Table of Content

10 August 2024, Volume 43 Issue 8

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Spatiotemporal variations of landscape pattern and emergency evacuation function of urban green space in Beijing from 2005 to 2020.

XU Huiting, XIE Junfei, LI Xinyu, LI Jiale, DAI Ziyun, DUAN Minjie

2024, 43(8):  2247-2256.  doi:10.13292/j.1000-4890.202408.038

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Based on the remote sensing data and population data of Beijing from 2005 to 2020, with the support of RS and GIS technology, we analyzed the changes of landscape pattern of urban green space and its emergency evacuation ability in different periods using the landscape pattern metrics. The results showed that the total area of urban green space in Beijing increased gradually from 2005 to 2020, with a higher growth rate from 2010 to 2015. The area of park green space showed similar characteristics. The auxiliary green space and protective green space showed a trend of increasing first and then decreasing, while the area of production green space presented a gradually decreasing trend. From 2005 to 2020, the large-scale green space patches with an area of larger than 50 hm² increased annually, which was conductive to emergency evacuation. From the perspective of spatial distribution, the nearest neighbor index of green patches in 2005, 2010, 2015 and 2020 all exceeded 1.5, and the spatial distribution of patches was relatively uniform. However, large green space patches (larger than 50 hm²) were mainly distributed in the central and northwest parts of Beijing, with less distribution in the southern part of Beijing, which should be comprehensively considered in the later planning and construction process of urban green space. In 2020, the population density in the core urban area was relatively large, and population density gradually decreased from the inside to the periphery. The population density in the southwest and northeast regions was relatively low. According to the service radius of 500 m, the coverage of green buffer zone in Beijing urban area in 2020 was 1076.36 km², accounting for 96.6% of total urban area, with only 38.06 km² service blind area, which was mainly distributed in the core urban area. Under the service radius of 1000 m, the service blind area was only 0.59 km², indicating a full coverage.





Monthly variations and driving factors of urban heat island in Changchun.

PAN Lizhi, YANG Chaobin, REN Zhibin, ZHANG Shuwen, XU Xinliang, KUI Tong, LIU Lifeng

2024, 43(8):  2257-2265.  doi:10.13292/j.1000-4890.202408.005

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Urban heat island effect (UHI) has become an important ecological and environmental problem that hinders the sustainable development of cities. However, few studies explored the seasonal variations of UHI in the cold regions of China, which limits the comprehensive understanding of UHI in different climate zones. Taking Changchun City of Jilin Province in northeast China as an example, Landsat 8 and GF2 images were selected as main remote sensing data, and four surface urban heat island intensity indices were proposed to characterize the urban thermal environment. The spectral unmixing, profile line analysis, and regression models were used to explore the impacts of potential driving factors on the monthly and seasonal variations of UHI. The results showed that: (1) The spatial pattern of the urban thermal environment in Changchun exhibited significant monthly and seasonal variations, with the highest land surface temperature (LST) of 39.44 ℃ in August and the lowest of -18.60 ℃ in December. The UHI effect was prominent in winter and summer, but not obvious in spring and autumn. (2) The intensity of UHI as expressed by different indices had great differences. Based on the index characterized by land use type, the intensity of UHI could reach as high as 10.56 ℃ in July. However, some months (February, March, and November) showed the reverse UHI with temperature in rural area being higher than that in urban area. (3) Vegetation and impervious surface area were important driving factors for the spatial and temporal variations of urban thermal environment. There was seasonal variation in the influencing mechanism, with the most significant correlation between UHI intensity and the two factors in the summer, and no effect in winter. (4) The LST of urban function zones showed monthly variations. Specifically, the industry zone had the highest LST. However, the human activities such as straw burning resulted in the highest LST in the croplands in some months. Our results elucidate the driving mechanisms of monthly and seasonal variations in the urban thermal environment, which is of great significance for the regulation of thermal environment ecology in cold regions.





Variations and influencing factors of vegetation net primary productivity in the main urban area of Chongqing under the background of urbanization.

LIU Tingting, YUAN Yanping, YE Xuchun

2024, 43(8):  2266-2274.  doi:10.13292/j.1000-4890.202408.008

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In recent years, eco-environment in the main urban area of Chongqing has undergone great changes due to the impacts of climate change and rapid urbanization. Based on MOD17A3 dataset of net primary productivity (NPP) from 2000 to 2020, combined with regional climate and land use data, we analyzed the variations of NPP in the main urban area of Chongqing and explored the impacts of climate and land use change by using the methods of trend analysis, correlation analysis, and quantitative attribution. Over the past 21 years, NPP showed a fluctuating upward trend, with total NPP increasing from 2.15 Tg C to 2.87 Tg C. The contribution of cropland to total NPP was the largest, reaching 65.30%, followed by forest (30.28%). Precipitation and temperature were positively correlated with NPP, and the relationship between precipitation and NPP was the most prominent, while solar radiation had no significant effect. In general, climatic factors were the dominant driving factors for the increase of total NPP. During the periods of 2000-2005, 2005-2010 and 2010-2015, climate change positively contributed to the increase of total NPP, with a contribution rate of 88.65%, 80.53%, and 90.93%, respectively. However, it showed an inhibitory effect on total NPP during 2015-2020, with a contribution rate of 35.95%. Land use change caused by urban expansion had a significant negative effect on total NPP change. The contribution rate of land use change to total NPP during 2000-2005, 2005-2010, 2010-2015, and 2015-2020 were 10.92%, 16.77%, 8.56%, and 56.51%, respectively. Moreover, the increases of landscape patch density and Shannon diversity index and the decrease of landscape aggregation had a promoting effect on increasing total NPP. Our findings are of great significance for understanding carbon sequestration capacity under the background of urbanization, and can provide theoretical basis for promoting regional ecological monitoring and protection and spatial planning.



Spatialtemporal variations of ecosystem service value and its driving factors in the Great Nanchang Metropolitan Area.

YANG Xiaofan, CAI Haisheng, ZHANG Xueling, ZUO Tengyun, CHEN Liting

2024, 43(8):  2275-2284.  doi:10.13292/j.1000-4890.202408.001

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Exploring the spatiotemporal variations in ecosystem service value (ESV) is beneficial to clarifying the focus of ecological conservation. Based on the land use data in 2000, 2010, and 2020, the spatial and temporal variations and driving factors of ESV in the Greater Nanchang Metropolitan Area were analyzed by using the equivalent factor, spatial autocorrelation and geographical detection methods. The results showed that land use change in the Greater Nanchang Metropolitan Area mainly displayed increases of construction land (+141.43%) and water area (+12.68%), and decreases of grassland (-12.25%) and cultivated land (-6.31%) from 2000 to 2020. The change type was mainly from forest land to grassland, and from cultivated land to construction land and water area. The ESV in the research area showed a trend of “decreasing first and then increasing”, with an overall increase of 164.38×10⁸ yuan, which was mainly due to the increase of water area and wetland area. From a spatial perspective, the ESV in Poyang Lake region was the highest, which decreased to the surrounding areas. The ESV in the western region was higher than that in the southern region. From the perspective of spatial autocorrelation of ESV, the local correlation showed a trend of “high in the center and low in periphery”, with high-high concentration areas being distributed in the Poyang Lake area, and low-low concentration areas mainly in the south of the study area. From 2000 to 2020, the spatial agglomeration effect of ESV in the study area gradually decreased. Vegetation cover change was a key factor affecting spatial variations of ESV in the study area, and natural and social factors interactively affected ESV spatial differentiation. Our results provide scientific basis for the ecological protection of regional territorial space.





Effects of urbanization intensity on forest vegetation characteristics and landscape pattern indices in Nanchang.

ZHONG Jialin, LI Xin, LIU Wei, ZHANG Foyi, HUANG Fei, XU Sheng, XIAO Shufen, WANG Qiong

2024, 43(8):  2285-2294.  doi:10.13292/j.1000-4890.202408.037

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Rapid urbanization is shaping urban forests and greenery in China, playing a fundamental role in driving vegetation characteristics and landscape patterns. In this study, we classified the level of urbanization intensity based on the proportion of impervious surface area and investigated 184 plots in the builtup area of Nanchang City. Vegetation and landscape indices were measured and analyzed within each plot. The results showed that landscape patterns and vegetation characteristics greatly differed among different urbanized areas. With increasing urbanization intensity, the landscape indices, including mean perimeter-area ratio, mean Euclidean nearestneighbor distance, and landscape division index, increased by 130.8%, 63.2%, and 92.4%, respectively, and the percentage of landscape type, largest patch index, and aggregation index decreased by 82.8%, 85.5%, and 22.3%, respectively. Moreover, the lowest tree height, diameter at breast height, and herbaceous richness were observed in heavily urbanized areas, whereas woody species density exhibited the opposite trend. The results of variation partition analysis revealed that the impervious surface area and landscape indices explained 0.8% and 17.1% of the variation in vegetation characteristics, respectively, whereas their interactions explained up to 82.1%. The results of Pearson correlation and redundancy analyses showed that changes in forest vegetation characteristics were strongly associated with mean perimeter-area ratio, percentage of landscape type, patch density, and landscape division index. Increasing the mean perimeter-area ratio could increase the richness and cover of herbaceous species in moderately and lowly-urbanized areas. From the perspective of landscape pattern, we proposed suggestions for protecting urban forests and enhancing plant diversity, aiming to provide references for maximizing the ecological services of urban forests.





Characteristics of urban invasive plants and their effects on plant diversity in the built-up area of Shen-zhen, China.

LI Jian, ZHUANG Chunxiao, YANG Fangfang, LU Shijun, QIU Lishan, ZHAO Juanjuan

2024, 43(8):  2295-2303.  doi:10.13292/j.1000-4890.202408.006

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Cities are the primary distribution areas of most invasive plant species and the important starting point of invasion for many invasive plant species. As one of the important issues in urban ecosystems, the composition of urban invasive plant species and their impacts on plant diversity have received increasing attention. With the built-up area of Shenzhen as a case study, we analyzed the species composition of urban invasive plants and their impact on plant diversity using data from 600 urban plant plots (100 m × 100 m). A total of 214 invasive plant species in 55 families and 153 genera were investigated, with herbaceous plants as the leading life type. Tree species Leucaena leucocephala, shrub species Lantana camara and Mimosa bimucronata, and herb species Mimosa bimucronata, Mimosa bimucronata, and Mikania micrantha were the most widespread invasive species. For herb quadrats with different invasive levels, Simpson dominance index, Shannon diversity index, Margalef richness index, and Pielou evenness index all exhibited the same order as severe invasion < moderate invasion < mild invasion. This study revealed the significant effect of mild invasion on urban herb diversity and the evident pattern of herb diversity decreasing trend with increasing invasion level. Our results and methods provide a reference for studying urban invasive plants and preventing urban alien plant invasions.





Agricultural alien invasive plants in Haidian district, Beijing.

ZHANG Yue, ZHANG Guoliang, ZHENG He, KONG Chuizhi, SONG Zhen, WANG Zhonghui, TIAN Chenxu, ZHANG Lichen, FU Weidong

2024, 43(8):  2304-2312.  doi:10.13292/j.1000-4890.202408.009

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Modern urban agriculture in Haidian District is much more frequently and directly affected by human beings, making it more susceptible to alien plant invasion. In this study, we improved the basic dataset of agricultural alien invasive plants in Haidian District and comprehended the invasive status of agricultural invasive plants, aiming to provide a basis for the prevention and control of alien invasive plants, biodiversity conservation, and ecological security management. We preliminarily surveyed alien invasive plants at 48 sites in five agricultural towns in Haidian District. We collected data of habitats, investigation area, species composition, and damage objects, consulting the literature to obtain characteristic information, such as origin and life form. According to the preliminary results, we selected 12 heavily harmful and widely distributed species, including Ipomoea purpurea and Amaranthus retroflexus, for plot inventory, and quantified the damage level by average coverage. A total of 18 families, 35 genera, and 55 species of invasive plants were recorded across the five agricultural towns in Haidian District. Dicotyledonous plants (16 families, 32 genera, and 52 species, accounting for 94.5%) were the dominant. Meanwhile, Compositae and Amaranthaceae were the dominant families, with 18 (32.7%) and 10 species (18.2%), respectively. Furthermore, annual herbaceous plants (37 species, 67.3%) were the most common life form. Most alien species originated from North America (29 species, 52.7%), followed by South America (17 species, 30.9%). Ipomoea purpurea, Amaranthus retroflexus, Ipomoea hederacea, Erigeron canadensis, Bidens bipinnata, Abutilon theophrasti, Amaranthus blitum, Amaranthus viridis, Helianthus tuberosus, Xanthium italicum, Galinsoga parviflora, and Galinsoga quadriradiata were all widely distributed (with occurrence frequency over 40%) and extremely harmful (other than Erigeron canadensis and Abutilon theophrasti). In Haidian District, there were numerous agricultural alien invasive plant species with wide distribution and serious damage. We suggest that field investigations and monitoring of alien invasive plants should continue, the professional ability of technicians should be improved, and the alien invasive plants list and science popularization education should be expanded.





Variation and influencing factors of PM_2.5 concentration during the heating period in Shenyang.

KONG Fanqing, WU Meiyang, QU Haiyan

2024, 43(8):  2313-2324.  doi:10.13292/j.1000-4890.202408.002

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With the continuous industrialization, hazy weather has occurred more and more frequently in major developed regions, which leads to the deterioration of atmospheric environment and seriously affects people’s daily life and health. Based on the recorded data of PM_2.5 concentration at the state controlled environmental air quality monitoring points in urban areas of Shenyang and meteorological data during the heating period of 2020-2021, we explored the spatial patterns and temporal dynamics of PM_2.5 at different environmental scales in Shenyang, as well as the influence of different meteorological factors and land use types on the variations of PM_2.5 concentration. The results showed that PM_2.5 concentrations in the urban areas displayed a spatial pattern of low in the north and high in the south. PM_2.5 concentrations during the heating period were in a decreasing order of March 2021 > January 2021 > February 2021 > December 2020 > November 2020. Temperature and relative humidity were significantly and positively correlated with PM_2.5 concentrations, and wind speed was significantly negatively correlated with PM_2.5 concentrations. At three different buffers, green space and water bodies were significantly negatively correlated with PM_2.5 concentrations, squares were significantly negatively correlated with PM_2.5 concentrations at 500 m and 1000 m buffer scales, and significantly negatively correlated with PM_2.5 concentrations at 2000 m buffer scale. The results of hierarchical regression analysis showed that temperature, relative humidity, and green space contributed the most to PM_2.5 concentration, which indicates that haze weather in Shenyang during the heating period is mainly affected by temperature and humidity, and that urban green space, water body, square and wind can significantly reduce PM_2.5 concentration. This study provides a reference for urban haze weather management and urban planning in Shenyang.





Scale effect of regulating mechanism of urban water bodies in improving thermal environment in Wuhan, China.

XIE Qijiao, YANG Chenzhe, REN Lu

2024, 43(8):  2325-2333.  doi:10.13292/j.1000-4890.202408.003

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It is of great significance to understand the regulation mechanism of urban water bodies on thermal environment for developing urban blue-green infrastructure system oriented to thermal environment improvement. This study detected the correlations between commonly-used landscape metrics and land surface temperature (LST) at different scales of 300 m×300 m, 1000 m×1000 m, and 3000 m×3000 m. The main influencing factors of water bodies in regulating thermal environment were identified and the regulation mechanisms were monitored accordingly. The results showed that: (1) Generally, LST was more stably and closely correlated with the landscape indices at class level than with those at landscape level. (2) At class level, the correlations between LST and the variables indicating water area, proximity and dispersion were stable and less affected by scale size, while those related to density, shape and edge characteristic of water bodies were scale-dependent. The variables at landscape level showed stronger correlations with LST with the increases of scale size, thus they were appropriate to explain the LST variation at a larger scale. (3) The main influencing factors and mechanism of water bodies on cooling thermal environment varied with scale size, showing an obvious scale effect. The area proportion of water bodies in landscape was the largest contributor to the cooling effect of water bodies at all studied scales, though the relative contribution decreased with the scale increasing. Additionally, the cooling effect of water system was influenced by water body shape and edge features at local scale (300 m) and by the proximity and distribution distance of water bodies at coarser scale (3000 m). (4) Considering the interactions between water bodies and other landscape elements, LST variation at local scale was mainly attributed to the area and spatial distribution distance of construction land. The cooling efficiency of water bodies was weakened by the surrounding impervious covers. At coarser scales, the area proportion of water bodies in landscape contributed more to thermal environment variation, which could combat the thermal deterioration caused by urbanization to a certain extent. These findings provide informative evidence for the planning of urban blue-green infrastructure system to adapt to climate change.





Estimation of the density and spatial distribution of soil organic carbon in urban vegetation based on Sentinel-2 imagery data.

DONG Ziyue, LIU Jianhong, LYU Xiaoqing, WANG Jun, MA Minfei, LI Jinnuo

2024, 43(8):  2334-2344.  doi:10.13292/j.1000-4890.202408.013

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Soil organic carbon density (SOCD) is an important index to evaluate the carbon sink function of soil. Studying vegetation SOCD is of great significance for exploring the impacts of human activities on soil carbon cycle in urban areas. Based on the SOCD data of 206 sampling points (0-20 cm) and Sentinel-2 remote sensing images in the main urban area of Xi’an, we established the optimal SOCD estimation models of trees, shrubs, and grasslands by using multiple linear, quadratic fitting, and exponential models. The vegetation SOCD in the study area was estimated based on the optimal models, the spatial distribution of vegetation SOCD were further analyzed. Results showed that the SOCD of the urban vegetation ranged from 0 to 16.47 kg·m^-2, with an average of 3.24 kg·m^-2. Overall, the SOCD showed a spatial distribution characteristic of “high on the edge and low in the middle”, with high spatial heterogeneity. There were large differences in SOCD among different vegetation types. The average SOCD of the three vegetation types followed a pattern of trees (3.75 kg·m^-2) > shrubs (2.72 kg·m^-2) > grasslands (2.04 kg·m^-2). There was a negative correlation between urban vegetation SOCD and urbanization intensity (P<0.001), and the average SOCD was higher in areas with higher vegetation coverage. In general, urbanization had a negative impact on vegetation SOCD. Increasing urban vegetation coverage is one of the effective means to improve SOCD. The combination of remote sensing technology and field survey methods can quickly and effectively estimate SOCD of trees, shrubs and grasslands in the study area, which provides a reference for soil carbon management in future urban development.





Infiltration characteristics of grassland in small watershed of purple soil in suburban Chongqing.

LIU Chunhong, WEI Jie, XIAO Xiwen, GOU Junfei, GAN Fengling, TANG Yao, BO Chunyue

2024, 43(8):  2345-2353.  doi:10.13292/j.1000-4890.202408.007

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To understand the effects of root system on the infiltration capacity of grasslands in a purple soil watershed, we conducted a one-dimensional infiltration experiment with four common herbaceous plants (Torilis scabra, Youngia japonica, Lolium multiflorum, and Sinosenecio oldhamianus) in suburb Chongqing. The relationship between the characteristics of plant root structure and the infiltration capacity of root soil complex was examined, and the Kostiakov, Mezencev, Horton, and Phillip infiltration models were used to simulate the infiltration process. The results showed that the infiltration processes of root soil complex and rootless soil decreased sharply at first and then decreased slowly until stable. The stable infiltration rate of root soil complex increased by 1.35-2.96 times compared with that of rootless soil. The infiltration rate of fibrous root soil complex was higher than that of taproot soil complex. Sinosenecio oldhamianus performed better in improving the infiltration performance of purple soil. Root length density, root surface area density, and root volume fractal dimension were significantly positively correlated with the initial, stable, average, and cumulative infiltration rates of the root soil complex (P<0.01). However, there was no significant correlation (P>0.05) between root volume density and soil initial infiltration rate, root weight density and stable infiltration rate. The Mezencev model was the most suitable to characterize the infiltration of root soil complex of the four herbaceous species and rootless soil (R²=0.99), followed by Kostiakov model, Horton model, and Philip model. Moreover, the Kostiakov, Philip, and Horton models performed better in simulating the infiltration of taproot soil complex than that of fibrous root soil complex. The results can provide a scientific basis for slope vegetation construction and soil erosion prevention in  purple soil areas.





Prediction methods of soil nitrogen spatial distribution in Xiong’an New Area.

GUO Xiaoxue, LIU Zhijun, GAO Dongli, XU Chengli, ZHANG Kexin, LIU Xianzhao

2024, 43(8):  2354-2364.  doi:10.13292/j.1000-4890.202408.004

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The spatial distributions of soil total nitrogen (STN) and available nitrogen (AN) contents are important factors influencing vegetation productivity. A total of 182 soil samples were collected from the upper and lower layers of 91 sampling points in the eastern part of the Xiong’an New Area. The distributions of STN content, AN content, soil total nitrogen density (STND), and available nitrogen density (AND) were predicted with four methods, i.e., kriging combined with land-use (KLU), ordinary kriging, inverse distance weighting (IDW), and radial basis function (RBF). The predictive accuracy of these methods was evaluated by the root mean square error (RMSE), mean absolute error (MAE), and correlation coefficient (R). Furthermore, the spatial distribution patterns of STN and AN contents and the regional reserves were assessed. The results showed that the vertical distribution of STN, AN content and density decreased with increasing soil depth. From a horizontal perspective, there were significant differences for STN and AN content and density among different land-use types (P<0.05). The KLU was the optimal interpolation method for predicting the spatial distribution of STN, AN content and density. In the upper layer of soil, the R values of KLU were 0.574 (STN), 0.426 (AN), 0.555 (STND) and 0.407 (AND), respectively, which were 0.350, 0.390, 0.304 and 0.310 higher than that of the other three interpolation methods on average. The RMSE of KLU was 0.2255 (STN), 21.5902 (AN), 0.0901 (STND), and 8.5365 (AND), respectively, with an average reduction of 0.0481, 3.7874, 0.0166, and 1.4236 compared with the other three interpolation methods; while the MAE of KLU was the best. KLU showed advantages also in the deeper soil layer.





Spatiotemporal variation of vegetation in forest-typed nature reserves in China and its response to climate change.

HOU Jing, HOU Peng, GAO Haifeng, XIAO Rulin, FU Zhuo, YANG Xu, CHEN Yan

2024, 43(8):  2365-2372.  doi:10.13292/j.1000-4890.202408.025

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Forest-typed nature reserves play an important role in supporting primary productivity, vegetation biomass, carbon storage, and biodiversity conservation, along with its crucial ecological functions. Understanding the ecological change in these regions could provide a fundamental and scientific basis for assessing the effectiveness of ecological protection initiatives. We comprehensively analyzed the spatiotemporal variations of fraction vegetation coverage (FVC), which was derived from MOD09 reflectance data in forest-typed reserves in China over the past 20 years. We employed trend analysis, nuclear density analysis, re-scaling range analysis to examine these changes. Correlation analysis was conducted to examine the relationship between these changes and climate patterns, using TerraClimate climate reanalysis data. The results showed that the average FVC in forest-typed nature reserves was 52.29% from 2000 to 2020, significantly higher than that of the non-farmland areas. There were significant differences in FVC among these reserves, with higher coverage in the south and lower coverage in the north. In general, 98.29% of these regions exhibited an increasing trend of FVC over the past 20 years. The sub-humid temperate and humid temperate ecological regions of Shanxi, northern Hebei, western Liaoning, and Shandong experienced faster increases in FVC, with an annual increasing rate of 0.61% and 0.58%·respectively, compared to average rate 0.26% per year of all reserves. The increase of FVC in these regions is expected to have strong sustainability in the future, while vegetation coverage in the southern China remained relatively stable. In terms of climatic factors, 44% of the reserves had exhibited varying degrees of warming trends over the past two decades. On average, air temperature increased by 0.013 ℃·a^-1, resulting in accelerated vegetation growth. Precipitation remained stable and had different effects on vegetation cover in different regions. In addition to the influence of rising temperature, a series of ecological projects have played a significant role in the restoration of vegetation in the sub-humid temperate regions with faster growth rate of vegetation coverage.





Spatiotemporal variation of vegetation coverage and its influencing factors in the dryhot valley of Jinsha River during 2010-2021.

ZHAO Donglin, ZHU Shirong

2024, 43(8):  2373-2381.  doi:10.13292/j.1000-4890.202408.023

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Due to the influence of topography, climate and human disturbance, the dry-hot valley ecosystem of Jinsha River is severely degraded, being a typical ecologically fragile area. With the MODIS-NDVI data during 2010-2021, we investigated the spatiotemporal variations and future trends of vegetation coverage in the dry-hot valley of the Jinsha River, as well as its relationship with climate change, human activities, and altitude factors, using trend analysis, residual analysis, and partial correlation analysis. The results showed that vegetation coverage in the study area had generally increased with a rate of 0.0093 a^-1 over the last 12 years. The area with an increasing trend in vegetation coverage was larger than that with a decreasing trend. The change types of vegetation coverage were mainly low fluctuation, and future changes in vegetation coverage will be dominated by an upward trend. Vegetation coverage was weakly positively correlated with temperature and precipitation in 60.23% and 60.26% of the region, respectively, but only 3.47% and 5.08% passing the significance test. Human activities generally had positive effects on vegetation coverage. Altitude influenced vegetation coverage in the Jinsha River dry-hot valley. The proportion of low and medium-low vegetation coverage showed an increase-decrease-increase trend with increasing altitude, while the proportion of high vegetation coverage was the opposite.





Effects of forest gap size on species diversity of vascular plants in shrub and herb layers of Picea crassifolia forest in Helan Mountains.

SHA Huan, LIANG Yongliang, PENG Niu, GAO Feng, LI Jingyao, WEI Wenxuan, PANG Danbo, CHEN Lin

2024, 43(8):  2382-2394.  doi:10.13292/j.1000-4890.202408.022

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Forest gaps are common in forest ecosystems, which are important sites for species regeneration. Forest gaps can change the spatial structure and plant community composition of forests, and is of great significance for species regeneration and forest succession. In this study, we analyzed the species diversity and distribution patterns of shrub and herb layers in 24 pairs of differentsized gaps and understory of a Picea crassifolia forest on the eastern slope of the Helan Mountains. The aims of this study were to elucidate the effects of gap size on species diversity of vascular plants and to reveal differences in the interaction network of shrub-regeneration seedling-herb co-occurring species within the forest gaps and understory. The results showed that dominant plant species in the understory of Picea crassifolia forest were Berberis dubia, Juniperus procumbens, Dasiphora fruticosa, and Lonicera microphylla. The seedlings of Picea crassifolia and Juniperus rigida dominated the regeneration layer. Carex was the dominant species in the herb layer. The number of species in the forest gaps was higher than that of understory, with the highest number of family, genus, and species of shrub and herb layers in the large gaps. The richness index of shrub layer increased with increasing forest gap size. The Shannon diversity index was highest at the medium-sized gaps (100-200 m²), and the Simpson index and Pielou index showed a decreasing trend with increasing forest gap size. The herb layer richness index, Shannon index, Simpson index, and Pielou index increased with increasing gap size, and were significantly higher than those of forest understory. Beta diversity tended to decrease and then increase with increasing gap size. The decomposed richness difference components contributed the most to the shrub and herb layers, and showed an increasing trend with increasing gap size. The network structure of forest gaps was larger, more complex, and more concentrated than that of the understory. A close symbiosis between herb-herb species was mostly formed in different-sized gaps and understory. The emergence of medium gap increased the interaction and symbiosis between regenerated seedlings, shrub and herb species. Forest gaps play a positive role in enhancing species diversity of vascular plants and species symbiosis in Picea crassifolia forest in the Helan Mountains. Forest gap with a size of 100-200 m² can improve species diversity and promote the regeneration of understory.





Effects of melatonin on photosynthetic efficiency, carbon assimilation, and hormones of Kandelia obovata seedlings under low-temperature stress.

YUE Danfei, ZHANG Huiyu, LIU Weicheng, PAN Xiaojiao, HAO Lulu, ZHENG Chunfang

2024, 43(8):  2395-2402.  doi:10.13292/j.1000-4890.202408.033

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We assessed the regulatory role of melatonin (MT) on photosynthetic efficiency, carbon assimilation, and hormone metabolism of Kandelia obovata seedlings under different low periods. To investigate the protective role of MT in photosynthesis and endogenous hormone balance, we sprayed 0.2 mmol·L^-1 MT on K. obovata seedlings subjected to low-temperature stress (8 ℃/-3 ℃) for 2, 4, and 6 days. The results showed that, with increasing stress duration, the regulatory role of MT on photosynthesis of K. obovata seedlings first increased and then decreased, reaching a maximum under low-temperature stress for 4 days. After 4 days of low-temperature stress, spraying MT increased net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), actual photochemical efficiency of PSⅡ (F_v/F_m), maximum photochemical quantum yield of PSⅡ (Ф_PSⅡ), and photochemical quenching coefficient (q_p) by 13.67, 2.40, 1.48, 2.03, 1.42 and 2.00 times, respectively. Spraying MT decreased the intercellular CO₂ concentration (C_i) and non-photochemical quenching coefficient (NPQ) of seedlings by 76.29% and 50.36%, respectively. Furthermore, spraying MT increased leaf photorespiration rate (R_p), CO₂ saturation point (CSP), carboxylation efficiency (CE), and maximum RuBP regeneration rate (J_max) in seedlings by 1.28, 1.09, 4.24, and 12.70 times, respectively. In addition, leaf endogenous MT, auxin (IAA), gibberellin (ABA), and abscisic acid (GA) were increased by 1.23, 1.24, 1.17, and 1.61 times respectively in seedlings sprayed with MT under low-temperature stress for 4 days. In conclusion, foliar spraying MT could improve photorespiration rate and photosynthetic carbon assimilation ability of K. obovata seedlings under low-temperature stress, increase endogenous hormone content, enhance photosynthetic capacity, and reduce the damage of low-temperature stress. However, such mitigation effects were dependent on the duration of low-temperature stress. Endogenous MT was positively correlated with P_n, T_r, F_v/F_m, Ф_PSⅡ, R_p, CE, J_max, IAA, GA, and ABA, indicating that endogenous MT plays an important role in regulating photosynthetic efficiency, carbon assimilation, and hormones.





Biogenic volatile organic compounds (VOCs) emission inventory and isoprene emission flux in spring of 11 common subtropical bamboo species.

WANG Chao, YANG Binkai, LI Li, CUI Bowen, WANG Fusheng, WANG Xiaoke

2024, 43(8):  2403-2413.  doi:10.13292/j.1000-4890.202408.020

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We examined the emission of volatile organic compounds (VOCs) of 11 common subtropical bamboo species by using a dynamic headspace sampling technique. Except for Bambusa multiplex cv. Fernleaf and Phyllostachys heterocycla cv. pubescens, the other nine species were all reported for the first time. The VOCs composition, relative contents, the pollution gases contained, and emission rates of isoprene (ISO) were analyzed. Given that the height of bamboo species would affect ISO emission, all bamboo species were divided as large, medium, and small groups and their ISO emission differences were also analyzed. The results showed that the compounds emitted from the 11 bamboo species could be classified into eight types, including hydrocarbons, alcohols, ketones, acids, esters, aldehydes, ethers, and other VOCs. In terms of total number of detailed compounds, 11 bamboo species emitted 339 kinds of compounds. Pseudosasa amabilis emitted the most diverse compounds (48 kinds), while Bambusa multiplex cv. Fernleaf emitted the least (11 kinds). No monoterpenes or sesquiterpenes were detected in 11 bamboo species. Seven bamboo species all emitted terpenes, all of which were composed of ISO. The VOCs components of 11 bamboo species contained six kinds of VOCs beneficial to human health and 16 kinds of air pollutants, among which Pseudosasa amabilis emitted the most kinds of pollutants and Phyllostachys heterocycla cv. pubescens emitted the largest relative contents. The ISO emission rates of the seven ISO-emitted bamboo species ranged from 0.16 to 7.75 μg·g^-1·h^-1. Phyllostachys heterocycla cv. pubescens had the highest ISO emission rates (7.75 μg·g^-1·h^-1), and the lowest was Pleioblastus china f. hisauchii (0.16 μg·g^-1·h^-1). Large bamboo species emitted more ISO than middle and small bamboo species, which was about six times of medium bamboo and 19 times of small bamboo.





Drought identification indicators for the critical growth period of mango in Panxi region.

YUAN Yue, CHEN Dongdong, DU Chengxun, LIAO Wei, RAN Jingjiang, LI Xiaowei

2024, 43(8):  2414-2420.  doi:10.13292/j.1000-4890.202408.039

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Considering water supply and demand situation of mango at different growth stages, the drought identification indicators of mango at flowering and fruiting stage and fruit expansion stage were determined using meteorological data, phenological data of mango and small samples of mango disaster data in Panxi region by cluster analysis and sample distance analysis. The validity of drought identification indicators was verified by T_test, reserved history sample test, typical station, and identification of typical years. The drought-triggering threshold at the flowering and fruiting stage and fruit expansion stage were 0.89 and 0.80, respectively. The drought indices extracted based on the drought identification indicators at critical growth stages were consistent with that in historical disaster samples. The identification accuracy of the identification indicators for the reserved historical samples was 81.5%, and the identification accuracy of the indicators for long time-series disaster samples of a typical station was 95%. The drought identification indicators can be used to drought disaster identification in typical years, and the accuracy of the indicator identification in drought areas in typical years was 85.7%. The results can provide technical support for drought monitoring and drought prevention and mitigation of mango in Panxi region.





Drought characteristics of spring maize during the whole growth period in Songnen Plain.

ZHANG Fuguo, DUAN Juqi, JIANG Zhihui, JIN Yazhong, ZHANG Youli

2024, 43(8):  2421-2432.  doi:10.13292/j.1000-4890.202408.014

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The drought characteristics and trend of spring maize in Songnen Plain were studied by using the meteorological data from 2001 to 2020 and the crop water deficit index (CWDI). The results showed that during the whole growth period of spring maize, the variation trend of precipitation and water demand in Songnen Plain was similar, both showed a trend of first rising and then decreasing, and peaked in mid-late July. CWDI showed a trend of decreasing first and then rising, and reached the lowest value in the mid-late July. Drought was more severe in the early and late stages of growth. A trend of drying occurred in whole growth stage, seeding-emerging stage, and heading-milking stage, while a trend of wetting occurred in emerging-heading stage and milking-ripening stage, with such trends being significant except for the emerging-jointing stage, and the drought gradually shifted to the late stage of growth. In each growth stage, the influence scope of light drought was predominant, followed by moderate drought, severe drought, and extreme drought. Spatially, drought occurrence frequency was generally higher in the west and lower in the east, and higher in the north and lower in the south. It is necessary to strengthen the monitoring and early warning of drought in the future and increase the input of drought disaster prevention, which can provide strong guarantee for stable yield and supply of maize.





Residents’ perception and willingness to participate in ecotourism development in Xiaoxiangling and surrounding areas of the Giant Panda National Park.

HU Jiayuan, ZHENG Haipeng, YANG Bing, DAI Qinlong, ZHOU Wenjia

2024, 43(8):  2433-2439.  doi:10.13292/j.1000-4890.202408.015

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The development of ecotourism through community participation can not only enhance the engagement and sense of belonging of local residents in ecotourism activities, but also strengthen their recognition and support for ecotourism, ultimately fostering harmonious coexistence between humans and nature. Taking the Xiaoxiangling area of the Giant Panda National Park as a case, we employed a combination of questionnaires and interviews to assess the current status of local ecotourism development and residents’ perceptions of ethnic culture, economic factors, and their willingness to participate in the development. At present, the residents’ participation in ecotourism in the study area is relatively low, with limited benefits. Ethnic culture perception significantly and positively influenced residents’ willingness to participate, with a path coefficient of 0.30 (P<0.01). Economic perception also significantly and positively affected residents’ willingness to participate, with a path coefficient of 0.65 (P<0.001). Additionally, economic perception partially mediated the positive impact of ethnic cultural perception on willingness to participate, with a mediating effect of 0.43 (P<0.01). To enhance residents’ willingness to participate, we recommend interventions in three key aspects: integrating ethnic culture into ecotourism, optimizing tourism products, and providing professional training. These recommendations would contribute to the sustainable development of national park and serve as a valuable reference for future initiatives.





Effect of phylogenetic distance from native plants on the herbivory of Solidago canadensis L. by phytophagous insects.

SHU Hongsuo, REN Dianting, HONG Hefang, WANG Jiang

2024, 43(8):  2440-2447.  doi:10.13292/j.1000-4890.202408.034

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Due to the genetic conservation of herbivory, phylogenetic distance between native plants and invasive plants may determine herbivory of invasive plants by native insects. However, how phylogenetic distance between native plants and invasive plants affects the herbivory of native insects on invasive plants is still unclear. We conducted manipulative experiments and field survey. We constructed artificial plant communities with distant and close phylogenetic distance to invasive plants (Solidago canadensis L.). Meanwhile, we conducted surveys on plant communities invaded by S. canadensis in Zhejiang, Fujian, Jiangxi, and Yunnan provinces. The proportion and intensity of insect feeding on leaves of S. canadensis were examined. Results of artificial experiments showed that phylogenetic distance and species types (native or invasive plants) significantly interacted to affect herbivory intensity. When the phylogenetic distance between the native plants and S. canadensis was close, the herbivory intensity of S. canadensis was significantly higher than that of native plants. When the phylogenetic distance between the native plants and S. canadensis was distant, the herbivory intensity of S. canadensis was significantly lower than that of native plants. Herbivory proportion had no significant difference between native and invasive plants in both artificial plant communities with close or distant phylogenetic distance with invasive plants. There were significant differences in the individual number of some insect species between genetically distant and genetically close groups. Results from the field survey showed that different regions and phylogenetic distance had significant effect on herbivory proportion and intensity. Plant species richness had no significant effect on herbivory proportion and intensity. The herbivory proportion and intensity had a significant negative correlation with phylogenetic distance in Zhejiang and Fujian, but no significant correlation in Yunnan. Our results indicate that phylogenetic distance can affect invasive plants by influencing herbivory of native insects. Therefore, more attention should be paid on the phylogenetic distance between native and invasive plants in future studies about invasibility of plant communities.





Effects of industrial vitamin C production-residue after evaporation on nitrogen utilization and quality of non-heading Chinese cabbage.

GE Xiaoyi, GAO Mingfu, XU Hui

2024, 43(8):  2448-2454.  doi:10.13292/j.1000-4890.202408.031

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Promoting the uptake and assimilation of nitrogen fertilizer is crucial for improving crop yield and quality. However, the effect of low-molecular-weight organic matters on soil nitrogen utilization by plants remains unclear. Here, we investigated the effect of industrial vitamin C production-residue after evaporation (RAE), which is mainly composed of small-molecule organic acids, on the utilization of soil nitrogen by non-heading Chinese cabbage (Brassica campestris ssp. chinensis). The results showed that RAE application increased nitrogen fertilizer agronomic efficiency, nitrogen fertilizer partial productivity, nitrogen fertilizer physiological efficiency, and nitrogen fertilizer apparent efficiency by 171.2%, 57.9%, 46.1%, and 86.1%, respectively. Plant growth was significantly promoted, with an increase of total nitrogen accumulation and biomass of leaves by 60.7% and 57.9%, respectively. Meanwhile, chlorophyll content was increased by 16.7%, and soluble protein and free amino acid contents were increased by 65.4% and 15.1%, respectively. Furthermore, the expression levels of nitrite reductase, glutamine synthetase, and glutamate synthase were up-regulated, indicating that photosynthesis was enhanced and inorganic nitrogen assimilation was significantly promoted. In conclusion, RAE could improve nitrogen use efficiency, yield and quality of non-heading Chinese cabbage. This study provided a scientific basis for resource utilization of RAE as a potential organic synergist for improving nitrogen fertilizer utilization.





Distribution and heavy metal accumulation of pioneer plants in lead-zinc tailings ponds in southern Guizhou.

OUYANG Jidi, HAN Zhiwei, WU Pan, LU Jiang

2024, 43(8):  2455-2464.  doi:10.13292/j.1000-4890.202408.032

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Ecological restoration of tailings ponds is crucial for improving biodiversity and reducing pollution from heavy metal sources in mining regions. To screen the pioneer plant species that can be used for ecological restoration of lead-zinc tailings in karst areas, we measured the diversity index and distribution characteristics of plant species in a new tailings pond and an old tailings pond in the centralized area of Niujiaotang lead-zinc tailings pond in southern Guizhou were selected as the study area. Seven pioneer plant species were evaluated and screened, and their bioconcentration factors (BCF) and translocation factors (TF) of Zn, Pb, Cd, Cu, As, and Sb in tailings were analyzed to explore their accumulation characteristics and ecological restoration potential. The results showed that the tailings in the study area were alkaline. Cd and Zn contents exceeded soil background values of Guizhou Province and local soil heavy metal contents by several times, and the contents of bioavailable Cd and Zn were the highest. A total of eight plant species belonging to eight genera and four families (Ilex crenata, Arundinella hirta, Eremochloa ciliaris, Imperata cylindrica, Saccharum arundinaceum, Equisetum hyemale, Miscanthus floridulus, and Bidens pilosa) were distributed in the study area, which were mainly from Gramineae. Seven pioneer species screened (except I. crenata) were herbs and the contents of Zn, Cd, Cu, and As exceeded the normal levels in plants. The BCF and TF of E. ciliaris, I. cylindrica, and E. hyemale were greater than one for Cu, the BCF and TF of M. floridulus and B. pilosa were greater than one for As. Similarly, the BCF and TF of S. arundinaceum were greater than one for Cu and As. The abovementioned species are Cu and As accumulator, respectively. The BCF of A. hirta was greater than one for Cu, but the TF was less than one, indicating it is a root hoarding plant. In conclusion, seven pioneer plant species in the study area showed strong tolerance and accumulation ability to Cu, As, and other heavy metals, and had certain potential to be used in ecological restoration.





Ecological risk assessment of heavy metals in groundwater in the Yanqi Basin.

MAMAT Muyassar, EZIZ Mamattursun, LI Xinguo

2024, 43(8):  2465-2471.  doi:10.13292/j.1000-4890.202408.016

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To identify the potential ecological risks of heavy metals in groundwater in inner river basin, we collected 67 groundwater samples from the Yanqi Basin and analyzed the concentrations of six heavy metals. The potential ecological risks of heavy metals were quantitatively assessed using the potential ecological risk index (RI) and the ecological risk warning index (IER). Results showed that the average concentrations of Cd and Ni in groundwater were equal to 1.4 times and 1.15 times of the Class III thresholds of the “Standard for Groundwater Quality (GB/T 14848-2017)”, respectively. The average values of the single potential ecological risk index (E_i) of heavy metals in groundwater were ranked Cd>Ni>Mn>Cr>Cu>Zn, being at a slight ecological risk. The average RI value of heavy metals in groundwater was 23.89, indicating a slight ecological risk level. The average value of the single ecological risk warning index (IER_i) of heavy metals in groundwater was ranked Cd=Mn>Ni>Cr>Zn>Cu, indicating a no warning level for all the analyzed heavy metals. The average IER value of heavy metals in groundwater was -3.87, indicating a no warning level. The E_i and IER_i index of each heavy metal in groundwater in the Yanqi Basin showed different spatial distribution patterns. Overall, Cd is the potential heavy metal with the highest ecological risk in the groundwater in the Yanqi Basin, which deserves attention.





Effect of nitrogen addition on soil phosphorus fractions of grassland in loess hilly region.

LU Xiaoyue, ZHU Yun, LI Jiangwen, DENG Jian, XU Liping, WU Linhao, ZHANG Dan

2024, 43(8):  2472-2479.  doi:10.13292/j.1000-4890.202408.029

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Phosphorus is one of the limiting nutrients for plant growth in terrestrial ecosystems. Nitrogen deposition can change the activity and bioavailability of phosphorus by regulating soil phosphorus cycle. However, the understanding of changes in soil phosphorus fractions and their influencing factors under nitrogen deposition is still limited. To reveal the effects of nitrogen addition on soil phosphorus fractions and its regulation pathways, we measured soil phosphorus fractions, soil physicochemical properties, soil microbial biomass, and phosphorus invertase activity in a three-year field experiment with different nitrogen addition levels in a loess hilly region. The results showed that the contents of moderately and highly labile phosphorus increased significantly with increasing nitrogen addition levels, while the contents of non-labile phosphorus decreased significantly. Organic phosphorus content significantly increased by 1.71%-5.14%, but inorganic phosphorus content significantly decreased. Nitrogen addition reduced soil pH. High nitrogen addition level promoted the accumulation of soil C, N, and P, and increased soil microbial biomass C, N, and P by 18.11%, 38.27%, and 41.73%, respectively. With increasing nitrogen addition levels, the activities of soil alkaline phosphatase, phosphodiesterase and phytase decreased first and then increased. Soil nutrients, pH, microbial biomass, and enzyme activities explained 68.64% of the variation of soil phosphorus fractions. Structural equation model analysis showed that nitrogen addition induced changes in soil microbial metabolizing substrate nutrients, which had significant effects on microbial biomass and the activities of phosphorus conversion extracellular enzymes, and co-regulated soil phosphorus fractions through these two pathways.





Review on root classification methods and its applications.

GAO Qiao, XU Gang, DUAN Baoli

2024, 43(8):  2480-2492.  doi:10.13292/j.1000-4890.202408.021

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The complexity and heterogeneity of roots are important characteristics that hinder root research. Various root classification methods have been developed to classify roots into relatively homogeneous subcategories for specific scientific questions and root traits. Each classification method aims to subdivide different root subcategories from different perspectives using different rules. When conducting root research, it is crucial to select an appropriate method based on research objectives and the homogeneity of obtained root subcategories. As each root classification method has its advantages and disadvantages and can provide useful information about root function, multiple root classification methods coexist. To choose a suitable root classification method, a comprehensive understanding of the advantages and relevance of different methods is necessary. However, there is a lack of comprehensive literature reports that compare root classification methods, which hinders root researchers from selecting appropriate methods. We addressed this gap by summarizing and comparing five classification methods of fine roots. We review the progress and direction for the application of fine root classification to facilitate root researchers in selecting appropriate classification methods when studying fine root physiological and ecological functions.





A review of soil carbon, nitrogen, phosphorus and stoichiometry studies in China.

WANG Jiarui, ZHOU Junju, ZHU Guofeng

2024, 43(8):  2493-2501.  doi:10.13292/j.1000-4890.202408.011

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Soil C, N, P contents and stoichiometric ratios reflect the quantity and quality of soil organic matter, as well as element balance and constraints, which is of great significance for understanding ecological specificity and stability. Here, we summarized and analyzed the research on the spatial and temporal variations of soil C, N, P and their ratios and the driving factors in China, aiming to clarify the evolution of soil C, N, P and stoichiometric ratios at different spatial and temporal scales in China, and prospected the future research focuses. Under the combined effects of hydrothermal factors, land use/cover types and soil physicochemical properties, soil C, N, P and stoichiometric ratios showed different patterns in spatial and temporal scales. We further elucidated the mechanisms underlying stoichiometric characteristics and the coupling patterns of biogeochemical cycles. Our review will provide strong theoretical support for further research in ecosystem ecology.





Research progress on remediation technology of petroleum contaminated soil.

LI Jun, HU Jian, MA Wenmin, WANG Peng, ZHENG Houyi, LU Ran

2024, 43(8):  2502-2512.  doi:10.13292/j.1000-4890.202408.028

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Industrialization has promoted the prosperity of global oil industry. However, soil pollution caused by oil production and utilization is becoming more and more serious. The green, economical, stable and efficient remediation technology of petroleum polluted soil has been developed. Based on the present situation and the harm of petroleum contaminated soil, we summarized the existing physical, chemical, biological, and combined remediation technologies and remediation mechanisms of petroleum contaminated soil. Meanwhile, we expounded the applicable conditions, advantages, and disadvantages of different restoration methods. Finally, we prospected the future deve-lopment direction and challenge of remediation technology of petroleum contaminated soil. This work provides a reference for the research of remediation of petroleum contaminated soil and the selection of engineering application technology.





Construction of additive biomass model of planted poplar trees considering plot effect.

LI Wenbo, XIE Longfei, DONG Lihu

2024, 43(8):  2513-2522.  doi:10.13292/j.1000-4890.202408.019

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Populus nigra × P. simonii is one of the important tree species with the characteristics of fast-growing and high-yield. The accurate estimation of its biomass is of great significance. Based on diameter at breast height (DBH) and tree height (H), we constructed two seemingly unrelated regression models (SUR) and seemingly unrelated mixedeffects models (SURM) introduced random effects of plots, respectively (SUR1 and SURM1: DBH as the independent variable; SUR2 and SURM2: DBH and H as independent variables), and analyzed the prediction accuracy of SURM models. The results showed that after adding H to the model, the simulation effect on the biomass of trunk, branch, and leaf was significantly improved (R² in the SUR model increased by 0.1%-1.6%, and R² in SURM increased by 0.6%-7.0%), but the improvement on bark and root was poor. After considering the random effects at the plot level, the fitting effect of branch, leaf, and root biomass in the model was significantly improved, with the R² of each component in the SURM model increased by 5.7%-16.5%, while the improvement effect of trunk and bark biomass simulation was small. In addition, the mixedeffects model using the plot level (SURM1) performed better than using two variables (SUR2) to predict biomass, and the fitting effect of each component of the SURM1 model was better than the SUR2 model (R₂ increased by 0.2%-9.9%). The SURM model was more accurate for the biomass fitting and prediction of each component than the SUR model. In practice, when using the SURM model for biomass prediction, considering the difficulty of obtaining biomass data, it was determined that four trees were randomly selected for the correction of random effects. The two types of SURM models proposed here were applicable to different data types, which can provide basic support for accurately assessing the biomass of Populus nigra × P. simonii.





Hyperspectral retrieval of leaf ecological stoichiometry of mangrove species with RF and BPNN models in Qinglangang Mangrove Nature Reserve, Hainan.

LI Huazhe, DOU Zhiguo, NIE Leichao, WANG Junjie, GAO Changjun, TANG Xiying, ZHAI Xiajie, LI Wei

2024, 43(8):  2523-2530.  doi:10.13292/j.1000-4890.202408.030

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Mangrove forest is a natural coastal defense barrier, which plays an irreplaceable role in coastal disaster prevention and mitigation. Therefore, it is important to understand the growth status of mangroves. The ecological stoichiometry of plants can reflect their nutrient storage and supply capacity. Applying hyperspectral data to quantify the ecological stoichiometry of mangrove plants and exploring the accuracy and stability of hyperspectral retrieval of leaves can provide a technical reference for rapid remote sensing monitoring of mangrove growth conditions. In this study, we collected hyperspectral data of leaves of three dominant mangrove species (Bruguiera sexangula, Ceriops tagal, and Rhizophora apiculata) in Qinglangang Mangrove Nature Reserve, Hainan, and retrieved the contents and stoichiometry of C, N, and P. The results showed that there were significant differences in the contents and stoichiometry of C, N, and P among the three species, indicating differences in nutrient utilization of the three mangrove species. The Random Forest (RF) model outperformed Back Propagation Neural Network (BPNN) model in retrieving C, N, P contents and their ecological stoichiometry considering R², RMSE and RPD. This study demonstrated that the contents and stoichiometry of C, N, and P in mangrove leaves could be accurately estimated by leaf hyperspectral data. RF model is recommended for the hyperspectral retrieval of mangrove ecological stoichiometry when considering model accuracy and robustness.





Estimation of soil organic matter content in Ningxia based on hyperspectral information.

DING Qidong, WANG Yijing, ZHANG Junhua, CHEN Ruihua, JIA Keli, LI Xiaolin

2024, 43(8):  2531-2538.  doi:10.13292/j.1000-4890.202408.040

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Soil organic matter (SOM) is a key indicator for soil fertility. To explore the estimation ability of hyperspectral information for soils with low SOM content, this study focused on the surface soil (0-20 cm) of Hongsibu and Xidatan in Ningxia, and used field hyperspectral reflectance and SOM content as data sources. Four mathematical transformations were performed on the original spectral reflectance: reciprocal transformation first-order differential (RTFD), logarithm transformation first-order differential (LTFD), logarithmic reciprocal first-order differential (LRFD), and first-order differential (FD). Correlation analysis (PCC) and stepwise regression (SR) were used to screen for the sensitive bands. A SOM estimation model was established based on principal component regression (PCR), partial least squares regression (PLSR), support vector machine (SVM), and geographic weighted regression (GWR). The correlation between the original spectral reflectance and SOM was significantly enhanced after mathematical transformation, with the largest increase in FD transformation. The combination of PCC and SR was used to screen sensitive bands, which greatly reduced the dimensionality of the data, reduced the computational difficulty of the model, and improved its estimation ability. Based on the LTFD-SVM model, the estimation performance was optimal, with modeling determination coefficients (R_c²) and validation determination coefficients (R_p²) of 0.7593 and 0.9321, respectively. The root mean square error (RMSE) and relative analysis error (RPD) of the validation set were 0.62 and 3.47, respectively. The results can provide a reference basis for quantitative monitoring of low-content SOM in the study region and similar regions.





Potential habitat analysis and conservation strategies of Pére David’s deer based on MaxEnt model.

YANG Liwen, ZHANG Yuanyuan, YANG Zheng, ZHONG Zhenyu, BAI Jiade, SANG Weiguo

2024, 43(8):  2539-2550.  doi:10.13292/j.1000-4890.202408.024

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Pére David’s deer (Elaphurus davidianus), an endemic rare species in China, is a successful case of the reintroduction of wild extinct species, which gave a mode of reintroduction of wildlife in biodiversity conservation. Understanding the potential habitat suitability of Pére David’s deer can provide ecological information and a scientific basis for its conservation and population propagation. In this study, 15 distribution sites of free/semi-free populations and 11 environmental variables that may affect the distribution of Pére David’s deer were used to predict the most likely potential habitat and analyze its limiting factors by contrasting two conditions: natural conditions and human disturbance conditions, based on the MaxEnt model. The results showed that the total potential habitat for Pére David’s deer under natural conditions reached 4791795.3 km², accounting for 49.8% of China’s total land area. The area of highly suitable habitat was 526056.3 km², accounting for 5.5% of the total land area of China and mainly distributed in the humid plains in the east-central region. Altitude, slope aspect, and vegetation type were the environmental factors with higher contribution. When considering human activity factors, the potential habitat of Pére David’s deer reduced by 13.5% of the total land area. The area of highly suitable habitat was reduced to 317808.3 km², accounting for only 3.3% of the total land area in China. The habitat showed an obvious trend of fragmentation. The range of suitable altitude values is decreased and moved to lower altitudes, and the optimal altitude threshold decreases from 647 m for natural conditions to 635 m for human-influenced conditions. There was no obvious negative correlation between the presence probability of Pére David’s deer and human disturbance variables, which may be related to the fact that the location of the protected area was artificially set and the reintroduced provenance spread sites were close to anthropic activity zone. Some suggestions were put forward, such as settingup protected areas, establishing a perfect circuit monitoring system of protected areas, developing ecological corridors, artificially intervening interspecies communication, strengthening resource allocation, and improving ecological compensation mechanism.