Table of Content

15 April 2023, Volume 34 Issue 4

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Special Features of Black Soil Protection and Agricultural Sustainable Development

Spatial and temporal variations of soil nutrients of cropland in Northeast China from the 1980s to the 2010s

WANG Shihao, XU Xinliang, HUANG Lin, ZHAO Guang

2023, 34(4):  865-875.  doi:10.13287/j.1001-9332.202304.010

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In recent years, the degradation of cropland soils in Northeast China, such as “thinned, barren, and hardened”, has become increasingly serious, with consequences on sustainable development of agriculture. Based on the data from Soil Types of China (1980s) and Soil Series of China (2010s), we examined the change patterns of soil nutrient conditions across different regions and soil types in Northeast China over the past 30 years through the statistical analysis of large samples. The results showed that: 1) from the 1980s to the 2010s, soil nutrient indicators in Northeast China changed to different degrees. Soil pH decreased by 0.03. Soil organic matter (SOM) content decreasd most prominently, by 8.99 g·kg^-1 or 23.6%. Soil total N (TN), total P (TP) and total K (TK) contents showed increasing trends, with increases of 17.1%, 46.8%, and 4.9%, respectively. 2) Changes in soil nutrient indicators differed across different provinces and cities. Soil acidification in Liaoning was the most obvious, with pH decreasing by 0.32. SOM content in Liaoning decreased most significantly, by 31.0%. Soil TN, TP, and TK contents in Liaoning increased most significantly by 73.8%, 248.1% and 44.0%, respectively. 3) The changes of soil nutrients varied greatly among soil types, with brown soil and kastanozems showing the greatest decrease in pH. The SOM content of all soil types showed a decreasing trend, with 35.4%, 33.8% and 26.0% reduction in brown soil, dark brown forest soil and chernozem respectively. The greatest increase in TN, TP and TK contents were observed in brown soil by 89.1%, 232.8%, and 48.5%, respectively. In summary, declining organic matter content and soil acidification were the core problems of soil degradation in Northeast China from the 1980s to the 2010s. Reasonable tillage methods and targeted conservation strategies are critically needed to ensure the sustai-nable development of agriculture in Northeast China.

Mechanisms of conservation tillage on nitrogen-fertilizer reduction and maize grain improvement in Mollisols of Northeast China: Insights from a ¹⁵N tracing study

MIAO He, YUAN Lei, YANG Miaoyin, HU Yanyu, CHEN Xin, HE Hongbo, ZHANG Xudong, XIE Hongtu, LU Caiyan

2023, 34(4):  876-882.  doi:10.13287/j.1001-9332.202304.032

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Conservation tillage is an important management practice to guarantee soil fertility in degraded Mollisols. It is still unclear, however, whether the improvement and stability of crop yield under conservation tillage can be sustainable with increasing soil fertility and reducing fertilizer-N application. Based on a long-term tillage experiment initiated in Lishu Conservation Tillage Research and Development Station by Chinese Academy of Sciences, we conducted a ¹⁵N tracing field micro-plot experiment to investigate the effects of reducing nitrogen application on maize yield and fertilizer-N transformation under long-term conservation tillage agroecosystem. There were four treatments, including conventional ridge tillage (RT), no-tillage with 0% (NT0), 100% (NTS) maize straw mul-ching, and 20% reduced fertilizer-N plus 100% maize stover mulching (RNTS). The results showed that after a complete cultivation round, the average percentages of fertilizer N recovery in soil residues, crop usage, and gaseous loss were 34%, 50%, and 16%, respectively. Compared with conventional ridge tillage, no-tillage with maize straw mulching (NTS and RNTS) significantly increased the use efficiency of fertilizer N in current season by 10% to 14%. From the perspective of N sourcing analysis, the average percentage of fertilizer N absorbed by crop parts (including seeds, straws, roots, and cobs) to the total N uptake reached nearly 40%, indicating that soil N pool was the main source of N for crop uptakes. In comparison with conventional ridge tillage, conservation tillage significantly increased total N storage in 0-40 cm by reducing soil disturbance and increasing organic inputs, and thus ensured the expansion and efficiency increment of soil N pool in degraded Mollisols. Compared with conventional ridge tillage, NTS and RNTS treatments significantly increased the maize yield from 2016 to 2018. In all, by improving fertilizer nitrogen utilization efficiency and maintaining the continuous supply of soil nitrogen, long-term management of no-tillage with maize straw mulching could achieve a stable and increasing maize yield in three consecutive growing seasons and simultaneously reduce environmental risks derived by fertilizer-N losses, even under the condition of 20% reduction of fertilizer-N application, and thus actualize the sustainable development of agriculture in Mollisols of Northeast China.

Effects of the construction of fertile and cultivated soil layer on soil fertility and maize yield in Albic soil

LU Xinchun, FAN Xinxin, ZOU Wenxiu, YAN Jun, CHEN Xu, HAN Xiaozeng, DENG Weina

2023, 34(4):  883-891.  doi:10.13287/j.1001-9332.202304.034

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We examined the effects of fertile soil layer construction technology on soil fertility and maize yield with a 3-year field experiment in Albic soil in Fujin, Heilongjiang Province. There were five treatments, including conventional tillage (T15, without organic matter return) and fertile soil layer construction methods [deep tillage (0-35 cm) with straw return, T35+S; deep tillage with organic manure, T35+M; deep tillage with straw and organic manure return, T35+S+M; deep tillage with straw, organic manure return and chemical fertilizer, T35+S+M+F]. The results showed that: 1) compared with the T15 treatment, maize yield was significantly increased by 15.4%-50.9% under fertile layer construction treatments. 2) There was no significant difference of soil pH among all treatments in the first two years, but fertile soil layer construction treatments significantly increased soil pH of topsoil (0-15 cm soil layer) in the third year. The pH of subsoil (15-35 cm soil layer) significantly increased under T35+S+M+F, T35+S+M, and T35+M treatments, while no significant difference was observed for T35+S treatment, compared with T15 treatment. 3) The fertile soil layer construction treatments could improve the nutrient contents of the topsoil and subsoil layer, especially in the subsoil layer, with the contents of organic matter, total nitrogen, available phosphorus, alkali-hydrolyzed nitrogen and available potassium being increased by 3.2%-46.6%, 9.1%-51.8%, 17.5%-130.1%, 4.4%-62.8%, 22.2%-68.7% under the subsoil layer, respectively. The fertility richness indices were increased in the subsoil layer, and nutrient contents of the subsoil layer were close to those of topsoil layer, indicating that 0-35 cm fertile soil layer had been constructed. 4) Soil organic matter contents in the 0-35 cm layer were increased by 8.8%-23.2% and 13.2%-30.1% in the second and third years of fertile soil layer construction, respectively. Soil organic carbon storage was also gradually increased under fertile soil layer construction treatments. 5) The carbon conversion rate of organic matter was 9.3%-20.9% under T35+S treatment, and 10.6%-24.6% under T35+M, T35+S+M, and T35+S+M+F treatments. The carbon sequestration rate was 815.7-3066.4 kg·hm^-2·a^-1 in fertile soil layer construction treatments. The carbon sequestration rate of T35+S treatment increased with experimental periods, and soil carbon content under T35+M, T35+S+M and T35+S+M+F treatments reached saturation point in the experimental second year. Construction of fertile soil layers could improve the fertility of topsoil and subsoil and maize yield. In term of economic benefits, combination application of maize straw, organic material and chemical fertilizer within 0-35 cm soil, cooperating with conservation tillage, is recommended for the Albic soil fertility improvement.

Effects of cyanobacteria- and moss-biocrusts on soil aggregate stability and splash erosion in croplands of the China Mollisols area

CAO Yousong, ZHANG Chenhui, XIAO Bo, SUN Fuhai

2023, 34(4):  892-902.  doi:10.13287/j.1001-9332.202304.018

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To investigate the effects of biocrusts development on aggregate stability and splash erosion of Mollisols and to understand its function in soil and water conservation, we collected biocrusts (cyano crust and moss crust) samples in croplands during the growing season and measured the differences in aggregate stability between biocrusts and uncrusted soil. The effects of biocrusts on reduction of raindrop kinetic energy were determined and splash erosion amounts were obtained with single raindrop and simulated rainfall experiments. The correlations among soil aggregate stability, splash erosion characteristics, and fundamental properties of biocrusts were analyzed. The results showed that compared to uncrusted soil, the cyano crust and the moss crust decreased the proportion of soil water-stable aggregates <0.25 mm by 10.5% and 21.8%, respectively, while their soil water-stable aggregates 5-10 mm were 4.0 and 8.8 times as that of uncrusted soil. In contrast to uncrusted soil, the macroaggregate content (R_0.25), mean weight diameter (MWD), and geometric mean diameter (GMD) of biocrusts were 31.5%, 76.2%, and 33.5% higher, respectively. In addition, biocrusts reduced raindrop kinetic energy by an average of 0.48 J compared to uncrusted soil. The breakthrough raindrop kinetic energy of cyano crust and moss crust were 2.9 and 26.2 times as that of uncrusted soil, while the reduction of raindrop kinetic energy by cyano crust with high biomass was 1.3 and 6.6 times as that of medium and low biomass, respectively. Under the single raindrop and simulated rainfall conditions, biocrusts reduced splash erosion amounts by 47.5% and 79.4%, respectively. The proportion of aggregates >0.25 mm in the splash soil particles of biocrusts (37.9%) was 40.3% lower than that of uncrusted soil, while the proportion of aggregates >0.25 mm decreased as biocrust biomass increased. Moreover, the aggregate stability, splash erosion amount, and fundamental properties of biocrusts were significantly correlated. The MWD of aggregates was significantly and negatively correlated with the splash erosion amount under single raindrop and simulated rainfall conditions, indicating that the improved aggregate stability of surface soil caused by biocrusts accounted for reducing splash erosion. The biomass, thickness, water content, and organic matter content of biocrusts had significant effects on aggregate stability and splash characteristics. In conclusion, biocrusts significantly promoted soil aggregate stability and reduced splash erosion, which had great significance to soil erosion prevention and the conservation and sustainable utilization of Mollisols.

Effects of no-tillage and different stover mulching amounts on soil microbial community and microbial residue in the Mollisols of China

LYU Fuze, YANG Yali, BAO Xuelian, ZHANG Changren, ZHENG Tiantian, HE Hongbo, ZHANG Xudong, XIE Hongtu

2023, 34(4):  903-912.  doi:10.13287/j.1001-9332.202304.033

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To investigate the effects of no-tillage and different amounts of stover mulch on soil microbial community composition and their residues, we set up a field experiment of different amounts of stover mulch under no-tillage on the long-term maize conservation tillage station located in the Mollisols area of Northeast China (built in 2007), including without stover mulch (NT0), 1/3 stover mulch (NT1/3), 2/3 stover mulch (NT2/3) and full stover mulch (NT3/3), and the conservation tillage (plowing without stover mulch, CT) as control. We analyzed phospholipid fatty acid, amino sugar biomarker and soil physicochemical properties at different soil layers (0-5 cm, 5-10 cm, 10-20 cm). The results showed that compared to CT, no-tillage without stover mulch (NT0) did not affect soil organic carbon (SOC), total nitrogen (TN), dissolved organic carbon and nitrogen (DOC, DON), water content, microbial community and their residue. The main effects of no-tillage and stover mulch were found in the topsoil. Specifically, the NT1/3, NT2/3 and NT3/3 significantly increased SOC content by 27.2%, 34.1% and 35.6%, respectively, phospholipid fatty acid content was significantly increased under NT2/3 and NT3/3 by 39.2% and 65.0%, respectively, and NT3/3 significantly increased the content of microbial residue-amino sugar by 47.2% in the depth of 0-5 cm compared with CT. The variations in soil properties and microbial community induced by no-tillage and different amounts stover mulch decreased with soil depth, with almost no difference in the 5-20 cm soil layer. SOC, TN, DOC, DON, and water content were the main factors influencing the composition of the microbial community and the accumulation of microbial residue. Microbial biomass was positively correlated with microbial residue, particularly fungal residue. In conclusion, all stover mulch treatments promoted SOC accumulation to different degrees. When there is sufficient stover, it is advisable to opt for no-tillage with full stover mulch, as it is most conducive to the increases of soil microbial biomass, microbial residue and SOC. In case when the amount of stover is inadequate, however, no-tillage with 2/3 stover mulch can still improve soil microbial biomass and SOC content. This study would provide practical guidance for stover management in conservation tillage and sustainable agricultural development in the Mollisols area of Northeast China.

Effects of long-term no-tillage on the functional potential of microorganisms involved in the nitrogen, phosphorus and sulfur cycles of black soil

GAO Yan, LIANG Aizhen, HUANG Dandan, ZHANG Yan, ZHANG Yang, WANG Yang, ZHANG Shixiu, CHEN Xuewen

2023, 34(4):  913-920.  doi:10.13287/j.1001-9332.202304.011

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Understanding the effects of different tillage practices on functional microbial abundance and composition in nitrogen (N), phosphorus (P) and sulfur (S) cycles are essential for the sustainable utilization of black soils. Based on an 8-year field experiment located in Changchun, Jilin Province, we analyzed the abundance and composition of N, P and S cycling microorganisms and their driving factors in different depths of black soil under no til-lage (NT) and conventional tillage (CT). Results showed that compared with CT, NT significantly increased soil water content (WC) and microbial biomass carbon (MBC) at soil depth of 0-20 cm. Compared with CT, NT significantly increased the abundances of functional and encoding genes related to N, P and S cycling, including the nosZ gene encoding N₂O reductase, the ureC gene performing organic nitrogen ammoniation, the nifH gene encoding nitrogenase ferritin, the functional genes phnK and phoD driving organic phosphorus mineralization, the encoding pyrroloquinoline quinone synthase ppqC gene and the encoding exopolyphosphate esterase ppX gene, and the soxY and yedZ genes driving sulfur oxidation. The results of variation partitioning analysis and redundancy analysis showed that soil basic properties were the main factors affecting the microbial composition of N, P and S cycle functions (the total interpretation rate was 28.1%), and that MBC and WC were the most important drivers of the functional potential of soil microorganisms in N, P and S cycling. Overall, long-term no tillage could increase the abundance of functional genes of soil microorganisms by affecting soil environment. From the perspective of molecular biology, our results elucidated that no tillage could be used as an effective soil management measure to improve soil health and maintain green agricultural development.

Characteristics of spring maize sap flow and its environmental influencing factors in typical mollisol area

ZHU Xiangming, PENG Wei, RAN Enhua, FU Meiling, ZHENG Yueheng, ZHANG Yu

2023, 34(4):  921-927.  doi:10.13287/j.1001-9332.202304.027

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Clarifying the variations of sap flow rate of spring maize in the typical mollisol area and its main control factors is of great significance to explore water consumption from transpiration and regulate field water management. In this study, we installed the wrapped sap flow sensors and TDR probes to continuously monitor the sap flow rate of spring maize during filling-maturity stage and soil water and heat conditions of topsoil. In combination with meteorological data collecting from a nearby automatic weather station, we analyzed the correlation between the sap flow rate of spring maize and environmental factors at different time scales. The results showed that the sap flow rate of spring maize in typical mollisol area had an obvious fluctuation of high diurnal and low nighttime. The instantaneous sap flow rate peaked at daytime, with a value of 139.9 g·h^-1, but being weak at nighttime. The starting time, closing time, and peak values of spring maize sap flow were significantly inhibited in cloudy and rainy days, compared with that in sunny days. On hourly scale, the sap flow rate was significantly correlated to solar radiation, saturated vapor pressure deficit (VPD), relative humidity, air temperature, and wind speed. On daily scale, only solar radiation, VPD, and relative humidity were significantly correlated with sap flow rate, with the absolute values of correlation coefficient being all above 0.7. Due to high soil water content during the observation period, the sap flow rate was not significantly correlated with soil water content and soil temperature of 0-20 cm layer, with the absolute values of correlation coefficient being less than 0.1. Under the condition without water stress, solar radiation, VPD, and relative humidity were the top three influencing factors of sap flow rate in this region, on both hourly scale and daily scale.

Original Articles

Effects of management intensities on soil aggregate stability and carbon, nitrogen, phosphorus distribution in Phyllostachys edulis forests

NI Huijing, CHU Haoyu, SU Wenhui, FAN Shaohui

2023, 34(4):  928-936.  doi:10.13287/j.1001-9332.202304.002

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Soil aggregates are the main sites for the decomposition of soil organic matter and the formation of humus. The composition characteristics of aggregates with different particle sizes are one of the indicators for soil fertility. We explored the effects of management intensity (frequency of fertilization and reclamation) on soil aggregates in moso bamboo forests, including mid-intensity management (T₁, fertilization and reclamation every 4 years), high-intensity management (T₂, fertilization and reclamation every 2 years), and extensive management (CK). The water-stable soil aggregates (0-10, 10-20, and 20-30 cm layers) from moso bamboo forest were separated by a combination of dry and wet sieving method and the distribution of soil organic carbon (SOC), total nitrogen (TN) and available phosphorus (AP) across different soil layers were determined. The results showed that management intensities had significant effects on soil aggregate composition and stability, and SOC, TN, AP distribution of moso bamboo forests. Compared with CK, T₁ and T₂ decreased the proportion and stability of macroaggregates in 0-10 cm soil layer, but increased that in 20-30 cm soil layer, while reduced the content of organic carbon in macroaggregates, the contents of organic carbon, TN and AP in microaggregates. Such results indicated that the intensified management was not conducive to formation of macroaggregates in 0-10 cm soil layer and carbon sequestration in macroaggregates. It was beneficial to the accumulation of organic carbon in soil aggregates and nitrogen and phosphorus in microaggregates with lower human disturbance. Mass fraction of macroaggregates and organic carbon content of macroaggregates was significantly positively correlated with aggregate stability, which best explained the variations of aggregate stability. Therefore, macroaggregates and organic carbon content of macroaggregates were the most important factors affecting the formation and stability of aggregates. Appropriate reduction of disturbance was beneficial to the accumulation of macroaggregates in the topsoil, the sequestration of organic carbon by macro-aggregates, and the sequestration of TN and AP by microaggregates, and improving soil quality and sustainable management in moso bamboo forest from the point of view of soil aggregate stability.

Effects of acid rain and root exclusion on soil organic carbon in Cunninghamia lanceolata and Michelia macclurei plantations

WANG Jiao, GUAN Xin, HUANG Ke, DUAN Xuan, CHEN Bohan, ZHANG Weidong, YANG Qingpeng

2023, 34(4):  937-945.  doi:10.13287/j.1001-9332.202304.016

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Acid rain is one of most serious environment problems in China. The types of acid rain have gradually transformed from sulfuric acid rain (SAR) to mixed acid rain (MAR) and nitric acid rain (NAR) in recent years. Roots are one source of soil organic carbon and play an important role in the formation of soil aggregates. However, the changes in acid rain type and the effect of root removal on soil organic carbon in forest ecosystems are poorly understood. In this study, we removed roots and simulated acid rain with different types (SO₄^2-:NO₃^- ratio of 4:1, 1:1, and 1:4) for three years in Cunninghamia lanceolata (CP) and Michelia macclurei (MP) plantations to analyze the changes of soil organic carbon and physical properties and to measure the size and mean weight diameter (MWD) of aggregates. Results showed that root removal in C. lanceolata and M. macclurei remarkably reduced soil organic carbon pool by 16.7 % and 21.5%, and soil recalcitrant carbon by 13.5% and 20.0%, respectively. Root removal substantially decreased the MWD and proportion and organic carbon content of soil macroaggregates in M. macclurei, but not in C. lanceolata. Acid rain did not affect soil organic carbon pool and soil aggregate structures. Our results indicated that roots promote soil organic carbon stabilization and that their contribution to the stability of soil organic carbon varies with forest types. Moreover, soil organic carbon stabilization is not affected by different types of acid rain in the short term.

Effects of warming on quantity and structure of litter-derived dissolved organic matter in subtropical natural Castanopsis kawakamii forests

ZHANG Yuhui, CHEN Juan, XU Chao, XIONG Decheng, YANG Zhijie, CHEN Shidong, MAO Chao

2023, 34(4):  946-954.  doi:10.13287/j.1001-9332.202304.006

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Litter-derived dissolved organic matter (DOM) is an important source of soil DOM, and the response of which to climate warming may change forest soil carbon and nitrogen dynamics, such as soil carbon and nitrogen mineralization. In this study, we conducted a field manipulative warming experiment in natural Castanopsis kawakamii forests. Combined with litter leaching solution collected in the field and ultraviolet-visible and three-dimensional fluorescence spectroscopy analyses, we explored the effects of warming on the content and structure of litter-derived DOM in subtropical evergreen broad-leaved forests. The results showed that litter-derived dissolved organic carbon and nitrogen content exhibited monthly dynamics, with the peak (in April) and the mean monthly content being 1.02 and 0.15 g·m^-2, respectively. Litter-derived DOM had higher fluorescence index and lower biological index, indicating the microbial-origin of DOM from litter. The litter DOM mainly included humic-like fractions and tryptophan-like substances. Warming did not affect the content, aromaticity, hydrophobicity, molecular weight, fluorescence index, biological index and humification index of DOM, suggesting neutral effect of warming on the quantity and structure of litter DOM. Warming also did not affect the relative contribution of main components in DOM, indicating that the temperature variation exerted no effects on microbial degradation. In summary, warming did not change the quantity and quality of litter-derived DOM in subtropical evergreen broadleaved forests, indicating warming had little effect on litter-derived DOM input to soil.

Spatial heterogeneity of soil available medium- and micro-elements in evergreen-deciduous broadleaved forest in karst

LIAN Ziwen, DU Hu, GU Junkun, ZENG Fuping, PENG Wanxia, YIN Lichu, LONG Qingzhi, LIU Kunping, SUN Rui, TAN Weining

2023, 34(4):  955-961.  doi:10.13287/j.1001-9332.202304.008

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Understanding the spatial heterogeneity of soil available medium- and micro-elements in karst area can provide a valuable theoretical guideline for soil nutrient management of karst ecosystem. We collected soil samples at a soil depth of 0-10 cm using grid sampling (20 m×20 m) in a 25 hm² (500 m×500 m) dynamic monitoring plot. We further analyzed the spatial variability of soil medium- and micro-elements and their drivers, with classic statistics analysis and geo-statistics analysis. The results showed that the average contents of exchangeable Ca and Mg and available Fe, Mn, Cu, Zn, and B were 7870, 1490, 30.24, 149.12, 1.77, 13.54, and 0.65 mg·kg^-1, respectively. The coefficient of variation of the nutrients ranged from 34.5% to 68.8%, showing a medium degree of their spatial variation. The coefficient of determination of the best-fit semi-variogram models of each nutrient was higher than 0.90, except for available Zn (0.78), indicating a strong predictive power for the spatial variation of the nutrients. The nugget coefficients for all the nutrients were less than 50%, showing a moderate spatial correlation, and the structural factors played a pivotal role. The spatially autocorrelated variation was within the range of 60.3-485.1 m, among which available Zn showed the lowest range and the deepest fragmentation degree. The spatial distribution of exchangeable Ca, Mg, and available B were consistent, with contents in the depression being significantly lower than that in other habitats. The contents of available Fe, Mn, and Cu declined with the increases of altitude and were significantly lower on the hilltop than in other habitats. The spatial variation of soil medium- and micro-elements was closely related to topographic factors in karst forest. Elevation, slope, soil thickness, and rock exposure rate were the primary drivers of spatial variation of soil elements and need to be considered in soil nutrient management of karst forestlands.

Soil C, N and P stoichiometry in different forest stand types in the middle and lower reaches of the Beijiang River, China

XU Tiaozi, YE Caihong, ZHANG Geng, ZHANG Zhongrui, ZHU Hangyong, HE Qian, DING Xiaogang

2023, 34(4):  962-968.  doi:10.13287/j.1001-9332.202304.001

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We examined the vertical distribution characteristics of soil organic carbon (C), total nitrogen (N), total phosphorus (P) and their ecological stoichiometric ratios in 0-80 cm soil profile under three forest stand types in the middle and lower reaches of the Beijiang River, including broad-leaved forest, coniferous forest, and mixed coniferous and broad-leaved forest. The results showed that soil C, N and P contents of the three forest stand types were 12.17-14.25, 1.14-1.31, and 0.27-0.30 g·kg^-1, respectively. The contents of C and N decreased with the increases of soil depth. The content of C and N in each soil layer showed that coniferous and broad-leaved mixed forest > coniferous forest > broad-leaved forest. There was no significant difference in P content among the three stand types, and there was no obvious variation in the vertical profile. The soil C/N, C/P, and N/P of the three forest types were 11.2-11.3, 49.0-60.3, and 4.5-5.7, respectively. There was no significant difference in soil C/N among the three stand types. The highest soil C/P and N/P were found in the mixed forest. There was no interaction between soil depth and stand type in affecting soil C, N, P contents and their stoichiometric ratios. There was significant positive correlation between C and N, and between N and C/P in each stand type and soil layer. Soil C/P and N/P had stronger ecological indicating effects on stand types. The coniferous and broad-leaved mixed forest was strongly limited by P availability.

Ecological stoichiometry of soil and microbial biomass carbon, nitrogen and phosphorus in tea plantations with different ages

ZHANG Guanhua, NIU Jun, YI Liang, SUN Baoyang, LI Jianming, XIAO Hai

2023, 34(4):  969-976.  doi:10.13287/j.1001-9332.202304.015

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The implementation of ecological engineering projects such as “Green for Grain” causes great changes in the cycling and stoichiometry of soil carbon (C), nitrogen (N), and phosphorus (P), with consequences on soil microbial biomass stoichiometric characteristics. However, the temporal dynamics and coordination of soil-microbial C:N:P stoichiometry are still unclear. In this study, we examined the variations of soil-microbial biomass C, N, and P with the tea plantation ages (<5 a, 5-10 a, 10-20 a, 20-30 a, and >30 a) in a small watershed in the Three Gorges Reservoir Area. We analyzed the relationships between their stoichiometric ratios, microbial entropy (qMBC, qMBN, qMBP), and stoichiometric imbalance (ratios of soil C, N, P stoichiometry to microbial biomass C, N, P stoichiometry). The results showed that with the increases of tea plantation ages, soil and microbial biomass C, N, P contents, soil C:N and C:P significantly increased, while soil N:P declined; the microbial biomass C:P and N:P increased first and then decreased, but microbial biomass C:N did not change. Tea plantation ages significantly affected soil microbial entropy and soil-microbial stoichiometry imbalance (C:N_imb, C:P_imb, N:P_imb). With the increases of tea plantation ages, qMBC first decreased and then increased, while qMBN and qMBP went up in a fluctuating pattern. The C-N stoichiometry imbalance (C:N_imb) and C-P stoichiometry imbalance (C:P_imb) increased significantly, while the N-P stoichiometry imbalance (N:P_imb) showed a fluctuating rise. Results of the redundancy analysis showed that qMBC was positively correlated with soil N:P and microbial biomass C:N:P, but negatively correlated with microbial stoichiometric imbalance and soil C:N, C:P; whereas qMBN and qMBP showed the opposite situation. The microbial biomass C:P was most closely related to qMBC, while C:N_imb and C:P_imb had greater effects on qMBN and qMBP.

Geographical variation of ecological stoichiometry and nutrient resorption in leaves of Pinus koraiensis and Fraxinus mandshurica

YAN Yuanyuan, GUO Qi, GUAN Junze, LIU Zhi, WANG Dongnan, GU Jiacun

2023, 34(4):  977-984.  doi:10.13287/j.1001-9332.202304.004

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In this study, we sampled leaves of coniferous species Pinus koraiensis and broad-leaved tree species Fraxinus mandshurica from four latitudes in northeastern China to investigate the carbon (C), nitrogen (N), phosphorus (P) stoichiometric characteristics and nutrient resorption efficiency and their potential relationships, as well as their responses to climatic and edaphic factors. The results showed that stoichiometric characteristics were species-specific, and that the C and N contents in leaves of F. mandshurica significantly increased with increasing latitude. The C:N of F. mandshurica and N:P of P. koraiensis were negatively correlated with latitude, but an inverse relationship was found for N:P of F. mandshurica. P resorption efficiency was significantly correlated with latitude in P. koraiensis. The spatial variation of ecological stoichiometry of these two species was mainly affected by climatic factors such as mean annual temperature and precipitation, while that of nutrient resorption was influenced by several soil factors such as soil pH and nitrogen content. Principal component analysis showed that P resorption efficiency of P. koraiensis and F. mandshurica was significantly negatively correlated with N:P, but positively correlated with P content. N resorption efficiency showed significantly positive correlation with P content but negative correlation with N:P in P. koraiensis. Compared with P. koraiensis, F. mandshurica was more inclined to fast investment and return in terms of leaf traits.

Effects of silicate application on rice growth, yield and quality under nighttime warming in southern China

LOU Yunsheng, YU Yujie, LIU Yan, YANG Huilin, ZHOU Dongxue

2023, 34(4):  985-992.  doi:10.13287/j.1001-9332.202304.013

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The main feature of climate warming is that nighttime warming is higher than the daytime warming. Nighttime warming reduced single rice production in southern China, while silicate application increased rice yield and stress resistance. It is still unclear regarding the effects of silicate application on growth, yield, and especially quality in rice under nighttime warming. We performed a field simulation experiment to investigate the effects of silicate application on tiller number, biomass, yield and quality of rice. Warming was set at two levels, ambient temperature (control, CK) and nighttime warming (NW). The open passive nighttime warming method was used, with rice canopy being covered with aluminum foil reflective film at night (19:00-6:00) to simulate nighttime warming. Silicate fertilizer (steel slag) was applied at two levels, i.e., Si₀(0 kg SiO₂·hm^-2) and Si₁(200 kg SiO₂·hm^-2). The results showed that, compared with the control (ambient temperature), average temperature at nighttime on rice canopy and at 5 cm soil layer increased by 0.51-0.58 ℃ and 0.28-0.41 ℃ during rice growing season, respectively. Nighttime warming decreased tiller number and chlorophyll content by 2.5%-15.9% and 0.2%-7.7%, respectively. In contrast, silicate application increased tiller number and chlorophyll content by 1.7%-16.2% and 1.6%-16.6%, respectively. Under nighttime warming, silicate application increased dry weight of shoot, total dry weight of the whole plant, and yield at grain filling-maturity stage by 64.1%, 55.3%, and 7.1%, respectively. Under nighttime warming, silicate application significantly increased milled rice rate, head rice rate, and total starch content by 2.3%, 2.5%, and 41.8%, respectively. Nighttime warming reduced rice yield by decreasing the number of effective panicles, seed setting rate, and 1000-grain weight, but increasing empty grains. Silicate application increased rice yield by increasing the number of effective panicles, filled grains per panicle, seed setting rate and 1000-grain weight, but reducing empty grains. In conclusion, silicate application could effectively alleviate the suppressive effects of nighttime warming on growth, yield, and quality of single rice in Southern China.

Effects of N fertilizer reduction combined with straw biochar application on the yield, Si, and N nutrition of double-cropping rice

NING Chuanchuan, CHEN Yuegui, LIU Rui, LI Tongxin, CHEN Hailang, TIAN Jihui, CAI Kunzheng

2023, 34(4):  993-1001.  doi:10.13287/j.1001-9332.202304.009

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Nitrogen (N) and silicon (Si) are important nutritional elements for rice. However, excessive N fertili-zer application and the ignorance of Si fertilizer are common in practice. Straw biochar is rich in Si, which can be used as a potential Si fertilizer. In this study, we conducted a consecutive 3-year field experiment to explore the effects of N fertilizer reduction combined with straw biochar application on rice yield, Si and N nutrition. There were five treatments: conventional N application (180 kg·hm^-2, N₁₀₀), 20% N reduction (N₈₀), 20% N reduction with 15 t·hm^-2 biochar (N₈₀+BC), 40% N reduction (N₆₀), and 40% N reduction with 15 t·hm^-2 biochar (N₆₀+BC). The results showed that compared with N₁₀₀, 20% N reduction did not affect the accumulation of Si and N in rice; 40% N reduction reduced foliar N absorption, but significantly increased foliar Si concentration by 14.0%-18.8%; while combined application of biochar significantly increased foliar Si accumulation, with an increase of Si concentration by 38.0%-63.3% and Si absorption by 32.3%-49.9%, but further reduced foliar N concentration. There was a significant negative correlation between Si and N concentration in mature rice leaves, but no correlation between Si and N absorption. Compared with N₁₀₀, N reduction or combined application of biochar did not affect soil ammonium N and nitrate N, but increased soil pH. Nitrogen reduction combined application of biochar significantly increased soil organic matter by 28.8%-41.9% and available Si content by 21.1%-26.9%, with a significant positive correlation between them. Compared with N₁₀₀, 40% N reduction reduced rice yield and grain setting rate, while 20% N reduction and combined application of biochar did not influence rice yield and yield components. In summary, appropriate N reduction and combined with straw biochar can not only reduce N fertilizer input, but also improve soil fertility and Si supply, which is a promising fertilization method in double-cropping rice fields.

Density and row spacing of short-season cotton suitable for machine picking in the cotton region of Yellow River Basin

LI Fengrui, ZHAO Wenchao, ZHANG Donglou, DONG Lingyan, WANG Ruming, QI Hongxin, ZHANG Chao, ZHANG Guijun, YANG Xiufeng, SHI Jialiang

2023, 34(4):  1002-1008.  doi:10.13287/j.1001-9332.202304.012

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To determine the suitable planting density and row spacing of short-season cotton suitable for machine picking in the Yellow River Basin of China, we conducted a two-year field experiment in Dezhou during 2018-2019. The experiment followed a split-plot design, with planting density (82500 plants·hm^-2 and 112500 plants·hm^-2) as the main plots and row spacing (equal row spacing of 76 cm, wide-narrow row spacing of 66 cm+10 cm, equal row spacing of 60 cm) as the subplots. We examined the effects of planting density and row spacing on growth and development, canopy structure, seed cotton yield and fiber quality of short-season cotton. The results showed that plant height and LAI under high density treatment were significantly greater than those under low density treatment. The transmittance of the bottom layer was significantly lower than under low density treatment. Plant height under 76 cm equal row spacing was significantly higher than that under 60 cm equal row spacing, while that under wide-narrow row spacing (66 cm +10 cm) was significantly smaller than that under 60 cm equal row spacing in peak bolling stage. The effects of row spacing on LAI varied between the two years, densities, and growth stages. On the whole, the LAI under the wide-narrow row spacing (66 cm+10 cm) was higher, with the curve declining gently after the peak, and it was higher than that in the two cases of equal row spacing in the harvest time. The change in transmittance of the bottom layer presented the opposite trend. Density, row spacing, and their interaction had significant effects on seed cotton yield and its components. In both years, seed cotton yield was the highest (3832 kg·hm^-2 in 2018, 3235 kg·hm^-2 in 2019) under wide-narrow row spacing (66 cm+10 cm), and it was more stable at high densities. Fiber quality was less affected by density and row spacing. To sum up, the optimal density and row spacing of short-season cotton were as follows: density with 112500 plants·hm^-2 and wide-narrow row spacing (66 cm+10 cm).

Effects of elevated atmospheric ammonia concentration on photosynthetic characteristics and grain yield in wheat under different nitrogen rates

ZHANG Pengfei, LIU Pengzhao, WANG Chenglong, DENG Mingzhu, LIN Yanrong, REN Xiaolong, CHEN Xiaoli

2023, 34(4):  1009-1014.  doi:10.13287/j.1001-9332.202304.017

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To evaluate the effects of nitrogen (N) application rates on the growth, photosynthetic traits and yield of winter wheat under elevated atmospheric ammonia (NH₃) concentrations could provide guidance for N management under high NH₃ environment. We conducted a split-plot experiment for two consecutive years (2020-2021 and 2021-2022) with top-open chambers. The treatments included two NH₃ concentrations [elevated ambient NH₃ concentration at 0.30-0.60 mg·m^-3 (EAM) and air NH₃ concentration at 0.01-0.03 mg·m^-3 (AM)] and two N application rates [recommended N dose (+N) and no N application (-N)]. We analyzed the effects of aforementioned treatments on net photosynthetic rate (P_n), stomatal conductance (g_s), chlorophyll content (SPAD value), plant height, and grain yield. The results showed that averaged across the two years, EAM significantly increased P_n, g_s, and SPAD values at the jointing and booting stages at the -N level by 24.6%, 16.3%, 21.9% and 20.9%, 37.1%, 5.7%, respectively, compared with AM. However, EAM significantly decreased P_n, g_s, and SPAD values at jointing and booting stages at +N level by 10.8%, 5.9%, 3.6% and 6.8%, 18.9%, 9.3%, respectively, over AM treatment. There was a significant effect of NH₃ treatment, N application rates and their interaction on plant height and grain yield. Compared with AM, EAM increased the average plant height and grain yield by 4.5% and 32.1% at -N level and decreased by 1.1% and 8.5% at +N level, respectively. In a nutshell, the eleva-ted ambient NH₃ concentration had positive effect on photosynthetic characteristics, plant height, and grain yield under ambient N condition, but a inhibitory effect under N application.

Impacts of Eucalyptus plantation on soil and water losses in a typical small watershed in mountainous area of southern China

SHU Chengbo, SHEN Yingli, LIU Gang, ZHANG Qiong, XU Jinghua, GUO Zhen

2023, 34(4):  1015-1023.  doi:10.13287/j.1001-9332.202304.021

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Unreasonable exploitation of artificial forest causes severe soil erosion in the mountainous areas of sou-thern China. The spatial-temporal variations of soil erosion in typical small watershed with artificial forest has signifi-cant implications for artificial forest exploitation and sustainable development of mountainous ecological environment. In this study, we used revised universal soil loss equation (RUSLE) and geographic information system (GIS) to evaluate the spatial and temporal variations of soil erosion and its key drivers of Dadingshan watershed in mountainous area of western Guangdong. The results showed that the erosion modulus was 1948.1 t·km^-2·a^-1 (belonging to light erosion) in the Dadingshan watershed. However, the spatial variation of soil erosion was substantial, with variation coefficient of 5.12. The maximal soil erosion modulus was 191127 t·km^-2·a^-1. Slight erosion (<500 t·km^-2·a^-1) accounted for 80.6% of the total watershed area. The moderate erosion and above (>2500 t·km^-2·a^-1) were mainly distributed in young Eucalyptus forest area with less than 30% of the vegetation coverage, which contributed nearly 75.7% of total soil erosion. During 2014-2019, the interannual variations of mean erosion of Dadingshan catchment was modest, but the spatial variation of soil erosion was large. Vegetation cover, slope, and rainfall were key drivers of such variation. The destruction of natural vegetation resulted by plantation exploitation was the primary cause of soil erosion in afforestation areas. Soil erosion significantly increased with the increases of slope gradient in the young forest area, which was aggravated by extreme rainfall. However, soil erosion gradually decreased with the increases of the age of Eucalypt plantation. Therefore, the hot spot of soil erosion was young forest areas of Eucalypt plantation with slope >25°, and the key period for soil erosion control was the first 2-3 years after Eucalyptus planting. We suggested that reasonable afforestation measures should be used in area with >25° slopes, and that the destruction of natural vegetation should be avoided on hillslope with >35° slope gradient. The road construction standards and forest management should be further improved to address the challenge of extreme rainfalls.

Extraction of tree crown parameters of high-density pure Cunninghamia lanceolata plantations by combining the U-Net model and watershed algorithm

LI Rui, SUN Zhao, XIE Yunhong, LI Haowei, ZHANG Yungen, SUN Yujun

2023, 34(4):  1024-1034.  doi:10.13287/j.1001-9332.202304.003

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As one of the important timber species in China, Cunninghamia lanceolata is widely distributed in southern China. The information of tree individuals and crown plays an important role in accurately monitoring forest resources. Therefore, it is particularly significant to accurately grasp such information of individual C. lanceolata tree. For high-canopy closed forest stands, the key to correctly extract such information is whether the crowns of mutual occlusion and adhesion can be accurately segmented. Taking the Fujian Jiangle State-owned Forest Farm as the research area and using the UAV image as the data source, we developed a method to extract crown information of individual tree based on deep learning method and watershed algorithm. Firstly, the deep learning neural network model U-Net was used to segment the coverage area of the canopy of C. lanceolata, and then the traditional image segmentation algorithm was used to segment the individual tree to obtain the number and crown information of individual tree. Under the condition of maintaining the same training set, validation set and test set, the extraction results of the canopy coverage area by the U-Net model and traditional machine learning methods [random forest (RF) and support vector machine (SVM)] were compared. Then, two individual tree segmentation results were compared, one using the marker-controlled watershed algorithm, and the other using the combination of the U-Net model and marker-controlled watershed algorithm. The results showed that the segmentation accuracy (SA), precision, IoU (intersection over union) and F1-score (harmonic mean of precision and recall) of the U-Net model were higher than those of RF and SVM. Compared with RF, the value of those four indicators increased by 4.6%, 14.9%, 7.6% and 0.05, respectively. Compared with SVM, the four indicators increased by 3.3%, 8.5%, 8.1% and 0.05, respectively. In terms of extracting the number of trees, the overall accuracy (OA) of the U-Net model combined with the marker-controlled watershed algorithm was 3.7% higher than that of the marker-controlled watershed algorithm, with the mean absolute error (MAE) being decreased by 3.1%. In terms of extracting crown area and crown width of individual tree, R² increased by 0.11 and 0.09, mean squared error decreased by 8.49 m² and 4.27 m, and MAE decreased by 2.93 m² and 1.72 m, respectively. The combination of deep learning U-Net model and watershed algorithm could overcome the challenges in accurately extracting the number of trees and the crown information of individual tree of high-density pure C. lanceolata plantations. It was an efficient and low-cost method of extracting tree crown parameters, which could provide a basis for developing intelligent forest resource monitoring.

Model construction for height to crown base of Larix olgensis based on mixed-effects model and quantile regression

YI Da, LI Fengri, MA Aiyun, LIN Fucheng, HAO Yuanshuo, DONG Lihu

2023, 34(4):  1035-1042.  doi:10.13287/j.1001-9332.202304.007

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Height to crown base is an important index reflecting the characteristics of tree crown. It is of great significance to accurately quantify height to crown base for forest management and increasing stand production. We used nonlinear regression to construct the height to crown base generalized basic model, and further extended that to the mixed-effects model and quantile regression model. The prediction ability of the models was evaluated and compared by the ‘leave-one-out’ cross-validate. Four sampling designs and different sampling sizes were used to calibrate the height to crown base model, and the best model calibration scheme was selected. The results showed that based on the height to crown base generalized model including tree height, diameter at breast height, basal area of the stand and average dominant height, the prediction accuracy of the expanded mixed-effects model and the combined three-quartile regression model were obviously improved. The mixed-effects model was slightly better than the combined three-quartile regression model, and the optimal sampling calibration scheme was to select five average trees. The mixed-effects model with five average trees was recommended to predict the height to crown base in practice.

Assessment on the declining degree of farmland shelter forest in a desert oasis based on LiDAR and hyperspectrum imagery

YANG Yuli, XIAO Huijie, XIN Zhiming, FAN Guangpeng, LI Junran, JIA Xiaoxiao, WANG Litao

2023, 34(4):  1043-1050.  doi:10.13287/j.1001-9332.202304.026

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We examined the growth decline and health status of farmland protective forest belt (Populus alba var. pyramidalis and Populus simonii shelterbelts) in Ulanbuh Desert Oasis by using airborne hyperspectral and ground-based LiDAR to collect the hyperspectral images and point cloud data of the whole forest belt respectively. Through correlation analysis and stepwise regression analysis, we constructed the evaluation model of the decline degree of farmland protection forest with the spectral differential value, vegetation index, and forest structure parameters as independent variables and the tree canopy dead branch index of the field survey as dependent variables. We further tested the accuracy of the model. The results showed that the evaluation accuracy of the decline degree of P. alba var. pyramidalis and P. simonii by LiDAR method was better than that by hyperspectral method, and that the evaluation accuracy of the combined LiDAR and hyperspectral method was the highest. Using the LiDAR method, hyperspectral method, the combined method, the optimal model of P. alba var. pyramidalis was all light gradient boosting machine model, with the overall classification accuracy being 0.75, 0.68, 0.80, and Kappa coefficient being 0.58, 0.43, 0.66, respectively. The optimal model of P. simonii was random forest model, random forest model, and multilayer perceptron model, with the overall classification accuracy being 0.76, 0.62, 0.81, and Kappa coefficient being 0.60, 0.34, 0.71, respectively. This research method could accurately check and monitor the decline of plantations.

Spatial and temporal effect and driving factors of ecosystem service trade-off in the Qingjiang River Basin, China

ZHANG Zizheng, ZHANG Lei, SUN Guiying, LIU Junxiang

2023, 34(4):  1051-1062.  doi:10.13287/j.1001-9332.202304.022

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Identifying the spatiotemporal differentiation characteristics of trade-offs/synergies relationships of ecosystem service in watersheds and their influencing factors is essential for ecosystem management and regulation. It is of great significance for the efficient allocation of environmental resources and the rational formulation of ecological and environmental policies. We used correlation analysis and root mean square deviation to analyze the trade-offs/synergies relationships among grain provision, net primary productivity (NPP), soil conservation, and water yield service in the Qingjiang River Basin from 2000 to 2020. Then, we analyzed the critical factors affecting the trade-offs of ecosystem services by using the geographical detector. The results showed that grain provision service in the Qingjiang River Basin presented a decreasing trend from 2000 to 2020, and that NPP, soil conservation, as well as water yield service showed an increasing trend. There was a decreasing trend in the degree of trade-offs between grain provision and soil conservation services, NPP and water yield service, and an increasing trend in the intensity of trade-offs between other services. Grain provision and NPP, soil conservation and water yield showed trade-off in the northeast and synergy in the southwest. There was a synergistic relationship between NPP with soil conservation and water yield in the central part and a trade-off relationship in the surrounding area. Soil conservation and water yield showed a high degree of synergy. Land use and normalized difference of vegetation index were the dominant factors in the intensity of trade-offs between grain provision and other ecosystem services. Precipitation, temperature, and elevation were the dominant factors in the intensity of trade-offs between water yield service and other ecosystem services. The intensity of ecosystem service trade-offs was not only affected by a single factor. In contrast, the interaction between the two services or the common factors behind the two services was the determining factor. Our results could provide a reference for developing ecological restoration planning strategies in the national land space.

Construction and optimization of ecological security network in the Shule River Basin, China

JIN Yinli, ZHOU Dongmei, ZHOU Fan, YANG Jing, ZHU Xiaoyan, MA Jing, ZHANG Jun

2023, 34(4):  1063-1072.  doi:10.13287/j.1001-9332.202304.020

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Construction and optimization of ecological security network is an efficient way to ensure regional ecological security and achieve sustainable development. Based on the morphological spatial pattern analysis method, circuit theory and other methods, we constructed the ecological security network of the Shule River Basin. The PLUS model was used to predict the land use change in 2030, with the aim to explore the current ecological protection direction and propose reasonable optimization strategies. The results showed that there were 20 ecological sources in the Shule River Basin, with a total area of 15774.08 km², accounting for 12.3% of the total area of study area. The ecological sources were mainly distributed in the south part of the study area. A total of 37 potential ecological corridors were extracted, including 22 important ecological corridors, which showed the overall spatial characteristics of vertical distribution. Meanwhile, 19 ecological pinch points and 17 ecological obstacle points were identified. We predicted that the expansion of construction land would continue to squeeze the ecological space by 2030, and identified 6 warning areas of ecological protection space to effectively avoid conflicts between ecological protection and economic development. After optimization, 14 new ecological sources and 17 stepping stones were added, and the circuitry, ratio of line to node and connectivity index of the ecological security network increased by 18.3%, 15.5%, and 8.2% respectively compared with those before optimization, forming a structurally stable ecological security network. The results could provide scientific basis for ecological security network optimization and ecological restoration.

Construction of ecological network based on MSPA-Conefor-MCR at the county scale: A case study in Yanqing District, Beijing, China

DU Xiaoyu, LYU Feinan, WANG Chunyu, YU Zhenrong

2023, 34(4):  1073-1082.  doi:10.13287/j.1001-9332.202303.023

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The acceleration of urbanization and the frequent occurrence of natural disasters have led to increasingly fragmented habitats and decreased ecological connectivity, which in turn hinder rural sustainable development. Constructing ecological networks is a key direction in the spatial planning. By strengthening source protection, corridor construction, and ecological control, it can effectively alleviate the contradiction between regional ecological and economic development imbalance and promote biodiversity enhancement. With Yanqing District as an example, we constructed the ecological network by means of the morphological spatial pattern analysis, the connectivity analysis software, and the minimum cumulative resistance model. We analyzed various network elements from a county perspective, and provide suggestions for the development of towns. The results showed that the ecological network of Yanqing District as a whole presented the distribution characteristics of “the Mountain and the Plain”. A total of 12 ecological sources were identified, covering an area of 1085.54 km², accounting for 54.4% of the total area. 66 ecological corridors were screened with a total length of 1057.18 km, including 21 important corridors and 45 general corridors, with the length of which accounting for 32.6% and 67.4%, respectively. 27 first-class ecological nodes and 86 second-class ecological nodes were identified, which were concentrated in “the Mountain” such as Qianjiadian and Zhenzhuquan. The distribution of ecological networks in different towns was closely related to their geographical environment and development orientation. The towns such as Qianjiadian and Zhenzhuquan were located in “the Mountain”, covering a wide range of ecological sources and corridors. Strengthening protection of ecological source was the focus of network construction, which can promote the coordinated development of ecology and tourism in towns. The towns such as Liubinbao and Zhangshanying were located at the junction of “the Mountain-Plain”, hence strengthening corridor connectivity was the main direction of network construction, which could promote the construction of ecological landscape in towns. The towns such as Yanqing and Kangzhuang were located in the “the Plain”, with serious landscape fragmentation due to the lack of ecological sources and corridors. Those towns need to build green livable towns through increasing ecological nodes and strengthening ecological restoration. This study enriched the construction of ecological networks at the county scale, explored the interface with spatial planning, strengthened ecological restoration and ecological control, which had reference value for promoting the sustainable development of towns and the construction of a multi-scale ecological network.

Equity evaluation of urban green space in the main urban area of Wuhan based on green view index

LIU Chang, WANG Yiting, GUO Xiaohua, WANG Liangfei

2023, 34(4):  1083-1090.  doi:10.13287/j.1001-9332.202304.025

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Green space is a kind of resource welfare. The evaluation of green space equity based on green view index (GVI) is important to ensure the equitable distribution of green resources. Taking the central urban area of Wuhan as the research object, based on multi-source data such as Baidu Street View Map, Baidu Thermal Map, and satellite remote sensing images, we evaluated the equity of spatial distribution of GVI in Wuhan by using the locational entropy, Gini coefficient and Lorenz curve. The results showed that 87.6% of the points in the central urban area of Wuhan were below the level of poor green vision, which mainly concentrated in Wuhan Iron and Steel Industrial Base of Qingshan District and south of Yandong Lake. The number of points reaching an excellent level was the least (0.4%), mainly concentrated around the East Lake. The overall Gini coefficient of GVI in the central urban area of Wuhan was 0.49, which indicated that the distribution of GVI was heterogeneous. The Gini coefficient of Hongshan District was the largest at 0.64, indicating a huge gap in the distribution of GVI, while the Gini coefficient of Jianghan District was the smallest at 0.47, with a large gap in the distribution. The central urban area of Wuhan had the most low-entropy areas for 29.7% and the least high-entropy areas for 15.4%. There were two-level differences in entropy distribution within Hongshan District, Qingshan District, and Wuchang District. The nature of land use and the role of linear greenery were the main factors affecting the equity of green space in the study area. Our results could provide theoretical basis and planning reference for optimizing urban green space layout.

Spatial and temporal variations of extreme climate index in the Songhua River Basin during 1961-2020

YU Shui, ZHANG Xiaolong, LIU Zhijuan, WANG Yan, SHEN Yanjun

2023, 34(4):  1091-1101.  doi:10.13287/j.1001-9332.202304.024

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Understanding climate change and extreme climate is of great significance for ensuring food security and socio-economic development of the Songhua River Basin. Based on the daily precipitation, maximum temperature and minimum temperature data during 1961-2020 from 69 meteorological stations in and around the Songhua River Basin, we analyzed the temporal and spatial variations of extreme temperature and precipitation in the Songhua River Basin using 27 extreme climate indices recommended by the World Meteorological Organization, and linear trend method, Mann-Kendall trend test and ordinary Kriging interpolation methodology. The results showed that, from 1961 to 2020, except for cold speel duration, the extreme cold index in the study area showed a downward trend, while the extreme warm index, extreme value index and other temperature indices showed an upward trend. The increasing trend of the minimum temperature was greater than that of the maximum temperature. Icing days, cold speel duration and warm speel duration showed an increasing trend from south to north, while the minimum value of maximum temperature and that of minimum temperature showed opposite spatial characteristics. The high value areas of summer days and tropical nights were mainly distributed in the southwestern region, while there was no obvious spatial variations of cool days, warm nights, and warm days. Overall, except for cold speel duration, other extreme cold indices had a rapid decreasing trend in the north and west of the Songhua River Basin. In the warm index, summer days, warm nights, warm days, and warm speel duration had a rapid upward trend in the north and west, and tropical nights had the fastest rise in the southwest. In the extreme value index, the maximum of temperature rose fastest in the northwest, while the minimum rose fastest in the northeast. Except for consecutive dry days, the rest of precipitation indices showed an increasing trend, and the fastest rising areas were mainly in the north-central part of the Nenjiang River Basin, while some areas in the south of the Nenjiang River Basin became dry. Heavy precipitation days, very heavy precipitation days, heaviest precipitation days, consecutive wet days, very wet day precipitation, extremely wet day precipitation, and annual precipitation showed a gradual decreasing pattern from southeast to northwest. Overall, the Songhua River Basin was warming and wetting, but there were some differences among different regions, especially the northern and southern parts of the Nenjiang River Basin.

Spatial and temporal dynamics of large natural lake areas and shoreline morphology in the Yellow River Basin

QU Zhi, LUO Manya, ZHAO Yonghua, YANG Shuyuan, HAN Lei, MU Qi

2023, 34(4):  1102-1108.  doi:10.13287/j.1001-9332.202304.019

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Given their important roles in the regulation and storage functions for river flow and in the regional ecological environment and ecosystem services, natural lakes are essential for the ecological protection and high-quality development of the Yellow River Basin. We used the Landsat TM/OLI remote sensing data to analyze the area changes of Dongping Lake, Gyaring Lake, and Ngoring Lake, three representative large natural lakes in the Yellow River Basin from 1990 to 2020. We used the landscape ecology approach to study the morphological characteristics of lake shoreline and shoreland changes and the relationship between the landscape indices. The results showed that the main areas of Gyaring Lake and Ngoring Lake were mainly in the trend of expansion, while the main area of Dongping Lake significantly reduced during 1990-2000 and 2010-2020. The changes in the area of lake all occurred mainly near the lake inlet of the river. The shoreline morphology of Dongping Lake was more complex, with the fragmentation and aggregation of shoreland landscape significantly changed. The circularity ratio of Gyaring Lake gradually decreased with the expansion of the lake area, and the number of patches in its shoreland changed significantly. The fractal dimension index-mean of the shoreland of Ngoring Lake was relatively high, the complexity of its shoreline landscape was stronger, and the number of patches had increased significantly from 2000 to 2010. Meanwhile, there was a significant correlation between certain lake shoreline (shoreland) landscape indices. The changes in circularity ratio and shoreline development coefficient caused changes in the patch density of shoreland.

Denitrification process of Casuarina root nodule endophyte Frankia

CHEN Hui, ZHU Cheng, LIN Hong-lian, MA Hongliang, YIN Yunfeng, GAO Ren

2023, 34(4):  1109-1116.  doi:10.13287/j.1001-9332.202304.005

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To examine the characteristic of denitrification in Frankia, a symbiotic nitrogen-fixing microbe associated with non-leguminous plants, and its role as a N₂O source or sink, Casuarina root nodule endophyte Frankia was isolated using sectioning method, which was then purely cultured to investigate the denitrification process under NO₃^- addition. The results showed that after addition of NO₃^- to the medium under anaerobic condition, the concentration of NO₃^- decreased with time, while the concentrations of NO₂^- and N₂O initially increased and then decreased over time. Key denitrification genes and nitrogenase gene were detected at 26 h, 54 h and 98 h during incubation. Abundances of these genes significantly differed among each other, and their dynamics were asynchronous. Redundancy analysis of the effect of NO₃^-, NO₂^-, N₂O concentrations on abundances of denitrification genes and nitrogenase gene indicated that 81.9% of the total variation in gene abundances could be explained by the first two axes. Frankia had a denitrifying activity under anaerobic condition, with denitrification genes, including nitrous oxide reductase gene (nosZ), being identified. Our results suggested that Frankia possessed a complete denitrification pathway and the ability of N₂O reduction under anaerobic condition.

Effects of plant community and altitude on food composition of Cervus elaphus wallichii during the withered grass period on the Tibetan Plateau, China

WEI Kaili, LIANG Xiaoping, YU Jingjing, WANG Lin, ZHOU Liangjun, LYU Zhonghai, ZHANG Minghai, ZHANG Weiqi

2023, 34(4):  1117-1122.  doi:10.13287/j.1001-9332.202304.028

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How Tibetan red deer (Cervus elaphus wallichii) acclimates to high altitude environment during the withered grass period is one of the challenges in maintaining their nutrient intake. It is an important basis to study the nutritional ecology of wild large ungulates in alpine ecosystems by investigating the changes in plant communities with altitude during the withered grass period and how these changes affect the food composition of Tibetan red deer. In this study, we selected the Tibetan red deer in Sangri County, Shannan region of Tibet as the research subject. We carried out field surveys on the altitude, plant communities, and feeding traces of the Tibetan red deer in March of 2021 and 2022 during the withered grass period on the Tibetan Plateau. Detrended correspondence analysis and canonical correspondence analysis were used to study altitudinal variations in plant communities and the regularity of food composition. The results showed that during the period of withered grass, Tibetan red deer ate primarily Salix daltoniana, Rosa macrophylla var. glandulifera and Dasiphora parvifolia. S. daltoniana accounted for more than 50% of the food composition, as the main food resources for red deer in withered grass period. In the low altitude area (4100-4300 m), plant community included Caragana versicolor, R. macrophylla and Berberis temolaica, and Tibetan red deer mainly ate R. macrophylla, C. versicolor and Artemisia wellbyi. In higher altitude area (4300-4600 m), plant community consisted of Rhododendron nivale, Rhododendron fragariiflorum, and Sibiraea angustata, and Tibetan red deer mainly fed on S. daltoniana, Salix obscura, and Carex littledalei. At different altitudes, the dominant plant species were the main food of Tibetan red deer. It is suggested that the changes of plant community composition with altitude directly affected food composition of Tibetan red deer, indicating different food composition patterns with altitude gradients.

Optimization of hydrolysis conditions of crop straw and its effect in Chlorella sorokiniana culture

LI Ruichun, JI Chunli, SU Sheng, CUI Hongli, ZHANG Chunhui, XUE Jinai, SUN Xiping, LI Runzhi

2023, 34(4):  1123-1129.  doi:10.13287/j.1001-9332.202304.029

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Taking straws of corn, wheat, and millet as raw materials, we pretreated them with alkaline hydrogen peroxide, and then hydrolyzed by cellulase and xylanase. We selected the total sugar content in the hydrolysate as the indicator to evaluate the hydrolysis of the straws from three crop species, and further optimized the conditions. Then, the hydrolysates of three types of crop straws were used as carbon source for Chlorella sorokiniana culture to assess their effects on microalgal cultivation. The results showed that the optimal hydrolysis conditions for the three crop straws were identified as solid-liquid ratio of 1:15, temperature of 30 ℃, and treatment time of 12 h. Under such optimal condition, the total sugar contents increased up to 1.677, 1.412, and 1.211 g·L^-1 in the corn, millet and wheat straw hydrolysate, respectively. The hydrolysates from the three crop straw could significantly increase both algal biomass and lipid content of C. sorokiniana. Corn straw hydrolysate had the best effect, with high levels of algal biomass (1.801 g·L^-1) and lipid content (30.1%). Therefore, we concluded that crop straw hydrolysates as carbon source could significantly promote microalgal biomass and lipid enrichment. The results could lay the foundation for the efficient conversion and utilization of straw lignocellulose raw materials, provide new knowledge for the resource utilization of agricultural wastes, as well as the theoretical basis for the efficient cultivation of microalgae using crop straw hydrolysates.

Trophic niche and potential carbon source of three reef-associated fishes of Zhongjieshan Islands

LIU Mingzhi, YANG Fan, JIANG Rijin, YIN Rui, WANG Jing, XIAO Yi, LING Ting, ZHU Shuailin

2023, 34(4):  1130-1136.  doi:10.13287/j.1001-9332.202304.014

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To clarify the trophic relationship of important rock fishes, we analyzed trophic niche of three typical rockfish species (Oplegnathus fasciatus, Sebastiscus marmoratus and Conger myriaster) in the Zhongjieshan Islands in summer 2020, based on the carbon and nitrogen stable isotope techniques. We calculated the contributions of major carbon sources [macroalgae, phytoplankton, suspended particulate organic matter (POM) and substrate organic matter (SOM)]. The results showed that: 1) the δ¹³C values of the three species ranged from -21.44‰ to -15.21‰, with an average value of (-16.85±1.12)‰, while the δ¹⁵N values ranged from 8.32‰ to 10.96‰, with an average value of (9.69±0.66)‰. There were significant differences in carbon and nitrogen stable isotopes among the three species. 2) There was small niche overlap between O. fasciatus and S. marmoratus, indicating that the interspecific competition was not intense. There was no overlap between C. myriaster and the first two, indicating feeding differentiation. 3) The total ecotone area, corrected core ecotone area, and food source diversity of C. myriaster were the highest, indicating that it had a more generalized diet and richer food sources. 4) With Mytilus coruscus as a baseline organism, the trophic level of C. myriaster was the highest (3.38), followed by S. marmoratus (3.09), and the trophic level of O. fasciatus was the smallest (3.00). 5) Results of the stable isotope mixture model (SIAR) showed that POM was the main carbon source of the three species, contributing 57.4%, 57.9%, and 92.0% of the total, respectively. In addition, the contribution rate of SOM was also high for O. fasciatus and S. marmoratus, which was 21.5% and 33.9%, respectively. This study could provide basic information and reference for understanding trophic structure and marine food web in Zhongjiashan Islands.

Influencing factors of predation on five keystone prey species in Haizhou Bay based on Delta-GAMMs

GAO Mingwei, DONG Xiuqiang, ZHANG Chongliang, XU Binduo, JI Yupeng, REN Yiping, XUE Ying

2023, 34(4):  1137-1145.  doi:10.13287/j.1001-9332.202304.030

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Trophic dynamics is one of the major regulators of fishery production in marine ecosystems, which is important for the implementation of ecosystem-based fisheries management. Based on data collected form bottom trawl surveys in Haizhou Bay and adjacent waters during autumn of 2011 and 2018, Delta-GAMMs (Delta-generalized additive mixed models) were constructed to evaluate the effects of biotic and abiotic factors on the predation of five key prey species (including Leptochela gracilis, Alpheus japonicus, Loligo spp., Larimichthys polyactis, and Oratosquilla oratoria) in the Haizhou Bay. Percent frequency of occurrence and predation pressure index were used to identify their major predators. Variance inflation factor and full subsets regression were analyzed to quantify the degree of multicollinearity between these factors. The results showed that the occurrence frequency of keystone prey species in the stomach of predators ranged from 8.5% to 42.2%, and the weight percentage ranged from 4.2% to 40.9%. The average deviance explanation rate of the “binomial” model was 16.1%, and the average deviance explanation rate of the “positive” model was 23.8%. Body length of predator, predator population density, and sea bottom temperature were important factors influencing prey-predator trophic interactions. Predator length was the most important factor, with feeding probability and weight percentage of keystone prey species all increasing with body length of predator. Feeding probability and weight percentage of key prey species decreased with predator population density. The effects of environmental factors such as sea bottom temperature, depth of water, latitude, and sea bottom salinity showed different trends, depending on the prey-predator assemblage. This study showed that the Delta-GAMMs was an effective method to explore the trophic interactions between prey and predators in marine ecosystems, and could provide a theoretical basis for the conservation and sustainable use of fisheries resources.

Reviews

Advances and perspectives on the research of starfish outbreaks in northern China

WANG Yu, GU Yanbin, GUO Hao, CAO Linquan, JIN Yuan

2023, 34(4):  1146-1152.  doi:10.13287/j.1001-9332.202304.031

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In recent years, starfish outbreaks occurred frequently in northern China, causing serious economic losses to marine aquaculture. The most common outbreak starfish species are Asterias amurensis and Asterina pectini-fera. We systematically reviewed the related studies by introducing the biological characteristics, current outbreaking status, and main impact of A. amurensis and A. pectinifera, and by discussing the causes, formation process, and migration pattern of starfish outbreaks in northern China. The early life history stage drives starfish outbreak. The increases of larval survival rate is the key leading to population outbreak. Population connectivity is the vital clue to reveal the source and dispersal of starfish populations. On this basis, we proposed several scientific and technical issues that should be addressed urgently, including the determination of the outbreak threshold, the traceability of starfish population, and the methods of monitoring, early warning and control. It would provide insight into the research on the mechanism of starfish outbreaks and the theoretical support for formulating prevention and treatment strategies for starfish outbreaks in northern China.