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    18 July 2017, Volume 28 Issue 7
    Water sources of Nitraria sibirica and response to precipitation in two desert habitats
    ZHOU Hai, ZHAO Wen-zhi, HE Zhi-bin
    2017, 28(7):  2083-2092.  doi:10.13287/j.1001-9332.201707.021
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    Nitraria sibirica usually exists in a form of nebkhas, and has strong ecological adaptability. The plant species has distinctive function for wind prevention and sand fixation, and resistance drought and salt. However, the water condition is still a limiting factor for the plant survival and development. In order to understand the water use strategy of the plant in different desert habitats, we selected the N. sibirica growing in sandy desert habitat and gravel desert habitat to study the seaso-nal variation of plant water sources and response to precipitation at the edge of the oasis of Linze in the Hexi Corridor. We measured the oxygen stable isotope of the plant stem water and the different potential water sources (precipitation, soil water and ground water), and used the IsoSource model to calculate the proportion of water sources from the potential water. The results showed that there were significant seasonal variation characteristics of δ18O value and water source of stem water for the plant in the two habitats. In the sandy habitat, the plant used more ground water in the less precipitation seasons including spring and fall, and more than 50% of the water sources absorbed from ground water. However, under the condition of gravel habitat, the plant could not achieve the ground water level depth of 11.5 m, and its water source was controlled by precipitation, which had large seasonal variability. The water sources of N. sibirica had significant responses to the change of precipitation in the two desert habitats. Following the rapid decrease of soil water content after the precipitation events, the plant in the sandy habitat turned to use the abundant ground water as the main sources of water, while the plant in the gravel habitat only used the less water from precipita-tion infiltration to the deep soil. Therefore, different water use strategies of the plant in the two habitats were the main reason for the difference in growth characteristics, and it had a strong ability of self-adjustment and adaptation.
    Water sources of dominant sand-binding plants in dry season in southern Horqin Sandy Land, China
    LIU Bao-qing, LIU Zhi-min, QIAN Jian-qiang, Alamusa, ZHANG Feng-li, PENG Xin-hua
    2017, 28(7):  2093-2101.  doi:10.13287/j.1001-9332.201707.030
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    It’s important to explore the water sources of sand-binding plants and their relationship to reveal the mechanism underling species coexistence and vegetation stability. In the present study, 12 sand-binding species in two typical habitats (fixed dune and dune slack) in southern Horqin Sandy Land were selected. The δD and δ18O values of plant water, rain water, ground water and soil water were determined, and the percentages of soil water at different depths used by plants were calculated with the IsoSource model. Our results showed that the δD and δ18O values of stem water were significantly different among various life forms in both habitats except for those of trees and shrubs in dune slack. From trees to grass, the depth of soil water contributed to main water source of plant became shallower in dune slack: trees and shrubs mainly used soil water in 50-150 cm or 30-50 cm layer, subshrubs mainly used soil water in 10-30 cm layer while grass relied on soil water of 0-10 cm layer. Shrubs mainly used soil water of 0-30 cm layer and subshrubs mainly used soil water around 50 cm at fixed dune. This study indicated that in dry season plants at fixed dune are more dependent on soil water of 0-50 cm layer compared with those in dune slack. The water sources of sand-binding plants are correlated with plant life form and root distribution range, and the later might play a more important role.
    Variations of water use efficiency and its relationship with leaf nutrients of different altitudes of Wuyi Mountains, China
    KONG Ling-lun, LIN Jie, HUANG Zhi-qun, YU Zai-peng, XU Zi-kun, LIANG Yi-fan
    2017, 28(7):  2102-2110.  doi:10.13287/j.1001-9332.201707.008
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    We determined the water use efficiency and nitrogen and phosphorus concentrations of plants at different altitudes (600, 900, 1300, 1500, 1800, 2000, 2100 m) in Wuyi Mountains to understand the relationship of water use efficiency with foliar nutrients. The results showed that plant water use efficiency increased with altitude, and the leaf δ18O of tree showed no significant variance with altitude. On the whole, leaf nitrogen concentration showed no obvious trend, while leaf phosphorus concentration at high altitude was significantly higher than that at low altitude. No significant relationship between water use efficiency and foliar nitrogen concentration was found in this study, but water use efficiency had a positive correlation with foliar phosphorus concentration. In conclusion, the change of water use efficiency was mainly caused by the difference in photosynthetic rate. The effect of water status on plant water use efficiency was not significant. The variances of leaf phosphorus concentrations along the altitudinal gradient may affect photosynthetic rate and in turn the water use efficiency of plant in this area.
    Difference of water relationships of poplar trees in Zhangbei County, Hebei, China based on stable isotope and thermal dissipation method
    MIAO Bo, MENG Ping, ZHANG Jin-song, HE Fang-jie, SUN Shou-jia
    2017, 28(7):  2111-2118.  doi:10.13287/j.1001-9332.201707.037
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    The water sources and transpiration of poplar trees in Zhangbei County were measured using stable hydrogen isotope and thermal dissipation method. The differences in water relationships between dieback and non-dieback poplar trees were analyzed. The results showed that the dieback trees mainly used shallow water from 0-30 cm soil layer during growing season while the non-dieback trees mainly used water from 30-80 cm soil layer. There was a significant difference in water source between them. The non-dieback trees used more water from middle and deep soil layers than that of the dieback trees during the dry season. The percentage of poplar trees using water from 0-30 cm soil layer increased in wet season, and the increase of dieback trees was higher than that of non-dieback trees. The contributions of water from 30-180 cm soil layer of dieback and non-dieback trees both decreased in wet season. The sap flow rate of non-dieback trees was higher than that of dieback trees. There was a similar variation tend of sap flow rate between dieback and non-dieback trees in different weather conditions, but the start time of sap flow of non-dieback trees was earlier than that of dieback trees. Correlation analysis showed that the sap flow rate of either dieback or non-dieback poplar trees strongly related to soil temperature, wind speed, photosynthetically active radiation, relative humidity and air temperature. The sap flow rate of die-back poplar trees strongly negatively related to soil temperature and relative humidity, and strongly positively related to the other factors. The sap flow rate of non-dieback poplar trees only strongly negatively related to relative humidity but positively related to the other factors. The results revealed transpiration of both poplar trees was easily affected by environmental factors. The water consumption of dieback trees was less than non-dieback trees because the cumulative sap flow amount of dieback trees was lower. Reduced transpiration of dieback trees couldn’t help to prevent poplar forest declining due to shallow water source.
    Retrospective analysis of the poplar plantation degradation based on stable carbon isotope of tree rings in Zhangbei County, Hebei, China
    SUN Shou-jia, LI Chun-you, HE Chun-xia, ZHANG Jin-song, MENG Ping
    2017, 28(7):  2119-2127.  doi:10.13287/j.1001-9332.201707.024
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    The Three-North Shelter Forest is an important ecological defense of Beijing-Tianjin-Hebei area. About four-fifths of poplar plantations declined and about a third of them were dying or already dead in the last ten years. The mortality of trees resulted in the decline of ecological function of poplar plantation. In this study, we investigated the differences of δ13C and intrinsic water-use efficiency (WUEi) values in the tree-ring between dieback and non-dieback trees with stable carbon isotope method. The cause of poplar plantation degradation and mortality was retrospectively ana-lyzed. The results showed that the diameter of poplar trees of nearly the same age decreased with the increase of degradation degree. The δ13C value of rings from dieback trees varied between -25.26‰ and -22.97‰, whereas that of non-dieback ones was -26.15‰ to -23.50‰. The δ13C values of dieback trees were higher than that of non-dieback ones from 1997. There was a nonsignificant difference of the WUEi between dieback and non-dieback tree-ring from 1997 to 2001. And the difference of WUEi between dieback and non-dieback tree was significant since 2002. The continuous occurrence of positive ΔWUEi(WUEidieback-WUEinon-dieback) values might be one of important factors for subsequent divergence of the dieback and non-dieback poplar trees. The WUEi of both dieback and non-dieback trees had no significant relationship to precipitation, relative humidity and ET0, while significantly related with air temperature and ground water depth. The retrospective ana-lysis results showed that extreme drought in 1997 was a threshold when poplar trees began to decline. The underground water was overused because of land use change, which increased the intensity and duration of the drought, thus accelerated the degradation and mortality of poplar trees.
    Tree-ring δ13C and water use efficiency of Platycladus orientalis in mountains of Beijing
    LU Wei-wei, YU Xin-xiao, JIA Guo-dong, LI Han-zhi, LIU Zi-qiang
    2017, 28(7):  2128-2134.  doi:10.13287/j.1001-9332.201707.013
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    Water use efficiency (WUE) is different among species and regions. Few literatures have been reviewed related to long-term WUE of Platycladus orientalis in mountainous areas of Beijing, China. Tree-ring δ13C of P. orientalis was used to determine the long-term variation of annual intrinsic water use efficiency (WUEi) and its response to environmental change. Combining with quantification of tree-ring width, the relationship between net carbon sequestration and WUEi of P. orientalis was eventually explored. The results showed that mean annual temperature increased with the increase of time from 1918 to 2013, whereas annual precipitation fiercely fluctuated. Tree-ring δ13C decreased and WUEi increased over time. WUEi was positively related and more sensitive to air temperature increasing than temperature decreasing. Correlation between WUEi and fluctuated annualprecipitation was ambiguous, which indicated the precipitation was not the main factor affecting WUEi. The de-trend tree-ring width of P. orientalis increased initially and then decreased, especially in recent 20 years. According to the correlation between WUEi and environmental factors, temperature resulted in stomatal conductance (gs) decreasing, which caused a reduction in evapotranspiration and an increase in respiratory loss, leading to the increase of WUEi and a down trend in net carbon sequestration and tree growth.
    Water source of typical plants in rocky mountain area of Beijing, China
    LIU Zi-qiang, YU Xin-xiao, JIA Guo-dong, LI Han-zhi, LU Wei-wei
    2017, 28(7):  2135-2142.  doi:10.13287/j.1001-9332.201707.012
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    Water is the key factor limiting plant growth in seasonal arid area. In order to analyze the water sources of community plant (Platycladus orientalis, Vitex negundo var. heterophylla, Broussonetia papyrifera and Lespedeza bicolor) in Beijing mountainous area, we measured hydrogen and oxygen stable isotope ratio (δD and δ18O) values of their xylem water and potential water sources. The results showed the four species had different water sources. P. orientalis mainly absorbed water from 40-60, 60-80 and 80-100 cm soil layers, and the utilization ratio of the three layers was 23.3%-25.9%. It still grabbed water from 0-20 and 20-40 cm soil layers with the utilization ratio of 12.3% and 13.0%, respectively. V. negundo var. heterophylla mainly absorbed 60-80 and 80-100 cm depth soil water, and the utilization rate was 51.9% and 25.2%, respectively, while it barely absorbed water in other soil layers. B. papyrifera mainly absorbed 0-20 and 20-40 cm depth soil water, and the utilization rate was 47.5% and 36.8%, respectively. L. bicolor used the water from five layers, and the utilization ratio of 0-20, 20-40 and 40-60 cm layer was 21.4%-22.8%, and that of 60-80 and 80-100 cm layer was 15.2%-18.3%, respectively. The competition was higher in mixed forest of P. orientalis and L. bicolor because they had similar water sources. It was better to mix V. negundo var. heterophylla and B. papyrifera because their water sources were complementary. The results could provide reference for the best combination of plant species to restore the damaged ecological environment.
    Foliar water use efficiency of Platycladus orientalis of different canopy heights in Beijing western mountains area, China
    ZHANG Yong-e, YU Xin-xiao, CHEN Li-hua, JIA Guo-dong, ZHANG Zhen-yao, SUN Li-bo, ZHANG Jie-ming, HOU Gui-rong
    2017, 28(7):  2143-2148.  doi:10.13287/j.1001-9332.201707.015
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    In this study, we focused on Platycladus orientalis, a widely distributed tree species in Beijing western mountains area, and precisely determined its foliar water use efficiency (including instantaneous water use efficiency derived from gas exchange and short-term water use efficiency obtained on carbon isotope model) by carefully considering the discrepancies of meteorological factors and atmosphere CO2 concentration and δ13C among different canopy heights, hoping to provide theoretical basis for carbon sequestration and water loss in regional forest ecosystem, and offer technical support for regional forest management and maintenance. The results showed that the foliar instan-taneous water use efficiency tended to increase with the increasing canopy height, following the order of the upper canopy > the middle canopy > the lower canopy. A variety of meteorological factors synergistically influenced stomatal movement, and stomatal conductance would in turn have an effect on foliar instantaneous water use efficiency. Foliar short-term water use efficiency also increased with increasing canopy height, following the order of the upper canopy > the middle canopy > the lower canopy. The differences of foliar short-term water use efficiency among different heights could be explained by discrepancies of environmental drivers and atmosphere CO2 concentration and δ13C. Platycladus orientalis leaves in upper canopy adapted to ambient condition by improving water use efficiency.
    Foliar water use efficiency of Platycladus orientalis sapling under different soil water contents
    ZHANG Yong-e, YU Xin-xiao, CHEN Li-hua, JIA Guo-dong, ZHAO Na, LI Han-zhi, CHANG Xiao-min
    2017, 28(7):  2149-2154.  doi:10.13287/j.1001-9332.201707.020
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    The determination of plant foliar water use efficiency will be of great value to improve our understanding about mechanism of plant water consumption and provide important basis of regional forest ecosystem management and maintenance, thus, laboratory controlled experiments were carried out to obtain Platycladus orientalis sapling foliar water use efficiency under five different soil water contents, including instantaneous water use efficiency (WUEgs) derived from gas exchange and short-term water use efficiency (WUEcp) caculated using carbon isotope model. The results showed that, controlled by stomatal conductance (gs), foliar net photosynthesis rate (Pn) and transpiration rate (Tr) increased as soil water content increased, which both reached maximum va-lues at soil water content of 70%-80% field capacity (FC), while WUEgs reached a maximum of 7.26 mmol·m-2·s-1 at the lowest soil water content (35%-45% FC). Both δ13C of water-soluble leaf and twig phloem material achieved maximum values at the lowest soil water content (35%-45% FC). Besides, δ13C values of leaf water-soluble compounds were significantly greater than that of phloem exudates, indicating that there was depletion in 13C in twig phloem compared with leaf water-soluble compounds and no obvious fractionation in the process of water-soluble material transportation from leaf to twig. Foliar WUEcp also reached a maximum of 7.26 mmol·m-2·s-1 at the lowest soil water content (35%-45% FC). There was some difference between foliar WUEgs and WUEcp under the same condition, and the average difference was 0.52 mmol·m-2·s-1. The WUEgs had great space-time variability, by contrast, WUEcp was more representative. It was concluded that P. orientalis sapling adapted to drought condition by increasing water use efficiency and decreasing physiological activity.
    Response of water sources in Platycladus orientalis and Vitex negundo var heterophylla system to precipitation events in mountain area of Beijing, China
    ZHAO Na, MENG Ping, HE Ya-bing, LOU Yuan-hai, YU Xin-xiao
    2017, 28(7):  2155-2163.  doi:10.13287/j.1001-9332.201707.011
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    This study aimed to qualify the potential water sources and their responses to seasonal precipitations for the system of Platycladus orientalis and Vitex negundo var. heterophylla by IsoSource model based on stable hydrogen and oxygen isotopic analysis in Jiufeng Mountain area of Beijing. The results showed that the 18O of water from 0-20 cm soil layer was enriched, whereas that was depleted as the soil layer deepened. P. orientalis used water mainly from 0-30 cm soil la-yer, being composed of rainwater 2-3 days before at the beginning of dry season. The water absorbed by P. orientalis and V. negundo sourced from 0-10 cm and 10-30 cm soil layer, which was fed on recent rainwater at the end of dry season. In wet season P. orientalis mainly accessed the soil water (from 0-40 cm layer, 59.3%) and recent rainwater (12.5%), while V. negundo drank the water from 0-30 cm soil layer derived from recent heavy rain. P. orientalis actively uptook the deeper soil water with time, until the end of growing season (November), its available water was from 60-80 cm soil layer and sourced from the rainwater happened 2-3 days before. Meanwhile, V. negundo completed its growing cycle and was on the brink of death. This system faced less competition for water use, stating its vertical water availability for climate adaptation in this region, which could reduce water and soil loss and minimize the instantaneous damage under heavy rainstorm attack.
    Variations and determinants of CO2 concentration and δ13C in Platycladus orientalis plantation in Beijing mountainous area, China
    LI Han-zhi, YU Xin-xiao, JIA Guo-dong, ZHAO Na, LIU Zi-qiang, LU Wei-wei, ZHANG Yong-e
    2017, 28(7):  2164-2170.  doi:10.13287/j.1001-9332.201707.014
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    This research employed off-axis integrated cavity output spectroscopy technique to observe CO2 concentration and δ13C values of planted Platycladus orientalis in Beijing mountainous area. We compared the variation between CO2 concentration and δ13C values in the plantation at different heights observed by every 0.5 h to explore how the CO2 concentration and δ13C values responded to the meteorological factors. The results showed that the CO2 concentration showed the pattern of “first decreased and then increased” after sunrise. The lowest value (352.5 μmol·mol-1) appeared at 16:00-16:30, while the maximum value (402.0 μmol·mol-1) was observed at about 5:00. However, the change of δ13C value was not significant and regular, which increased firstly and then decreased in the surface layer while opposite for the canopy. Atmospheric CO2 concentration decreased with the increasing height. In the height of 0, 2, 5, 8, 12.5 and 18 m, the average daily value was 386.5, 369.9, 368.2, 367.8, 367.9 and 367.9 μmol·mol-1, respectively. In contrast, the δ13C values tended to rise correspondingly with height with the average daily value being -16.0‰, -13.7‰, -13.5‰, -13.5‰, -13.1‰ and -13.3% at 0, 2, 5, 8, 12.5 and 18 m, respectively. The stepwise regression analysis showed that temperature and humidity were the main factors for the changes of atmospheric CO2 concentration and δ13C values. The saturated vapor pressure difference (VPD) affected the concentration of CO2 in the forest and wind speed could affect it on the canopy. However, soil moisture, soil electric conductivity and net solar radiation affected the CO2 concentration and δ13C values in surface layer. All these environmental factors influenced CO2 concentration and δ13C values through their influences on the photosynthesis and respiration.
    Stable hydrogen and oxygen isotope compositions in soil-plant-atmosphere continuum (SPAC) in rocky mountain area of Beijing, China
    DENG Wen-ping, ZHANG Jie, ZHANG Zhi-jian, HU Shao-chang, GUO Jin-rong, LIU Yuan-qiu, KONG Fan-qian, ZHANG Yi
    2017, 28(7):  2171-2178.  doi:10.13287/j.1001-9332.201707.018
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    The stable hydrogen and oxygen isotopes are environmental isotopes, which widely exist in various kinds of water. Their relative abundance variation in water can indicate the water circulation and mechanism of water use in plant. This research selected two major kinds of greening tree species, evergreen coniferous Platycladus orientalis and deciduous broad-leaved Quercus variabilis, in Beijing mountainous area, and the water movement process in soil-plant-atmosphere continuum was investigated by the variation characteristics analysis of stable hydrogen and oxygen isotope compositions in precipitation, soil water, groundwater, plant stem water and leaf water. The results showed that the meteoric water line equation of the study area was δD=7.17δ18O+1.45 (R2=0.93), and the soil evaporation line equation was δD=3.85δ18O+1.45 (R2=0.76). A certain degree of evaporation fractionation existed in the processes of rainfall infiltration into soil water. In different seasons, the δD and δ18O values of precipitation, soil water and spring water had different variation regularity. In rainy season, the mean δD and δ18O values were in order of precipitation> spring water>soil water, with the precipitation and soil water supplied spring water together; in dry season, the order was precipitation > soil water > spring water, and the precipitation and spring water both contributed to soil water. The δD and δ18O fitting line equations of stem water of P. orienta-lis and Q. variabilis were respectively δD=5.03δ18O-30.78 and δD=3.0δ18O-48.92. The uptake water of Q. variabilis was more enriched than that of P. orientalis, and the depth of Q. variabilis water uptake in soil profile was shallower than P. orientalis. The leaf water isotopic variation of Q. varia-bilis was more sensitive to atmospheric environment, with the kinetic isotopic fractionation of Q. variabilis being more enriched than that of P. orientalis, but they had the same response to variation of environmental condition.
    Responses of the natural abundance of carbon and nitrogen isotopes of Quercus mongolica leaf and soil to elevated CO2
    SUN Jian-fei, DAI Wei-wei, HE Tong-xin, PENG Bo, JIANG Ping, HAN Shi-jie, BAI E
    2017, 28(7):  2179-2185.  doi:10.13287/j.1001-9332.201707.039
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    The rising atmospheric CO2 concentration significantly changed soil nitrogen (N) cycling which is important for us to predict the carbon (C) sequestration potential of terrestrial ecosystems. The natural abundance of N isotope as an integrative indicator of ecosystem N cycling processes can effectively indicate the effect of elevated CO2 on soil N cycling processes. Here, we used an open top chamber experiment to examine the effects of elevated CO2for ten years on the natural abundance of Quercus mongolica, soil and microbial biomass C and N isotopes in northeastern China. Our results showed that elevated CO2 significantly changed soil N cycling processes, resulting in the increase of microbial and leaf δ15N; stimulated the decomposition of 13C-enriched soil organic C, and offset the effect of more 13C-depleted plant photosynthetic C inputs, resulting in unchanged δ13C of soil dissolved organic C and microbes under elevated CO2. These results indicated that elevated CO2 likely increased the mineralization of soil organic matter, and the system is getting more N-limited.
    Hydrological characteristics of calcareous soil with contrasting architecture on dolomite slope of Northwest Guangxi
    ZHANG Xing, WANG Ke-lin, FU Zhi-yong, CHEN Hong-song, ZHANG Wei, SHI Zhi-hua
    2017, 28(7):  2186-2196.  doi:10.13287/j.1001-9332.201707.028
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    The traditional hydrology method, stable hydrogen and oxygen isotope technology, and rainfall simulation method were combined to investigate the hydrological function of small experimental plots (2 m×1.2 m) of contrasting architecture in Northwest Guangxi dolomite area. There were four typical catenary soils along the dolomite peak-cluster slope, which were the whole-sand, up-loam and down-sand, the whole loam, up-clay and down-sand soil types, respectively. All the experimental plots generated little amounts of overland runoff and had a high surface infiltration rate, ranging from 41 to 48 mm·h-1, and the interflow and deep percolation were the dominant hydrological progress. The interflow was classified into interflow in soil clay A and C according to soil genetic layers. For interflow in soil clay A, matrix flow was generated from the whole-sand, up-loam and down-sand, up-clay and down-sand soil types, but preferential flow dominated in the whole-loam soil type. As for interflow in soil clay C, preferential flow dominated in the whole-loam, up-clay and down-sand, up-loam and down-sand soil types. The soils were shallow yet continuously distributed along the dolomite slope. The difference of hydrological characteristics in soil types with different architectures mainly existed in the runoff generation progress of each interface underground. It proved that the a 3-D perspective was needed to study the soil hydrological functions on dolomite slope of Northwest Guangxi, and a new way paying more attention on underground hydrological progress should be explored to fully reveal the near-surface hydrological processes on karst slope.
    Runoff and nitrogen loss characteristics in soil-epikarst system on a karst shrub hillslope
    ZHU Xiao-feng, CHEN Hong-song, FU Zhi-yong, WANG Ke-lin, ZHANG Wei, XU Qin-xue, FANG Rong-jie
    2017, 28(7):  2197-2206.  doi:10.13287/j.1001-9332.201707.029
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    With the development of the binary structure of karst landforms, surface water is largely drained with rapid loss of nutrients. However, the pathway and mechanism of nutrient loss remain elusive. From a three-dimensional (vegetation-soil-epikarst system) perspective of a critical zone in karst area, this study conducted rainfall induced runoff and nitrogen loss monitoring during monsoon in karst shrub slopes. Isotope-based (D and 18O) hydrograph separation method was applied to partition the ratio of ‘old’ and ‘new’ water in main hydrological path. The main results were summarized as follows. Deep percolation and interflow were the dominant hydrological pathways, accoun-ting for 71% and 9% of total rainfall amount, respectively. In contrast, surface runoff occupied less than 2%. Both deep percolation and interflow were dominated with 85% and 61% of old water, respectively. The highest nitrate concentration occurred in deep percolation (1.97 mg·L-1), while the highest ammonium nitrogen concentration occurred in interflow (1.18 mg·L-1). Deep percolation contributed 89.4% of total nitrogen loss, which was significantly higher than that of surface runoff and interflow. Old water ratio showed a significant positive correlation with nitrate nitrogen concentration, ammonium nitrogen concentration, and total nitrogen loss, suggesting it might be the main agent driving nitrogen migration for the whole soil-epikarst system in karst hillslopes. The results would provide scientific basis for rational allocating water resources and developing nutrient loss control technology in karst region of southwestern China.
    Deuterium isotope characteristics of precipitation infiltrated in the West Ordos Desert of Inner Mongolia, China
    CHEN Jie, XU Qing, GAO De-qiang, MA Ying-bin, ZHANG Bei-bei, HAO Yu-guang
    2017, 28(7):  2207-2214.  doi:10.13287/j.1001-9332.201707.003
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    Understanding the soil-profile temporal and spatial distribution of rainwater in arid and semiarid regions provides a scientific basis for the restoration and maintenance of degraded desert ecosystems in the West Ordos Desert of Inner Mongolia, China. In this study, the deuterium isotope (δD) value of rainwater, soil water, and groundwater were examined in the West Ordos Desert. The contribution of precipitation to soil water in each layer of the soil profile was calculated with two-end linear mixed model. In addition, the temporal and spatial distribution of δD of soil water in the soil profile was analyzed under different-intensity precipitation. The results showed that small rainfall events (0-10 mm) affected the soil moisture and the δD value of soil water in surface soil (0-10 cm). About 30.3% to 87.9% of rainwater was kept in surface soil for nine days following the rainfall event. Medium rainfall events (10-20 mm) influenced the soil moisture and the δD value of soil water at soil depth of 0-40 cm. About 28.2% to 80.8% of rainwater was kept in soil layer of 0-40 cm for nine days following the medium rainfall event. Large (20-30 mm) and extremely large (>30 mm) rainfall events considerably influenced the soil moisture and δD value of soil water in each of the soil layers, except for the 100-150 cm layer. The δD value of soil water was between those δD values of rainwater and groundwater, which suggested that precipitation and groundwater were the sources of soil water in the West Ordos Desert. Under the same intensity rainfall, the δD value of surface soil water (0-10 cm) was directly affected by δD of rainwater. With increasing soil depth, the variation of soil water δD decreased, and the soil water of 100-150 cm kept stable. With increasing intensity of precipitation, the influence of precipitation on soil water δD lasted for a longer duration and occurred at a deeper soil depth.
    Spatial variation of soil carbon and stable isotopes in the southern margin desert of Junggar Basin, China
    WANG Na, XU Wen-qiang, XU Hua-jun, FENG Yi-xing, LI Chao-fan
    2017, 28(7):  2215-2221.  doi:10.13287/j.1001-9332.201707.002
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    The southern margin desert of Junggar Basin in the central arid region of Asia was selec-ted as the study area. To gain insight into the distribution characteristic of stable carbon isotope and the relationship between the change of soil carbon and the distance to oasis of soil organic carbon (SOC) and soil inorganic carbon (SIC), three belt transects were set according to the distance between the desert and the oasis in edge, middle and hinterland of the desert respectively, and collected the soil profile samples with depth of 2 m. The results indicated that the SOC content reduced with the soil depth, and the variation with the distance to oasis was the edge> the middle> the hinterland. The δ13C value of SOC varied in the range of -21.92‰ to -17.41‰, and decreased with the depth; the range in the middle and hinterland was -25.20‰ to -19.30‰, and increased then declined with the depth. Therefore, we could infer that the C3 plants played a dominant role in the central of desert, and had experienced the succession from C3 plants to C4 plants. The average content of SIC was 38.98 g·kg-1 in the edge of desert, which was about 6.01 folds as large as the content in the hinterland. This indicated that a large number of SIC with 0-2 m depth were clustered in the edge of the desert. The δ13C value of SIC increased first then decreased with the soil depth, and enriched in the bottom layer, which was mainly affected by the original carbonate content and soil carbon dioxide.
    Effects of clipping on nitrogen allocation strategy and compensatory growth of Leymus chinensis under saline-alkali conditions
    ZHENG Cong-cong, WANG Yong-jing, SUN Hao, WANG Xin-yu, GAO Ying-zhi
    2017, 28(7):  2222-2230.  doi:10.13287/j.1001-9332.201707.040
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    Soil salinization and overgrazing are two main factors limiting animal husbandry in the Songnen Grassland. Leymus chinensis is a dominant rhizome grass, resistant to grazing as well as to-lerant to salt stress. Foliar labeled with 15N-urea was used to study the nitrogen allocation strategy and compensatory growth response to clipping under saline-alkali conditions. The results showed that the total absorbed 15N allocated to the aboveground part was more than 60%. Compared with the control treatment (no saline-alkali, no clipping), saline-alkali increased the distribution of 15N by 5.1% in root; the 15N distribution into aboveground in the moderate clipping and saline-alkali treatment was 11.6% higher than that of the control, exhibiting over-compensatory growth of aboveground biomass and total biomass, however, 15N allocated to stem base was significantly increased by 9.5% under severe clipping level and saline-alkali addition, showing under-compensatory growth of shoot, root and total biomass. These results suggested that L. chinensis adapted to mode-rate clipping by over-compensatory growth under salt-alkali stress condition. However, L. chinensis would take a relatively conservative growth strategy through the enhanced N allocation to stem base for storage under severe saline-alkali and clipping conditions.
    Composition and distribution characteristics of stable carbon isotope in typical riparian grassland ecosystem
    WU Jian, SHA Chen-yan, WANG Min, WU Jian-qiang, TAN Juan, QI Xiao-bao, HUANG Shen-fa
    2017, 28(7):  2231-2238.  doi:10.13287/j.1001-9332.201707.004
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    Plant-soil carbon stable isotope characteristics of riparian herbaceous ecosystem were ana-lyzed by measuring the δ13C value of plant tissues from four typical riparian herbaceous plants, which were Cynodon dactylon, Trifolium repens, Festuca arundinacea and Imperata cylindrical, and that of soil organic carbon (SOC) from different vertical depths along Dongfeng Port River in Qingpu District, Shanghai. The result showed that T. repens and F. arundinacea were C3 plants while C. dactylon and I. cylindrical were C4 plants. There was no significant difference between the δ13C va-lue of stem and leaf, litter and root of the four herbaceous plants. The surface SOC δ13C value of C3 and C4 plants strips showed different trends with soil depth, which could be related to the background SOC δ13C value, soil carbon stable isotope fractionation effect and plant root distribution depth as well. Plant input was the main source of SOC and the δ13C composition of plant organisms had direct effect on the SOC δ13C value. The δ13C value of plant components were significantly correlated with the δ13C value of SOC. The SOC content and δ13C value were significantly correlated in the four herbaceous plants strips. The SOC content and δ13C value showed linear negative correlation in C3 plant strips and linear positive correlation in C4 plant strips.
    Effects of nitrogen-supply levels on leaf senescence and characteristics of distribution and utilization of 13C and 15N in Fuji 3 apple grafted on different stocks
    CHEN Qian, DING Ning, ZHU Zhan-ling, PENG Ling, GE Shun-feng, JIANG Yuan-mao
    2017, 28(7):  2239-2246.  doi:10.13287/j.1001-9332.201707.005
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    Two-year-old potted Fuji 3 apple trees on different rootstocks [Fuji 3/M. micromalus Makin (joe), Fuji 3/M7 (semi-dwarf) and Fuji 3/M26/M. micromalus Makin (dwarf)] were used to study leaf morphology and photosynthesis and the characteristics of distribution and utilization of 13C and 15N at different nitrogen supply levels (0N, 25%N and 100%N, the N content in 100% N treatment was the same as that in Hoagland complete nutrient solution) under sand culture condition. The main results were as follows: At shoot growth cessation stage in autumn, the leaf chlorophyll content (SPAD), leaf nitrogen content and photosynthetic rate were found the highest in Fuji 3/M. micromalus Makin, followed by Fuji 3/M7, and the lowest was found in Fuji 3/M26/M. micromalus Makin under the same nitrogen stress treatments (0N and 25%N), however, under normal nitrogen treatment (100%N) Fuji 3/M26/M. micromalus Makin had the highest leaf SPAD value, photosynthetic rate and the nitrogen content, followed by Fuji 3/M7, and the lowest was found in Fuji 3/M. micromalus Makin. The leaf SOD and CAT activities showed Fuji 3/M. micromalus Makin > Fuji 3/M7 > Fuji 3/M26/M. micromalus Makin under the same nitrogen stress treatments, but showed Fuji 3/M26/M. micromalus Makin > Fuji 3/M7 > Fuji 3/M. micromalus Makin under the normal nitrogen treatment. There were significant differences in the distributions of 15N and 13C in root and leaf in the 3 scion-stock combinations, and the distribution rates of 15N and 13C in roots were the highest under nitrogen stress treatments and in the order of Fuji 3/M. micromalus Makin > Fuji 3/M7 > Fuji 3/M26/M. micromalus Makin. The distribution rates of 15N and 13C in leaves were the highest under the normal nitrogen treatment and in the order of Fuji 3/M26/M. micromalus Makin > Fuji 3/M7 > Fuji 3/M. micromalus Makin. The 15N utilization ratio differed significantly among the 3 scion-stock combinations under different nitrogen application levels and was in the order of Fuji 3/M. micromalus Makin (44.3%, 37.5% and 31.4%)> Fuji 3/M7 (38.8%,30.7% and 26.6%) > Fuji 3/M26/M. micromalus Makin (32.0%,27.2% and 22.5%).
    Effects of different nitrogen application rates on 15N-urea absorption, utilization, loss and fruit yield and quality of dwarf apple
    CHEN Qian, DING Ning, PENG Ling, GE Shun-feng, JIANG Yuan-mao
    2017, 28(7):  2247-2253.  doi:10.13287/j.1001-9332.201707.001
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    Seven-year-old ‘Yanfu3’/M26/M. hupehensis Rehd. seedlings and 15N trace technique were used to explore the characteristics of 15N-urea absorption, utilization, loss and fruit yield and quality under different nitrogen application rates (N100, N200 and N300). The main results were as follows: the plant growth, 15N absorption, utilization and loss differed significantly under different treatments. The plant leaf chlorophyll content (SPAD value), photosynthetic rate (Pn), total N content of leaves and the biomass, as well as the root-shoot ratio of N200 treatment were obviously higher than the N100 and N300 treatments. Significant differences were observed in the 15N derived from fertilizer (Ndff value) of different organs under different nitrogen application rates. The Ndff of fruits (flowers), leaves, one-year-old branch, and perennial branches in each measurement period was N100 >N200>N300, while that of the roots at full-bloom and spring shoot growing slowly stage was N100 >N200>N300, and in a trend of N200 >N100>N300 at autumn shoot growing stage, fruit rapid-swel-ling stage and fruit maturity stage. At fruit maturity stage, plant 15N nitrogen utilization ratio of N200 treatment was 23.6%, which was obviously higher than the N100 (16.3%) and N300 (14.4%) treatments, with the 15N loss rate of 56.4%, obviously lower than the N100 (60.6%) and N300 (66.1%) treatments. There were significant differences among the treatments in fruit mass, yield per plant, soluble solid, fruit firmness, soluble sugar, titratable acids and sugar-acid ratio of different nitrogen rates, and the N200 treatment showed the best performance, followed by the N300 treatment, and then the N100 treatment.
    Effects of different potassium levels on growth and NO3- uptake and utilization of Malus hupehensis seedlings
    TIAN Ge, WANG Fen, PENG Ling, HE Liu, JIANG Yuan-mao, GE Shun-feng
    2017, 28(7):  2254-2260.  doi:10.13287/j.1001-9332.201707.009
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    In order to explore the effects of potassium fertilizer on the absorption and utilization of nitrogen fertilizer, and provide theoretical basis for scientific fertilization in apple orchard, Malus hupehensis seedlings were used to study the effects of different potassium levels (K0, K1, K2, K3, K4, K5, and K6 equivalent to 0, 2, 4, 6, 8, 10, and 12 mmol·L-1 K+, respectively) on growth and NO3- uptake and utilization using the track technology of 15N and non-damage microtest technique. The results showed that root vigor, nitrate reductase activity and root morphological index of seedlings in K3 treatment were significantly higher than those in the other treatments. The 15N derived from fertilizer (Ndff) in different organs of M. hupehensis seedlings was significantly different among treatments, and the Ndff values of root, stem and leaf appeared in K3 treatment were the highest, being 1.36, 1.33 and 1.47 times as those of the K0 treatment, respectively. With the increase of potassium application rate, the 15N utilization rate of seedlings were firstly increased and then decreased, and reached the highest value (23.3%) in K3 treatment, which was 3.04 times as that of K0 treatment. The results of non-damage microtest technique showed that there was a strong absorption of NO3- in K3 treatment (19.34 pmol·cm-2·s-1), while a clear trend of outflow was observed in the potassium deficiency (K0) and high potassium (K6) treatments. Therefore, the deficit or excess of potassium could inhibit the uptake and utilization of nitrogen, while appropriate potassium could promote root growth, enhance the activity of nitrate reductase, and then increase the absorption of nitrogen by seedlings.
    Effects of nitrogen application on decomposition and nutrient release of returned maize straw in Guanzhong Plain, Northwest China
    HUANG Ting-miao, WANG Zhao-hui, HOU Yang-yi, GU Chi-ming, LI Xiao, ZHENG Xian-feng
    2017, 28(7):  2261-2268.  doi:10.13287/j.1001-9332.201707.010
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    With 15N isotope labeled maize straw in nylon net bags and buried in the wheat field at two N rates of 0 and 200 kg N·hm-2, the effects of nitrogen application on the decomposition of straw dry matter and the release dynamics of carbon, nitrogen, phosphorus and potassium (C, N, P and K) after maize straw retention were investigated in the winter wheat-summer maize rotation system in Guanzhong Plain, Shaanxi, China. Results showed that N application did not affect the decomposition of the returned straw C and dry matter, but promoted the release of P and inhibited the release of N and K from straw during sowing to wintering periods of winter wheat. From the grain filling to the harvest of winter wheat, the decomposition of the returned straw and the release of N, P and K were not affected, but the release of straw C was significantly enhanced by N application. The release dynamic of straw C was synchronized with the decomposition of the dry matter, and the C/N of straw declined gradually with the extension of wheat growing. Until the harvest of winter wheat, the accumulative decomposition rate of straw dry matter was less than 50%, and the total straw C release rate was around 47.9% to 51.1%. The C/N ratio of the returned straw was decreased from 32.2 to 20.2 and 17.9, respectively at N rates of 0 and 200 kg N·hm-2. From sowing to harvest of winter wheat, the net release of N, P and K from the straw was observed. The N release was 7.2-9.4 kg·hm-2 and 12.7%-16.6% of the total straw N, and the P release was 1.29-1.44 kg·hm-2 and 29.0%-32.4% of the total straw P, while a great deal of K was released quickly, with approximately 80% of the straw K released before wintering, 51.8-52.5 kg·hm-2 and 90.5%-91.7% of the total straw K released at wheat harvest. It was suggested that the K fertilizer application should be decreased for the winter wheat due to the great amount K release from the returned maize straw, and an extra amount of N and P fertilizer should be applied under the straw retention cropping system.
    Effects of soil water condition on N2O emission and its sources in vegetable farmland of North China Plain
    DING Jun-jun, ZHANG Wei, LI Yu-zhong, LIN Wei, XU Chun-ying, LI Qiao-zhen
    2017, 28(7):  2269-2276.  doi:10.13287/j.1001-9332.201707.026
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    To understand the mechanisms of agricultural N2O emission, we investigated the N2O emission dynamics, the N2O isotope signatures, and the site preference value under different soil water conditions in the vegetable farmland of North China, by using the stable isotope technique and the acetylene inhibition method. The results demonstrated that N2O emission was significantly affec-ted by the water condition, and N2O emissions from soil with water-filled pore space (WFPS) of 70% were significantly higher than that with 50% WFPS. N2O emission occurred mostly in the early stage of fertilization, and decreased rapidly in the later stage of fertilization. At 50% WFPS, nitrification was the major process generating N2O during the early fertilization stage, accounting for approximately 90% of the N2O emission. However, the contribution of nitrification decreased sharply, whereas denitrification became the dominant process, accounting for 80% of the N2O emission 7 days after the fertilization. On the other hand, at 70% WFPS, denitrification was the main process releasing N2O during the early fertilization stage, decreasing from 70% to 40% and then gradually increasing to 80% 10 days after the fertilization. Overall, N2O emission was mainly dominated by the denitrification. The effect of different water treatments on soil nitrification and denitrification took place mainly in the early stage of fertilization, and N2O emission was gradually dominated by the denitrification at the later stage. These results suggested we could reduce N2O emission by approp-riately reducing the amount of irrigation in the vegetable farmland of North China.
    Effects of soil pH on the competitive uptake of amino acids by maize and microorganisms
    MA Qing-xu, WANG Jun, CAO Xiao-chuang, SUN Yan, SUN Tao, WU Liang-huan
    2017, 28(7):  2277-2384.  doi:10.13287/j.1001-9332.201707.033
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    Organic nitrogen can play an important role in plant growth, and soil pH changed greatly due to the over-use of chemical fertilizers, but the effects of soil pH on the competitive uptake of amino acids by plants and rhizosphere microorganisms are lack of detailed research. To study the effects of soil pH on the uptake of amino acids by maize and soil microorganisms, two soils from Hangzhou and Tieling were selected, and the soil pH was changed by the electrokinesis, then the 15N-labeled glycine was injected to the centrifuge tube with a short-term uptake of 4 h. Soil pH had a significant effect on the shoot and root biomass, and the optimal pH for maize shoot growth was 6.48 for Hangzhou red soil, while it was 7.65 for Tieling brown soil. For Hangzhou soil, the 15N abundance of maize shoots under pH=6.48 was significantly higher than under other treatments, and the uptake amount of 15N-glycine was also much higher. However, the 15N abundance of maize shoots and roots under pH=7.65 Tieling soil was significantly lower than it under pH=5.78, but the uptake amount of 15N-glycine under pH=7.65 was much higher. The microbial biomass C was much higher in pH=6.48 Hangzhou soil, while it was much lower in pH=7.65 Tieling soil. According to the results of root uptake, root to shoot transportation, and the competition with microorganisms, we suggested that although facing the fierce competition with microorganisms, the maize grown in pH=6.48 Hangzhou soil increased the uptake of glycine by increasing its root uptake and root to shoot transportation. While in pH=7.65 Tieling soil, the activity of microorganisms was decreased, which decreased the competition with maize for glycine, and increased the uptake of glycine by maize.
    Contribution of soil water at various depths to water consumption of rainfed winter wheat in the Loess tableland, China
    CHENG Li-ping, LIU Wen-zhao
    2017, 28(7):  2285-2291.  doi:10.13287/j.1001-9332.201707.007
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    Soil water and stem water were collected in jointing and heading stages of the rainfed winter wheat in the Changwu Loess tableland, and the stable isotopic compositions of hydrogen and oxygen in water samples were measured to analyze the contribution of soil water at various depths to water consumption of winter wheat. The results showed that the isotopes were enriched in soil and wheat stem water in comparison with that in precipitation. Under the condition of no dry layer in soil profile, the contributions to wheat water consumption in jointing and heading stages were 5.4% and 2.6% from soil water at 0-30 cm depth, 73.4% and 67.3% at 60-90 cm depth (the main water source for winter wheat), and 7.9% and 13.5% below 120 cm depth, respectively. With the wheat growth, the contribution of soil water below the depth of 90 cm increased. It was concluded that soil evaporation mainly consumed soil water in 0-30 cm depth and wheat transpiration mainly consumed soil water below 60 cm depth in the experimental period. In the production practice, it is necessary to increase rainwater storage ratio during the summer fallow period, and apply reasonable combination of nitrogen and phosphorus fertilizers in order to increase soil moisture before wheat sowing, promote the wheat root developing deep downwards and raise the deep soil water utilization ratio.
    Food web foundation and seasonal variation of trophic structure based on the stable isotopic technique in the marine ranching of Haizhou Bay, China
    XIE Bin, LI Yun-kai, ZHANG Hu, ZHANG Shuo
    2017, 28(7):  2292-2298.  doi:10.13287/j.1001-9332.201707.019
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    Stable isotope technique was applied to investigate the small and medium-size consumers including not only fish, shrimps, crabs, cephalopods, snails and bivalves, but also the specimens of their potential carbon sources, which were collected in the marine ranching area of Haizhou Bay during the spring of 2015. IsoSource model was adopted to calculate the contribution of potential carbon sources to the consumers. Biospeciemens collected in the summer of 2014 were compared with those in the spring of 2015, aiming to analyze the seasonal variation in the trophic structure of food web. Six quantitative community indices were calculated based on the isotope values of the organisms in Haizhou Bay. The results showed that the δ13C values of consumers ranged from -18.9‰ to -17.1‰, and the δ13C values of three potential food sources ranged from -18.1‰ to -23.4‰ in the spring of 2015. The calculation results of IsoSource model further demonstrated that the phytoplankton was the most important carbon source for consumers (80.8%), followed by sediment organic matter (10.8%) and particulate organic matter (8.4%). There was a significant difference in the δ13C values between the biospecimens in the summer of 2014 and those in the spring of 2015, while no significant difference was observed in δ15N values. Trophic structure of community-wide differed remarkably in different seasons indicated by the six quantitative community indices. The δ13C range, total area, mean nearest neighbor distance and standard deviation of nearest neighbor distance of the community were much higher in 2014 than those in 2015, but the δ15N range and mean distance to centroid showed no significant change. The trophic structure redundancy was lower in the summer of 2014 compared with that in the spring of 2015, however, the diversity of food resources was higher in the summer of 2014.
    Impacts of dominated landscape types on hydrogen and oxygen isotope effects of spring water in the Hani Rice Terraces
    JIAO Yuan-mei, LIU Cheng-jing, LIU Xin, LIU Zhi-lin, DING Yin-ping
    2017, 28(7):  2299-2306.  doi:10.13287/j.1001-9332.201707.022
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    Analysis of hydrogen and oxygen stable isotopes is an effective method to track the water cycle in watershed. Impact of landscape pattern on the isotope effects of spring water is a new interdisciplinary topic between landscape ecology and isotope hydrology. Taking the Quanfuzhuang River basin located in the core area of UNESCO World Cultural Heritage of Honghe Hani Rice Terrace as the object, collecting the monthly samples of 78 points of spring water and 39 precipitation at altitude of 1500 m (terraces), 1700 m (terraces) and 1900 m (forest) from March 2015 to March 2016, we analyzed the hydrogen and oxygen stable isotopes of water samples under the different landscape types. The results indicated that the dominated landscape types were forests and rice terraces, being 66.6% and 22.1% of the whole landscape area respectively, and they had a spatial vertical pattern of forest located at the mountain top and rice terraces at the down-slope. The correlation analysis showed that the spring water not only came from the precipitation, but also from other water sources which had a more positive δ18O and δD values, the spring water in up-slope forests mainly came from precipitation, while that in down-slope rice terraces came from precipitation, ri-ver water, rice terrace water and under ground water. Therefore, the mixing effects of spring water δ18O and δD were more significant in rice terraces. The overall altitude effect of the hydrogen and oxygen stable isotopes in spring water was obvious. The linear decreasing rates of δ18O and δD values were -0.125‰·(100 m)-1and -0.688‰·(100 m)-1, respectively. The deuterium surplus value increased with the altitude because of the impacts of landscape pattern and the local cycle of water isotopes. In summary, the dominant landscape types had a significant impact on the hydrogen and oxygen isotopes of spring water, which could be used as response indicator to reveal the impacts of landscape pattern on hydrological process.
    Identification of the critical coastal conservation areas with ecological significance based on Pb stable isotope signatures analysis
    QIAN Qing-teng, LI Cheng-wei, ZHAO Meng, FANG Shu-bo
    2017, 28(7):  2307-2314.  doi:10.13287/j.1001-9332.201707.032
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    Pb stable isotope signatures analysis can be used to identify its sources precisely and the spatial transportation process to achieve precise management of target areas. In this study, 12 surface (0-10 cm) soil samples (3-5 replications for each site) were collected on the Yancheng coast. Pb isotopes (206Pb, 207Pb and 208Pb) and Pb contents were analyzed by inductively coupled plasma mass spectrometry. Results showed that the soil Pb contents were as high as 1.7 times of the background Pb content value. Referencing the national criteria of GB 15618-2008, the study area was polluted by Pb to a relatively serious extent. The analysis indicated that main Pb sources of the area were local, including Sheyang Power Plant, Shuangdeng Paper Mill Sewage Plant, and Huafeng industrial area near Wanggang. Based on the normalized difference vegetation index (NDVI) and distance analysis, we figured out the key patterns of Yancheng coast to cope with the press sources.
    Characterization of trophic position of red-crowned crane (Grus japonensis) influenced by the food resource exhausting
    LUO Jin-ming, WANG Yong-jie, WANG Wen-feng, GAO Zhong-yan
    2017, 28(7):  2315-2320.  doi:10.13287/j.1001-9332.201707.038
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    The trophic relations of the red-crowned crane species in Zhalong Wetland, northeastern China may change significantly withrapid decrease of biological resources. In this paper, the influence of food resource exhausting on the trophic levels of this vulnerable species was determined by using stable isotope (δ13C and δ15N) methods. The results indicated that the mass of δ13C and 15N in the red-crowned cranes were in the range of -17.8‰ to -18.5‰ and 6.9‰ to 8.1‰, respectively. The dominant food chain length of large water fowls in the ecosystem of Zhalong Wetland was 3.8±0.2 in average, of which the examined species, i.e., red-crowned cranes were 3.1 in average, with the range of 2.9 to 3.3. The annual fluctuation range of δ15N values in the red-crowned cranes was from 7.4‰ to 8.8‰ (with the gap of approximately 1.4, which was below the threshold 3.4 that was considered as a trophic level significant change in an ecosystem), indicating the trophic level of this vulnerable species did not change significantly with the losses of large area of their habitats and foods. Nevertheless, the rapid decrease of the target species population with the food resource exhausting indicated that the conflict of food demand of the red-crowned cranes versus resource need of local residents should be resolved for better protecting this extinguishable species.
    Feeding habits of the marbled rockfish Sebastiscus marmoratus in the marine ranching off Ma’an Archipelago, China
    WANG Kai, LI Chao-wen, WANG Zhen-hua, ZHAO Jing, ZHANG Shou-yu
    2017, 28(7):  2321-2326.  doi:10.13287/j.1001-9332.201707.035
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    Marine ranching is considered as an efficient tool to protect and restore the coastal fishe-ries resource. In order to assess the ecological impacts of the construction of marine ranching on rocky fishes, the feeding habits of Sebastiscus marmoratus collected at the marine ranching area off Ma’an Archipelago were studied using stomach contents analyses and stable isotope analyses. Results showed that S. marmoratus mainly preyed on amphipoda, crabs and cephalopods before the construction of marine ranching. The dominant prey species were Caprella sp., Loligo japonica, Charybdis japonica, Petrolisthes japonicas and Amphiura vadicola. Proportion of crabs in the diet of S. marmoratus increased with the increase of fish size, whereas the proportion of amphipoda decreased. After the construction of marine ranching, S. marmoratus fed mainly on crabs, amphipoda, and fishes. The dominant prey species were C. bimaculata, C. japonica, Caprella sp. and Thryssa kammalensis. Proportions of fishes and crabs in the diet of S. marmoratus increased with the increase of fish size, whereas the proportion of amphipoda increased and then decreased. Results of the stable isotope analyses suggested that S. marmoratus populations in the marine ranching area off Ma’an Archipelago could be divided into three feeding groups based on size variations: <10.0 cm BL, 10.0-14.0 cm BL, and ≥14.0 cm BL. The mean trophic level of S. marmoratus was estimated as 3.40.
    Application of stable isotopes (δ13C and δ15N) in studies on heavy metals bioaccumulation in Daya Bay food web
    DU Sen, ZHOU Yan-yan, ZHANG Li
    2017, 28(7):  2327-2338.  doi:10.13287/j.1001-9332.201707.016
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    The Daya Bay is a typical subtropical bay in Southern China, and chronically stressed by heavy metal pollution. The bioaccumulation of heavy metals in Daya Bay ecosystem is still unclear. In this study, heavy metals (Cr, Co, Ni, Cu, Zn, Ag, Cd, Pb) and stable isotopes (δ13C and δ15N) were analyzed in seawater, sediment, and organisms (planktons, benthos and nektons) sampled from Daya Bay in June and December of 2015, in order to illuminate the influences of heavy metals to Daya Bay ecosystem and the basic information of environmental monitoring and risk assessment. Results showed that the major source of matter in the organisms in Daya Bay was originated from the ocean, while the freshwater input was limited. The food chain of Daya Bay was short and the highest trophic level was 3.48. The nekton predators (e.g. fish) in Daya Bay were omnivorous, and preferred benthic feeding habit in the winter. The levels of heavy metals in environment and organisms generally did not exceed the criteria according to the National Agriculture Products and the National Water Quality of China, except Zn and Pb in seawater and Cd in two crustaceans (Oratosquilla oratoria and Oratosquilla interrupta). Cr, Co, Ni, Zn, Cd and Pb were found to be biominimized along the Daya Bay food web. Cu was biominimized in the summer, but this trend was not significant in the winter. There was no significant correlation between Ag concentration and trophic level in both seasons, in contrast, there was a potential biomagnification of Ag in crustacean. Overall, the levels of heavy metals in Daya Bay ecosystems were relatively low, and further attention should be paid to Zn, Ag, Cd and Pb.
    Otolith carbon and oxygen stable isotopes in laboratory-reared Schizothorax kozlovi
    HE Yong-feng, WU Xing-bing, WANG Xu-ge, ZHU Yong-jiu, YANG De-guo
    2017, 28(7):  2339-2343.  doi:10.13287/j.1001-9332.201707.023
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    In order to investigate the role of otolith carbon (δ13C) and oxygen (δ18O) stable isotopes in identification of freshwater fish stocks, otolith δ13C and δ18O of cultured Schizothorax kozlovi at different ages were measured by stable isotope mass spectrometer. The relationships between otolith δ13C / δ18O and environment were discussed. The results showed that δ13C and δ18O values of S. kozlovi at age 1+ were not significantly correlated with otolith mass, but both were significantly different between lapillus and asteriscus. The average lapillus δ13C and δ18O values of S. kozlovi at different ages were (-9.58±0.06)‰ and (-8.33±0.17)‰, respectively. There was no significant difference of lapillus δ13C and δ18O between the sexes, but with significant difference among diffe-rent ages. The correlation of δ13C with δ18O was an effective method in identification of different culture stocks of S. kozlovi, which indicated the isotopic signatures of otolith could be used as a method to identify freshwater fish stocks.
    Reviews
    A review on development of stable isotope technique in the studies of N2O formation mechanism
    LIN Wei, FANG Fu-li, ZHANG Wei, DING Jun-jun, LI Yu-zhong, XU Chun-ying, LI Qiao-zhen
    2017, 28(7):  2344-2352.  doi:10.13287/j.1001-9332.201707.031
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    As one of three major greenhouse gases, nitrous oxide (N2O) has solicited substantial attention. Stable isotope has been widely used to explore the sources of N2O emissions. Here, we briefly introduced the microbial processes involved in N2O emissions, and the main influencing factors. We further summarized the development of N2O isotope signature of δ15N, δ18O and SP (site preference of 15N in different positions of N2O molecule) in exploring the N2O formation mechanism. The application of these techniques, especially the SP values, is still at the primary stage in China. Therefore, this paper focused on the development of the isotope ratios analysis in partitioning N2O sources from foreign countries, and put forward suggestions on the future research in China.
    Isotope analysis of ammonium and nitrate: A review on measured methods and their application
    LIU Dong-wei, TU Ying, FANG Yun-ting
    2017, 28(7):  2353-2360.  doi:10.13287/j.1001-9332.201707.036
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    In the past several decades, a variety of methods have been developed for measuring the isotopic composition of ammonium (δ15N) and nitrate (δ15N and δ18O). This review summarized the advantages and disadvantages of these methods. Nowadays, the most popular method for measu-ring δ15N of ammonium is the combined hypobromite (BrO-) and hydroxylamine (NH2OH) me-thod, while for δ15N and δ18O of nitrate is the denitrifier method and the sodium azide (NaN3) me-thod. These methods convert NH4+ or NO3- into nitrous oxide (N2O) and measure its isotopic compositions, with higher analytical precision because of the lower background concentration of atmospheric N2O. Accordingly, these methods are suitable for the samples with lower N concentration, and normally require 10-60 nmol N. The development of new methods for measuring N isotopic composition has greatly stimulated the studies in nitrogen cycling worldwide.
    Challenges and probable solutions for using stable isotope techniques to identify plant water sources in karst regions: A review
    NIE Yun-peng, CHEN Hong-song, WANG Ke-lin, SCHWINNING Susanne
    2017, 28(7):  2361-2368.  doi:10.13287/j.1001-9332.201707.017
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    Karst regions, which account for about 15% of the terrestrial surface area, are characte-rized by specific hydrogeological structure different from most non-karst regions. Thus, many research methods that are used in non-karst regions cannot be directly used in karst regions. This issue is especially relevant to research on plant water sources. In this paper, origins and possible solutions to the common problems associated with research on water sources used by karst plant species were reviewed. Four questions were addressed: 1) why is it important to determine plant water source in karst regions? 2) Why are stable isotopes used? 3) What are the challenges associated with using stable isotopes in karst regions? 4) What are the probable solutions for these challenges? This review emphasized the advantages of using stable isotope techniques to identify sources of water used by karst plant species and the challenges associated with satisfying the prerequisites of this method. It is suggested that sources of water used by plant species in karst regions need not to be divided into specific depths and the method of identifying sources of water used by plant species based on their hydrologic properties was much applicable.
    A review of water and carbon flux partitioning and coupling in SPAC using stable isotope techniques
    XU Xiao-wu, YU Xin-xiao, JIA Guo-dong, LI Han-zhi, LU Wei-wei, LIU Zi-qiang
    2017, 28(7):  2369-2378.  doi:10.13287/j.1001-9332.201707.025
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    Soil-vegetation-atmosphere continuum (SPAC) is one of the important research objects in the field of terrestrial hydrology, ecology and global change. The process of water and carbon cycling, and their coupling mechanism are frontier issues. With characteristics of tracing, integration and indication, stable isotope techniques contribute to the estimation of the relationship between carbon sequestration and water consumption in ecosystems. In this review, based on a brief introduction of stable isotope principles and techniques, the applications of stable isotope techniques to water and carbon exchange in SPAC using optical stable isotope techniques were mainly explained, including: partitioning of net carbon exchange into photosynthesis and respiration; partitioning of evapotranspiration into transpiration and evaporation; coupling of water and carbon cycle at the ecosystem scale. Advanced techniques and methods provided long-term and high frequency measurements for isotope signals at the ecosystem scale, but the issues about the precision and accuracy for measurements, partitioning of ecosystem respiration, adaptability for models under non-steady state, scaling up, coupling mechanism of water and carbon cycles, were challenging. The main existing research findings, limitations and future research prospects were discussed, which might help new research and technology development in the field of stable isotope ecology.
    Investigation on effects of elevated atmospheric CO2 concentration on plant-soil system carbon cycling: Based on stable isotopic technique
    ZHANG Rui, ZHAO Yu, HE Hong-bo, ZHANG Xu-dong
    2017, 28(7):  2379-2388.  doi:10.13287/j.1001-9332.201707.034
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    Elevated atmospheric CO2 affects plant photosynthesis process and biomass accumulation, furthermore alters the distribution of photosynthetic carbon (C) above- and below-ground. The formation and turnover of soil organic carbon (SOC) depends on the input of photosynthetic C, so the change of plant physiology and metabolism caused by increasing CO2 concentration will further affect the balance of SOC pool. Therefore, stable isotope 13C technique is powerful for clarifying the influence of elevated atmospheric CO2 on C cycling in plant-soil system, including the distribution of photosynthetic C among plant organs, and the transformation and accumulation of photosynthetic C in soil. This review summarized research focused on the effects of elevated atmospheric CO2 on C cycling in terrestrial ecosystems based on 13C natural abundance or 13C tracing technique, including: 1) isotopic fractionation effect in plant photosynthesis; 2) the distribution of photosynthetic C in plant organs; 3) the transformation and stabilization of photosynthetic C in SOC driven by microbial process. Clarifying the above processes and controlling mechanisms is essential to predict long-term influence of elevated CO2 on C cycling and evaluate the source-sink function of SOC in terrestrial ecosystems.
    Research progress on food sources and food web structure of wetlands based on stable isotopes
    CHEN Zhan-yan, WU Hai-tao, WANG Yun-biao, LYU Xian-guo
    2017, 28(7):  2389-2398.  doi:10.13287/j.1001-9332.201707.027
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    The trophic dynamics of wetland organisms is the basis of assessing wetland structure and function. Stable isotopes of carbon and nitrogen have been widely applied to identify trophic relationships in food source, food composition and food web transport in wetland ecosystem studies. This paper provided an overall review about the current methodology of isotope mixing model and trophic level in wetland ecosystems, and discussed the standards of trophic fractionation and baseline. Moreover, we characterized the typical food sources and isotopic compositions of wetland ecosystems, summarized the food sources in different trophic levels of herbivores, omnivores and carnivores based on stable isotopic analyses. We also discussed the limitations of stable isotopes in tra-cing food sources and in constructing food webs. Based on the current results, development trends and upcoming requirements, future studies should focus on sample treatment, conservation and trophic enrichment measurement in the wetland food web, as well as on combing a variety of methodologies including traditional stomach stuffing, molecular markers, and multiple isotopes.
    Selection of isotopic baselines in marine ecosystems
    GONG Yi, CHEN Ling, LI Yun-kai
    2017, 28(7):  2399-2404.  doi:10.13287/j.1001-9332.201707.006
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    Stable isotope analysis has been widely used in marine food web studies. An appropriate isotopic baseline is essential for calculating diet or trophic position of marine organisms when using stable isotopic data. This paper provided an overview of the selection of isotopic baselines for four ty-pical marine ecosystems, i.e. estuary and bay, neritic zone, oceanic zone, and deep sea. The interferential factors of baseline selection and the significance of compound specific stable isotope in minimizing the effects of temporal-spatial variations of isotopic baseline were summarized, and the issues needed to be solved in this field and several directions for further research were presented. It would provide a beneficial reference for further research on stable isotope ecology in marine ecosystems.