDVI data from 2001 to 2018, we extracted the fade stage of vegetation in Inner Mongolia and the characteristics of its temporal and spatial changes using the Logistic curve maximum curvature method of the cumulative normalized difference vegetation index (NDVI). We analyzed the responses of fade stage to climatic factors and NDVI at the ecological zone level. The results showed that the fade stage in Inner Mongolia occurred between the day of year (DOY) 260 and 280 during the study period. It was DOY 270-280 in the forest ecological zone, and was delayed from the south to north. The fade stage in the grassland ecological zone was the earliest and ranged between DOY 257 and 273, and was delayed from the northeast to southwest. The fade stage in the desert ecological zone ranged between DOY 270 and 283, which was delayed from the northeast to southwest. From 2001 to 2018, the fade stage in three ecological zones showed an insignificant delaying trend. Spatially, vegetation productivity decreased from the northeast to southwest, with a larger area of an increasing temporal trend than that of a decreasing trend. The fade stage in the entire Inner Mongolia and three ecological zones was greatly affected by precipitation during the two or three months before the fade stage and was positively correlated with the pre-season average temperature, maximum temperature, and minimum temperature, respectively. The increases/decreases in vegetation productivity in August and September delayed/advanced the fade stage in entire Inner Mongolia and three ecological zones. In contrast, the increases/decreases in vegetation productivity in June and July advanced/delayed the fade stage in the grassland and desert ecological zone.
    Community structure and species composition in a subtropical evergreen broad-leaved forest in Wuchaoshan, Hangzhou, Zhejiang Province, China
    TIAN Li-xin, WU Chu-ping, YANG Shao-zong, XU Yue, HUANG Ji-hong, DING Yi, ZANG Run-guo
    2020, 31(6):  1909-1915.  doi:10.13287/j.1001-9332.202006.001
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    The numerical classification and ordination of plant communities can reveal the relationship between plant distribution and environment, with implications on vegetation restoration and forest management. Community types were classified using a clustering method based on 45 forest dynamic plots with each area of 0.04 hm2 in Wuchaoshan, Hangzhou, Zhejiang Province, China. The ordination of plant community and the relationship between communities and edaphic variables (soil nutrient availability and topography) were explored using redundancy analysis. Results showed there were three community types in the study area, including Schima superba community type, Quercus fabri-Symplocos anomala community type, and Cyclobalanopsis glauca community type. Stem density and basal area of trees were not significantly different among those community types. Species richness in the C. glauca community was higher than that in S. superba community, but not significantly different from the Q. fabri-S. anomala community. Results from the redundancy analysis showed that community distribution was significantly related to edaphic factors. Topographic and soil factors accounted for 46.4% of the total variation in community distribution while total soil phosphorus, available phosphorus, available potassium, elevation, slope, aspect, and canopy openness had significant effects on community composition. Total soil phosphorus, available potassium, and altitude were the main factors influencing community distribution in Wuchaoshan. 53.6% of the total variation in community distribution were not explained, perhaps due to anthropogenic disturbance.
    Density and spatial distribution of seedlings and saplings in different gap sizes of a sprucefir mixed stand in Changbai Mountains, China
    HE Dan-ni, YANG Hua, WEN Jing, XIE Rong
    2020, 31(6):  1916-1922.  doi:10.13287/j.1001-9332.202006.004
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    In August 2019, we investigated natural regeneration (seedlings height between 0.2 m and 1 m; saplings ≥1 m in height and <5 cm in DBH) inside canopy gaps (n=48) in a plot (0.36 hm2) established in a typical mixed spruce-fir conifer broadleaved stand. To examine the short-term effects of gap size (small <20 m2, medium 20-50 m2, large 50-120 m2, and extra large >120 m2) on the regeneration density and growth (height and ground diameter) of Korean pine (Pinus koraiensis), Ezo spruce (Picea jezoensis) and Khingan fir (Abies nephrolepis), the kernel density estimation was used to examine their spatial distribution within gaps. The results showed that spruce and fir regeneration density generally decreased with the increases of gap size (significant effect only on saplings). The density of spruce and fir saplings in small gaps was 0.34 and 1.74 trees·m-2, respectively. In contrast, the density of Korean pine was not affected by gap size. The effects of gap size on seedling and sapling growth were strongest in Khingan fir and weakest in Korean pine, with greater height and ground diameter in larger gaps. Within a given canopy gap, the Korean pine and Ezo spruce saplings in small, medium, and large gaps were taller and had larger DBH in the northeastern corner of the expanded gap than in other sections, whereas those in extra large gaps had the highest growth in the northwestern part of the core gap. Small gaps favoring seed germination and seedling establishment could be created through selective removal of Khingan fir, which should be expanded later to larger sizes (>50 m2) to enhance sapling growth. Further monitoring would be required to understand the long-term effects of gap size on natural regeneration of spruce-fir forest.
    Community structure of Quercus aliena var acuteserrata forest in the Taibai Mountain, China
    YU Wen, YAN Yan, LIU Xiao-yun, ZHANG Shuo-xin
    2020, 31(6):  1923-1932.  doi:10.13287/j.1001-9332.202006.003
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    Qinling Mountains are biodiversity hotspots in China, with rich vegetation resources and species diversity. To clarify the mechanism underlying biodiversity maintenance during vegetation restoration in this area, we established two permanent plots with each area of 100 m×150 m in the Q. aliena var. acuteserrata secondary forest (SF) and primary forest (PF) in the northern slope of Taibai Mountain in 2016, following the standardized protocols by CTFS (the Center for Tropical Forest Science). We analyzed community composition and structure with measuring all trees with DBH ≥ 1 cm. 2839 and 2840 trees were recorded in the SF and PF plots, respectively. Trees in those two plots belong to 29 families, 45 genera, 65 species and 21 families, 37 genera, 47 species, respectively. The proportions of occasional species and rare species were 38.4% and 24.6% in the SF plot, and 40.4% and 19.2% in the PF plot. Most of the trees were distributed in northern temperate zones, and the proportions of genera were 46.6% and 48.7% in the SF and PF plots, respectively. The diameter of Q. aliena var. acuteserrata in both plots followed a unimodal distribution (more young trees than old ones). The diameter distributions of companion species (e.g., Sorbus alnifolia, Acer davidii, Cornus kousa, and Staphylea holocarpa) were inverted “J” shapes, indicating that those populations could have complete life history. In the pair correlation function g(r) analyses, the aggregation of dominant species were the strongest at 0-2 m scale in the two plots when r=10 m. The degree of aggregation gradually weakened with increasing scale. The population distribution patterns of the dominant species were random or uniform when the scale increased to certain value. The average uniform angle index (W) were 0.56 and 0.58 in the SF and PF, respectively. Trees in the communities followed an aggregated distribution. The average W of the community and dominant species in the SF were smaller than that in the PF, indicating weaker species aggregation in the SF. The average dominance in the SF and PF was both 0.47, indicating that the stands were in a co-dominant state. The average mingling was 0.70 and 0.57 in the SF and PF, respectively, which belonged to high and moderate mingling. Species richness, community stability and spatial distribution patterns of forest community could be affected by human disturbance. The role of interspecific interaction, effects of habitat heterogeneity on species coexistence, and variation of community structure should be considered during vegetation restoration of disturbed forest community.
    Hollow-bearing characteristics of Populus euphratica in the lower reaches of Tarim River, China
    Reyila Mumin, Tayierjiang Aishan, Umut Halik
    2020, 31(6):  1933-1940.  doi:10.13287/j.1001-9332.202006.009
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    We analzyed the hollow ratio of tree trunks, tree hole parameters, and its distribution characteristics among different DBH and tree height classes in a long-term monitoring plots of Populus euphratica forest at the Argan section in the lower reaches of Tarim River. The results showed that P. euphratica in the study area had a high hollow ratio, in that trees with hollowness accounted for 56% of the total individuals, with a absolute value of 159 tree·hm-2. The hollow ratio of P. euphratica showed significant difference among different DBH classes and tree height classes. The hollow ratio was positively correlated with DBH, and negatively correlated with tree height. The density of P. euphratica with hollowness was 560 ind·hm-2 and 2 ind·tree-1. Most of tree holes appeared on the tree trunk (57.1%) and mainly in the middle of the trunk (31.3%). The hole with a diameter of 5-15 cm accounted for the largest proportion (38.2%). The total number of tree holes, the number of tree holes per tree, and the diameter of holes were positively correlated with DBH and negatively correlated with tree height. The distribution of different tree hole types among different DBH classes and tree height classes was different, with inconsistent changing trends. The distribution of tree holes showed significant difference acorss orientations, with most of which mainly toward the west. The occurrence rate of tree hollow in P. euphratica desert riparian forest was more serious. The larger the DBH of poplar tree was, the more obvious the degree of hollow. Therefore, it is of great significance to strengthen the conservation of young poplar trees and to restore degraded desert riparian forests.
    Effects of sodium salt stress on seed germination of typical annuals in a desert-oasis ecotone of Hexi Corridor, China
    WANG Guo-hua, GUO Wen-ting, GOU Qian-qian
    2020, 31(6):  1941-1947.  doi:10.13287/j.1001-9332.202006.006
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    We assessed the effects of different concentrations of salts (0, 40, 80, 120, 160 and 200 mmol·L-1) on the seed germination and re-germination of six typical annuals (Gramineae: Setaria viridis, Chloris virgata and Eragrostis minor; Chenopodiaceae: Bassia dasyphylla, Salsola ruthenica and Corispermum mongolicum) in autumn of current year and next spring, with NaCl and NaHCO3 as neutral sodium salt and alkaline sodium salt. The results showed that NaCl and NaHCO3 significantly affected seed germination of the six species. The inhibition effect of NaHCO3 on seed germination was stronger than NaCl. When the concentration of NaHCO3 reached to 160 mmol·L-1, germination rates of the six species were low. However, when the concentration of NaCl reached to 200 mmol·L-1, the germination rates of the six species were still high. The germination (2.8%-20.0%) and re-germination rates (3.3%-20.0%) in current autumn were much lower than those in next spring, with values of 21.7%-81.6% and 5.0%-41.1%, respectively. In autumn, most of the current year’s seeds kept dormancy, but the dormancy weakened in next spring. The salt tolerance of seeds of the six annual species was in the order of C. virgata > S. viridis > S. ruthenica > B. dasyphylla > C. mongolicum > E. minor.
    Effects of nitrogen and phosphorus addition on soil microbial community and amino sugar in a temperate forest on Changbai Mountain, Northeast China
    YANG Jing-yi, WANG Xu, SUN Li-fei, WANG Chao, BAI E
    2020, 31(6):  1948-1956.  doi:10.13287/j.1001-9332.202006.007
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    We carried out an experiment including nitrogen addition (N, 50 kg N·hm-2·a-1), phosphorus addition (P, 25 kg P·hm-2·a-1) and both nitrogen and phosphorus addition (NP, 50 kg N·hm-2·a-1+25 kg P·hm-2·a-1) in a natural Korean pine broad-leaved mixed forest on Changbai Mountain to examine the effects of single and combined N and P additions on soil microbial community composition and amino sugar. The results showed that N and P addition significantly reduced total microbial biomass by 19.5% and 24.6% in the organic layer of soil, while P addition significantly reduced the biomass of bacteria and fungi by 23.8% and 19.3%, respectively. In the mineral layer, N, P and NP addition significantly increased total microbial biomass by 94.8%, 230.9%, and 115.0% respectively, while the biomass of bacteria and fungi were significantly increased under all the treatments. The fungi to bacteria ratio (F/B) was significantly increased in the organic layer by N addition, while was decreased in the mineral layer soil by NP addition. The Gram-positive bacteria to Gram-negative bacteria ratio showed positive response to N, P and NP addition. Soil amino sugars responded differently to different treatments. N, P and NP addition significantly decreased glucosamine content by 41.3%, 48.8% and 36.4% in the organic layer, while N and NP addition increased muramic acid content by 43.0% and 71.1%, respectively. The contents of glucosamine and muramic acid in the mineral layer did not change significantly in response to N addition but increased significantly in response to both P addition and NP addition. The glucosamine to muramic acid ratio in the organic layer significantly decreased under fertilization treatments, indicating that N and P addition increased the relative contribution of bacteria to soil organic carbon accumulation. The changes in soil amino sugar contents were closely related to the change in microbial community composition after N and P addition, both of which were affected by changes in soil chemical properties.
    Responses of soil intracellular and extracellular urease activities to carbon additions in chernozem
    YU Chun-jia, JIANG Dong-qi, TIAN Mu-yu, CHEN Zhen-hua, ZHANG Yu-lan, WANG Jian, JIANG Hui, CHEN Li-jun
    2020, 31(6):  1957-1962.  doi:10.13287/j.1001-9332.202006.037
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    Urease in soil, as the most important enzyme catalyzing urea hydrolysis, plays an important role in nitrogen supply of grassland ecosystems. While the effects of different carbon additions on extracellular urease in grassland soil are well understood, their effects on soil intracellular urease remain unknow. Moreover, whether the responses of intracellular and extracellular urease to carbon additions are consistent need to be clarified. With a field experiment in Hulun Buir grassland of Inner Mongolia, we investigated soil intracellular and extracellular urease activities in chernozem under four treatments, including carbon-free (C0), 250 (C250), and 500 (C500) kg C·hm-2·a-1, using glucose as carbon source. Further, we analyzed their relationships with soil properties. Carbon additions significantly increased soil intracellular urease activity and its ratio to total urease activities and total urease activity, but did not affect soil extracellular urease activities. There was significant positive correlation between soil intracellular urease activity and microbial biomass, suggesting that the increases of soil intracellular urease activities were mainly caused by the increases of microbial biomass. Results of structural equation modeling (SEM) analysis showed that carbon additions indirectly increased soil intracellular urease activities by affecting microbial biomass.
    Influencing factors of phosphate solubilizing capacity of Aspergillus niger and optimization of its culture condition
    SUN Ran, ZHANG Su, WU Chen-lin, LI Zhu, XIAO Yang
    2020, 31(6):  1963-1970.  doi:10.13287/j.1001-9332.202006.033
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    In this study, we investigated factors affecting the phosphate solubilizing capacity of Aspergillus niger. A strain named A. niger Xj-2 was isolated by single-spore isolation, with phosphate solubilizing capacity of 539.90 mg·L-1 in liquid medium. The simulated process of fermentation kinetics showed that phosphate concentration reached equilibrium after 4 d cultivation, indicating that the optimal fermentation time was around 4 d. Phosphate solubilization capacity of strain Xj-2 in different phosphorus-source culture media followed the order: calcium phosphate (539.90 mg·L-1)>zinc phosphate (238.45 mg·L-1)>ferric phosphate (182.64 mg·L-1)>phosphate rock power (71.80 mg·L-1) > aluminum phosphate (24.40 mg·L-1). We further examined the optimal condition of strain Xj-2 for phosphate solubilization by response surface optimization combined with single factor experiments. Results showed that the influence of various factors on the phosphate solubilizing capacity of strain Xj-2 was in the order: carbon source > microbial density > pH. The maximum phosphate solubilizing capacity (616.81 mg·L-1) could be achieved under the following condition with 10.00 g·L-1 glucose, 0.79 g·L-1 urea, 35 ℃, the initial pH of medium 6.0, 3.8% microbial density and 160 r·min-1 rotating speed.
    Effects of “Grain for Green” program and coal mining on sediment production in a typical small watershed of Yushenfu Mining Region, Northwest China
    WANG Xiao-tong, ZHANG Jia-qiong, YANG Ming-yi, WANG Yong-ji
    2020, 31(6):  1971-1979.  doi:10.13287/j.1001-9332.202006.016
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    Soil erosion in the ecologically fragile zone is severely affected by the intensified coal mining activities in the Yushenfu Mining Region of the Loess Plateau. Soil erosion controlling projects such as the “Grain for Green” program are continuously implemented by the government, which has effectively mitigated or even controlled soil erosion. Coal mining results in new environmental problems, which has changed the erosion characteristics and sediment transport in watersheds. In this study, we identified the sediment source trapped behind the check dam using a composite fingerprinting approach and clarified the impact of “Grain for Green” program and coal mining on variation of the amount and sources of sediment during two decades, in a representative check-dam which controlled the watershed of Laoyeman. The two decades were divided into two stages, i.e. an earlier decade (1990-1999) and a later decade (2000-2010) with respect to the implement of the “Grain for Green” program in the flood couplets sequence established during the running of the dam. The annual average thickness of flood couplets during 2000-2010 decreased from (42.7±29.9) cm to (16.6±13.7) cm during 1990-1999, and the annual sediment deposition per unit area (square meter) at the sampling site reduced from 579.9 kg·m-2 to 245.8 kg·m-2. The main source of sediment was gully wall (averaged 79.2%±10.1%) during the study period. However, compared with sediment sources during 1990-1999, the contribution of sediment from slope during 2000-2010, which was greatly affected by the “Grain for Green” program, showed an increasing trend (average annual contribution increased by 7.4%). According to the coaling mining and the variation of rainfall erosivity, our results indicated that under the combined effects of the “Grain for Green” program and decreases of rainfall erosivity, the intensity of sediment production in the watershed was substantially decreased. Coal mining had important impacts on sediment contribution from the slope, and obviously affected soil erosion controlling effects of the “Grain for Green” program. It is obvious that coal mining has increased the risk of erosion and sediment production on the slope, and that soil erosion control on the slope should focus on areas affected by coal mining.
    Soil enzyme activities and their stoichiometry of typical plantations in mid-subtropical China
    SHI Li-juan, WANG Hui-min, FU Xiao-li, KOU Liang, MENG Sheng-wang, DAI Xiao-qin
    2020, 31(6):  1980-1988.  doi:10.13287/j.1001-9332.202006.008
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    We measured the activities of six kinds of enzyme, including β-glucosidase (BG), β-N-acetyl-glucosaminidase (NAG), leucine aminopeptidase (LAP), acid phosphatase (AP), polyphenol oxidase (POX), peroxidase (POD), as well as enzyme stoichiometric ratios and soil physical and chemical properties at 0-10 and 10-20 cm layers across typical Pinus massoniana plantation, Pinus elliottii plantation and mixed plantation of P. massoniana and Schima superba (broadleaved-conifer mixed plantation) in mid-subtropical China. Key factors driving the variation in soil enzyme activity and stoichiometry among different stand types were investigated. The results showed that the activities of soil BG and LAP were significantly affected by stand type. Soil BG activity at 10-20 cm soil layer was significantly higher in P. elliottii plantation than in P. massoniana plantation, while the activity of LAP was highest in the P. massoniana plantation. Soil BG/(NAG+LAP) and BG/AP at 10-20 cm layer of P. elliottii plantation were significantly higher than those of P. massoniana plantation, while (NAG+LAP)/AP of P. massoniana plantation was significantly higher than those of P. elliottii plantation and mixed plantation. The vector length of enzyme stoichiometry at 10-20 cm soil layer was significantly different among stand type, with an order of P. elliottii plantation > broadleaved-conifer mixed plantation > P. massoniana. The vector angles of enzyme stoichiometry in the three plantations were greater than 45°, with the vector angle in the P. elliottii plantation at 10-20 cm soil layer being significantly greater than that of the P. massoniana plantation. Results from redundancy analysis showed that soil carbon quality index and the ratio of soil organic carbon to total phosphorus (C/P), soil water content and C/P were the key factors affecting soil enzyme activity and stoichiometry at 0-10 and 10-20 cm soil layers, respectively. The quantity and quality of soil carbon and phosphorus, and soil water content played a key role in regulating nutrient cycling in mid-subtropical plantation ecosystem.
    Characteristics of humidity and temperature variations and CO2 exchange of mobile dunes at different space-time scales in Horqin sandy land, China
    YANG Xiao-jun, LIU Ting-xi, WANG Guan-li, DUAN Li-min, LI Dong-fang, HUANG Tian-yu
    2020, 31(6):  1989-1998.  doi:10.13287/j.1001-9332.202006.015
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    Terrestrial carbon cycle plays a key role in driving climate change and ecosystem carbon balance. Understanding the variations of humidity and temperature and CO2 exchanges are meaningful to reveal the law and mechanism of regional carbon cycles in deserts. We examined the near surface humidity, temperature variations, and CO2 exchanges by eddy covariance and Bowen ratio systems in a typical mobile dune of Horqin sandy land. We analyzed the relationships between water-heat and CO2 exchanges of 0 to 10 m vertical height at daily and seasonal scales were analyzed. The results showed that the vertical variations of near surface temperature ranged from 0.4 ℃ to 2 ℃ and decreased with the increases of height from April to September, but with an opposite pattern in other months. The seasonal variation of air relative humidity was greater than 40%. During the growing season of 2018, the averaged daily net ecosystem carbon exchange (NEE) was -0.02 mg·m-2·s-1. The annual averaged daily NEE was 0.003 mg·m-2·s-1, indicating that the mobile dunes were carbon sources at the whole year scale. The vertical differences of temperature and humidity well fitted the NEE. The inflexion points of the fitting curve were at 10% humidity and 0.5 ℃ temperature, respectively. At the scalem of the year, the NEE fitting result of temperature was better than that of humidity, with the inflexion points at 17 ℃ and 65% humidity, respectively. In the growing season, the near surface vertical temperature difference was negative, which would inhibit CO2 absorption of mobile dunes. The circumstances of high humidity would promote the absorption of atmospheric CO2. Across different time and vertical height, the variations of humidity and temperature were closely related to CO2 exchanges, which affected carbon sink and source of mobile dunes. Carbon budget was more sensitive to temperature than humidity.
    Remote sensing monitoring and evaluation of spatial and temporal changes of ecological environment in Hangjin Banner, Inner Mongolia, China
    ZHOU Ling-mei, WANG Shi-hang
    2020, 31(6):  1999-2006.  doi:10.13287/j.1001-9332.202006.018
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    With the ecological environment problems being increasingly prominent and globalized, more and more attention is paid to environmental protection. Remote sensing technology is important in monitoring and evaluating ecological environment. In this study, based on the Landsat image data of 1992, 2000, 2008 and 2017, the remote sensing ecological index (RSEI) was constructed to monitor and evaluate the quality of ecological environment in Hangjin Banner, Inner Mongolia, aiming to provide a theoretical basis for local ecological environment protection. The results showed that from 1992 to 2017, the quality of ecological environment in Hangjin Banner was generally poor, with RESI grades of poor and inferior. The mean value of RESI increased from 0.31 (1992) to 0.37 (2008) and then decreased to 0.30 (2017). During the period, the change range was mainly from one grade to the next. In terms of spatial distribution, the regions with poor ecological environment quality were mainly in the desert plains of the central and western regions, that with good ecological quality mainly along the Yellow River and in the southeast, and that with large fluctuation of ecological quality grade mainly in the desert edge along the Yellow River and in the hilly and gully regions in the east. During the research period, the center of gravity of each ecological grade in Hangjin Banner substantially shifted, with spatiotemporal fluctuations. Our results suggest that ecological environment of Hangjin Banner was fragile and unstable. Ecological construction can promote the quality of ecological environment, but resources and land use should also be reasonably allocated.
    Quantitative analysis of the effects of human activities on vegetation in the Beijing-Tianjin sandstorm source region under the climate change
    YU Lu, WU Zhi-tao, DU Zi-qiang, ZHANG Hong, LIU Yong
    2020, 31(6):  2007-2014.  doi:10.13287/j.1001-9332.202006.005
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    It is of great practical significance for regional ecological management to understand the quantitative impacts of human activities on vegetation under climate change. Based on GIMMS NDVI3g data, meteorological data (temperature, precipitation) and standardized precipitation evapotranspiration index (SPEI), we used correlation analysis and trend analysis to examine the spatio-temporal variation of vegetation and its driving factors in different periods from 1982 to 2014 in the Beijing-Tianjin sandstorm source region. Regression analysis and residual analysis were used to quantify the impacts of human activities on vegetation changes in different sub-regions. The results showed that from 1982 to 2014, the degradation status in 77.1% of degraded vegetation was significantly improved and 64.1% of vegetation had an increasing trend in the study area, with mean annual NDVI decreasing from southeast to northwest. Vegetation coverage increased in 74.5% of the areas after the implementation of the Beijing-Tianjin sandstorm source control project, with mountains in northern Shanxi showing the most obvious increases. Among all the climate factors, rainfall had the strongest correlation with vegetation change. Human activities, such as ecological engineering, played an active role in most areas, especially in mountains of northern Shanxi, where the contribution of human activities reached 94.9%.
    Research basis of ecological thresholds and regime shifts in China
    LI Dai-kui, HE Ping, XU Jie, HOU Li-ping
    2020, 31(6):  2015-2028.  doi:10.13287/j.1001-9332.202006.017
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    Non-linear changes widely occur in ecosystems, which manifest as sudden changes in system state with increasing pressure. To explain these changes, ecologists proposed the concepts of ecological threshold and regime shift, and continuously improved the theory and method system. Mechanistic and empirical studies further deepen our understanding for evolution mechanism of the complex system, which begun to be implemented into the environmental management. In recent decades, a large number of quantitative studies on stress-response in various types of ecosystems in China. Results from those studies are closely related to the theory paradigms of ecological threshold and regime shift in essence. Based on the “China Ecological Thresholds and Alternative Stable States Database”, we screened and summarized the relevant ecological thresholds and explained the mechanisms underlying regime shift for 10 ecosystem types, including river, lake, wetland, forest, grassland, estuary and ocean, farmland, desert, city, and tundra. We linked case studies with theory paradigms of ecological threshold and regime shift with the aim to integrate multi-field scientific achievements and resources as the basis for ecosystem complexity research, and promote their application in ecological monitoring, ecological security early warning, and ecological standards innovation.
    Evaluation of sustainable development of eco-economic systems in China based on emergy analysis
    MA Wen-jing, LIU Juan
    2020, 31(6):  2029-2038.  doi:10.13287/j.1001-9332.202006.038
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    We comprehensively evaluated the sustainable development level in China from 2006 to 2016 based on emergy theory. According to the differences in the proportion of primary energy input, all the provinces in China were divided into four groups for inter-provincial comparison to further examine the impacts of primary energy input on the sustainable development. The results showed that under the high economic development, the continuous increase in the primary energy input rate enhanced the environmental load rate of Chinese eco-economic system from 2.78 to 3.13. Meanwhile, the increases in imports led to a decline in emergy yield rate and a decline in emergy sustainable index to 5.40. Results of inter-provincial comparison showed that the trend of emergy per area was generally consistent with the change in the primary energy input rate. Currently, economic development in most provinces was dependent on energy consumption. Among them, sustainable development in cities with dual characteristics of highly developed economics and significant environmental pressures was not optimistic, including Beijing and Shanghai. Provinces in southern China with lower energy input and higher emergy yield were stronger in sustainable development, with Jiangsu as the most representative province. Consequently, improving the efficiency of energy utilization in inland provinces, adjusting the mode of economic development and appropriately slowing down the intensity of economic development could fully alleviate the contradiction between economic growth and environmental protection, and thus steadily achieve sustainable development of ecology and economy.
    Impacts of industrial agglomeration on eco-efficiency in resource-based areas: An empirical study based on nine typical resource-based provinces in China
    YAN Xiao, TIAN Yu, LI Rong-jie
    2020, 31(6):  2039-2048.  doi:10.13287/j.1001-9332.202006.014
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    The contradiction between ecological environment and industrial economic development is extremely prominent in resource-based areas. We conducted an in-depth research on the effects and mechanisms of different types of industrial agglomeration on eco-efficiency in nine typical resource-based provinces (Shanxi, Inner Mongolia, Heilongjiang, Guizhou, Yunnan, Shaanxi, Qinghai, Ningxia and Xinjiang) from 2006 to 2015, including specialization, related and unrelated diversification. The results showed that the specialization had a negative impact on eco-efficiency. The industrial specialization degree of all provinces except Ningxia showed a downward trend, which was conducive to the improvement of eco-efficiency. The impacts of related diversification on eco-efficiency were characterized by a U-shaped curve. The degrees of related diversification in Shanxi, Qinghai and Ningxia were less than the critical value of 1.49, which inhibited the improvement of eco-efficiency. Other provinces had crossed the inflection point, with a promotion role of related diversification on eco-efficiency. The unrelated diversification had a negative impact on eco-efficiency. The degrees of unrelated diversification in Shanxi, Guizhou, Shaanxi, and Heilongjiang declined slightly, which was conducive to the improvement of eco-efficiency. In other provinces, the unrelated diversification increased significantly, which was not conducive to the improvement of eco-efficiency. Our results could provide theoretical basis for path selection and policy formulation of industrial green transformation in resource-based regions.
    Principles of “ecological living water” to purify sewage and its application in black and smelly water treatment of Yangzhou
    LI Rong-fu, SUN Long-sheng, KOU Xiang-ming, LI Zhang-lin, WANG Shu-guang
    2020, 31(6):  2049-2056.  doi:10.13287/j.1001-9332.202006.035
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    To explore the fundamental way of black and odorous water treatment, based on the study of the purification function of natural water body and the analysis of root cause and direct cause of black and odorous water body, we elaborated the scientific connotation and ecological function of “ecological living water”, and fully revealed the scientific principle and technical advantages of “ecological living water” for sewage treatment. “Ecological living water” was the original ecological water control in situ. Through the rapid water reaeration, the micro-ecosystem of living water was created. Meanwhile, with the support of micro-speed circulating water, the continuous and efficient purification was realized. The practice of black and odorous water treatment in Yangzhou showed that, 3-5 days after the treatment of “ecological living water”, the black and odorous water was completely eliminated and transformed into “green water”. 15-20 days after the treatment, water quality reached the national surface water class Ⅲ water standard. Therefore, “ecological living water” may be a kind of sustainable water control technology system with investment of less resources and equipment, fast pollution control speed, low operation cost, good water control effect and both symptoms and treatment.
    Spatial response of lake water quality to multi-scale landscape pattern of lakeside zone in agricultural watershed
    LI Kun, XIE Yu-jing, SUN Wei, WANG Xiang-rong, LI Zhao-hua, WANG Ling
    2020, 31(6):  2057-2066.  doi:10.13287/j.1001-9332.202006.036
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    Understanding the response of water quality in lake to landscape pattern at different spatial scales in agricultural watershed is of great significance to water quality management. In this study, we classified seven riparian buffer zones of lakeside zone by ArcGIS and RS in the Honghu Lake, according to the five functional areas. The landscape metrics were analyzed at multiple buffer widths using Fragstats software. Mathematical statistical methods and models such as redundancy analysis were used to explore spatial relationship between water quality and landscape patterns. Results showed that: 1) The effect of landscape patterns on water quality was scale-dependent at multiple buffer widths. The highest total explanatory power between landscape characteristics and water quality was found at the 200 m buffer width, accounting for 86.1% of the total, which was the most effective spatial scale affecting water quality. 2) The landscape configuration (e.g., largest patch index, patch density) was more associated with water quality than landscape composition (e.g., the percent of landscape and evenness index). 3) The impacts of different landscape types on water quality varied. Agriculture land, affected by topography and cultivation mode, was the main influencing factor on the degradation of water quality at smaller buffer widths from 100 m to 500 m. Forests with higher density and area had more purification effect on water pollutants at the wider buffer widths from 1000 m to 5000 m. The impacts of grassland on water quality was similar with that of forests, but densely distributed urban land contributed to water quality degradation at the same buffer widths. This study could provide scientific reference for water quality management and landscape planning of lake basin in agricultural areas.
    Nitrogen and phosphorus stoichiometry of aquatic macrophytes in Kaidu River of Xinjiang and the potential influencing factors
    PENG Qing-wen, YAN Zheng-bing, LUO Yan, LI Kai-hui, HAN Wen-xuan
    2020, 31(6):  2067-2075.  doi:10.13287/j.1001-9332.202006.031
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    Nitrogen (N) and phosphorus (P) are two common mineral elements constraining plant growth. Nutrients in aquatic macrophytes are mainly absorbed from water and sediments, and thus elemental composition in plant tissues can reflect the nutritional status in freshwater ecosystems. Kaidu River is an important river flowing through the alpine meadows, deserts, and desert oases in Xinjiang. Herein, samples of aquatic macrophytes, water, and sediments across the Kaidu River were collected. Foliar stoichiometric characteristics of N and P in plants were examined among life forms and phylogeny. The differences and correlations among the stoichiometric characteristics of plants, water bodies, and sediments in the upstream and downstream and across different land use types were elaborated. Results showed that the means of leaf N and P concentrations and N/P mass ratio were 24.9 mg·g-1, 2.49 mg·g-1, and 12.6, respectively. There were significant differences in the leaf N and P stoichiometry among various life forms. Specifically, leaf N and P concentrations in submerged species were significantly higher than that in floating-leaved species and emergent species. The N/P of floating-leaved species was 19.2 and significantly higher than that in other two life-forms, indicating that their growth might be limited by P. Leaf N and P concentrations were higher in the upstream than in the downstream. Nitrogen contents in water and sediment were the higher in the upstream of the river. Compared with the river reaches in farming areas, the higher N and P concentrations of aquatic macrophytes in the grassland regions might be related to the higher contents of organic matter in grassland soils and of animal slurries from flocks and herds, suggesting that grazing exerted larger impact on the stoichiometric characteristics of the Kaidu River ecosystem. Our findings highlighted that overgrazing might accelerate the deterioration of water quality in the upstream of the Kaidu River, disturb the balance of N and P in the aquatic ecosystem, and potentially influence the biogeochemical cycling.
    Overwintering distribution and its environmental determinants of small yellow croaker based on ensemble habitat suitability modeling
    LIU Zun-lei, YANG Lin-lin, YUAN Xing-wei, JIN Yan, YAN Li-ping, CHENG Jia-hua
    2020, 31(6):  2076-2086.  doi:10.13287/j.1001-9332.202006.034
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    Small yellow croaker is a trans-boundary fish resource shared by China and South Korea. Information on the distribution and preferred habitats of overwintering populations is lacking, parti-cularly in southern waters of Yellow Sea where the species is regulated together by China and South Korea. We simulated the geographic distribution under current condition with eight species distribution models (SDM) based on the presence-absence data and five environmental variables. The performance of model’s prediction was evaluated using the area under the receiver operating characteris-tic curve (AUC) based on 5-fold cross-validation. Ensemble SDMs were constructed using a weighted average of eight habitat suitability model types to identify core areas with high probability of small yellow croaker occurrence. The results suggested that predictions based on presence-absence data generally perform better than those based on presence-only data and classical regression models under-performed compared to machine learning approaches. Among all the approaches that supported presence-absence data, support vector machine was the best performing technique and GLM was the worst. The ensemble model outperformed individual SDM models, demonstrating higher effectiveness of ensemble modelling approaches than individual models in reducing the predictive uncertainty. Salinity and temperature were important factors in predicting the overwintering distribution of small yellow croaker. The core areas with high probability of occurrence were concentrated in three areas, the open waters of southern Yellow Sea, the open waters of northern East China Sea, and the coastal sea of Zhejiang Province. Coastal waters in southern Yellow Sea and open waters in central and southern East China Sea were not suitable for overwintering of small yellow croaker. Our results provided a basis for predicting the potential overwintering distribution to guide spatial planning in support of sustainable utilization of small yellow croaker.
    Ecomorphological traits explaining the competition exclusion between Oryzias and mosqui-tofish
    XIAO Qiao-zhi, CHEN Li-juan, JIN Jin-jin, Qiu Yu-ping, CHEN Guo-zhu
    2020, 31(6):  2087-2097.  doi:10.13287/j.1001-9332.202006.040
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    The theory of ecomorphology predicts that species with similar morphological traits can occupy similar ecological niche, which may cause competitive exclusion. To apply this theory into fish invasion ecology research is of significance for understanding the interaction between native and invasive species. Here, we compared the morphological difference between two native (Oryzias pectoralis, Oryzias curvinotus) and one invasive species (Gambusia affinis) to explore the competitive exclusion among them. The results showed that despite O. pectoralis and O. curvinotus were sympa-tric species, they varied in spatial distribution. Such a result supported the theory of ecomorphology, which predicts that two species with similar morphological traits might have strong competition. Moreover, their population density exhibited a significant negative relationship with that of G. affinis. The morphology of G. affinis and both Oryzias species were more similar when comparing to other fish in the assemblage. Results from the cluster analysis showed that G. affinis and Oryzias species were close in a branch, with extremely low spatial niche overlap between invasive mosquitofish and native Oryzias species. There was significant negative correlation between the population abundance of mosquitofish and Oryzias species. All the results suggested that mosquitofish led to population decline of both Oryzias species, due to the ecomorphological similarity. More studies are needed to better understand the mechanisms of G. affinis invasion in habitats of native Oryzias species.
    Reviews
    Research advances in model simulation and data assimilation of water and carbon fluxes in land surface vegetation
    FAN Hua-ye, LI Ying, ZHANG Ting-long, GAO Huan-lin, HU Shuai
    2020, 31(6):  2098-2108.  doi:10.13287/j.1001-9332.202006.012
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    Accurately estimating water and carbon fluxes is of great significance for the research in land surface water and carbon cycles. However, it is very challenging. The estimation accuracy needs further improvement. Both traditional model simulation and site observation methods have advantages and disadvantages, which need to be examined in combination. Data assimilation integrates observations into models based on physics laws to obtain the optimal estimates of model state variables and parameters as much as possible, and provides an effective way for their combination. In this review, we traced the research progress for process models assimilated with multi-source observational data of land surface water carbon fluxes and analyzed the domestic and foreign research status of land surface process models focused on water carbon fluxes, data assimilation algorithms, and assimilation of land surface carbon flux data. We summaried problems in this research area, including insufficient coordination of multi-source observation data, relatively simple assimilation strategy, lacking fusion of assimilation models, and limited assimilation scale. The future development directions and trends were analyzed and prospected from five aspects, including assimilation strategy, model selection, data expansion, scale effect, and scientific calculation. This work would provide more comprehensive background information for scholars in this field, and arouse common concerns.
    Vegetation and soil characteristics of degraded alpine meadows on the Qinghai-Tibet Pla-teau, China: A review
    LI Jun-hao, YANG Guo-jing, WANG Shao-ping
    2020, 31(6):  2109-2118.  doi:10.13287/j.1001-9332.202006.002
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    Alpine meadows account for 46.7% of grassland area on the Qinghai-Tibet Plateau, which is an important part of grasslands in China. Under the effects of climate change and human activities in recent years, alpine meadow has been degraded seriously. Vegetation and soil have shown different degradation trends. At large spatial scales, the degraded alpine meadows are characterized by decreases of vegetation coverage, increases of weed vegetation, soil degradation and even desertification. At the micro-scale, soil particle size, soil microorganisms, and soil enzymes in degraded alpine meadows changed. We analyzed the changes of vegetation and soil during the degradation of alpine meadow ecosystems by considering species diversity, plant community structure, plant biomass, soil physical properties, soil microorganisms, soil enzymes, and soil nutrients. We put forward some uncertainties in the current research and problems that needed further study. This review provided a scientific basis for a comprehensive understanding of the degradation mechanisms and patterns of alpine meadows, effective intervention in alpine meadow, and restoration of ecological function.
    Impacts of Spartina alterniflora invasion on coastal wetland ecosystem: Advances and prospects
    XIE Xue-feng, SUN Xiao-min, WU Tao, JIANG Guo-jun, PU Li-jie, XIANG Qi
    2020, 31(6):  2119-2128.  doi:10.13287/j.1001-9332.202006.032
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    Coastal wetland, affected by the interaction of land and marine ecosystems, is a typical fragile and sensitive zone. Spartina alterniflora is the most successful invasive species in global coastal zone, with important impact on coastal wetland ecosystems. We systematically summarized available literature, and reviewed the effects of S. alterniflora invasion on biogeochemical cycling (soil carbon, nitrogen, phosphorus cycling, and soil heavy metal migration) and biological community (microorganisms, plants, and animals) in coastal wetlands. Then, three perspectives were proposed for the future research: 1) strengthening the mechanism of the impact of S. alterniflora invasion on ecosystem health of coastal wetlands; 2) focusing on the coupling mechanism of the interaction between S. alterniflora community and coastal wetland environment in the context of global change; 3) carrying out long-term positioning monitoring to clarify the responses of coastal wetlands at different stages of S. alterniflora invasion. This review could provide guidance for the ecological utilization and management of S. alterniflora.
    Research advances in physiological toxicity of graphene on plants
    WENG Yi-neng, JIANG Nan, LI Jia-xin, YING Zhi-ning, DU Shao-ting
    2020, 31(6):  2129-2138.  doi:10.13287/j.1001-9332.202006.041
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    Graphene is one of the most popular carbon nanomaterials that widely used in many fields due to its unique physical and chemical properties. The expanding production and application of graphene materials has led to their inputs into the environment, with increasing risks of environment and human health. Therefore, elucidating the potential toxic effects of graphene and the related mechanism are of significance to evaluate its ecological risk and bio-safety. To date, many studies have reported the physiotoxicological effects of graphene on plants. Literature showed that graphene had concentration-dependent effects on the physiological response of plants, including seed germination, growth, oxidative stress, photosynthetic characteristics, plant hormones, and metabolic processes. In the future, it is necessary to establish a widely accepted phytotoxicity evaluation system for the safe manufacture and use of graphene.