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    10 August 2020, Volume 39 Issue 8
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    The relationship between ecological environments recorded by pollen and Neolithic cultures in the representative areas of China during the Holocene: A review.
    WANG Kai, MA Yu-zhen, LI Dan-dan, MENG Hong-wei, GUO Chao
    2020, 39(8):  2467-2477. 
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    The relationship between ecological environments and Neolithic cultures during the Holocene is a hot topic in academic community, due to its profound theoretical and practical significance for the regional sustainable development. Pollen records and archaeological sites with chronology data in the representative areas of China were comprehensively analyzed to uncover their relationship. Our preliminary conclusions were as follows: (1) The warm and humid climate conditions during the middle Holocene facilitated the cultural development. (2) The East Asian Monsoon significantly contributed to the development of Neolithic cultures. The regional topography and water condition also affected the development of regional culture to a certain extent. (3) A global climatic and cultural event obviously exhibited at ca. 4.3-4.2 ka BP. Decreases in solar radiation and changes in East Asian Monsoons in winter and summer in the middlelate Holocene were the main drivers for environmental changes and the decline even collapse of Neolithic cultures. (4) High-resolution pollen records, systematic dating of archaeological sites, and coupling mechanism of ecological environment and cultural development need further investigation.
    Changes of organic C and N stable isotope and their environmental implication during the past 100 years of Lake Yilong.
    WU Han, CHANG Feng-qin, ZHANG Hu-cai, DUAN Li-zeng, ZHANG Xiao-nan, PENG Wei, ZHANG Yun, LIU Qi, LIU Feng-wen
    2020, 39(8):  2478-2487. 
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    Based on the analysis of organic C, N stable isotope, C/N ratio, TOC, and TN from core sediments (YLH-1) in Lake Yilong, combined with the stage features of human activities, we analyzed the origin of organic matter and the stagebased evolution process of lake ecosystem during the past 100 years. The results showed that the organic C and N stable isotope values varied from -25.9‰ to -22.5‰ and 0.5‰ to 4.7‰, respectively, and the range of C/N ratio was between 16.4 and 20.4. Such results suggested that aquatic macrophyte was main origin of organic matter, with relatively little contribution of algae and terrestrial sources. The decline in δ13C values suggested that the process of intensified eutrophication, which may be related to CO2 produced by algae due to the degradation of organic matter. The increase in δ15N was attributed to the increasing sewage, the application of fertilizers, and atmospheric nitrogen deposition. The historical evolution of Lake Yilong ecosystem could be divided into three stages. From the 1880s to the early 1960s, primary production level was relatively low and water quality was good, with weak human influence. From the mid1960s to 1990s, with the intensified human activities, the lake productivity rapidly increased, eutrophication was aggravated, water quality was deteriorated, and the intensity of algal blooms increased. Since the 1990s, the lake was at high production level and serious eutrophication state. Future work should pay attention to the impacts of human activities on the lake ecological environment. The management of lake ecosystem should be emphasized to improve the quality of eco-environment.  
    Vegetation succession and its response to climate changes since the Last Glacial Maximum on the Loess Plateau of Central Gansu, Northwest China.
    WU Hui-ning, ZHANG Cai-xia, ZHAO Hai-kuo, ZHANG Lei-lei, ZHAO Li
    2020, 39(8):  2488-2500. 
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    The Earth experienced an integrated climate cycle from cold to warm since the Last Glacial Maximum (LGM), which is a key period in the previous global change research. This study focused on vegetation succession and its climate response pattern since the LGM to provide scientific basis for the strategic deployment of ecological environment construction on the Loess Plateau, by utilizing the highresolution pollen records of fluvial and lacustrinesubaqueous loess sedimentary sequence of the Huining XG section from the Loess Plateau in the Central Gansu. Results from this study are significant for the further investigation of regional climate change mechanisms, as well as prediction of future climate change. The pollen records from the XG section revealed that vegetation succession in the Loess Plateau of Central Gansu since the LGM could be: desert steppe (the cold glacial maximum epoch)→coniferous sparse forest/forest steppe→forest steppe dominated by coniferous broadleaved mixed forest→coniferous broadleaved mixed forest (the warm intermaximum glacial epoch)→coniferous sparse forest steppe→steppe/desert steppe. The corresponding climate response pattern could be: cold and dry→relatively warm and humid→relatively warmer and wet→most warm and wet→cool but slant dry→relatively cold and dry. Overall, the forest/sparse forest steppe zone in the study area has been advanced and retreated many times from southeast to northwest since the LGM, along with the changes of climate in cold or warm and dry or humid. The climax community of regional vegetation is coniferous broadleaved mixed forest, which developed under the suitable climate period of Middle Holocene. A large area of coniferous broadleaved mixed forest also developed in a long term during the Early and Middle Holocene. During Late Holocene, vegetation degenerated into steppe/desert steppe, which may be attributed to the natural response of continuous climate drying or could be a result of the vicious circle caused by the anthropogenic destruction of natural forest and grassland vegetation.
    Environmental implication of magnetic susceptibility of lacustrine sediments in Lake Chaonaqiu, Liupan Mountain.
    YU Ke-ke, WANG Le, SHENG En-guo, LIU Bin, LIU Xing-xing, LAN Jiang-hu
    2020, 39(8):  2501-2508. 
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    In the research of paleoclimate of lacustrine sediments, higher magnetic susceptibility (MS) value indicates stronger erosion and load capacity of surface runoff, and infects more precipitation and humid climate indirectly. On the contrary, lower MS value indicates weaker erosion and load capacity of surface runoff, and infects less precipitation and arid climate indirectly. We identified the environmental indication of MS using multiproxy indices retrieved from sediments in Lake Chaonaqiu in Loess Plateau. The results correlated well with the records from tree-rings in neighboring regions, and showed that higher MS values indicate weaker erosion and load capacity of surface runoff and that lower MS values indicate stronger erosion and load capacity of surface runoff. The environmental indication significance of lake sediment MS is multi-solvent, due to the complex sedimentary environment. This is mainly determined by the bedrock, vegetation cover, and rainfall pattern of the basin. Therefore, various factors affecting MS should be fully considered in different lakes and combined with other indicators for comprehensive identification.
    Optical microscopic characteristics of Zygophyllaceae pollen from western Inner Mongolia and their taxonomic implications.
    HOU Yu-er, YONG Zi-juan, WANG Wei, CHEN Dong-xue, MA Yu-zheng, HE Jiang
    2020, 39(8):  2509-2517. 
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    To clarify the morphological differences of pollen among genera in the family Zygophyllaceae, we examined optical microscopic characteristics of pollen from six species, including Tribulus terrestrisL.,Nitraria tangutorum Bobr., Sarcozygium xanthoxylonBunge, Peganum harmala L., Tetraena mongolica Maxim., and Zygophyllum mucronatum Maxim. from western Inner Mongolia. Classification and regression tree (CART) analysis was performed on the quantified data of main pollen characteristics to explore the relationships between the classifications of pollen morphology and their taxonomic classification in ‘Flora of China’. The results showed that the grains of Zygophyllaceae pollen were mainly smallsized and spherical, subprolata, or prolate. The apertures of pollen were 3-colporate, 3-pseudocolporate, and pantoporate. The exine ornamentations of pollen were reticulate and striate. Most pollen grains had colpus membranes. The polar axis of Tetraena mongolica and Zygophyllum mucronatum was shorter, while the equatorial axis was longer than that reported in literature. The results of CART classification tree were quite different from the classification of ‘Flora of China’, suggesting that the pollen morphological characteristics, which are less evolved with environmental change, can be used as a potential proxy to reveal the phylogenetic relationship of plant species.
    Surface pollen spectrum in intermountain basin of Middle Tianshan, Xinjiang, China.
    LANG Qing, YAO Fu-long, YANG Hai-jun
    2020, 39(8):  2518-2527. 
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    Based on the pollen spectrum of 58 topsoil samples collected in intermountain basin of the Middle Tianshan and a plantcommunity quadrat survey, we analyzed the relationship between topsoil pollen assemblages and modern vegetation distribution in this region. The results showed that: (1) The pollen assemblages were consistent with modern vegetation distribution. Based on the results of cluster analysis, the study area could be divided into five zones with increasing elevation, namely desert grassland, mountain grassland, mountain forest, subalpine meadow, and alpine scree vegetation. Axis 1 of the principal component analysis revealed that humidity was an important factor driving the formation of these vegetation zones. The pollen assemblages differed significantly among vegetation zones, with Chenopodiaceae Artemisia, ArtemisiaPoaceae Chenopodiaceae, PiceaArtemisiaPoaceaeChenopodiaceae (Picea>25%), CyperaceaeAlchemillaArtemisiaPoaceaeChenopodiaceae, and ArtemisiaChenopodiaceae CyperaceaeAlchemillaPoaceae pollen assemblages dominating the desert grassland, mountain grassland, mountain forest, subalpine meadow, and alpine scree vegetation zones, respectively. (2) Artemisia, Chenopodiaceae, Poaceae, Picea, Cyperaceae, and Alchemilla are the representative species in intermountainbasin of the Middle Tianshan, which can serve as important reference for palaeoenvironment reconstruction.Artemisia and Chenopodiaceae were over represented, while Poaceae was opposite. (3) The factors affecting the distribution and content of topsoil pollen in the vegetation zones were complex, with the pollen of Piceabeing greatly affected by the westerly circulation and those of Artemisia and Chenopodiaceae being significantly affected by human activities.
    Interactive effects of shortterm warming and precipitation exclusion on undergrowth vegetation biomass in a Chinese fir (Cunninghamia lanceolata) plantation in midsubtropical China.
    LI Chao, LIN Wei-sheng, YANG Zhi-jie, LIU Xiao-fei, CHEN Shi-dong, ZHENG Wei, JI Yu-huang
    2020, 39(8):  2528-2537. 
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    We examined the interactive effects of soil warming and precipitation exclusion on understory vegetation biomass in Chinese fir (Cunninghamia lanceolata) plantation in subtropical China, with factorial treatments of soil warming (W, +5 ℃ above the ambient temperature) and 50% of precipitation exclusion (P) in a mesocosm experiment. The results showed that soil warming, precipitation exclusion and their interaction had significant effects on understory vegetation biomass. The above and belowground biomass increased significantly in the treatments of W and WP, with the increasing proportion being higher in W treatment. The P treatment significantly decreased belowground biomass. Root/shoot ratio decreased in the treatments of W, P and WP. The responses of above and belowground biomass and root/shoot ratio were primarily caused by the increase of soil temperature. However, the changes of dissolved carbon and nitrogen and mineral element concentrations of soil solution might directly affect undergrowth biomass. The increase in undergrowth biomass of different parts in the W treatment was significantly related to the decreases of the concentrations of Al3+, Fe3+ and Ca2+, while the increases of Al3+ and Na+ concentrations in P treatment might reduce belowground biomass. This study focuses on the main and interactive effects of increasing temperature and precipitation exclusion on the undergrowth biomass of Chinese fir plantation from the perspective of soil nutrient composition changes. The results can provide important theoretical basis for study of carbon cycling and forest management under the background of climate change.
    Water-use efficiency in a mixed conifer-broadleaf forest ecosystem in lower subtropical China.
    HUANG Jian-iang, DENG Yong-hong, ZENG Xiao-ping, MENG Ze, ZHANG Qian-mei, LI Yue-lin
    2020, 39(8):  2538-2545. 
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    Mixed conifer-broadleaf forest is a transitional type from coniferous forest to zonal evergreen broadleaved forest in subtropical area of southern China. Research on water use efficiency (WUE) of forest ecosystem is helpful in predicting the impacts of environmental change on water and carbon processes in lower subtropical China. In this study, the changes of WUE and the effects of main environmental factors in the mixed coniferbroadleaf forest ecosystem during 2005 to 2010 were analyzed based on the eddy covariance system installed at the Dinghushan ForestEcosystem Research Station. The results showed that, at the annual scale, mean annual WUE of the mixed coniferbroadleaf forest was (2.85±0.22) g C·kg-1 H2O. The seasonal trend of WUE presented a typical single-peak curve, with the highest values occurring in spring and winter, followed by autumn, and the lowest values in summer. The highest monthly WUE was 4.75 g C·kg-1 H2O in January 2006, while the lowest was 1.45 g C·kg-1 H2O in July 2007. WUE showed a decreasing trend during the study period (2005-2010). The annual WUE was significantly correlated with air temperature and vapor pressure deficit (VPD) during the dry season (November-January of the next year), while WUE was significantly correlated with photosynthetically active radiation (PAR) in the wet season (from June to September) (P<0.001). These results are helpful to clarify carbonwater coupling in forest ecosystems in lower subtropical China and provide scientific basis for ecosystem management in the context of climate change.
    Leaf N and P resorption efficiency of major subalpine coniferous species on the eastern Tibetan Plateau, China.
    CAI Qin, DING Jun-Xiang, XIAO Juan, YIN Hua-Jun
    2020, 39(8):  2546-2555. 
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    Understanding the characteristics of leaf nitrogen (N) and phosphorus (P) resorption efficiency is crucial for understanding nutrient cycling and plant nutrient use strategy in forest ecosystems. In this study, foliar and litter samples of 24 coniferous species were collected on the eastern Tibetan Plateau. Leaf N and P resorption efficiency of coniferous species was analyzed, combined with soil N and P contents and climatic data (mean annual temperature and mean annual precipitation). Our results showed that leaf N resorption efficiency was slightly higher than that of leaf P, indicating that coniferous species were generally Nlimited. The resorption efficiency of leaf N and P significantly differed with species, being the highest for Pinus species. Leaf N and P resorption efficiency showed a similar variation pattern along the environmental gradients, significantly decreasing with increased altitude, and increasing with increased average annual temperature, but showing no correlation with latitude and mean annual precipitation. With increasing soil N and P contents, leaf N and P resorption efficiency exhibited a significantlydecreasing trend, indicating that trees can improve nutrient resorption efficiency to reduce their dependence on soil nutrient limitation. From the perspective of nutrient resorption efficiency, this study enhances the cognitive level of ecological adaptation strategies and nutrient storage mechanisms of alpine plants in a changing environment.
    Effects of restoration duration, understory vegetation and seasons on soil nitrogen transformation in Pinus massoniana forests.
    HUANG Qiao-ming, HUANG Jun, LYU Mao-kui, XIONG Xiao-ling, ZHANG Shi-liang, XIE Jin-sheng
    2020, 39(8):  2556-2564. 
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    Vegetation restoration can effectively prevent soil erosion and improve ecological environment in eroded red soil regions. Enhancement of soil nitrogen (N) mineralization capacity and N availability is a key pathway to improve the growth and development of vegetation in barren soil, which is of great significance to ecosystem restoration of eroded land. The amount and rate of soil net N mineralization in Pinus massoniana forests under different recovery years (Y0, Y16, and Y34) and different treatments of understory vegetation (Dicranopteris dichotoma) were examined by in situ closedtop core incubation method. The interactive effects of vegetation restoration years, understory vegetation cover, and seasonal changes on soil N mineralization were analyzed. The results showed that vegetation restoration improved soil nutrients in the erosion-degraded land. The highest value of net N mineralization appeared in summer and autumn, but negative value was observed in spring. Vegetation restoration significantly increased the amount of soil net N mineralization, with ammonification playing a dominant role in the process of net N mineralization. The net ammonification rate and net mineralization rate showed similar seasonal pattern. The nitrification rate decreased with increasing recovery years. The amount and rate of net N mineralization in the forest gap without vegetation cover were lower than that in the forest covered with D. dichotoma. The removal of D. dichotoma reduced the amount and rate of net N mineralization. Results of analysis of variance showed that recovery years, seasons, and their interaction significantly affected the amount and rate of soil net N mineralization (P<0.001), but the manipulation of D. dichotoma had no effects (P>0.05). Soil N transformation in P. massoniana forest changed seasonally, and thus forest management should be carried out in accordance with seasonal change. D. dichotoma coverage under the forest plays an important role in the soil N recovery of P. massoniana forest.
    Distribution and impact factors of carbon and nitrogen contents in light fractions of topsoil on the central and eastern Tibetan Plateau.
    YANG Xue-mei, YANG An, XING Wen-cong, WANG Xiao-xia, LIU Xiao-long, Khan M.G. Mostofa, LI Jun
    2020, 39(8):  2565-2573. 
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    The light fraction (LF) of soil is sensitive for identifying changes in soil due to human activities or environmental changes. To explore the distribution and influencing factors of soil LF content on the central and eastern Tibetan Plateau, we measured the LF, heavy fraction (HF) and its carbon and nitrogen content and C/N ratio of topsoil at different vegetation types. We further analyzed the relationships between the carbon and nitrogen content, C/N ratio of LF and environmental factors. The results showed that the contribution of LF to total soil organic matter was small (2.11%). The content of LF in topsoil at different vegetation types followed the order of forest land > alpine meadow > alpine steppe > desert. The average contents of soil LF organic carbon (LFOC) and HF organic carbon (HFOC) in all sampling sites were 27.23% and 2.39%, respectively, with highest content in the forests (31.73% vs. 2.64%). LFOC was the lowest in desert (24.63%), whilst HFOC was the lowest in alpine meadow (2.30%). The average contents of LF total nitrogen (LFTN) and HF total nitrogen (HFTN) were 1.22% and 0.12%, respectively, being highest in alpine meadow (1.28% vs. 0.12%) and lowest in forests (1.14% vs. 0.10%). The average value of the LF C/N ratio and HF C/N ratio was 27.67 and 11.59. C/N ratio in both LF and HF (36.95 vs. 15.15) was the highest in the forests, whilst was the lowest in LF of alpine meadow (25.45) and in HF of alpine steppe (10.03). These results imply that humification degree of forests is high and the available nitrogen content is low, while an opposite pattern was found for alpine meadows and alpine steppe. The contents and distribution of the LF in topsoil on the central and eastern Tibetan Plateau significantly varied across vegetation type, while soil pH is the most important environmental factor affecting LF carbon and nitrogen contents.
    Imbalance of soil elements drives the degradation of alpine grasslands.
    LIU Min, SUN Jing-guo, XU Xing-liang
    2020, 39(8):  2574-2580. 
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    Imbalance of soil elements is one of the major factors driving alpine grassland degradation. Clarifying the processes and mechanisms for the imbalance of soil elements is important for the restoration and sustainable use of degraded alpine grasslands. To achieve this, we analyzed basic soil physicochemical properties across a chronosequence: a 1-year enclosed site as short-term restoration stage, a 6-year enclosed site as medium restoration stage, and a 15-year enclosed plot as long-term restoration stage in typical alpine grasslands in the Qinghai-Tibet Plateau. Restoration of degraded grassland did not change soil pH, but increased soil waterholding capacity and electricity. Soil organic C and total N contents changed greatly across the restoration stage, while soil P content remains unchanged. With increasing restoration duration, C∶N, C∶P and N∶P ratios and available N (especially ammonium) in soil remarkably increased. The ammonium content at long-term restoration stage was 3.1 times higher than that after one-year restoration. The restoration of degraded grasslands greatly increased aboveground biomass, resulting in the increased soil C and N inputs through plant litter and rhizodeposition. Increased C and N inputs by plants triggered rapid C and N turnover in soil. Such a strong positive feedback help restore the degraded alpine grasslands. These findings indicate that imbalance of soil elements should be responsible for the degradation of alpine grasslands, providing an important basis for the restoration of degraded alpine grasslands and sustainable use of alpine grasslands.
    Effects of Stellera chamaejasme on small scale community composition and soil physical and chemical properties in degraded grassland.
    CUI Xue, PAN Yao, WANG Ya-nan, ZHENG Xiao-na, GAO Ying
    2020, 39(8):  2581-2592. 
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    Overgrazing has resulted in degradation of grassland ecosystems, with the consequences of decreased dominance of foraging grasses and increased dominance of some poisonous species. As an indicator of grassland degradation, the impacts of poisonous species on adjacent plant species and soil environment are one of the important scientific issues in ecological research. To better explore the impacts of poisonous species in the restoration process of degraded grassland ecosystem, we selected the fenced and restored Leymus chinensis grasslands in Hailaer naturereserve as the research object. According to branch number of S. chamaejasme (a poisonous plant) per unit area, plant communities were classified into three types: community with high-density, low-density, and without S. chamaejasme, to investigate community species composition and soil physicochemical characteristics. The results showed that: (1) High density of S. chamaejasme altered plant community composition at small spatial scale by increasing Shannon index and Patrick index, which indicated the significant effects of S. chamaejasme on species richness. (2) With increasing S. chamaejasme density, the association properties of some Gramineaespecies and S. chamaejasme were changed. The association properties of Poa annua,Stipa baikalensis and S. chamaejasmewere changed from positive to negative, while that of Koeleria litvinowiiand S. chamaejasme was changed from no association to negative. The associations amongLeymus chinensis, Cleistogenes squarrosa, Achnatherum sibiricumand S. chamaejasme were unchanged. (3) S. chamaejasme could alter the relative importance of plant families in the community. Increased S. chamaejasme dominance enhanced the importance value of Leguminosae and Rosaceae, but decreased that of Compositae.There was no obvious change of Gramineae in importance value. (4) The presence of S. chamaejasme affected soil total nitrogen and pH. The community with low density S. chamaejasme had significantly higher soil total nitrogen content than the other two groups. It also had significantly higher soil pH than the community without S. chamaejasme. There were no significant differences in total carbon, available nitrogen and phosphorus in soils among all the three types of plant communities. The smallscale change of soil physicochemical properties might be responsible for promoting vegetation restoration in degraded grasslands.  
    Dynamics and influencing factors of endophytic bacterial community in leaves of Lycium barbarum during different growth periods.
    GOU Qi, LYU Yan, ZHANG Tao, LI Jing-yu, ZHAO Hui-jun, LIU Jian-li
    2020, 39(8):  2593-2601. 
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    To explore dynamics and influencing factors of endophytic bacterial community in leaves of Lycium barbarum at different growth stages, endophytic bacterial community in young, mature and old leaves of Lycium barbarum were examined using the high-throughput sequencing. Canonical correspondence analysis and variance partitioning canonical correspondence analysis were used to analyze the effects of three environmental factors on the dynamics of endophytic bacteria community, including the living conditions of host plants represented by climatic factors, the physiological status of host plant’s organs represented by photosynthesis parameters, and the endophytic bacteria living micro-environmental condition in host plants represented by nutrients that can be utilized by microorganisms. The results showed that 28 phyla, 52 classes, 118orders, 249 families, 503 genera, 738 species and 978 OTUs of endophytic bacteria were found during three growth periods. The alpha diversity and richness of OTU were the highest in the young leaves, decreased with the ages of leaves, and being at a relatively low level in mature and old leaves. The class γProteobacteria of phylum Proteobacteria dominated the endophytic bacteria in the leaves. In addition, genus Stenotrophomonas in family Xanthomonas, genus Pseudomonas in family Pseudomonadaceae, and genusPantoea in family Enterobacter were dominant in young, mature, and old leaves, respectively. The endophytic bacteria OTUs in mature and old leaves were mainly inherited from the preceding growth period. The function of endophytic bacteria changed slightly with the growth stage of leaves. The environmental factors affecting the composition of endophytic bacterial community differed across growth stages, with foliar nutrients having the greatest impact. The endophytic bacteria in leaves of Lycium barbarum responded to the changes of in vivo and in vitro environment during different growth stages based on each characteristic of endophytic bacterial community. The living micro-environmental condition of endophytic bacteria in host plants was the main factor affecting the dynamics of endophytic bacterial community in leaves of Lycium barbarum.
    Effects of soil water stress on emergence and seedling growth of spring soybean.
    LI Xiu-fen, MA Shu-qing, LI Yun-feng, YU Hai, XU Li-ping, CHEN Feng-tao, ZHANG Hong-wei, ZHAI Mo
    2020, 39(8):  2602-2609. 
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    We carried out a field soil moisture control experiment in central Jilin Province in 2017 and 2018 to explore the effects of drought on seedling emergence speed, seedling rate and seedling growth during spring sowing to seedling period, and the spring drought index, with the final aim to guide the spring drought assessment and drought control irrigation. Soil moisture was controlled by rainproof sheds and artificial water spraying. There were seven soil moisture levels and one natural rain-fed treatment. We measured soil moisture, emergence date, emergence ratio, plant height, leaf age and biomass. The effects of soil moisture on emergence date, emergence ratio and seedling growth potential were analyzed by regression method, and the evaluation index of soybean spring drought was established accordingly. The results showed that soybean emergence date, emergence rate, plant height, leaf age and aboveground biomass were closely related to soil moisture in the sowing layer. Under the range of experiment treatment (soil moisture was less than 24%), with every 1% decrease of soil moisture, the emergence date was delayed for 1-2 d, the emergence rate was decreased by 1.6%, and the relative leaf age, seedling height and aboveground biomass were decreased by 6.1%, 5.4% and 10.2%, respectively. Suitable soil moisture for soybean emergence ranged between 20% and 23%, and for seedling growth ranged between 21% and 24%. The indicators of light, moderate, severe and extreme drought in spring were as follows: soil humidity in 0-10 cm was 16%-17%, 14%-15%, 12%-13% and <12%, respectively; in 0-20 cm was 17%-18%, 15%-16%, 13%-14% and <13%, respectively.
    Effects of neighborhood complexity on the responses of wheat seedlings to root exudates-mediated kin recognition.
    WEI Jia-he, CHEN Bin
    2020, 39(8):  2610-2615. 
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    To investigate the responses of wheat seedlings to kin recognition in a complex neighborhood composed by both kin and stranger individuals, we conducted an experiment with hydroponically growing two wheat cultivars exposed to root exudates which varied with three levels of relatedness (i.e. intra-cultivar, inter-cultivar and inter-species), and two levels of neighborhood complexity (i.e. all individuals from either the same level of relatedness or a mixture with half of them from intracultivar and the other half from inter-cultivar/specific). The results showed that both relatedness and neighborhood complexity significantly affected specific leaf area (SLA) and specific root length (SRL) of wheat seedlings, and they interactively affected SLA, total root length, SRL, and mean root diameter. These morphological trait values in the kinstranger-mixed neighborhood were either significantly higher/lower or unchanged, as compared to those in the pure kin neighborhood and pure stranger neighborhood. Furthermore, these kin recognition induced responses were cultivar-dependent. Our results suggest that the growth and competitive strategies of wheat in response to a relatedness-mixed neighborhood are not simply at the average status between pure kin and pure stranger neighborhoods.
    Phenotypic selection on flower traits of Aconitum gymnandrum (Ranunculaceae).
    LU Ning-na, MA Yan, MENG Xiu-xiang
    2020, 39(8):  2616-2621. 
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    To uncover the evolutionary mechanism of floral traits, it’s necessary to analyze the intensity and direction of phenotypic selection. Through manipulating the width of lateral sepals of Aconitum gymnandrum(Ranunculaceae) and phenotypic selection analysis, we examined the relationship between floral traits and fitness of A. gymnandrum. The results showed that, after increasing the width of lateral sepals, the visitation rate of pollinators was significantly decreased, but seed number per flower did not change. Lateral sepals affected pollen export mainly through pollinator attraction rather than seed production. Phenotypic selection estimated through female fitness showed significant linear selection differential on the flower traits except entry width. There was significant linear selection gradient on flower number and plant height, and only flower number was observed with significant nonlinear selection, showing directional selection on plant height and stabilizing selection on flower number. Individuals with taller stature and intermediate flower number would have higher seed production.
    Seed heteromorphism and population maintenance strategy of invasive plant Cenchrus pauciflorus.
    QU Ting, TIAN Xun, ZHOU Li-ye
    2020, 39(8):  2622-2628. 
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    Cenchrus pauciflorus Benth. is one of the most invasive weeds in Horqin Sandy Land. To explore the seed heteromorphism and population maintenance strategy of C. pauciflorus, we assessed the biological characteristics and germination traits of seeds, and the effects of artificial removal on the germination of P-type seeds. The results showed that two or more seeds were detected in the same bur of the C. pauciflorus (most contained two seeds). One type of seeds was bigger and looks like mango (type M), and the other type was smaller and looks like plum (type P). Seed length, width, height and weight were significantly higher for M-type seeds than P-type seeds. However, the variations of seed characteristics for P-type seeds were higher than M-type seeds. In natural habitats, the probability of one seed (M-type) germinated in one bur reached 93%, while the rate of two seeds (both M-type and P-type) germinated in the same bur was only 7%. We did not detect three seeds germinated in the same bur in the natural habitats. In laboratory germination experiment, the germination rate of one seed germinated in one bur was 69.3%, that of two seeds germinated in the same bur was 22.2%, and that of three seeds germinated  in the same bur was 8.5%. Results from the field artificial removal experiment showed that clipping C. pauciflorus seedlings in spring had weak effect on its population size, while clipping C. pauciflorus adult plants in summer significantly reduced the population size of C. pauciflorus. The germination rate of P-type seeds was only 20.15% after removal of the radicle and germ of the germinated M-type seeds. Our results indicated that P-type seeds may play a unique role in maintaining C. pauciflorus population, which is subject to environmental factors and with a threshold.
    Modular biomass ofBromus inermisin different areas on the northern slope of Tianshan Mountain.
    GONG Ke, JIN Gui-li, WANG Yu-xiang, LIU Wen-hao, MA Jian
    2020, 39(8):  2629-2635. 
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    Modular biomass allocation is a resource allocation strategy for plants in response to heterogeneous environment. Combined with field investigation and indoor measurement, we analyzed the difference of modular biomass of Bromus inermis in five sites on the northern slope of Tianshan Mountain to explore the variation of modular biomass. The results showed that the biomass and allocation of modules varied across different sites, with stem biomass and its allocation having the highest variation. Biomass allocation of vegetative modules was larger than that of reproductive modules, while biomass of aboveground modules was higher than that of underground modules (P<0.05). Modular biomass allocation was closely related to environmental factors. Aboveground biomass was more suitable to reflect the accumulation of stem biomass. In conclusion, biomass allocation of B. inermis was not stable across different grasslands, indicating its strong adaptability to environment.
    Water quality assessment in the habitat of Tylototriton kweichowensis.
    LI Lin-zhi, CHEN Hu, WANG Cun-lu, CHEN Jing, ZHANG Hong-mei, YANG Yi-wei, GUO Cheng
    2020, 39(8):  2636-2645. 
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    To assess water quality of Tylototriton kweichowensis habitats and the environmental factors affecting its habitat selection, the physical and chemical indices, including As water temperature, pH, DO, TN, TP, NH3-N, CODMn, Cu, Hg, Pb, Cr, Cd, Mn, Zn and As, were measured in seven distribution sites and two contrast sites in the demonstration area for comprehensive management of rocky desertification in Salaxi of Bijie City, Guizhou Province in May, August and October of 2019. Single factor evaluation method and Nemerow comprehensive pollution index were used to evaluate water quality. The results showed that water quality of three sites was classified into class III, with the pollution degree being in alert level; one into class IV, being slightly polluted; five into worse than class V, being severely polluted. The indices thatexceeded the limit include pH, DO, TN, TP, NH3-N, CODMn and Mn, among which TN and NH3-N were the main factors causing poor water quality. By comparing the environmental factors of the two control sites, water temperature and pH were important factors affecting the habitat selection of T. kweichowensis, with water environment with temperature lower than 13 ℃ or pH<6 being not suitable for the survival of T. kweichowensis.

     

    Fish assemblage and biotic integrity assessment in Shihoudian Lake.
    SHI Lei, ZHU Hao, YE Shao-wen, WANG Pu-ze, LIU Jia-shou, LIU Xing-guo, LI Zhong-jie
    2020, 39(8):  2646-2656. 
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    Fish-based index of biotic integrity (F-IBI) has been widely used in the health assessment of rivers and lakes, which is of great significance for regional ecological restoration and protection. From October 2018 to July 2019, we sampled fish community in Shihoudian Lake, the experimental area of Baiyangdian Lake. Combing with FIBI and ABC curve (abundancebiomass comparison curves), we comprehensively evaluated fish community composition characteristics and water health status. A total of 30 species were recorded, belonging to 4 orders and 10 families. Cyprinidae had 21 species, accounting for 70% of the total number of fish species. The F-IBI evaluation results showed that three sites were evaluated as “good to excellent” in the Bai yangdian Lake experimental area, three sites as “good”, four sites as “general to good”, five sites as “general”, eight sites as “poor-general”, three sites as “poor”, and no sites as “excellent” or “extremely poor”. Overall, autumn and spring showed “generalgood”, and summer showed “poorgeneral”. The ABC curves revealed obvious crossover trend, indicating that the overall state and that both spring and summer were moderately disturbed. The abundance curve in autumn remained above the biomass curve, indicating that autumn was in a serious interference state. Compared with the period between 1950s and 1970s, F-IBI of Baiyangdian Lake showed a downward trend. Overfishing, water pollution, and extreme climate were important factors driving the changes of Baiyangdian fish communities. Fishing forbidden zone should be delimited and the closed fishing season should be extended to strengthen the protection and sustainable use of fish resources.
    Effects of mother plant traits of Taxus chinensis on the diversity of bird visitors in the Meihuashan Nature Reserve, Fujian Province, China.
    ZHANG Shuai, FAN Yue-zheng, WANG Zheng
    2020, 39(8):  2657-2662. 
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    Plant traits are important factors shaping bird diversity in fragmented habitats, with consequences on ecosystem function. Chinese yew (Taxus chinensis) is catalogued as endangered species in IUCN and as vulnerable to extinction in China. Most natural populations of T. chinensis show a scattered distribution near villages in southern China. In this study, we used the methods of line transects and sampling points to investigate the potential effects of fruit amounts, canopy density and height of T. chinensis on the diversity of bird visitors in the yew ecological garden of Meihuashan Nature Reserve. A total of 67 bird species were recorded in the garden, including 45 frugivorous bird species. The composition of bird community and dominant bird species differed across patches (bamboo patch and evergreen broad-leaved forest patch) and years. A total of 21 bird species visited the mature trees of T. chinensis, whose diversity was strongly affected by plant traits. Fruit amount was positively related to the individuals and species richness of birds. Population size of bird visitors was positively correlated with plant canopy density. Our results highlighted the importance of plant traits in shaping frugivore diversity, which could affect plant recruitment in fragmented habitats.
    Effects of wildflower strips on ground-dwelling spider diversity in Beijing suburban cropland.
    GUO Bing-ru, FU Dao-meng, QI Shao-fan, YU Zhen-rong, NIE Zi-jin, ZHU Li
    2020, 39(8):  2663-2670. 
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    Spider is an important natural enemy group in croplands, whose biodiversity is affected by diverse factors at field scale. The wildflower strips in field margin could improve rural aesthetics, but their effectiveness in maintaining spider diversity remains poorly understood in China. In this study, eight pairs of focal fields with similar agricultural management and landscape composition were selected. In each pair, one field was selected next to a wildflower strip previously established as part of the focal field, and the other field next to habitats without flower resource was selected. We captured spiders in the fields to figure out factors that influence spider diversity. Wildflower strips increased cropland spider diversity, especially within the fields. The distribution of dominant spider species was not correlated with wildflower strip shapes, but positively correlated with species richness and width of wildflower strips. Our results indicated that the construction of field margin wildflower strips can increase spider diversity, and thus contribute to the biological control of insect pests.
    Spatiotemporal characteristics and driving factors of urban heat islands in Guangdong-Hong Kong-Marco Greater Bay Area.
    DENG Yu-jiao, DU Yao-dong, WANG Jie-chun, XU Jie, XIE Wei-si
    2020, 39(8):  2671-2677. 
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    The urban heat island is a hot social issue during the construction of Guangdong-Hong Kong-Macao Greater Bay Area. The study of the driving factors for the heat island is an important scientific issue. Based on satellite remote sensing data, we quantitatively analyzed the spatiotemporal distribution of urban heat islands in GuangdongHong KongMarco Greater Bay Area. The driving factors of urban heat islands were analyzed by the multiple regression. The results showed that the urban heat island effect in Greater Bay Area increased significantly from 2003 to 2018, with an annual increase of the heat island intensity of 0.05 ℃ and an annual increase of the heat island area of 0.18%. For seasonal variation of urban heat islands, the intensity was the strongest in summer and the weakest in winter. The heat island area was the largest in summer, and second largest in winter. The heat island area was mainly distributed in Dongguan, Shenzhen, the junction of Guangzhou and Foshan, the north of Zhongshan, and the central part of Huizhou. Theresults of multiple regression analysis showed that the altitude had the most significant impact on urban heat islands, followed by the light index, normalized vegetation index, and aerosol optical thickness in a descending order. The light index was a positive driving factor, whereas the rest were negative driving factors.
    Quantitative characteristics of roadside tree canopy cover under the background of urban expansion: A case study of Beijing.
    ZHANG Wen, LI Xiao-ting, MA Jie, JIA Bao-quan
    2020, 39(8):  2678-2690. 
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    Roadside tree canopy (RTC) is the most important component of urban tree canopy (UTC). In this study, we constructed an evaluation system of RTC quantitative change from a perspective of the relationship between RTC quantitative change and urban expansion, which can provide basis for urban planning and road green space system management. Based on quantitative relationships between RTC and road, impervious surface, UTC and possible UTC (PUTC), we established five evaluation indices. The spatial distribution analysis and evaluation were carried out for regions between ring roads in the main urban area of Beijing. The results showed that the growth of RTC area was remarkable from 2002 to 2013, with a change index of the RTC area being 2.142, and the coverage rate increasing from 21.62% to 35.00%. The overall RTC growth showed obvious dominant response compared with the urban impervious surface change and the road weighting change. The overall I (impervious surface) response index was 1.879, and the R (road) response index was 1.736. The RTC showed weak dominant response compared with the overall growth of UTC and the decrease of potential UTC area, with overall U (UTC) response index of 1.055 and P (possible UTC) utilization index of 1.06. RTC area change index, I response index, R response index, and P utilization index all showed an increasing trend from inside to outside urban expansion. U response index was basically balanced between ring road areas, while the other indices had obvious differences. The difference of RTC area change index was the biggest between ring road areas. R response index showed the most significant correlation with RTC area change index. The RTC area changed greatly in urban outskirts, and its response advantage to road and urban impervious surface changes all showed a more significant trend from the inside to outside. New roads and impervious surfaces had higher RTC coverage. There was no correlation between U response index and RTC growth rate. The difference of RTC between ring roads in the main urban areas of Beijing was significant, with a promoted demand in the innercity, and especially the lagged demand inside the 2nd ring road which needed to be concerned. RTC position and tendency advantage in the overall urban tree canopy cover need to be strengthened, especially in regions inside the 3rd ring road. Leaving room for RTC growth was compressed. Exploring potentials of impervious surface in built-up areas is an important approach to RTC subsequent growth.
    Prediction of suitable distribution area of Eurasian Spoonbill in Northeast China based on MaxEnt model. #br#
    LI Min, LI Xiu-ming, XU Jia-hui, XUE Lin, WU Ai-ming, PAN Kai-jun, MIN Xiao-ming, LI Yu-tai, QIAN Fa-wen
    2020, 39(8):  2691-2703. 
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    Eurasian Spoonbill (Platalea leucorodia) is a national grade II protected wildlife species in China, with fragmented breeding habitats. In recent years, under the background of global climate change, the area of wetlands in Northeast China, as the main breeding area of Eurasian Spoonbill, has been reduced due to over-exploitation of groundwater and reclamation of wetlands. It is necessary to formulate a scientific protection plan to reduce the habitat fragmentation of Eurasian Spoonbill in Northeast China. Here, we analyzed the habitat suitability and main influencing factors of Eurasian Spoonbill in Northeast China using MaxEnt model and GIS technology. Thearea under the receiver operating characteristic curve (AUC) of the subjects achieved 0.918 in the training samples and 0.945 in the test samples, suggesting its high prediction ability and suitability for predicting the potential habitats of Eurasian Spoonbill. The results showed that the main environmental factors affecting the distribution of breeding habitats of Eurasian Spoonbill were altitude(36.8%) and vegetation coverage (32.6%), followed by isothermality (11.5%), the distance from lake (8.6%), and precipitation in the driest season (4.0%). The less impacting factors were the distance from road (2.7%), the wettest monthly precipitation (2.4%), the distance from residential area (0.8%), land use type (0.4%), and the distance from river (0.2%). The suitable habitats of Eurasian Spoonbill in Northeast China are concentrated in low altitude, suitable climate, and close to water source. The distribution of protected areas (nature reserves and wetland parks) suitable for Eurasian Spoonbill habitats was clear. Our results provide scientific basis for the protection of Eurasian Spoonbill, and provide suggestions for the management of its habitats.
    Ecologically suitable habitats and population characteristics of Cercidiphyllum japonicum in China. #br#
    ZENG Chao-yue, ZHONG Qian-juan, WANG Chong-yun, HU Yan-ping, WU Ming-hui, MENG Wei, PENG Ming-chun
    2020, 39(8):  2704-2712. 
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    Cercidiphyllum japonicum is one of the second-class national protected plant species in China, with extremely low ability of regeneration in isolated natural populations. The prediction of its suitable habitats can provide a scientific basis for delineating management units of C. japonicum in different regions. Based on the geographical distribution data of C. japonicum in China, 22 environmental indicators were adopted in the MaxEnt model to predict its potential suitable habitats in China. We further compared the population structure of C. japonicum in different regions to clarify the ecological factors determining its distribution and population characteristics. The results showed that the potential suitable habitats of C. japonicum were mainly located in the western margin of the Sichuan Basin, Shennongjia, Qinling-Daba Mountains, and isolated hills in east China. Climatic and topographic factors had a joint influence on the distribution of C. japonicum. The factors which had main contribution to its potential suitable habitats included annual precipitation, the minimum temperature in the coldest month, slope, and altitude. Results of principal component analysis showed that the 11 populations surveyed in different regions could be divided into three groups, including populations in Qinling-Daba Mountains, populations in the western margin of Sichuan Basin, and populations in eastern China. Environmental factors had different effects on population density and survival rate of C. japonicum at different growth stages, with stronger correlation between population characters and climate factors at the early growth stage.
    Spatiotemporal variations of water conservation capacity in Ruoergai Plateau.
    YUAN Yue, ZHANG Liang, CUI Lin-lin
    2020, 39(8):  2713-2723. 
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    The Ruoergai Plateau has an important function in water conservation. In this study, water conservation was simulated using water balance method based on meteorological and remote sensing data. We analyzed the spatiotemporal changes of water conservation function and its influencing factors in Ruoergai Plateau during the period 2001-2017. Results showed that the amount of water conservation (AWC) varied greatly, gradually increasing from the north to the south. During the study period, the proportions of the AWC per unit area <100, 100-200, 200-300, 300-400, 400-500 and >500 mm were 15.43%, 63.66%, 18.66%, 2.22%, 0.03% and 0,respectively. The average AWC in different regions was following the order of Aba Tibetan and Qiang Autonomous Prefecture > Hongyuan County > Rouergai County > Maqu County > Luqu County. The average AWC per unit area in the Ruoergai Plateau showed a slight upward trend. The proportions of the areas with significant decrease, moderate decrease, slight decrease, almost constant, slight increase, moderate increase and significant increase in water conservation were 50.64%, 16.81%, 11.64%, 5.20%, 4.52%, 7.31% and 3.88%, respectively. The AWCs in Aba Tibetan and Qiang Autonomous Prefecture and Rouergai County showed an increasing trend, while the other three counties (Maqu, Luqu, and Hongyuan) showed a decreasing trend during 2001-2017. Precipitation and elevation were the major factors driving spatiotemporal changes of water conservation function.
    Spatiotemporal change of land ecological security in Hunan based on DPSIR.
    WANG Wen-xuan, LI Ming-xiao
    2020, 39(8):  2724-2736. 
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    An index system was constructed based on the “DriversPressureStateImpactResponse” (DPSIR) model, with nature, economy, society, environment, and landscape pattern being considered. The comprehensive weight matterelement analysis model was used to evaluate land ecological security in Hunan and to analyze the characteristics and driving factors of its spatiotemporal change. The results showed that the areas with unsafe and relatively unsafe land ecology were mainly concentrated in center and west of Hunan, while the relatively safe area was in the northeast in 2000. The west and south parts of Hunan were upgraded to the relatively safe level, while the north central parts were in critically safe level in 2016. Therefore, the spatial differences in land ecological security in Hunan were temporally reduced. The land ecological security in Hunan presented a development trend from relatively unsafe to relatively safe, with unstable status. The ecological security levels of driving force, pressure, state and response systems were all improved. The impact system was in critically safe level, which was slightly decreased, indicating a weak capacity of bearing disturbance. The steady development of land ecological security in Hunan was guaranteed by the improvement of economic density, per capita income of rural residents, per capita GDP, per capita public green area of cities, degree of agricultural mechanization and sewage treatment rate, which was mainly restricted by the natural growth rate of population, urbanization rate, non-point source pollution of agriculture, landscape pattern of land use, and rate of scientific and technological investment. Topography and land-use landscape pattern were the fundamental factors accounting for the spatial variations of land ecological security.
    Nitrous oxide production and emission mechanisms in key interfaces of canyon-reservoirs during stratification period.
    GAO Die, CHEN Sai-nan, LI Si-liang, LIU Xiao-long, LI Jun, BAI Li, YANG Jing, WANG Zhong-liang
    2020, 39(8):  2737-2747. 
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    Nitrogen (N) dynamics at different interfaces in canyon reservoirs during the thermal stratification period substantially influence the authentic quantification of N2O emission in the cascade reservoir system. We examined various N species (NO3--N, NH4+-N), dissolved N2O concentration, and dissolved oxygen (DO) in water samples collected from three reservoirs (Hongjiadu, Dongfeng, and Wujiangdu) during thermal stratification period in the upper reaches of Wujiang River. The results showed that N2O concentrations were 14.3-64.4, 16.5-35.7, and 17.0-70.8 nmol·L-1 in Hongjiadu, Dongfeng and Wujiangdu reservoirs, respectively. Theseresults indicated that all three reservoirs act as N2O source to the atmosphere. There was a significant correlation between ΔN2O and apparent oxygen utilization (AOU) in the whole profile of Dongfeng reservoir as well as above the hypoliminion (0-58 m) of Wujiangdu reservoir. This suggested that N2O production is primarily dominated by nitrification. The vertical distribution of DO, NO3--N, and N2O in hypoliminion of Wujiangdu and Hongjiadu reservoirs showed that N2O production in the hypoliminion of Wujiangdu Reservoir could mostly result from denitrification driven by insitu NO3-, while that of Hongjiadu Reservoir could mainly result from denitrification driven by the exogenous NO3- from upper layer water. N2O emission fluxes in the waterair interfaces in Hongjiadu, Dongfeng and Wujiangdu reservoirs were 0.4, 0.5 and 0.4 μmol·m-2·h-1, respectively. They were significantly higher than former measured values that conducted ten years ago. This implies that the enhanced N2O emission could presumably come from reservoir aging, water regulation of the reservoirs, and enhanced biogeochemical transformation of organic matter under climate changes. The N2O emission fluxes during power generation in July were 0.19×104, 1.6×104 and 6.7×104 mol in the outflow waters of Hongjiadu, Dongfeng and Wujiangdu reservoirs, respectively. The enhanced discharge of N2O from outflow waters may be affected by the joint scheduling and water regulation between the reservoirs in the cascade-developed river-reservoir system.
    Pollution and potential ecological risk of heavy metals in surface dust in Korla, Xinjiang.
    HAYRAT Adila, EZIZ Mamattursun, NASIRDIN Nasima, JIN Wan-gui
    2020, 39(8):  2747-2758. 
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    A total of 54 surface dust samples were collected from Korla. The contents of six heavy metals (Hg, Cd, As, Pb, Cr and Cu) in those samples were determined. The pollution levels and potential ecological risk of heavy metals in surface dust were evaluated using Nemerow pollution index (NPI), ecological risk index (HRI), and ecological risk warning index (IER). Results showed that the average contents of Hg, Cd, Pb, Cr and Cu in the surface dust in Korla exceeded the corresponding background values of Xinjiang soils by 3.71, 1.87, 1.96, 1.14 and 1.29 times, respectively. Among them, the surface dusts were highly polluted by Hg, lowly polluted by Cd, Pb, Cr, Cu, and slightly polluted by As. The average NPI value fell into the high pollution level. Results of ecological risk assessment indicate that Hg in surface dust fell into high ecological risk level, while Cd fell into moderate ecological risk level, and As, Pb, Cr, and Cu fell into low ecological risk level. The average value of HRI was 232.23, being at the moderate risk level. According to the classification of ecological risk warning degree, Hg in surface dust fell into low ecological warning status, while Cd, Pb, Cu, and Cr fell into early ecological warning status, As fell into no ecological warning status. The average value of IER was 4.91, being at a moderate ecological warning status. Spatial distribution of heavy metals showed that areas with high pollution and ecological risk levels were mainly distributed in the northern part in the study area. Overall, the pollution risk of heavy metals in surface dust in Korla was relatively low.
    Distribution characteristics and risk assessment of three PAEs in Dahuofang Reservoir.
    NIU Ming-fen, WANG Zheng-yan, MA Jian, CHEN Xin, LI Na
    2020, 39(8):  2759-2767. 
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    Dahuofang Reservoir is a major drinking water source in Liaoning Province, the water safety of which is important for this area. In this study, we collected water samples from the reservoir and three main inflow rivers and measured the contents of phthalic acid esters (PAEs). After that, we analyzed the spatial distribution and seasonal variation of PAEs. The results showed that the PAEs content in the reservoir area increased first and then decreased from east to west. In the three rivers, there was a gradual increase trend of PAEs content from upstream to downstream. The PAEs showed seasonal variation, with an order of summer>spring>autumn. Dibutyl phthalate (DBP) was detected in all sampling locations. DBP and di2ethylhexyl phthalate (DEHP) had a certain homology and were negatively related to the concentration of total nitrogen and total phosphorus in water. The results of risk exposure model showed that the non-carcinogenic risk index of DBP in Dahuofang Reservoir was far less than 1, which would not be harm to human body.
    Simulation on water infiltration and redistribution of sandy soil improved by sludge. #br#
    HUANG Dian-nan, ZHAO Chao-yue, ZHANG Yu-xin, LI Lin, JIAO Mei-yi, CHEN Ming-ming, HOU Wen-tao, FU Jin-xiang
    2020, 39(8):  2768-2775. 
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     The mixing of sludge and sandy soil is a way to improve desertified soil. Understanding the pattern of water infiltration and redistribution in the composite soil would facilitate project improvement. To ensure the applicability of simulation software in practical engineering, we analyzed the pattern of water infiltration and redistribution of a mixture of sludge and sand with a 1∶4proportion under simulated rainfall process. The experimental process was simulated by using Hydrus-1D soil moisture simulation software. The simulated data were compared with the measured data to verify the applicability of Hydrus-1D software in simulating sediment composite soil water infiltration to select a suitable model. The results showed that the Hydrus-1D software can predict water characteristic curve of composite soil. Basic soil property parameters were obtained, including residual water content (θr), saturated water content (θs), air intake value reciprocal (α), pore size distribution index (n), and hydraulic conductivity (KS). In the whole process of water infiltration simulation, water content of sand soil and composite soil graduallyincreased to a stable status close to but not equal to saturated water content. In the simulation test of water infiltration within 0-30 minutes, the difference between the measured curve and the simulated curve was not significant. After 60 minutes, the difference between the measured curve and the simulated curve in the simulation test of water redistribution in each soil layer was large. These results indicate that the software can simulate water infiltration, but not water redistribution.
    Research advances on response strategies of Pomacea canaliculata to predator stress and the involved mechanism.
    GUO Jing, ZHANG Jia-en
    2020, 39(8):  2776-2784. 
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    The apple snail,Pomacea canaliculata, is a cosmopolitan alien invasive species. It was introduced to mainland China in 1981 and has caused serious damage to aquatic crop production and ecosystem functioning. Phenotypic plasticity may play an important role during the invasion ofP. canaliculata, which help invaders to increase their environmental adaptation and tolerance. Phenotypic plasticity frequently involves predatorinduced defenses. In this paper, the response strategies and underlying mechanisms of P. canaliculata against predator stresses were reviewed and summarized from three aspects: behaviors (defense, growth, reproduction, learned predator recognition), morphology (shell shape and strength), and physiology and biochemistry (eggs, antioxidant system). The response diversity and sexual dimorphism of P. canaliculataunder predation were highlighted, and the predator-induced energy distribution and trade-off mechanisms were discussed. Finally, we proposed research priorities on the interaction mechanisms of P. canaliculata with its predators, technological developments and performance evaluation of biological control.
    Effects of ricecrab coculture on field ecological environment and rice growth: A review. #br#
    MIAO Wei, LIU Jia-min, ZHANG Jia, TANG Liang, ZHANG Wen-zhong, XU Zheng-jin
    2020, 39(8):  2785-2791. 
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    Rice-crab coculture is a mature model of integrated aquaculture system in China. Rice-crab coculture can produce higher economic value and also has a significant impact on the field ecological environment and rice growth. However, the underlying mechanisms are not fully understood. Here, we reviewed the effects of rice-crab coculture on field gas emission, nutrient cycling, and ecological benefit. We further focused on rice variety selection, water and fertilizer management, rice yield and quality. The following prospects should be paid more attention in future studies: integrative ecological environment; the combination of large-scale field experiment and small-scale simulation experiment; mechanism and the overall effect of ricecrab coculture; long-term field research. Future research should focus on synergy, quality and efficiency, for better understanding the effects of ricecrab coculture on ecological environment and rice growth.
    Screening differentially expressed proteins in root tips in response to methylmercury stress by iTRAQ technique and their bioinformatics analysis.
    LONG Shui-ting, WEI Yan, XU Xiao-hang, LIU Lin, QIU Guang-le
    2020, 39(8):  2792-2801. 
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    To understand the molecular mechanism of rice (Oryza sativa L.) in response to methylmercury (MeHg) stress, we analyzed the expressed proteins in root tips of rice Liangyou 302 under MeHg stress using isobaric tags for relative and absolute quantitation (iTRAQ) and liquid chromatographytandem mass spectrometry (LC-MS/MS). Differential proteins were elucidated in view of bioinformatics and molecular biology. The results showed that a total of 3508 proteins were quantified in both the control and MeHg treatment. According to fold change (≥1.20 or ≤0.83) andP<0.05, a total of 88 differentially expressed proteins were identified, out of which 32 proteins were upregulated and 56 proteins were down-regulated. There were 15 differentiallyexpressed proteins associated with the characteristic of metal ion binding, including 12 knownproteins of germination like proteins, lipoxygenase, and three unknown proteins. Results from the molecular functions of gene ontology (GO) suggested that differentially expressed proteins were mainly involved in catalytic activity, binding and transport activity, while the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway exhibited that they were significantly enriched in protein processing in endoplasmic reticulum, oxidative phosphorylation, starch and sucrose metabolism, and phenylpropanoid biosynthesis. Our results provide insight into regulating absorption of MeHg in rice.
    Monitoring effectiveness of halfduplex PIT telemetry technology.
    ZHANG Jian, WANG Yi-chuan, KE Sen-fan, BAI Yan-qin, TAN Jun-jun, LIU Zhi-xiong, CHENG Bi-xin, SHI Xiao-tao
    2020, 39(8):  2802-2809. 
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    As an important method monitoring fish passage efficiency with high reliability, precision, and automation, passive integrated transponder (PIT) telemetry has been widely used. During field monitoring, a crucial issue for ensuring data accuracy is how to maintain high-precision monitoring under interference from external environment. Based on video data on fish passing the PIT antenna, we tested the monitoring effectiveness of the halfduplex (HDX) PIT telemetry system, and analyzed the effects of the number and movement direction of fish on the accuracy of the HDX PIT telemetry system. The results showed that the monitoring effectiveness of the HDX PIT telemetry system was satisfactory. The mean error time of the tested fish through antenna with two sizes (Ⅱ, big size; Ⅰ, small size) was (0.40±0.46) s (Mean±SD), with the maximum error being 2.53 s. The number of crossing fish significantly affected the detection efficiency of antenna with two sizes. When a fish passed through the antenna, the detection efficiency of antenna Ⅱ and Ⅰ was 97.3% and 93.9%, respectively. When the number of fish increased to eight, the detection efficiency of antenna Ⅱ and Ⅰ decreased to 7.5% and 3.1%, respectively. The direction of crossing fish affected the detection efficiency of antenna Ⅰ, but not on that of antenna Ⅱ. We provide feasible suggestions to promote reliability of monitoring data for PIT telemetry system.
    Snow cover identification and area change in mountainous regions based on Sentinel-2 time series data.
    ZHANG Yan-li, ZHANG Li-ping
    2020, 39(8):  2810-2820. 
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    Snow cover is an important indicator of global climate change, and also an important freshwater resource in the arid regions of northwest China. Satellite remote sensing is an important way for snow cover identification and area change monitoring due to its large-scale, short-period, and repeated observations. Compared with Landsat TM, Sentinel2 image has advantages of higher radiation resolution, spectral resolution and spatial resolution, and higher time resolution, which undoubtedly is an important data source for snow research. At small and medium scales, the radiation brightness of highresolution satellite is affected not only by atmospheric attenuation such as atmospheric water vapor and aerosol, by topographical factors such as terrain shading, slope, aspect, but also by the surface bidirectional reflectance distribution function (BRDF), which distorts the surface information. Based on the digital elevation model (DEM), the atmosphere correction and topographic correction preprocessing were carried out synchronously on the basis of the surface BRDF characteristics using the mountain radiative transmission model, with 20 Sentinel-2 images of the middle section of Tianshan Mountain in China from May 2017 to April 2018. Then, snow cover information was accurately extracted by the normalization difference snow index NDSI and the snow reflectance threshold method in the green and nearinfrared bands. This method effectively eliminates the effects of water bodies, dense vegetation, shadows, and low radiance pixels on the recognition of snow. Moreover, combined with historical weather data, the variation characteristics of snow cover in the study area were analyzed within one year. Our results have great significance to the research on changes of surface reflectance and energy balance as well as terrestrial ecological environment caused by snow melting.