Table of Content

10 February 2020, Volume 39 Issue 2

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Spatiotemporal dynamics of China’s grassland NPP and its driving factors.

LIU Yang-yang, ZHANG Zhao-ying, TONG Lin-jing, WANG Qian, ZHOU Wei, WANG Zhen-qian, LI Jian-long

2020, 39(2):  349-363. 

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Grassland NPP in China from 2000 to 2015 was simulated based on the CASA model, incorporated with MODIS and meteorological data. Trend analysis, coefficient of variation and Hurst index were used to examine the temporal and spatial dynamics, stability and persistence of grassland NPP. The main influencing factors of grassland NPP change in China were identified. The results showed that grassland NPP increased significantly from 2000 to 2015, with an average change rate of 1.53 g C·m^-2·a^-1. Grassland NPP changed abruptly after 2011, with an obvious increase trend. Grassland NPP showed spatial heterogeneity, being lower in Northwest and higher in Southeast China. Areas with low NPP value were concentrated in most areas of Tibet Plateau and central Inner Mongolia. The area with increased grassland NPP accounted for 81.21% of the total grassland area, mainly distributed in the central region of Tibet Plateau and most areas of Loess Plateau. The regions with stable grassland NPP were mainly concentrated in Gannan region of Gansu Province and most of eastern Qinghai Province, while the unstable regions were mainly distributed in most areas of Tibet Plateau, central part and Hulunbuir of Inner Mongolia. The result of Hurst index analysis showed that grassland NPP in northern Xinjiang and most regions of Loess Plateau would continue to increase or decrease, while the future change of grassland NPP in southern Qinghai, central Inner Mongolia and Heilongjiang would be antisustainable. The average NPP values of alpine and subalpine meadow and meadow were 578.8 and 565.31 g C·m^-2·a^-1, respectively, while that of desert grassland was 122.61 g C·m^-2·a^-1. The increase in grassland NPP in most areas of China is mainly controlled by precipitation, while the increased temperature has a certain inhibition on grassland NPP. Human activities such as the reduction of overgrazing and the implementation of returning farmland to grassland exert important influence over the increases of grassland NPP.

Temporal and spatial distribution of aboveground biomass of vegetation and quantitative analysis of impact factors in semi-arid grassland basin.

ZHANG Jun-yi, LIU Ting-xi, LUO Yan-yun, DUAN Li-min, LI Wei, YANG Lu, Buren Scharaw

2020, 39(2):  364-375. 

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Xilin River Basin is the most representative area of typical steppe in Inner Mongolia. Characterizing the dynamics of aboveground biomass and its relationship with environmental factors can provide basic data for the research of ecosystem carbon cycling and a theoretical frame for rational use and management of grassland. Xilin River Basin locates in semiarid region. With filed empirical data, the methods of correlation analysis, classification and regression tree, nonlinear regression analysis were used to quantitatively analyze the relationship between aboveground biomass and its key driving factors in the upstream and downstream of the basin at different times (around June 20, July 5, July 20, and August 6 of 2016). The results showed that: (1) Aboveground biomass changed most significantly in July, with a peak on August 6. The aboveground biomass of the upper, middle and lower basin on August 6 were 79.64, 74.87, 69.34 g·m^-2 respectively. Biomass showed a decreasing tendency from the southeast to the northwest. (2) Key factors affecting aboveground biomass at different times in the upstream of the basin were precipitation in April, soil water content on July 5, soil water content on July 20, and Simpson index on August 6. The Simpson index had a negative effect on aboveground biomass, while all other factors had positive effects on aboveground biomass. Corresponding key factors accounted for 77%, 72%, 79%, and 65% of the variation of aboveground biomass, respectively. (3) Longitude, precipitation in June, precipitation in July, and precipitation in July were the key factors affecting aboveground biomass of the downstream on June 20, July 5, July 20, and August 6, respectively. All the factors had a significant positive correlation with aboveground biomass. Corresponding key factors accounted for 88%, 75%, 85%, and 82% of the variation of aboveground biomass, respectively. Our results provide a reference for the analysis of the temporal and spatial variation of plant biomass at a large scale and provide data for in depth research and long-term monitoring of grasslands.

Response of vegetation productivity patterns to rainfall in different habitats along a desert-oasis transition zone.

JI Shu-xin, QIAO Rong-rong, BAI Xue-lian, WANG Li-xiang, CHANG Xue-li

2020, 39(2):  376-383. 

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Landscape pattern analysis is an important method to understand the occurrence and development of ecological processes. In this study, we investigated the responses of vegetative productivity patterns of a gravel desert and a sandy desert (with a size of 1650 hm² each) in the desertoasis transition zone to sporadic rainfall events by using the MODIS data from June 22 to June 29, 2017. The internal landscape changes of these two habitats were different from each other. The area without increase of vegetation productivity (NDVI) in the gravel desert habitat was larger than that in sandy desert habitat. The change of vegetation productivity mainly occurred in the range of 0-0.01 in the gravel desert habitat, with its fluctuation area between 612.5 and 1200 hm². For the sandy desert habitat, the increase of vegetation productivity was concentrated above 0.01, and the fluctuation area ranged from 150 to 1587.5 hm². The landscape of the gravel desert habitat tended to be fragmented over time after rainfall events in the arid area, while the pattern of simple patches dominated the sandy desert habitat landscape.

The characteristic of species composition and community structure of low-altitude evergreen broad-leaved forest in Dagang Mountain, Jiangxi Province.

SONG Qing-feng, WANG Bing, NIU Xiang, LUO Zhi-wei

2020, 39(2):  384-393. 

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We investigated species composition, spatial distribution, biodiversity, and community structure of tree layer in an evergreen broad-leaved forest at low elevation in Dagang Mountain Ecological Station in Jiangxi Province. The results showed that: (1) Plant density was 1667 individuals·hm^-2 and there were 22 families, 34 genera and 41 species. Lauraceae, Fagaceae and Theaceae were most abundant, accounting for 52.49% of the total abundance. In addition, each species had a regular spatial distribution under the influence of environmental factors, disturbance factors and biological characteristics. (2) Simpson index, Shannon index, Pielou evenness index and Menhinick richness index were 0.896, 2.674, 0.725 and 0.978, respectively, which were lower than other evergreen broad-leaved forests in subtropical regions. (3) The height and diameter classes of trees showed an inverted “J” type distribution, which represented a typical heterogeneous forest structure and a relatively stable community structure. For each species, the height class and diameter class of trees had several distribution forms. For example, diameter distribution of Machilus pauhoi followed Poisson distribution, while Castanopsis fargesii followed multi-peak distribution. (4) This community was in the near climax community stage, with constructive species of C. fargesii, M. pauhoi and Symplocos sumuntia. In terms of tree height class and diameter class distribution, these three species had stable population structure, which was beneficial to the stable development of the whole community. Our results were helpful for understanding the variation of resource competition in the succession process of multispecies composition, providing scientific support for exploring forest community succession and its maintenance mechanism and the enhancement of ecosystem services.

Effects of topographical factors on species diversity across Dacrydium pectinatum natural community in Hainan Island.

LIU Hao-dong, CHEN Qiao, XU Zhi-yang, LIU Yang, JIANG Yi, CHEN Yong-fu

2020, 39(2):  394-403. 

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Environmental filters play a crucial role in the formation of species diversity patterns. Exploring the relationship between species distribution and environmental factors are important for reasonable management of forests. In this study, we analyzed species abundance, α diversity index, dominant population spatial pattern, and interspecific association with thirty Dacrydium pectinatum fixed plots in Bawangling National Nature Reserve, Hainan Island. A speciesenvironment relationship model (redundancy analysis, RDA) was built through species abundance data and topographic factors data. The results showed that D. pectinatum natural community had a rich species pool, including 187 tree species, 39 shrub species, and 36 herb species. The diversity index exhibited the pattern of tree layer > shrub layer > herbaceous layer, and was significantly higher than the midhigh latitude forest community. The evenness index was low. The species were mostly small-density populations. The importance values of all populations were low, with few dominant species. In addition, 10 dominant populations exhibited a pattern of cluster distribution, and their aggregate intensity and interspecific association were closely related. Results of Spearman analysis showed that the structure and diversity of the natural D. pectinatumcommunity in Bawangling were unstable. There might be intense interspecific competition and frequent species turnover in the future succession. The RDA model results showed that canopy density, elevation and slope aspect were the primary factors affecting species distribution, with dominant effects of canopy density. Our results suggest that some humanassisted measures can be adopted for biodiversity conservation, such as creating forest gaps to increase light utilization rate and reasonable thinning to increase seedling survival.

Population distribution pattern and spatial correlation of Kobresia humilis and Leontopodium nanum at different elevations.

ZHANG Ya-ya, LIU Min-xia, LI Bo-wen, XIA Su-juan, SUN Rui-di, SONG Jia-ying, LI Quan-di

2020, 39(2):  404-411. 

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Understanding the distribution pattern and spatial correlation of plant population is important for revealing the relationships between plant population and environmental factors, its own characteristics, and interspecific interaction. In this study, three plots were set up along an elevation gradient (2900, 3500, 3800 m). The population spatial distribution pattern and interspecific correlation of Kobresia humilis and Leontopodium nanum at different elevations were analyzed by Ripley K function. The results showed that: (1) The importance value, coverage and abundance of K.humilis showed an increasing trend, while that of L. nanum decreased with increasing altitude. (2) At different altitudes, K.humilis showed aggregated distribution at all the studied scales, with different degrees of aggregation among altitudes. L. nanum showed aggregated distribution at 2900 m and at the scale of 0-2.8 m, but its aggregation intensity gradually decreased with increasing scale, and finally changed to random distribution at 3500 m. At 3800 m, L. nanum showed an aggregated distribution at the 0-2 m scale and a random distribution at the 2-5 m scale. (3) K.humilis and L. nanum showed a positive correlation each other at the 0-1.1 m scale, but no correlation at larger scales at 2900 m, and a negative correlation at all the studies scales of 3500 m. At 3800 m, there was no correlation between the two species at the scale of 0-1.4 m and a negative correlation at larger scales, with the correlation increased with increasing scale.

Response of NDVI to SPEI at different temporal scales in Northeast China.

LUO Xin-lan, LI Ying-ge， YIN Hong， SUI Ming

2020, 39(2):  412-421. 

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Vegetation plays a vital role in terrestrial ecosystems. The frequency of drought event has gradually increased in recent years, which has negative impacts on vegetation growth. This study evaluated the response of vegetation growth in Northeast China to drought based on the correlation between normalized difference vegetation index (NDVI) and standardized precipitation evapotranspiration index (SPEI) from 1982 to 2015. The results showed that the maximum correlation coefficient (R_max) between NDVI and SPEI in annual and seasonal scales was the largest in the grassland region of Inner Mongolia (western Northeast China), followed by the Changbai Mountains (eastern Northeast China) and the Northeast Plain (centraleast part of Northeast China). The temporal scales with R_max were SPEI-12 and SPEI-24, indicating that drought has long lag effects on vegetation. The NDVI in growing season and summer was most sensitive to SPEI, and then decreased in spring and autumn. The NDVI in May-July had high proportion of significant correlations with SPEI-24, while NDVI in August-October exhibited high proportion of significant correlations with SPEI-06. Different vegetation types responded differently to drought. Forest NDVI showed a negative correlation with SPEI in different months and at different scales, while grasslands and croplands mainly showed positive correlations.

Characteristics of soil carbon pool management indices under different vegetation types in karst mountainous areas of North Guangxi.

TENG Qiu-mei, SHEN Yu-yi, XU Guang-ping, ZHANG Zhong-feng, ZHANG De-nan, ZHOU Long-wu, HUANG Ke-chao, SUN Ying-jie, HE Wen

2020, 39(2):  422-433. 

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To provide a basis for the eco-environment construction in karst mountain area, we examined the variation of soil labile organic carbon pool and carbon pool management index (CPMI) across different types of vegetation, including Cyclobalanopsis glauca secondary forest, shrub, Pinus massoniana forest, bamboo forest, grassland, cropland and bare land in the karst rocky mountain area of Northwest Guangxi. The results showed that: (1) Soil carbon storage and the contents of total nitrogen and available nitrogen in C. glauca secondary forest were significantly higher than that of the other plantations. Soil bulk density was lower than that of the other vegetation types except cropland. (2) The contents of soil organic carbon (SOC) and labile organic carbon (LOC) in all vegetation types decreased with increasing soil depth. The SOC content in 0-40 cm soil layer was 1.07-29.76 g·kg^-1, which decreased in the following order of C.glauca secondary forest > shrub >P.massoniana forest > bamboo forest > grassland > cropland > bare land. LOC content was 0.58-13.77 g·kg^-1, which decreased in the order of C. glauca secondary forest>shrub>P. massoniana forest>bamboo forest>cropland>grassland>bare land. The SOC/LOC was the lowest in the C. glauca secondary forest and highest in the cropland. (3) The CPMI decreased first and then increased, and decreased again with increasing soil depth. The mean value of CPMI in the 0-40 cm soil layer followed the order: C.glauca secondary forest>shrub>P. massonianaforest>cropland>bamboo forest>grassland>bare land. (4) Vegetation type, soil depth and their interaction had significant effects on CPMI and carbon pool characteristics. Our results indicate that soil organic carbon content and soil carbon pool stability could be improved efficiently by increasing vegetation cover and reducing disturbance from human activities in karst mountain area of North Guangxi.

A comparative study of temperature and humidity characteristics of mountain forest and open land at various elevations in Ailao Mountain and Yulong Snow Mountain.

ZHANG Peng, ZHANG Yi-ping, SONG Qing-hai, XU Kun, HUANG Hua, LIU Wei-wei, LUO Qi

2020, 39(2):  434-443. 

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We monitored air temperature and air relative humidity and analyzed the microclimate effects and elevational patterns in different forest ecosystems at various elevations in Ailao Mountain and Yulong Snow Mountain. The results showed that the annual dynamics of air temperature inside the forest and in open land at various elevations in two mountains showed an inverted U shape and air temperature of rainy season (May-October) was higher than that of dry season (November-April). In general, open lands had higher air temperature than forests. Forests at all elevations in Ailao Mountain had stronger effects on temperature than that in Yulong Snow Mountain. The absolute difference of air temperature between forest and open land generally increased with elevation. Air temperature inside forest in Ailao Mountain was lower than that in open land at annual scale, while Yulong Snow Mountain showed a same pattern except 3450 m. Thus, Ailao Mountain and Yulong Snow Mountain forests showed cooling regulation effects to a certain extent. Vertical lapse rate of temperature in Ailao Mountain forest (0.52 ℃·100 m^-1) was slightly higher than that in open land (0.50 ℃·100 m^-1), but was lower than that in Yulong Snow Mountain forest (0.55 ℃·100 m^-1) and open land (0.56 ℃·100 m^-1). Annual dynamics of air relative humidity of forest and open land at various elevations in two mountains also showed an inverted U shape. The relative humidity was higher in rainy season than in dry season, and lower in open land than in forest, with a similar pattern of air temperature. Moreover, air relative humidity at higher elevation was higher than that at lower elevation at annual scale. Both Ailao Mountain and Yulong Snow Mountain forests showed cooling and humidifying regulation effects. Ailao Mountain forests had the stronger cooling regulation effect but lower humidifying regulation effect than the Yulong Snow Mountain forests.

Changes in water holding capacity of Salix paraplesia woody debris with diameter classes in riparian zone of subalpine forest.

JIANG Yu-rui, TAN Bo, YANG Wan-qin, CHANG Chen-hui, WANG Zhuang, WANG Qin, LI Jing-yu1, YU Lin

2020, 39(2):  444-450. 

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To understand the water holding capacity of woody debris in the riparian zone of subalpine forest, water absorption process and water holding capacity of S alix paraplesia woody debris with six different diameter classes (>30, 30-20, 20-10, 10-5, 5-2 and 2-1 cm) were measured in the subalpine riparian zone of Wanglang National Nature Reserve by water immersion method. The results showed that the maximum water holding capacity across all diameter classes varied from 1024.78 to 2674.67 g·kg^-1. Water holding capacity from high to low was in order of 10-5, 20-10, 30-20, >30, 2-1, and 5-2 cm. The saturated water content increased over time during the process of water absorption, and the water absorption rate decreased. Woody debris with 30-5 cm diameter classes had good water holding capacity and water absorption capacity. In conclusion, retention of woody debris with larger diameter in the riparian zone is beneficial to improving the function of water conservation.

Influence of stand structure of Pinus massoniana on canopy hydrological effect.

YUAN Xiu-jin, XIAO Wen-fa, LEI Jing-pin, WANG Xiao-rong, HU Wen-jie, CUI Hong-xia, PANG Hong-dong, PAN Lei

2020, 39(2):  451-459. 

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Understanding the hydrological effects of forest across different stand structures and the main influencing factors can provide scientific support for forest management. We set up 14 plots with each area of 20 m×30 m in Pinus massonianaforests in the Jiulingtou Forest Farm located in Three Gorges Reservoir Area of China. We measured canopy interception, stemflow and throughfall, and assessed their stand characteristics. Pearson’s correlation analysis, principal component analysis and redundancy analysis were used to analyze the effects of stand structure (leaf areaindex, basal area, crown area, tree height, canopy density, stand density, mixing degree, size ratio, and competition index) on canopy interception rate, throughfall rate, stemflow rate. During the study period (June-October), the total amount of rainfall was 1008.4 mm, with interception, throughfall and stemflow accounting for 16.3%, 82.3% and 1.4% of the rainfall, respectively. Leaf area index, basal area and crown area were positively correlated with canopy interception rate (P<0.05), and negatively with throughfall rate (P<0.05). There were significant negative correlations between stemflow rate and tree height and canopy density (P<0.05), and a significant positive correlation between leaf area index and stand density (P<0.05). The results of the redundancy analysis showed that the combination of structural variables explained 59.6% of the redistribution of hydrological effect. Results of the Monte Carlo displacement test showed that canopy interception rate and throughfall rate were mainly affected by the combination of structural variables, such as forest stock volume. Higher the canopy interception rate and lower throughfall were correlated with larger forest stock volume. The stemflow rate was mainly affected by competition status and horizontal structure (R²=0.46, P<0.05) and forest stock volume (R²=0.51,P<0.05). The canopy hydrological effect was closely related to stand structure. Forest stock volume and water conservation effects were higher when the stand grew better.

Effects of rainfall characteristics on rainfall partitioning in Castanopsis hystrixplantation.

LEI Li-qun, ZHENG Lu, NONG You, LIU Shi-ling, LI Hua, HUANG De-wei

2020, 39(2):  460-468. 

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To provide basic hydrological data for sustainable management of south subtropical forest plantations, we measured rainfall, throughfall and stemflow in a 34year old Castanopsis hystrix stand in Guangxi Youyiguan Forest Ecosystem Research Station from January to December 2017. The results showed that total annual rainfall was 945.9 mm, with throughfall, stemflow and canopy interception accounting for 43.9%, 0.5% and 55.6% of total rainfall, respectively. The minimum rainfall that produced throughfall and stemflow was 0.6 and 3.8 mm, respectively. Rainfall had seasonal fluctuation, with the penetration rate being the lowest in summer and the highest in winter, and the stemflow rate and canopy interception rate showing opposite pattern. Small and short rainfall events led to low net rainfall input and high canopy interception. Among the four rainfall factors (rainfall amount, rainfall intensity, rainfall duration, and pre-rain drying period), rainfall amount had the strongest effect on rainfall distribution pattern. Rainfall intensity had a significant impact on stemflow rate. Rainfall duration had a significant impact on throughfall rate and canopy interception rate. Pre-rain drying period had no significant impact on the three components of rainfall distribution pattern. Results of multiple linear regression analysis showed that the response of the three components of rainfall partitioning to rainfall characteristics was not synchronized, with stemflow being less affected by rainfall characteristics than throughfall and canopy interception.

Community dynamics of an alien invasive plant species Tithonia diversifolia.

CHEN Jian, WANG Si-hai, YANG Wei, WU Chao

2020, 39(2):  469-477. 

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Community dynamics could reveal current status and future tendency of alien invasive species. Tithonia diversifolia, an alien invasive shrub species that is widely distributed in the tropical and subtropical regions of China was examined to understand the establishment and dynamics of T. diversifolia communities. We investigated the community characters with random survey of plots in the typical distribution area of T. diversifolia and analyzed the relationships between community characters and time span of establishment. The results showed that: (1) Old branches suppressed the production of young branches and controlled the community development after the community had developed to certain stage. (2) The mean stembase diameter of branches negatively correlated with cluster density and branch density (P<0.01) and positively correlated with aboveground biomass (P<0.01). The infructescence density did not correlate with mean stem-base diameter of branches (P>0.1). (3) Soil total K and available P concentrations were significantly increased (P<0.05) with the development of T. diversifolia community, whereas the concentrations of soil organic matter, total N, and hydrolysableN showed an insignificant decreasing trend (P>0.1). In conclusion, with the increases of colonization time, cluster density and branch density decreased, community aboveground biomass increased, and community infructescence amount per unit area unchanged. T. diversifolia community could occupy the invaded area in the long term, with consistent influence on soil nutrient composition.

Effects of drought stress and rehydration on physiology and biochemistry of leaf color in four species of Commelinaceae.

DENG Lei, WEN Min, GUO Wei, LIU Ping, XU Yu-fen, HONG Lan, HAN Rui-hong, WANG Gang, SUN Yan-jun

2020, 39(2):  478-486. 

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Four species (Belosynapsis ciliata, Murdannia simplex, Murdannia loriformis and Callisia repens) from Commelinaceae were used as experimental materials to explore the effects of drought stress and rewatering on the leaf physiological and biochemical characteristics of leaf color, aiming to provide basis for plant cultivation and breeding. The results showed that the content of anthocyanin in Belosynapsis ciliata and Murdannia simplex significantly increased under drought stress, and decreased to some extent after rewatering. There was no change of anthocyanin content in Murdannia loriformis and Callisia repens. The chlorophyll content of four species increased first and then decreased, and increased after rewatering; but still lower than that in CK. The carotenoid content of Belosynapsis ciliata and Murdannia simplexincreased first and then decreased, while it increased first, decreased and then increased for the other two species. The total antioxidant capacity of Belosynapsis ciliata and Mrdannia simplex increased with drought stress, while that of Murdannia loriformis and Callisia repens increased first and then decreased. The chalcone isomerase activity of the four species increased first and then decreased, and it was nonlinearly related to anthocyanin content. The phenylalanine ammonia lyase activities of Belosynapsis ciliata and Murdannia simplex increased, while that of Murdannia loriformis and Callisia repens decreased. The soluble sugar content of Belosynapsis ciliata and Murdannia simplex decreased first and then increased under drought stress, while that of Murdannia loriformis and Callisia repens increased. The increases of malondialdehyde content in Murdannia loriformisand Callisia repens were much higher than that inBelosynapsis ciliata and Murdannia simplex.

Compensatory growth of tomato after high temperature and high humidity stress.

YUAN Chang-hong, YANG Zai-qiang, ZHAO He-li

2020, 39(2):  487-496. 

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A three-factor orthogonal experiment of temperature, relative humidity, and duration was carried out to examine the combined effects of high temperature and high humidity stress on tomato “Jinguan 5”. There were four levels of temperature: 32 ℃/22 ℃, 35 ℃/25 ℃, 38 ℃/28 ℃, 41 ℃/31 ℃ (day/night temperature), three levels of air relative humidity: 50%±5%, 70%±5%, 90%±5%, and four durations (3, 6, 9, 12 d), with 28 °C/18 °C and 50%-55% relative humidity as control (CK). Sampling was carried out at 7, 14, 21 and 28 d after high temperature and high humidity stress. We measured growth index, antioxidase activity and chlorophyll content. The results showed that after high temperature stress, dry weight of tomato decreased significantly, and leaf area increased significantly when the treatment was at 35, 38 and 41 °C. Dry weight of tomato at 41 °C was 12.89% lower than that of CK. After high temperature treatment, the contents of chlorophyll a, chlorophyll b and carotenoids were lower than that of CK, and SOD, POD and CAT activities were higher than that of CK. With the increase of temperature, enzyme activities increased first and then decreased. The activities of SOD, POD and CAT were the highest at 38 ℃, which increased by 121.14%, 35.41% and 55.13%, respectively. Under the same temperature conditions, tomato grew best at the RH70% treatment. SOD, POD, CAT activity and chlorophyll content at RH70% were significantly higher than that at RH50% and RH90%. Appropriate high temperature could promote the growth of tomato and increase antioxidant enzymes. The growth of tomato was overcompensated when temperature was below 32 °C, but it was severely suppressed when temperature exceeded 38 °C. Under high temperature, increasing humidity could alleviate the stress of high temperature on plants to someextent, but such effect was limited and could not compensate the damage of high temperature stress.

Effects of groundwater depth on root system and dry matter accumulation of maize in central Liaoning Province.

SUN Shi-jun, SUI Wen-hua, CHEN Wei, SU Tong-yu, TAI En-bo, ZHANG Qi, MENG Wei-zhong

2020, 39(2):  497-506. 

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To examine the effects of different groundwater depths on dry matter accumulation and root growth of maize, seven groundwater depth treatments (1.0 m (D1.0), 1.5 m (D1.5), 2.0 m (D2.0), 2.5 m (D2.5), 3.0 m (D3.0), 3.5 m (D3.5) and 4.0 m (D4.0)) were set up with groundwater simulation system at the Irrigation Experimental Center of Liaoning Province, Shenyang, China. We measured maize dry matter accumulation, maize root growth and yield. The results showed that: (1) Root length, root surface area and root volume increased with maize growth under all treatments. There were significant differences among the treatments. Root diameter increased first and then decreased at the filling-mature stage. (2) Dry matter accumulation of stem and leaf decreased first and then increased with increasing groundwater depth in jointing stage and fillingmature stage of maize. Dry matter accumulation of maize stem and leaf under D2.0 treatment was the lowest, with a decrease of 7.2%-19.5% compared with other treatments. The dry matter accumulation of maize ear under D2.5 treatment was the lowest, being 9.8%-24.8% lower than other treatments. Dry matter of roots under D2.0 treatment at tasseling and silking stage was the highest, being 7.2%-54.2% higher than other treatments. (3) Maize yield decreased first and then increased with increasing groundwater depth. The D1.0 treatment attained the highest yield, which was 365-1790 kg·hm^-2 higher than other treatments. The D3.0 treatment had the lowest yield. (4) Results from multiple regression and path analysis showed that groundwater affected maize yield by affecting root growth and dry matter accumulation. Maize yield had a significantly positive relationship with root length and root diameter at tasseling and silking stage, and a significantly negative relationship with root surface area, dry matter accumulation of stem and leaf at tasseling and silking stage, and root surface area at filling-mature stage of maize. Our results can provide theoretical basis for improving maize yield in Liaoning plain and similar areas under different groundwater depths.

Effects of straw returning in conjunction with different nitrogen fertilizer dosages on corn yield and soil properties.

WANG Xue-min, LIU Xing, HAO Li-ying, XIE Hong-tu, ZHANG Guang-na, CHEN Zhen-hua, ZHANG Yu-lan

2020, 39(2):  507-516. 

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The combination of returning agricultural biomass into soil and reducing application dosage of chemical fertilizer can effectively improve soil quality. Considering the speciality and importance of black soil in Northeast China, a splitplot design experiment was set up in the Conservation Tillage Research and Development Station of the Chinese Academy of Sciences (black soil area, Jilin Province), which combined different straw returning modes with nitrogen fertilizer (N) addition levels. We analyzed crop yields, physicochemical properties and biological properties (0-20 cm) of soils. The feasibility of reducing nitrogen fertilizer dosage on the base of straw returning was discussed. There were six treatments of straw returning modes in the main plots: control (CK), full straw mulching without tillage (NT), crushing straw incorporation directly (SD), addition of compost from straw insitu (SC), addition of biochar from straw insitu (BC), and 9/10 straw +1/10 compost (SDC). The subplots, i.e., fertilizer dosages included: conventional NPK chemical fertilizer (N100); 20% reduction of N fertilizer (N80) (N content of straw was close to 20%); 40% reduction of N (N60, with conventional phosphorus, potassium fertilizer). Straw cooperation modes and N levels significantly interacted to affect maize biomass, maize yield, soil physical and chemical properties (pH, organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP)), and enzyme activities (dehydrogenase, α-glucosidase, β-glucosidase, β-1,4-N-acetylglucosidase, acid phosphomonoesterase and alkaline phosphomonoesterase). Straw cooperation had significant main effects (P<0.05), while N dosage had no significant effect on the examined variables. Among treatments with chemical application alone, N reduction treatment decreased maize biomass and yield and enhanced TP content and activities of N-acetylglucosidase and alkaline phosphatase, but had no significant effect on pH, SOC, TN, and activities of dehydrogenase, αglucosidase, βglucosidase, and acid phosphatase. Straw returning in conjunction with conventional NPK fertilizer (N100) increased soil pH, SOC, TN, and TP (P<0.05), and enhanced activities of dehydrogenase, α-glucosidase and acid phosphomonoesterase to a certain extent, with some treatments having no such effects. Straw returning modes combined with N reduction (N80, N60) had no negative impact on the maize biomass and yield, and enhanced soil pH, SOC, TN and TP (P<0.05). NT with N reduction enhanced β-glucosidase and acid phosphatase activities. SC with N reduction significantly increased activities of β-glucosidase, acid phosphatase and alkaline phosphatase. SDC with N reduction significantly enhanced activities of β-glucosidase and alkaline phosphatase. It is concluded that short-term combined treatment of straw returning and nitrogen reduction application stabilized crop yield, slowed soil acidification, and maintained SOC, TN and TP contents. Therefore, straw cooperation in conjunction with N application reduction has great ameliorative effects on soil nutrient storage, supply, and transformation.

Effects of physicochemical characteristics of water body on phytoplankton community in Hongfeng Lake in Guizhou Province.

JIN Zu-xue, WANG Jing-fu, LI Qiu-hua, ZHANG Rui-xue, LIU Yong, YU Ping-ping, CHEN Quan, CHEN Jing-an

2020, 39(2):  517-526. 

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To clarify the relationship between water physicochemical characteristics and phytoplankton community in Hongfeng Lake, water samples were monthly collected and analyzed at three sites (DB, HYD, and HW) in 2014. The trophic level index (TLI), algal abundance, and evaluation criteria for lake trophic type were used to evaluate the eutrophic level of Hongfeng Lake. The correlation between environmental factors and the abundance of phytoplankton were analyzed. The results showed that: (1) A total of 105 species (belonging to seven phyla) of phytoplankton were identified in the lake, dominated by cyanobacteria, green algae, and diatom. (2) Algae abundance peaked in spring and autumn, with Pseudanabaenasp. being the dominant specie in most months, followed by Scenedesmus bijugatus, Chlorella vulgaris and Cyclotella sp. (3) The eutrophic level of Hongfeng Lake ranged from mesotrophic to moderate eutrophication. (4) Results of correlation analysis showed that water temperature, dissolved oxygen, total nitrogen concentration, and water transparency were the major factors influencing the abundance of algae. Our results provide important scientific foundation for water environment protection and eutrophication control in Hongfeng Lake.

Phytoplankton community structure and its relationship with environmental factors in Xin’anjiang River Basin (Tunxi section).

ZHANG Guo-qing, YANG Yu-ling, TANG Ai-guo, WANG Li, DING Tao, WANG Heng-xing, MENG Yang, LU Sha-long, DONG Li-li, DUAN Shuang-quan, LI Wei

2020, 39(2):  527-540. 

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We investigated the seasonal variation of phytoplankton community structure and its relationship with environmental factors in Xin’anjiang River Basin (Tunxi section) from 2017 to 2018. A total of 160 species (including variants) from 96 genera belonging to seven phyla were identified, among which, Chlorophyta (72 species from 42 genera), Bacillariophyta (49 species from 26 genera) and Cyanophyta (19 species from 15 genera) were dominant. Photosynthetically active radiation (PAR), UVA and UVB had the highest intensity in summer, followed by spring, autumn and winter. The pH, dissolved oxygen, and water temperature differed among seasons. The concentration of ammonia nitrogen (NH₃-N) concentration and turbidity were significantly higher in winter than that in other seasons. There was no significant difference in total phosphorus (TP) concentration and oxidation reduction potential among the four seasons. Chlorophyll a and carotenoid concentrations varied spatially and temporally, with higher concentrations in summer and winter than in spring and autumn. The Shannon index, Simpson index, Margalef index and Pielou index did not change across seasons and sampling sites. Water quality was between the criteria of type I and type III, with most of which being located in type I and type II. The pollution indicator species showed a mesosaprobic zone. Shannon index and Margalef index revealed a slight pollution or nonpollution status of the studied area. Water quality of Xin’anjiang River Basin (Tunxi section) was generally in good condition according to the comprehensive analyses of both chemical and biological indices. Redundancy analysis results showed that the number of phytoplankton species in each phylum  had positive relationship with NH₃-N and TP, where UVB had a strong negative relationship with Bacilariophyta. PAR, UVA, UVB and water temperature were the main factors regulating phytoplankton abundance, which had positive relationship with  abundance of Bacillariophyta, Dinophyta and Euglenophyta but negative relationship with  abundance of Chloropyta, Cyanobacteria, Chrysophyta and Cryptophyta.

Effects of water content on the abundance and activity of autotrophic microbes in purple soil.

WEI Wan-ling, CHENG Yong-yi, ZHOU Zhi-feng, WANG Ming-xia

2020, 39(2):  541-548. 

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With cbbL (ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) large-subunit gene) and RubisCO (1,5-bisphosphate ribulose carboxylase) enzyme as markers, we investigated the effects of soil water content on the abundance and activity of soil autotrophic microbes in an indoor incubation experiment for 28 days. There were four treatments with different soil water contents (mass percentage of water to dry soil), including 10% (W₁₀), 15% (W₁₅), 25% (W₂₅), and waterlogging (WL). Soil samples were harvested after 3, 7, 14, and 28 days of incubation, with soil organic carbon content, cbbL abundance, and RubisCO enzyme activity being measured. The results showed that soil cbbL abundance increased with increasing soil water content during the first 14 days. WL treatment had the highest cbbL abundance during the whole period of incubation. At the initial stage of incubation (day 3), there was no significant difference of soil RubisCO enzyme activity among these treatments (P<0.05). At the end of incubation (day 28), however, RubisCO enzyme activity in the treatments with lower water content (W₁₀ and W₁₅) was significantly lower than that in the treatments with higher water content (W₂₅ and WL; P<0.05). Soil organic carbon content (F=11.91,P=0.03), cbbL abundance (F=42.33,P<0.01), and RubisCO enzyme activity (F=51.55,P<0.01) significantly varied among different treatments. Soil cbbL abundance and RubisCO enzyme activity were positively correlated (R²=0.23,P<0.01), and both of them were negatively correlated with soil organic carbon content. Our results indicated that soil water content played an important role in controlling the abundance and activity of soil autotrophic microbes, which should be valuable for further mechanistic understanding of responses of soil carbon transformation to soil moisture variation.

Coupling effects of ionic strength and water saturation on transport and distribution of Escherichia coli in porous medium.

KANG Jia, YANG Li-qiong, SHI Ya-nan, ZHUANG Jie

2020, 39(2):  549-558. 

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Ionic strength and water saturation have significant impacts on transport and deposition of bacteria in porous medium. In this study, column breakthrough experiments with IVIS Spectrum System were performed to investigate the effects of ionic strength and water saturation on transport and retention of target bacteria Escherichia coli T7 under three levels of ionic strength (2, 50, 100 mM) and two levels of water saturation (85%, 100%). At same ionic strength, the migration of E. coli T7 under saturated condition was stronger than that under unsaturated condition.M_eff of saturated and unsaturated column was 34% and 8% at 100 mM, respectively. In line with above results, the onesite kinetic estimated parameterk_att of unsaturated column was 7.7 times higher than the corresponding values of saturated column at 100 mM. Results of DLVO and capillary force showed that decrease of E. coli T7 migration under unsaturated condition was caused by adsorption of airwater interface due to capillary force. In saturated column, increase of ionic strength promoted deposition of E. coli T7. With ionic strength increasing from 2 mM to 100 mM, M_res of saturated column increased from 47% to 58%, with decrease of electrostatic repulsion and increase of radius of E. coli T7 being the causes. Increase of ionic strength promoted deposition of E. coli T7 under unsaturated condition, which was more significant than that under saturated condition. With ionic strength increasing from 2 mM to 100 mM, M_res of unsaturated columns enhanced from 46% to 84%. Increase of M_res under unsaturated condition was 2.5 times higher than that under saturated condition. The main reasons were decreasing of electrostaticrepulsion and increasing of capillary force. Results of IVIS Spectrum System showed that deposition of E. coli T7 was more significant at inlet of saturated columns, and increasing ionic strength promoted retention. The retention profiles of saturated column were prone to be exponential gradually over time. The retention profiles were non-monotonic in unsaturated column. As ionic strength decreased, the position of max retention quantity moved to outlet of the columns.

Behavior patterns and affecting factors of wintering common cranes inhabiting paddy fields of Poyang Lake.

GONG Hao-lin, SHAO Ming-qin, LU Ping, ZHU Guang-chen, DAI Nian-hua, ZENG Jian-hui

2020, 39(2):  559-566. 

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We analyzed the daily wintering behavior patterns and their affecting factors in common crane (Grus grus) inhabiting paddy field near Poyang Lake from October 2018 to March 2019, using focal sampling methods. Foraging (77.45%), vigilance (11.17%), and grooming (7.82%) were the main behaviors of cranes, with the predominant patterns being: foraging vigilance foraging and foraging grooming foraging. The time budget and duration spent for foraging by juvenile cranes was significantly higher than that of adult cranes (P<0.01). This is probably due to lower feeding efficiency in young cranes and longer total foraging time and individual foraging duration. The vigilance behavior of adult cranes (P<0.01) was significantly greater than that of juvenile cranes, with no significant difference in the duration of vigilance behavior betweenjuvenile and adult individuals. The frequency and time budget of vigilance in adult cranes during foraging intervals were significantly greater than that of juvenile cranes (P<0.05). This result indicates that adult cranes protected the safety of juvenile cranes by increasing the number of vigilance scans. The duration and time budget of foraging behaviors increased throughout the overwintering period. Locomotion was increased throughout the wintering period, which was related to the availability of food resources. Reduced intensities of human activities, such as grazing domestic ducks, would decrease foraging difficulty for cranes. There were significant differences in locomotion behavior among different crane families and during foraging intervals, which may be related to the differences of food resources. In terms of the activity rhythms, foraging behavior was generally at a high level during the daytime, with small peaks at 10:00-10:59, 12:00-12:59, and 16:00-16:59. Vigilance behavior remained at a stable level. A peak in grooming behavior occurred after a peak of foraging behavior because cranes groom after becoming fatigued from foraging. The behavioral rhythm of juvenile cranes was different from that of adults, with the foraging behavior of adults being more rhythmical and that of juvenile cranes is more random. This is related to the lack of foraging experience. The peak of vigilance behavior in young cranes occurred in the trough of such behavior in adult cranes, which may relate to the consistence of the vigilance in the whole family group.

Comparison of functional responses and biological characteristics between exotic species Clarias gariepinus and native species Silurus asotus.

ZHU Bing-tao, XU Meng, LIU Chao, GU Dang-en, YU Fan-dong, YANG Ye-xin, HU Yin-chang, MU Xi-dong

2020, 39(2):  567-575. 

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The Pearl River system is one of the rivers being most severely invaded by exotic aquatic animals in China. While the invasive species are diverse, the impacts of exotic fish on local fish resources has not been effectively evaluated. Comparative functional response is considered as an effective approach to quantify the potential ecological impacts of exotic species. In this study, adopting a manipulated experiment, we compared the functional responses of an exotic species, Clarias gariepinus and a native species, Silurus asotus. Cirrhinus molitorella, Megalobrama hoffmanni and Ctenopharyngodon idellus were used as feeding materials with bait density of 1, 2, 4, 8, 16, and 32, and three replicates for each treatment. We analyzed the types of functional responses, constructed the curve of functional response and fitted the parameters of the functional response. In addition, food conversion efficiency and biological characteristics of C. gariepinus and S. asotus were compared. The results showed that both C. gariepinus and S. asotus exhibited Type II functional response. Compared with S. asotus, C. gariepinus had a higher rate of unit resource consumption, i.e., a stronger attack rate (P<0.05), while there was no significant difference in the handling time between the two species (P=0.272). Food conversion efficiency of C. gariepinus was significantly lower than that of S. asotus (P<0.05). There was no significant difference in the relative growth rate between both species (P=0.762). Our results provide a basis for future systematic assessment of the ecological impact of C. gariepinus and can serve as a reference for quantifying resource consumption rate and potential ecological impacts of otherexotic fishes.

The effects of temperature on anesthetic effect of juvenile Chinese sturgeon (Acipenser sinensis).

GUAN Min, ZHANG De-zhi, RAO Jun, TANG Da-ming

2020, 39(2):  576-585. 

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Using MS-222 as an anesthetic, we investigated the effects of temperature on the anesthetic effect of juvenile Chinese sturgeon (Acipenser sinensis). The effects of water temperature (15, 20 and 25 ℃) on the effective anesthetic concentration, the time of induction and resuscitation, the longest anesthesia survival time and the final anesthesia status of juvenile Chinese sturgeon were examined. The effects of air temperature (4, 12 and 20 ℃) on the recovery time and the longest air exposure time of juvenile Chinese sturgeon were examined. The results showed that the optimum concentrations of MS-222 on juvenile Chinese sturgeon at 15, 20 and 25 ℃ were 100-240, 80-140 and 60-130 mg·L^-1, and the longest anesthesia retention time were 11 min, 7 min and 70 s, respectively. With the increases of water temperature, the time of enema and the longest anesthesia retention time of juvenile Chinese sturgeon were significantly decreased. Recovery time decreased first and then increased, with no significant correlation between recovery time and temperature. The final anesthetic level of juvenile Chinese sturgeon increased with the increase of MS-222 concentration. With increasing air temperature, the longest air exposure and survival time of juvenile Chinese sturgeons decreased significantly, and the recovery time increased significantly. The longest air exposure survival time of juvenile Chinese sturgeon at 4, 12 and 20 ℃ were 60, 28 and 14 min, respectively. Water temperature significantly affected the anesthetic effect of juvenile Chinese sturgeon. Air temperature significantly affected the recovery time and the longest air exposure survival time of Chinese sturgeon. The effect of water temperature on anesthesia effect should be fully considered during the anesthesia of Chinese sturgeon. In the manual operation of Chinese sturgeon, the effects of air temperature on the air exposure survival time of Chinese sturgeon should be fully considered to avoid accidental damage or death of fish.

Diversity and spatiotemporal distribution of soil microarthropod communities in forests on the eastern slope of Gongga Mountain.

ZHOU Yu-zhen, WU Peng-fei

2020, 39(2):  586-599. 

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We examined the spatiotemporal variations in taxonomic composition and diversity of soil microarthropod communities under four vegetation types along the altitude gradient on the eastern slope of Gongga Mountain. The vegetation types included evergreen broad-leaved forest (EBF, at an altitude of 1930 m), deciduous broad-leaved forest (DBF, 2343 m), coniferous and broad-leaved mixed forest (CBF, 2780 m), and dark coniferous forest (DCF, 3160 m). Soil microarthropods were investigated in March, May, July, October and December, 2012. A total of 8581 individuals of soil microarthropods were collected and classified into 8 classes, 28 orders, 114 families and 145 taxa or genera. The microarthropods were dominated by Paranurophorus, which accounted for 24.26% of the total individuals. The microarthropod communities on the eastern slope of Gongga Mountain showed higher taxonomic richness and unique zonal characteristics compared to those of forest ecosystems in subtropical and temperature zones. The results of principal component analysis and similarity indices showed that soil microarthropod community structure were similar among the four forest types, but the similarity declined with the increasing of relative altitude among the different forests. The density, richness and Shannon index of soil microarthropod communities decreased with increasing altitude, with lower richness and Shannon index of dark coniferous forest than those of the other forests. Moreover, the density, richness, Shannon index and Simpson index of soil microarthropod communities were higher in March and December than in May, July and October, with significant differences among the sampling months. Soil organic matter, available P, pH, soil temperature and moisture were the main factors driving the spatial distribution of the density and diversity of soil microarthropods. Our results indicated that soil microarthropod community on the eastern slope of Gongga Mountain had higher taxonomic richness and unique zonal characteristics, and their community structure, density and diversity index were more sensitive to seasons than to vegetation types.

Suitable distribution of endangered species Pseudotaxus chienii (Cheng) Cheng (Taxaceae) in five periods using niche modeling.

ZHANG Wen-xiu, KOU Yi-xuan, ZHANG LI, ZENG Wei-dong, ZHANG Zhi-yong

2020, 39(2):  600-613. 

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Changes in the distribution of organisms throughout different geological times have been widely investigated by niche modeling. This knowledge is of great importance for biodiversity conservation in front of anthropogenic global warming. Pseudotaxus chienii (Cheng) Cheng is an endangered plant species scattered in southeast China. In this study, we reestablished its distribution ranges in five periods (Last Interglacial, LIG; Last Glacial Maximum, LGM; MidHolocene, MH; current and future) using 34 presence records by niche modeling based on 19 bioclimatic factors. The results showed that precipitation of driest month was the key bioclimatic factor affecting its distribution, suggesting that this species prefers a humid climate with a short dry season. During the LIG, P. chienii distributed widely in southeastern China. During the LGM, the distribution area of P. chienii expanded to Zhejiang, Fujian, the east of Guizhou, and the optimal distribution in the central China (Jiangxi and Hunan) decreased. During the MH, the optimal distribution area was decreased than that in the LGM, with more serious habitat fragmentation than that in LIG. In the future, the suitable distribution area of P. chienii will decrease under the predicted warming climate. The species will shrink to the higher elevations, and the suitable area of middle and low altitude (below 600 m) will disappear largely. Our results present an important insight into the response of P. chienii to climate changes, and provide a guideline for the conservation of this endangered species.

Identification of urban ecological space in South Jiangsu based on GIS: A case study of Suzhou.

XU Hua-lian, GAO Wei-long, CHEN Si, CHEN De-chao

2020, 39(2):  614-624. 

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Urban ecological space is indispensable in maintaining urban ecosystem balance, providing ecosystem services for the city, and improving life quality of urban residents. Reasonable delimitation of urban ecological space is important for constructing sustainable land spatial pattern and maintaining the balance between economic development and ecological construction. In this study, based on the evaluation of ecosystem services and ecological sensitivity, we delimited the ecological space of Suzhou by selecting the targeted evaluation indices and evaluation models, based on RS and GIS technology. The results showed that total area of ecological space in Suzhou is 4543.64 km², accounting for 52.48% of the city’s total area. The buffer area is 2465.11 km², accounting for 28.47% of the total area. Statistic analysis by Fragstats 4.2 showed that there were 2877 patches in the ecological space, indicating obvious fragmentation of ecological space in Suzhou. The statistic results of land use types of ecological space showed that ecological space was occupied by about 13% of urban construction land.

The effect and mechanism of sponge city construction on heat island mitigation: A case study of Jiaxing.

HUANG Chu-dong, LI Dan-jun, CHEN Qian-hu, WANG Xian-ping

2020, 39(2):  625-634. 

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Mitigating urban heat island effect by sponge city construction has become one of the important issues in the research area of global climate change. Jiaxing is among one of the earliest members of national pilot sponge cities of China. With the land surface temperature of Jiaxing retrieved from Landsat 8 images in 2013, 2015, 2017 and 2018, we evaluated the mitigation effect of sponge city construction on the urban heat island of Jiaxing. The relationship between structural indicators of sponge city construction and relative heat island intensity at small andmedium scales was analyzed by Pearson correlation analysis, regression analysis and grey comprehensive correlation analysis. The results showed that the construction of sponge city obviously alleviated heat island effect of Jiaxing, with enhanced mitigation effect following the improvement of sponge city construction. The effects of structural indicators for sponge city construction from largest to the least were in the order of proportion of effective impervious area, proportion of sinking green belt, proportion of green area and proportion of permeable pavement. Considering the effectiveness of urban heat island mitigation and the economy of the project, there were differences in the thresholds of different indicators. The proportion of effective impervious area should be lower than 0.45. The proportion of green area should be higher than 0.35. The proportion of permeable pavement should be controlled at about 0.4. The application proportion of the sinking green space should be as large as possible. Based on those results, we put forward some suggestions to mitigate the urban heat island effect.

Carbon and nitrogen accumulation characteristics of sediment in higher-place shrimp pond.

WANG Zi-ai, TANG Shao-xia, CHEN Ke-ke, FU Yu-xuan, ZHENG Miao, YANG Chun-yan

2020, 39(2):  635-644. 

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To clarify the environmental impacts of higher-place shrimp pond aquaculture, we analyzed the concentrations of total nitrogen (TN), total carbon (TC), and total organic carbon (TOC) in the sediments sampled from three types of shrimp aquaculture in the Dongying Town of Haikou City. The sediments were sampled from four layers: 0-5 cm (t1), 5-10 cm (t2), 10-15 cm (t3), and 15-20 cm (t4). The concentrations of TC, TOC, TN in the soil outside the embankment of shrimp ponds were 5.66, 6.95 and 2.49 times higher than that of 〖JP2〗shrimp ponds, respectively, a phenomenon caused by the infiltration of wastewater from the higherplace shrimp〖JP〗 ponds. Additionally, the concentrations of TC, TOC and TN in the sediments were 7.36, 8.68 and 4.41 times higher than the background value, which was caused by accumulation of baits and shrimp excrement. The concentrations of TN, TC and TOC in the sediments of the bottom auxiliary sand were the highest in the surface layer and 2 to 27 times higher than that in the deep soil. In the bottom auxiliary cement shrimp pond, the concentrations of TN, TC and TOC in the crack were the highest in the third layer of soil, showing a trend of t3>t1>t2>t4. The concentrations of TN, TC and TOC on the outer side of shrimp pond dike showed a significant decrease from the surface layer to the deep layer. The TOC and TN in the surface sediments in shrimp ponds and the residues of bait and shrimp dung during culture were seriously exceeded the standard after the discharge of wastewater. The organic nitrogen and organic index of surface sediments of the unwashed shrimp pond after draining wastewater were classified as III moderate pollution and Ⅱ mild pollution, while both organic nitrogen and organic index of the bait and shrimp manure residues during the culture were classified as IV heavy pollution. The organic index in the lateral soil of the shrimp ponds embankment was III moderate pollution, while organic nitrogen rating was IV heavy pollution. The C∶N ratio in the sediments of the shrimp pond was low, which was conducive for the formation of humus stemmed from residual baits and biological excretions in sediments. If humus is not cleaned in time, it will reduce aquaculture water quality.

CH₄ and N₂O production potentials of sediments in Cyperus malaccensis marsh and reclaimedshrimp pond of Minjiang River estuary.

LI Ling, YANG Ping, TAN Li-shan, TONG Chuan

2020, 39(2):  645-654. 

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Reclamation of estuarine wetlands into aquaculture ponds has been an important eco-environment problem in coastal areas, with consequences on carbon and nitrogen cycling of estuaries. In this study, we measured methane (CH₄) and nitrous oxide (N₂O) production potentials of the surface sediments form Cyperus malaccensis marsh and reclaimed shrimp pond in the Shanyu shoal of the Minjiang River estuary by anaerobic incubation experiment from May 2016 to March 2017. The results showed that CH₄ production potentials of surface sediments from the C. malaccensismarsh and shrimp ponds varied from 0.33 to 215.2 and 0.13 to 9.41 ng·g^-1·d^-1, with mean values of 40.07±23.00 and 2.16±0.98 ng·g^-1·d^-1, respectively. CH₄ production potentials in autumn and summer were higher than that in spring and winter.  N₂O production potentials of the sediments in the C. malaccensis marsh and shrimp ponds ranged from 0.43 to 0.80 ng·g^-1·d^-1 and 0.45 to 0.84 ng·g^-1·d^-1, with mean values of 0.58±0.01 and 0.61±0.01 ng·g^-1·d^-1, respectively. CH₄ production potential of the sediments from C. malaccensis marsh was significantly higher than that from shrimp ponds (P<0.01). There was no significant difference in N₂O production potentials between the two ecosystems (P>0.05).

Research progresses in effects of climate warming on soil fauna community structure.

ZHANG Hui, WU Hai-tao

2020, 39(2):  655-664. 

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The global average temperature is continuously becoming warming, with far-reaching impacts on ecosystems. As one of the most abundant biological components in terrestrial ecosystems, soil fauna plays a vital role in environmental indications and biogeochemical cycles. Numerous studies have shown that climate warming has profound effects on soil fauna community structure, though the underlying mechanisms are not fully understood. This review summarized research progress and proposed that climate warming would affect soil fauna community structure through changing the growth, development and reproduction of soil fauna; the habitats and environments; food resources; and food web structures. Furthermore, we proposed that the following prospects should be paid more attention in future studies: (1) sensitive areas to climate change; (2) longterm field observations; (3) new sampling techniques for soil fauna; (4) applications of isotopic and high-throughput sequencing approaches; (5) analysis of functional traits of soil fauna; (6) potential effects of climate warming on the ecological function of soil fauna.

Nitrogen pollutant removal by riparian buffer zone: A review.

WANG Qiong, FAN Kang-fei, FAN Zhi-ping, LI Fa-yun, WANG Jun, WANG Shan-xiang, TANG Ya-ni

2020, 39(2):  665-677. 

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Nitrogen (N) is one of the most important pollutants in water. Riparian buffer zone, an ecological zone between terrestrial and aquatic ecosystems, performs excellently in removing N pollutants and thus is an effective way to control N output to water. Here, we introduced the process of N migration in riparian zone. The removal mechanisms of N by riparian buffer zone were elucidated from the perspective of physical, chemical and biological processes. We summarized research methods, removal efficiency and influencing factors of N reduction by riparian zone. Vegetation structure, soil permeability, and water holding characteristics, riverbank width and slope were the main factors affecting N removal by physical processes. Vegetation type, seasonal dynamics, and plant growth were the factors affecting N removal by plant assimilation. Soil temperature, organic carbon content, pH, nitrate and oxygen content contents were the main factors affecting N removal by denitrification. Finally, the problems in the current research and the future application were discussed.

Recent progress on the beneficial acclimation hypothesis.

PENG Min-rui, HUANG Yan, XIA Ji-gang

2020, 39(2):  678-683. 

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The beneficial acclimation hypothesis (BAH) claims that all acclimation changes would enhance the physiological performance or fitness of individual organisms. In other words, animals acclimated to a particular environmental condition would enhance performance or functional fitness at that condition in comparison with animals acclimated to other environmental conditions. Although intuitively appealing, several studies challenged the generality of this hypothesis. Here, we expounded the definition and connotation of BAH, and summarized the main positive supporting evidence as well as the negative evidence in BAH verification. Furthermore, we proposed the prospects of future theoretical and experimental research on BAH verification.

Effects of osmopriming on drought tolerance of alfalfa seeds based on hydrotime model analysis. 

TIAN Yu, ZHAO Xiao-chen, ZHANG Hong-xiang

2020, 39(2):  684-689. 

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Osmopriming is often used to improve seed viability and stress tolerance. We quantified the osmopriming effects on drought tolerance of alfalfa (Gongnong No. 1) seeds, with polyethylene glycol (PEG 6000) as the priming agent. Four constant temperatures (10, 15, 20 and 25 ℃) and six drought levels (0 (distilled water as the control), -0.2, -0.4, -0.6, -0.8, and -1.0 bar) were set up for routine germination experiment. Alfalfa seeds were primed with polyethylene glycol (PEG 6000) and then dehydrated before germinati〖HJ*3〗on experiment. The hydrotime model was used to calculate the relevant parameters. The results showed that the osmopriming accelerated the germination rate of alfalfa seeds. The primed seeds had a fast germination speed under conditions of low water potential. With respect to water potential model parameters, the cumulative potential of the primed alfalfa seeds was lower than that of un-primed seeds. The lowest water potential of alfalfa seeds was decreased after priming. Our results indicated that osmopriming could decrease water potential requirement of seed germination and thus enable primed seeds germinate at lower water potential than unprimed seeds, which could improve drought resistance of seed germination.

Monitoring and assessment of drought in arid area in northwest China based on FY-3C and TRMM Data.

ZHANG Jing, WEI Wei, PANG Su-fei, GUO Ze-cheng, LI Zhen-ya, ZHANG Xue-yuan, WANG Jing

2020, 39(2):  690-702. 

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Based on soil moisture (VSM), land surface temperature (LST) data of FY-3C/MWRI (microwave imager) and precipitation data of TRMM3B43 in the growing season (April-October) during 2015-2017, three indices of Precipitation Condition Index (PCI), Temperature Condition Index (TCI) and Soil Moisture Condition Index (SMCI) were obtained through downscaling and normalization. The three indices were merged to establish a Microwave Integrated Drought Index (MIDI), which was used to assess drought status in the arid regions of northwest China. The results showed that: (1) Temporally, drought occurred in the arid regions of Northwest China every year from 2015 to 2017, with the dominance of extreme drought and heavy drought. Spatially, drought events had obvious regional differentiation. The degree of drought increased from east to west, and the trend of change was slightly aggravated and then alleviated. (2) From the perspective of spatiotemporal evolution, 10.57% of area in the arid northwest China became wetter during 2015-2017, and 12.87% of the area became drier. Drought within a single year was continuously reduced from April to August, and continued to increase from August to October. (3) The MIDI index had a better detection effect than the single drought index on short-term drought in the study area. The correlation of MIDI index with Humidity Index was optimal, with a high actual agreement rate in space. Our results provide a basis for drought monitoring and related research using other microwave remote sensing data.

Evaluation of ecological function for urban plant communities based on functional traits.

SONG Chen-chen, LIU Shi-yan, ZHAO Juan-juan, LI Ming-juan, JIANG Nan, CHEN Jing

2020, 39(2):  703-714. 

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Functional traits are important foundation for the ecological functions of plants. Functional diversity based on functional traits is an important indicator for assessing biodiversity and plant functions. With the investigation data of 587 treeshrub plots and 1779 herb plots in the builtup area of Shenzhen, we analyzed plant community types and their functional traits, compared functional diversity of plants from the perspective of four ecological functions, including dust retention, noise attenuation, temperature reduction and humidity increase, and biodiversity conservation. The results of TWINSPAN classification showed that among the 41 tree-shrub community types and 54 herb community types, there were nine tree-shrub community types with ≥10 plots and 15 herb community types with ≥30 plots. The analyses on indicator species and dominant species in communities by plots showed that functional traits of trees and shrubs were commonly broadleaf (100%), evergreen (79.47%), small crowns (93.04%), nonNfixing plants (90.54%), leaf glabrous or hairless (76.95%), and herb plants were mostly small fruit (97.07%), dried fruit (91.33%), and nonNfixing plants (93.9%). The orders of functional diversities for different types of green space were roughly opposite for treeshrub and herb. The highest functional diversities of dust retention, noise attenuation, temperature reduction andhumidity increase and biodiversity conservation for trees all presented in park green space. For shrubs, the highest values were found in residential zone, park, road and park green space. For herbs, the highest values of the first three functions were found in wasteland, and that of the last one was in residential green space. Community structures of wasteland were different with other green space. Our results suggest that the construction of green space in the builtup area of Shenzhen should pay more attention to functional diversity of residential and institutional green space. This study provides reference for the evaluation of urban vegetation function, planning and design of green space, selection of plant species, urban biodiversity conservation, and ecosystem service improvement.