Table of Content

15 July 2022, Volume 33 Issue 7

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CONTENTS

CONTENTS

2022, 33(7):  1728-1728. 

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Special Features of biological soil crusts

Bryophyte diversity and microhabitat characteristics of bryophyte-dominated biological soil crusts development in water-wind erosion crisscross region of the northern Loess Plateau, China

WANG Yan-feng, XIAO Bo, WANG Wan-fu, YU Xing-xing, ZHANG Xue

2022, 33(7):  1729-1737.  doi:10.13287/j.1001-9332.202207.004

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Microhabitat factors play an important role in regulating bryophyte species distribution and the development of bryophyte-dominated biological soil crusts (hereafter bryophyte crusts). We investigated the distribution and development of bryophytes in eight microhabitats in the water-wind erosion crisscross region of the Loess Pla-teau. We used the line intercept transects to explore and quantify the influencing pathways of microhabitat factors on bryophyte diversity and analyzed the influencing pathways of plant cover, slope aspect, and slope gradient by using structural equation model to quantify influencing coefficients. Our results showed that: 1) The Patrick, Shannon, Pielou, and Simpson indcies of bryophytes under plant canopy were 63.4%, 66.6%, 91.0%, and 68.3% lower than that without plant canopy, respectively, while the thickness, biomass, and chlorophyll content of bryophyte crusts were 0.5, 0.2, and 1.3 times higher than that without plant canopy, respectively. 2) The Patrick, Shannon, Pielou, and Simpson indexes of bryophytes on the north slope were 0.6, 0.9, 5.6, and 0.9 times higher than those on the south slope, while the thickness, biomass, and chlorophyll content of bryophyte crusts were 0.3, 0.3, and 0.6 times higher than those on the south slope, respectively. 3) As the slope increasing from 14° to 34°, the Patrick, Shannon, Pielou, and Simpson indexes of bryophyte were decreased by 59.8%, 84.1%, 57.3% and 68.0%, and the thickness, biomass, and chlorophyll content of bryophyte crusts were decreased by 15.2%, 25.0%, and 16.5%, respectively. 4) The importance of the three microhabitat factors on bryophyte diversity and the development of bryophyte crusts followed an order of plant canopy cover > slope aspect > slope gradient. The primary influencing pathway varied among the microhabitat factors. In conclusion, plant cover, slope aspect, and slope gradient significantly affected the distribution of bryophytes species and developmental level of bryophyte crusts through direct and indirect pathways. Therefore, full consideration should be given to microhabitat conditions when using bryophyte crusts to control desertification.

Seasonal differences in vegetative regeneration of three desiccation-tolerant mosses in the Loess Plateau and its mechanism

GUO Yue-wei, ZHAO Yun-ge, QIAN Xu-kun, WAN Yang-zhuo-qun, WANG Shan-shan

2022, 33(7):  1738-1746.  doi:10.13287/j.1001-9332.202207.011

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Bryophytes have been used in many fields, such as landscaping and soil and water conservation. How-ever, few studies focused on moss regeneration and its influencing factors, which retards the application study. Three common desiccation-tolerant mosses (Barbula unguiculata, Didymodon vinealis, and Didymodon tectorum) in the Loess Plateau region were collected across four seasons. We measured vigor index of new shoots, representing vegetative regeneration capacity, and physiological indices, which included the contents of chlorophyll, soluble sugar, soluble protein and malondialdehyde (MDA), to determine seasonal differences in regeneration capacity and physiological characteristics of the three mosses, as well as their relationships. The results showed that, 1) vegetative regeneration of mosses showed significantly seasonal differences. The vigor index of the three mosses in summer were the lowest, averagely decreased by 56.1%, 48.4%, and 10.1% compared with that in autumn, winter, and spring, respectively. The vigor index of the three mosses in the same season showed interannual variation. 2) There were considerable differences in the regeneration capacity of mosses across species. D. tectorum and B. unguiculata had the highest and lowest vigor indices, respectively. In terms of regeneration capacity, B. unguiculata had the largest seasonal and interannual variations. 3) The physiological characteristics of mosses had seaonal variations. The mosses collected in the summer had the highest MDA content but the lowest contents of soluble sugar and soluble protein. 4) Seasonal variations in desiccation-tolerant moss regeneration were mostly due to soluble sugar. Our results showed seasonal variations of vegetative propagation capacity, and highlighted the role of soluble sugar as a critical factor influencing vegetative propagation of mosses. These findings could provide scientific support for moss protection and artificial cultivation.

Leaf spreading duration and its influencing factors for two Pottiaceae species in hilly Loess Plateau, Northwest China

YANG Xiao-li, ZHAO Yun-ge, GUO Ya-li, LIANG Yin-li

2022, 33(7):  1747-1754.  doi:10.13287/j.1001-9332.202207.002

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Mosses are poikilohydric plants. The duration of leaf spreading time is a key factor affecting their growth and development in the field. The dynamics of field growth and development and influencing factors of mosses in arid and semi-arid areas are largely unknown. In the study, we examined leaf spreading situation under natural conditions from September 5th to November 25th for Didymodon vinealis and Barbula unguiculata, two common species in hilly Loess Plateau. The results showed that the leaves of both species showed a regular diurnal dynamic change of ‘spreading-closing-spreading’ from September to October, and that the average leaf closing time of D. vinealis in the morning was 0.68 hours earlier than that of B. unguiculata, while leaf spreading time was delayed by 1.79 hours in the afternoon. Both species spread their leaves for longer time in the rainy season. The average leaf spreading duration of D. vinealis was 251 min, which was 30.4% lower than B. unguiculata of 361 min. The relative humidity near the surface was the key factor affecting leaf spreading duration. The morphological structure of moss species would affect leaf spreading duration. Compared with D. vinealis, B. unguiculata was relatively short, with a large proportion of costa in leaves, and the mosaic structure of stem cortex cells was more prominent. The humidity threshold during leaf spreading of B. unguiculata (54.3%) was lower than that of D. vinealis (60.1%). The leaf spreading duration was mainly affected by humidity. B. unguiculata was more adaptable to the environment than D. vinealis.

Spatial distribution and the influencing factors of organic carbon of biological crusts on regional scale in Mu Us sandy land, China

PANG Jing-wen, BU Chong-feng, GUO Qi, JU Meng-chen, JIANG Man, MO Qiu-xia, WANG He-ming

2022, 33(7):  1755-1763.  doi:10.13287/j.1001-9332.202207.017

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As an important soil cover in deserts, biological crusts play a central role in ecosystem function such as nutrient cycling, nitrogen fixation, and carbon sequestration. Many biological crust organisms could fix CO₂ through photosynthesis to improve soil organic carbon content. There is a knowledge gap in the origin of soil organic carbon (SOC) from biological crusts on a regional level, which restricts the prediction of soil carbon pool. Based on 45 plots in the Mu Us sandy land (42200 km²), we measured the SOC content and soil organic carbon density (SOCD) of two types of typical biological crusts (moss crusts, algal crusts) and their underlying soils, and analyzed together with the climate data, soil and vegetation factors to investigate the spatial distribution characteristics and controlling factors of organic carbon of biological crusts at the regional scale. The results showed that: 1) biological crusts significantly increased SOC and SOCD compared with bare ground. Moss crusts and the underlying SOC (4.93 g·kg^-1) and SOCD (0.41 kg·m^-2) were higher than those of algal crusts (1.89 g·kg^-1, 0.18 kg·m^-2). 2) On the regional scale, the SOC and SOCD of biological crusts had clear spatial distribution characteristics, demonstrating a banded distribution and block mosaic from northeast to central and west to southeast. 3) The SOC and SOCD of biological crusts and their underlying soils were mainly affected by climate, soil and vegetation conditions, while the main controlling factors depended on the types of biological crusts. The SOC and SOCD of moss crust were controlled by annual maximum temperature and potential evapotranspiration, whereas those of algal crusts were controlled by water vapor pressure.

Effects of biological crusts on soil organic carbon in sandlands under a precipitation gradient

JIANG Man, BU Chong-feng, GUO Qi, JU Meng-chen, PANG Jing-wen, MO Qiu-xia, WANG He-ming

2022, 33(7):  1764-1772.  doi:10.13287/j.1001-9332.202207.033

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Biological crusts (Biocrusts) are important surface active coverings in arid and semi-arid regions, which affect the content of soil organic carbon (SOC), SOC labile fractions and stability of SOC through photosynthetic carbon fixation. At present, studies on the variation characteristics of SOC, SOC labile fractions and the stability of SOC in biocrusts are rather limited. In this study, two types of typical biocrusts (moss crusts and algae crusts) were selected along a precipitation gradient from northwest to southeast in the Mu Us Sandland (straight line distance 188 km) by measuring soil organic carbon (SOC), soil microbial biomass carbon (MBC), water soluble carbon (DOC), particulate carbon (POC), easily oxidizable carbon (ROC). We aimed to explore the effects of biocrusts on the stability of SOC and carbon decomposition across the precipitation gradient. Results showed that:1) Two types of biocrusts significantly increased the contents of SOC, MBC, DOC, POC, ROC and stability of SOC. Moss crusts increased SOC contents by 1.6 to 2.6 times as that of algae crusts. 2) The lowest SOC contents of the two types of biocrusts were 6.43 g·kg^-1 and 14.50 g·kg^-1 respectively, which showed an increasing trend with increasing precipitation along the gradient. 3) With the increases of precipitation, the decomposition time of moss litters gradually decreased. The decomposition coefficient of moss litters during the study period (From July to Feb-ruary of the next year) ranged from 0.010 to 0.014, which was significantly lower than that of vascular plants. The carbon release of moss litters from northwest to southeast was 8.09, 10.89, 12.88 g·kg^-1, respectively. 4) Results of canonical correspondence analysis showed that water vapor partial pressure, actual evapotranspiration, annual average temperature, subsurface short-wave radiation, potential evapotranspiration and vapor pressure difference were the key climate factors affecting the content of SOC and its active components. Silt content was the main soil factor affecting the content of SOC and its active components.

Characteristics of biocrusts in croplands and their effects on surface soil disintegration in the black soil region of Northeast China

ZHANG Chen-hui, XIAO Bo, LI Sheng-long, WANG Yan-feng, CAO You-song

2022, 33(7):  1773-1782.  doi:10.13287/j.1001-9332.202207.012

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We selected typical croplands in the black soil region of Northeast China to analyze the characteristics of biocrusts during the growing season, including species composition, thickness, coverage, and biomass (chlorophyll content). We collected bareground soil and biocrusts samples with chlorophyll content of 5-15, 15-25, 25-35, and 35-50 mg·g^-1, and measured the soil disintegration rate and soil maximum disintegration ratio of each sample using a force gauge in the laboratory. The results showed that: 1) biocrusts dominated by algae and moss were frequently developed in the croplands, with Stigeoclonium and Bryum capillare as the most common species, respectively. The thickness and biomass of algal crusts were significantly lower than moss crusts, with a successional trend from algal crusts to moss crusts. 2) The coverage, thickness, and biomass of biocrusts in croplands were negatively correlated with the frequency and intensity of tillage disturbance. For instance, the values of those characterisitics were only 27.8%, 1.52 mm, and 6.49 mg·g^-1 on average, respectively, in traditional tillage croplands, and increased to 83.5%, 2.74 mm, and 34.16 mg·g^-1, respectively, in the croplands with conservational tillage. 3) Biocrusts considerably reduced the disintegration of surface soil, particularly in the layer of biocrusts. Compared to the bareground soil, the soil disintegration rate of biocrusts, with four levels of biomass (with chlorophyll content of 5-15, 15-25, 25-35, and 35-50 mg·g^-1), was reduced by 43.1%, 50.1%, 55.5%, and 59.8%, respectively, while the soil maximum disintegration ratios were reduced by 11.4%, 17.7%, 33.2%, and 36.6%, respectively. 4) Soil disintegration rate and maximum disintegration ratio were significantly and negatively correlated with the biomass and thickness of biocrusts, indicating that the impacts of biocrusts on soil disintegration were primarily caused by the improvements in physical properties of surface soil. In conclusion, biocrusts were frequently deve-loped in croplands in the black soil region of Northeast China, owing to less disturbance following the conversion from traditional tillage to conservational tillage. They had the potential to protect surface soil against disintegration and improve soil anti-scourability, which was critical for soil conservation in croplands in this region.

Responses of moss biocrusts respiration to simulated grazing and trampling disturbance with different intensities on the fenced forestland of Loess Plateau, China

DOU Wei-qiang, XIAO Bo, WANG Yan-feng, JIANG Zi-hao, YU Xing-xing, LI Sheng-long

2022, 33(7):  1783-1790.  doi:10.13287/j.1001-9332.202207.009

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The changes in soil properties caused by grazing and trampling are important reasons for the changes in soil respiration rates, carbon fixation, and emission. However, the effects of different intensities of grazing and trampling on biocrusts respiration rate are unclear. In this study, we simulated grazing and trampling disturbances of 10%, 30%, 50%, and 70% intensity on moss biocrusts developed in aeolian sandy soil on Loess Plateau, with undisturbed moss biocrusts serving as a control. The changes in respiration rate of moss biocrusts were monitored continuously, and its responses to different disturbance intensities were analyzed. The results showed that: 1) moderate disturbance stimulated moss biocrusts respiration, while heavy disturbance inhibited that. The respiration rate of moss biocrusts was increased by 41.1% and 22.2% at disturbance intensities of 10% and 30%, but was decreased by 8.9% and 15.3% at disturbance intensities of 50% and 70%, respectively. 2) The trampling disturbance significantly changed soil temperature but did not affect soil water content. In comparison to the control, soil temperature of biocrusts was decreased by 0.4 and 1.2 ℃ at disturbance intensities of 10% and 30%, but it was increased by 1.1 and 1.0 ℃ at disturbance intensities of 50% and 70%, respectively. 3) The respiration rate of moss biocrusts showed a significant exponential relationship with soil temperature and a linear positive relationship with soil water content under different disturbance intensities. However, the correlation between respiration rate of moss biocrust and the characteristics of moss biocrust was not significant. Soil temperature and water content could explain 70.6%-96.3% and 49.1%-70.0% of the total variation of respiration rate of moss biocrusts, respectively. In conclusion, grazing and trampling affected the respiration rate of moss biocrusts, with short-term moderate grazing and trampling would have positive effects. On the other hand, excessive grazing and trampling would reduce the rate of moss biocrust respiration. As a result, future studies on soil carbon balance of the Loess Plateau should consider the effects of grazing and trampling on biocrust respiration.

Effects of moss biocrusts on soil-microbe-ectoenzyme stoichiometric characteristics in a subtropical area

ZHANG Guan-hua, YI Liang, SUN Bao-yang, LI Jian-ming, SHEN Sheng-yu

2022, 33(7):  1791-1800.  doi:10.13287/j.1001-9332.202207.029

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The formation and development of biological soil crusts (biocrusts) potentially affect the cycles and stoichiometric characteristics of soil carbon (C), nitrogen (N), and phosphorus (P). However, it is still unclear how soil microbes adapt to such changes. In this study, we examined the effects of moss-dominated biocrusts coverage (0, 1%-20%, 20%-40%, 40%-60%, 60%-80%, and 80%-100%) on soil physicochemical properties, soil microbial biomass, and ectoenzyme activities [β-1, 4-glucosidase (BG), β-1, 4-N-acetyl glucosidase (NAG), acid phosphatase (AP)] in two soil layers (0-5 and 5-10 cm) in the Three Gorges Reservoir area, as well as the covariations of soil-microbe-ectoenzyme C:N:P stoichiometry. The results showed that biocrust development significantly increased soil clay content, water stable aggregates, soil C, N, P contents, and significantly decreased soil bulk density and sand content. Microbial biomass C, N, P and ectoenzyme activities were significantly increased with increasing biocrust coverage. Soil depth did not affect soil physicochemical properties and C:N:P, but significantly affected microbial biomass, ectoenzyme activities, BG:AP and NAG:AP. Soil C, N and P contents were significantly positively correlated with microbial biomass and ectoenzyme activities, negatively correlated with BG:NAG, while positively correlated with NAG:AP, but had no significant correlation with microbial biomass C:N:P. There was no significant correlation between soil-microbe and microbial-ectoenzyme C:N:P. BG:NAG:AP decreased gradually with the increase of C:N:P stoichiometric imbalance between microbe and soil. This study indicated that the microbial metabolism was co-limited by N and P and with stronger P limitation. Microbes could maintain homeostasis by adjusting their own biomass and ectoenzyme C:N:P to adapt to changes in soil ecological stoichiometry driven by biocrust development.

Seasonal dynamics of the physicochemical properties of biological crusts exopolysaccharides and the microbial community structure

LIU Zhe, YE Xing-wang, WANG Ji-ping, CHENG Yong-tao, QIAN Long, XIAO Jing-shang, WU Li

2022, 33(7):  1801-1809.  doi:10.13287/j.1001-9332.202207.016

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Exopolysaccharides (EPS), an important substance of cyanobacteria in resisting stresses, are the main form of carbon storage in biocrusts and play an important role in material cycling and stability of biocrusts. In this study, the biocrusts in different seasons (January, April, July, October) were collected from Gurbantunggut Desert, and the dynamics of EPS content, composition, morphological characteristics and microbial community structures were analyzed. The results showed that: 1) The excretion of EPS showed obvious seasonal dynamics. The EPS contents in January, April, July and October were 81.72, 52.46, 76.77, 70.54 μg·cm^-2, and the chlorophyll a contents were 2.7, 4.94, 4.2 and 5.98 μg·cm^-2, respectively. Cyanobacteria allocated more fixed organic carbon to EPS in winter and summer, and more to their own biomass accumulation in spring and autumn. 2) EPS in biocrusts of each season was composed of seven kinds of monosaccharides. The sum of relative mole percentages of glucose and galactose was 46%-56%, much higher than the other five monosaccharides. The monosaccharide compositions of EPS were significantly affected by temperature and precipitation. There was no significant difference in the Fourier infrared spectra of EPS in biocrusts across different seasons. 3) The observation results of atomic force microscope showed that more filamentous and thick rope-like structures occurred in EPS in July and October, while the EPS showed block-like morphology in January and April. 4) The results of 16S rDNA high-throughput sequencing showed that Cyanobacteria and Microcoleus were the dominant bacterial phyla and genus in biocrusts in all the four seasons, with significantly higher relative abundance than other bacterial phyla and genera. The relative abundance of Proteobacteria was significantly positively correlated with the relative mole percentages of fucose and galactose, indicating that the composition of monosaccharides affected heterotrophic bacteria in crusts. In deserts, environmental factors such as temperature and moisture changed significantly across seasons. The physicochemical properties of biocrust exopolysaccharides and the seasonal dynamics of bacterial communities were controlled by multiple factors, such as temperature, moisture, and light.

Litter decomposition and its effects on soil microbial community in Shapotou area, China

YANG Gui-sen, ZHANG Zhi-shan, ZHAO Yang, SHI Ya-fei, HU Rui

2022, 33(7):  1810-1818.  doi:10.13287/j.1001-9332.202207.003

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We investigated the decomposition characteristics of Eragrostis minor, mosses, and leaves of Artemisia ordosica with litterbag method in the sand-binding revegetation area, southeastern edge of the Tengger Desert, and further examined their effects on soil microbial communities using the Illumina MiSeq sequencing method. The results showed that the decomposition duration and litter types significantly affected litter decomposition rate. Mosses had the lowest decomposition rate, with a mass loss ratio of only 15.4% after decomposition for 13 months. The average decomposition rates of E. minor and leaves of A. ordosica were 4.9 and 3.4-fold of that of mosses, respectively. During decomposition for 11 months, the dominant bacterial phyla were Actinomycota and Proteobacteria, while that of the fungal community was Ascomycota. Moss decomposition significantly increased the relative abundance of Bacteroidetes and Chloroflexi, but remarkedly decreased the abundance of Basidiomycetes. The diversity and richness of bacterial and fungal communities significantly increased after litter decomposition. The compositional changes of fungal community were significant among litters, but that of bacterial community was not. There was a negative correlation between decomposition rate and the diversity and richness of bacterial and fungal communities. Plant polysaccharides, total phosphorus, soil pH, microbial biomass nitrogen, and soil ammonium content were the main factors affecting microbial community structure. Litter decomposition changed the composition and interspecific similarity within microbial communities, as well as increased the diversity and richness of soil microbial communities, and thus would promote the restoration of soil habitat.

Relationship between community composition and water infiltration of biological soil crusts in the hilly Loess Plateau, China

WANG Shan-shan, ZHAO Yun-ge, MING Jiao, ZHANG Zi-hui, GUO Ya-li

2022, 33(7):  1819-1826.  doi:10.13287/j.1001-9332.202207.007

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Biological soil crusts (biocrusts) are the mixed community composed of different ratios of cyanobacteria, mosses, and lichens at the slope scale in the Hilly Loess Plateau region. Biocrusts significantly affect water infiltration in this area. The relationship between infiltration rate and community structure of mixed biocrusts is unknown, which would hinder the assessment of soil permeability of biocrusts at the slope scale. We measured the stable infiltration rate of cyanobacteria, moss, and mixed biocrusts with different proportions of cyanobacteria and moss including moss coverage of <15%, 15%-30%, 30%-45%, 45%-60% and >60%, respectively. The principal component analysis and path analysis were used to understand the influencing factors of stable infiltration rate of mixed biocrusts, and to clarify the relationship between the stable infiltration rate and the community structure of mixed biocrusts. The results showed that the saturated hydraulic conductivity of cyanobacteria and moss crusts was 0.66 mm·min^-1 and 2.40 mm·min^-1, respectively. The stable infiltration rates of mixed biocrusts with moss coverage <15% to >60% were 0.80-2.30 mm·min^-1. The stable infiltration rate of mixed biocrusts at the slope scale depended on moss coverage and its improvement on soil pore structure, with the correlation coefficients being 0.636 (P=0.011) and 0.835 (P=0.000) respectively. Herein, the saturated hydraulic conductivity and coverage of cyanobacteria and moss confirmed the weighted prediction of water infiltration volume (y) i.e., a significant correlation (r=0.945) with the measured water infiltration volume (x) of mixed biocrusts. The linear fitting of measured and predicted water infiltration volume of mixed biocrusts was y=0.85x (R²=0.98, P<0.05). This study clarified the relationship between water infiltration of mixed biocrust community composition and individual biocrust composition, which provided a scientific basis for accurately evaluating the hydrological process of biocrusts in this area.

Effects of simulated grazing disturbance on soil water infiltration of biocrust slope in the hilly Loess Pla-teau, China

GU Kang-min, ZHAO Yun-ge, ZHANG Zi-hui, JI Jing-yi, GUO Ya-li

2022, 33(7):  1827-1834.  doi:10.13287/j.1001-9332.202207.010

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Water is the key factor for vegetation restoration in the Loess Plateau region. Biological soil crust (biocrust), a widely distributed soil surface cover, significantly affects soil infiltration. Disturbance would affect soil water infiltration of biocrust. The effects of different intensities of disturbance on soil water infiltration of biocrust are still unclear. By simulating the trampling disturbance of sheep, we examined the effects of disturbance intensity (10%, 20%, 30%, and 40%) estimated by the coverage of broken biocrust on the surface cover of biocrust slope in the Hegou catchment of Wuqi County, Shaanxi Province. Soil water infiltration under different intensities were measured by the linear source infiltration method. The influence mechanisms of disturbance on soil water infiltration of biocrust slope were investigated with a structural equation model and correlation analysis. Results showed that compared to that without disturbance, the coverage of cyanobacterial crust was increased by 33.6% at 10% of disturbance intensity, no difference at 20% of disturbance intensity, and decreased by 36.1% and 75.0% at 30% and 40% of disturbance intensities, respectively. Litter coverage was increased by 34.3% under 40% of disturbance intensity, while that of other treatments were not changed. Surface roughness was decreased by 22.3%, 11.1%, and 5.6% at 10%, 20%, and 30% of disturbance intensities, respectively, but increased by 8.2% at the 40% of disturbance intensity. The initial infiltration rate at 40% of disturbance intensity was 77.1% higher than that without disturbance, while other treatments had no significant difference at the initial infiltration rate. Furthermore, distur-bance did not affect the stable and average infiltration rate. Our results confirmed that disturbance mainly promoted the initial infiltration by reducing the coverage of cyanobacterial crust, increasing the coverage of litter, and changing soil roughness. This study would provide scientific basis for the management of biocrust of rehabilitated lands in the Loess Plateau region.

Effects of moss biocrust on soil water infiltration in the Three Gorges Reservoir Area, China

ZHANG Guan-hua, YI Liang, DING Wen-feng, WANG Yi-ran, NIU Jun, LI Jian-ming, SUN Bao-yang

2022, 33(7):  1835-1842.  doi:10.13287/j.1001-9332.202207.001

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We examined the effects of moss-dominated biocrusts on soil infiltration properties in Wangjiaqiao watershed of the Three Gorges Reservoir Area. Five levels of coverage (1%-20%, 20%-40%, 40%-60%, 60%-80% and 80%-100%) were set, with a nearby bare land as the control. We collected soil samples and conducted infiltration process observation by double cutting ring method. The results showed that biocrusts could appreciably increase soil cohesion, porosity, clay content, water-stable aggregates and organic carbon of topsoil, but significantly reduce soil bulk density and sand content. Biocrusts promoted soil water infiltration, with the initial infiltration rate (I_i), stable infiltration rate (I_f), average infiltration rate and cumulative infiltration amount being two times or more of that in bare land. Withbiocrust coverage increasing, soil infiltration properties firstly increased and then decreased, and peaked at 40%-60% coverage level. Results of path analysis indicated that I_i was mainly affected by biocrust coverage, soil bulk density, and organic carbon content, while I_f was mainly affected by biocrust coverage and soil bulk density. The simulation results of four infiltration models demonstrated that Horton model was the best fitting on the water infiltration process of biocrusted soil in the Three Gorges Reservoir Area.

Water repellent characteristics of physical and biological crusts and their effects on water infiltration

ZHONG Xiang-yan, SHI Hui, LI Xuan, ZHAO Yi-jian

2022, 33(7):  1843-1852.  doi:10.13287/j.1001-9332.202207.013

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Soil crust is a normal natural phenomenon with different water hydrophilicity and repellency due to different formation mechanism, thus affecting soil hydraulic characteristics and hydrological cycle. In this study, we measured water repellent characteristics of physical and biological crusts under different vegetations in the field using water drop penetration time (WDPT). The surface morphology of crusts was observed using scanning electron microscopy, and the infiltration characteristics of crusts and their non-crust soils (control) was evaluated with micro-infiltration device. The results showed that: 1) The average WDPT of physical crusts and the control soils was 3.3 s and 0.9 s, respectively, indicating that both were hydrophilic. The average WDPT of biological crusts ranged from 20.9 s to 140.9 s, which was 2.8 to 19 times that of control, and that under Diospyros lotus and Robinia pseudoacacia was 134.5 s and 140.9 s, respectively. 2) Compared with the control, the cumulative infiltration amount, average infiltration rate and moisture absorption force of physical crusts decreased by 0-4.3%, 3.5%-5.1%, and 27.2%-90.1%, respectively, while those of biological crusts decreased by 0-25%, 1.4%-28.2% and 36.0%-84.9%, respectively. 3) Regardless of the presence of crusts or not, there were “hockey-stick-like” curves by using Philip model to fit infiltration data. Before the WRCT point in the “hockey-stick-like” curve, the point source infiltration was mainly horizontal diffusion. After the WRCT point, the infiltration was mainly vertical diffusion. The presence of soil crust prolonged the formation time of the turning point. In all, physical crusts formed by inorganic mineral particles blocking the surface soil did not affect water repellency, while biological crusts that reflected the effects of hydrophobic organic compounds on soil structure enhanced its water repellency. Both physical crusts and biological crusts decreased the cumulative infiltration amount and average infiltration rate of soil. Compared with the control, physical crusts mainly affected soil hygroscopicity, but with limited effects on the steady infiltration rate. Biological crust decreased soil hygroscopicity and increased steady infiltration rate.

Characteristics of runoff and infiltration processes on slope with intergrown biocrusts and herbs

DAN Chen-xi, ZHANG Qiong, LIU Chang, GUO Zhen, LIU Gang

2022, 33(7):  1853-1860.  doi:10.13287/j.1001-9332.202207.015

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Biocrusts and herbs coexist in arid and semi-arid areas, playing an important role in soil and water conservation. However, the combined effects of biocrusts and herbs on process and mechanism of runoff and infiltration on slope are still unclear. In this study, simulated rainfall experiments with four treatments, including bare soil, biocrusts, Stipa bungeana and S. bungeana+biocrusts, were designed to investigate runoff, infiltration process and hydrodynamic characteristics of herbs and biocrusts on slope. The results showed that the runoff under the two treatments with biocrusts was stable. The total runoff of four treatments was in the following order: biocrusts > S. bungeana+biocrusts > bare soil > S. bungeana, indicating that biocrusts could inhibit soil infiltration and S. bungeana could promote soil infiltration. At soil depths of 16 cm and 24 cm, the cumulative infiltration of biocrusts treatment was significantly less than that of S. bungeana+biocrusts treatment, suggesting that with the increases of soil depth, S. bungeana reduced the negative effect of biocrusts on soil infiltration. The Froude number was greater than 1 under bare soil and less than 1 under other treatments, which was subcritical flow. Compared with the runoff kinetic energy of the bare soil treatment, the treatments of biocrusts, S. bungeana, and S. bungeana+biocrusts were reduced by 83.3%, 59.5%, and 88.1%, respectively. The variations of hydrodynamic parameters indicated that the role of biocrusts is greater than S. bungeana in regulating runoff.

Changes of soil water budget in the area covered by biological soil crusts in Mu Us sandy land, China

YUE Yan-peng, CHENG Long, SUN Ying-tao, PANG Ying-jun, WU Bo, SHI Lin, HE Jin-jun, JIA Xiao-hong

2022, 33(7):  1861-1870.  doi:10.13287/j.1001-9332.202207.014

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Exploring and quantifying the impacts of biological soil crusts on soil hydrological processes and soil water budget in semi-arid ecosystems can provide a theoretical basis for vegetation restoration and reconstruction in deserts. Based on continuous observation of soil water content in different types of areas covered by biological soil crusts (e.g., algae, moss) and bare sand in the Mu Us sandy land during the growing season (May to October) from 2018 to 2020, we examined the effects of biological soil crusts on soil water budget at a depth of 0-40 cm. Results showed that algae and moss crusts significantly reduced soil water supplement below 40 cm by rainfall and increased soil water evaporation loss, compared with that under bare sand. In the relatively wet year (2018), the amount of soil water expenditure (seepage+evaporation) covered by bare sand and the various types of biological soil crusts was less than that of rainfall, resulting in net soil water income. In the relative dry years (2019 and 2020), the amount of soil water expenditure covered by dominant algae and moss crusts was higher than that of rainfall, causing net soil water deficit, but opposite for bare sand. Biological soil crusts led to the imbalance of soil water budget of 0-40 cm depth and even soil water deficit in relatively dry years, which may lead to the succession of plant communities to be dominated by shallow-rooted plants in this area.

Reduction of flow velocity by biological soil crust of revegetated grassland in the hilly Loess Plateau, China

GUO Ya-li, ZHAO Yun-ge, GAO Li-qian, YANG Kai, SUN Hui, GU Kang-min

2022, 33(7):  1871-1877.  doi:10.13287/j.1001-9332.202207.008

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Biological soil crusts (biocrusts) are the common cover in arid and semiarid areas. Together with plants, biocrusts affect runoff and flow velocity. However, few studies have focused on the effects of the co-covering of plant and biocrust (plant+biocrust) on the flow velocity, with a knowledge gap in the study of driving factors for slope erosion in arid and semiarid areas. In this study, simulated rainfall experiments were used to investigate the effects of biocrust and three types of biocrusts (more cyanobacteria less moss, more moss less cyanobacteria, and moss) on the flow velocity of revegetated grassland in the hilly Loess Plateau. The results showed that plant and plant+biocrust significantly reduced flow velocity, with that of plants and plant+biocrust being 70.7% and 83.1% lower than bare soil. The reduction benefits of plant and biocrust on flow velocity were 70.7% and 12.4%, respectively, when they were co-covered. Biocrust composition under plant cover affected flow velocity. The reduction benefits of more cyanobacteria less moss, more moss less cyanobacteria, and moss crust on flow velocity were 11.5%, 12.4%, and 19.4%, respectively. There was a significant negative correlation between flow velocity and moss coverage and a significant positive correlation between flow velocity and cyanobacteria coverage. The relationship between moss cove-rage (x) and flow velocity (y) was y=-2.081x+0.03 (R²=0.469). The moss coverage was a key factor affecting the flow velocity of co-covering of plant and biocrust slope with similar plant coverage (40%±10%). In conclusion, biocrusts under plant cover significantly slowed flow velocity, and the effect magnitude was related to its composition, implying that the role of biocrusts should be considered in understanding the mechanism underlying slope erosion in revegetated grassland.

Representative landscape indices of biological soil crusts distribution in the hilly Loess Plateau of China

JI Jing-yi, ZHAO Yun-ge, ZHANG Wan-tao, GU Kang-min

2022, 33(7):  1878-1884.  doi:10.13287/j.1001-9332.202207.005

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Landscape indices can quantitatively describe the distribution characteristics of biological soil crusts (biocrusts). However, there are too many landscape indices, with high redundancy. We investigated 58 plots of biocrusts with different distribution patterns in the Hegou watershed of Wuqi County, Shaanxi Province, located in the hilly Loess Plateau. First, we calculated 15 common landscape indices, and selected representative landscape indices that could describe the biocrust landscape pattern and had specific ecological significance, based on correlation analysis, factor analysis, and sensitivity analysis. The reliability and rationality of the representative landscape indices were verified with data of the different biocrusts coverage in the Yingwoshanjian watershed of Yangjing Town, Dingbian County, Shaanxi Province. The results showed that 10 of the 15 landscape indices had significant correlations. Total edge (TE) and edge density (ED) were not significantly correlated with number of patches (NP), patch density (PD), clumpiness (CLUMPY), and interspersion juxtaposition index (IJI), respectively. The percentage of landscape (PLAND), ED, patch cohesion index (COHESION), and splitting index (SPLIT) described the spatial distribution characteristics of biocrust from coverage, length, connectivity, and fragmentation, respectively. The cumulative contribution of the three common factors represented in describing the spatial distribution of biocrusts was 91.6%. The study identified the representative landscape indices that could quantify the complexity of biocrusts distribution and thus would provide a theoretical basis for studying the pattern evolution of biocrusts and their relationship with ecological processes.

Eco-physiological functions of soil microbial biofilms: A review

A La-sa, GAO Guang-lei, DING Guo-dong, ZHANG Ying, CAO Hong-yu, DU Yu-jia

2022, 33(7):  1885-1892.  doi:10.13287/j.1001-9332.202207.006

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Soil microbial biofilms (SMBs) are a biological community of soil bacteria and their accumulative extracellular polymeric substances (EPS), which are the initial status and the most important components of biological soil crusts. SMBs, as the most common mode of soil bacterium survival, not only greatly contribute to the survival of free-living cells, but also stick to soil particles and roots, performing a variety of important ecological functions. Based on the structure and composition analysis of SMBs, we gave a summary of eco-physiological functions of SMBs involving soil quality and plant health. SMBs have higher metabolic activity than free-living cells. It promotes EPS secretion and organic turnover, which is important for soil fertility, pollutant decomposition, and aggregate formation. SMBs help improve plant nutrient utilization and stress resistance through the synergy of microorganisms, promotion of plant growth, promoting substance secretion and immobilization of EPS. In the future, it will be critical to uncover the micro-mechanisms underlying SMBs’ eco-physiological functions and to screen functional soil bacterium strains.

Original Articles

Water sources of Picea schrenkiana and Berberis heteropoda in the Tianshan Mountains in summer

GULHANAT·Bolatbek, CHANG Shun-li, BAHJAYNAR·Tiemerbek, ZHANG Yu-tao

2022, 33(7):  1893-1900.  doi:10.13287/j.1001-9332.202207.032

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Water use patterns of trees and shrubs in the Picea schrenkiana coniferous forest remain unclear, due to a lack of quantitative analysis on water use dynamics. In this study, the xylem water hydrogen and oxygen stable isotope compositions of P. schrenkiana and the companion shrub species Berberis heteropoda were measured to detect their water sources. The IsoSource model was used to analyze the relative contribution of each potential water source for both species during summer. The results showed that during July, P. schrenkiana and B. heterocarpa mainly extracted water from the 0-60 cm soil layer due to the relatively sufficient soil water content, with the relative contributions being 73.8% and 63.2% for the two species, respectively. In August, with the decreases in soil water content, water source of P. schrenkiana remained stable, and the relative contribution of soil water above 60 cm was 69.5%. In contrast, B. heterocarpa reverted to water source from deeper soil layer, with the relative contribution of shallow soil (0-20 cm) water decreasing to 14.3% and that of middle (20-60 cm) to deep (60-100 cm) soil water increased to 67.7%. In September, with the increases of water content in the shallow soil layer, both species extracted water from shallow soil layers, with the relative contribution reaching to 95.0%. In summary, P. schren-kiana exhibited typical shallow root characteristics, while B. heterocarpa extracted water from the 0-100 cm soil profile and could flexibly change its water source corresponding to changes in soil water content to cope with changing environmental water condition.

Effects of melatonin on photosynthetic properties and osmoregulatory substance contents of cucumber seedlings under salt-alkali stress

WU Peng, LYU Jian, YU Ji-hua, LIU Na, LI Jin-wu, JIN Li, JIN Ning, WANG Shu-ya

2022, 33(7):  1901-1910.  doi:10.13287/j.1001-9332.202207.028

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To determine the mitigating effects of exogenous melatonin on salt-alkali stress in cucumber, we mea-sured photosynthetic characteristics and osmoregulatory substance content of cucumber leaves under salt-alkali stress, using ‘Xinchun 4’ cucumber as the test material and a salt-alkali complex (NaCl:Na₂SO₄:Na₂CO₃:NaHCO₃ = 1:9:1:9) to simulate stress. The results showed that compared with the normal seedlings, the exogenous application of 10 μmol·L^-1 melatonin significantly increased the contents of chlorophyll, soluble sugar, and soluble protein, as well as net photosynthetic rate, stomatal conductance, transpiration rate, photosystem Ⅱ maximum photochemical efficiency, actual photochemical efficiency, apparent photosynthetic electron transfer rate, and photochemical burst coefficient of cucumber seedlings under 40 mmol·L^-1 salt-alkali stress, but decreased intercellular CO₂ concentration, non-photochemical burst coefficient, and sucrose, fructose, starch, and proline contents by 11.1%, 13.8%, 12.7%, 27.5%, 1.3% and 32.8%, respectively. Moreover, the activities of key enzymes for carbon assimilation (including ribulose-1,5-bisphosphate carboxylase/oxygenase and fructose-1,6-bisphosphate esterase) were significantly increased, whereas the mRNA expression levels of Rubisco subunits (CsrbcS and CsrbcL), CsFBA, CsRCA, CsFBPase and CsTK were downregulated. In conclusion, exogenous melatonin could increase the contents of chlorophyll and osmoregulatory substance, photosynthetic chemical efficiency, and key carbon assimilation enzyme activities of cucumber seedlings under salt-alkali stress, thereby enhance photosynthetic capacity and reduce the stress-induced plant damage. The results would provide theoretical basis for anti-saline plant cultivation.

Impacts of biochar and phosphorus application on soil phosphorus availability and soybean phosphorus uptake

KUANG Xi-zhi, DENG Wei-ming, TANG Le-le, HUANG Qi, CAI Kun-zheng, TIAN Ji-hui

2022, 33(7):  1911-1918.  doi:10.13287/j.1001-9332.202207.018

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Biochar is beneficial to soil phosphorus (P) availability and crop growth, but the effects vary greatly across different soil types. We investigated the effects of rice straw biochar (4% of total mass) and P application (0, 30, and 90 kg P·hm^-2) on soil P availability, phosphomonoesterase activity, and soybean P uptake by using lateritic red soil (pH 4.91) and cinnamon soil (pH 7.24) as test materials. The results showed that biochar application at different P levels significantly increased available P and total P in both soils. Biochar application with 30 kg P·hm^-2 increased soil available P with maxima at 192.6% and 237.1% in lateritic red soil and cinnamon soil, respectively. Biochar application with 30 kg P·hm^-2 in lateritic red soil significantly increased the activity of alkaline phosphomonoesterase by 78.9%, decreased the content of active organic P by 39.3%, and subsequently stimulated soybean P absorption and growth. Biochar amendment significantly reduced active organic P content in cinnamon soil, but did not affect soil phosphomonoesterase activity and plant growth. The content of active organic P was significantly negatively correlated with soil available P content. In summary, the effect of biochar on soil P availability varied across different soil types (lateritic red soil > cinnamon soil) and P levels (better at 30 kg P·hm^-2). Our results could provide scientific basis for a promising application of biochar in reducing the amount of P fertilizer and increasing soybean P uptake, especially in lateritic red soil.

Effect of reed-biochar application on ammonia volatilization from different types of soils

HU Wang, ZHAO Hang, ZHOU Xuan, WANG Yi-zhe, ZHANG Han-feng, ZHANG Yu-ping

2022, 33(7):  1919-1926.  doi:10.13287/j.1001-9332.202207.031

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The application of straw biochar in farmland in Dongting Lake area can realize the resource utilization of straw and reduce environmental risk. In 2020, a rice pot experiment was conducted to investigate the effects of different biochar application levels on ammonia volatilization rate, cumulative ammonia volatilization, pH value, and NH₄⁺-N concentration in surface water. Six levels of reed (Miscanthus lutarioriparius) biochar amount, i.e., 0%, 1%, 2%, 4%, 6% and 8% of soil weight of the 0-20 cm column, were applied in two typical paddy soils in sou-thern China, i.e., reddish clayey soil derived from quaternary red soil and granitic sandy soil derived from granite. Compound fertilizer was applied at a rate of 200 kg N·hm^-2. The results showed that biochar application resulted in significant differences in the rate and cumulative amount of ammonia volatilization between the two soils and among different biochar treatments. For the granitic sandy soil, peak ammonia volatilization under different biochar treatments appeared at the second day after fertilization, which was decreased by 23.6%-53.4%. For the reddish clayey soil, peak ammonia volatilization appeared between the 7th to 13th day after fertilization, which increased with biochar addition level. The rate of ammonia volatilization from the granitic sandy soil was generally higher than that from the reddish clayey soil. For the granitic sandy soil, addition of <4% biochar could inhibit the ammonia volatilization and cumulative volatilization amount, with the greatest reduction (46.9%) at the treatment with 2% biochar addition. The addition of biochar did not affect the pH value of surface water at the early stage of rice growth. For the reddish clayey soil, the pH value and NH₄⁺-N concentration in the surface water increased with biochar addition level, resulting in the increases of ammonia volatilization rate and cumulative volatilization amount by 1.3-10.5 times. Biochar addition level was the key factor affecting ammonia volatilization from the two soils. Elovich equation could well fit the variation trend of cumulative ammonia volatilization with time for the two soils, with the correlation reaching extremely significant level for each treatment. Overall, the application of reed biochar could suppress ammonia volatilization from the granitic sandy soil which was nearly neutral in acidity, while would promote ammonia volatilization via increasing pH value and NH₄⁺-N concentration of surface water for the acidic reddish clayey soil. Therefore, appropriate dosages of reed biochar should be selected for different types of soil in order to reduce nitrogen loss.

Simulation of soil desiccation effects and production water footprint of apple orchards in different precipitation areas of the Loess Plateau, China

WEN Hui-xian, ZHAO Xi-ning, GAO Fei

2022, 33(7):  1927-1936.  doi:10.13287/j.1001-9332.202207.030

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To clarify the desiccation effect of deep soil and water footprint of crop production in two typical dry-farming apple orchards on the Loess Plateau of China, with Luochuan County in semi-humid region and Mizhi County in semi-arid region as two typical apple planting areas, we used the WinEPIC model to quantitatively simulate and analyze the variations of soil moisture from 0 to 15 m and water footprint of apple production during 1980-2020. The results showed that annual yield of mature orchards in Luochuan and Mizhi followed an “S” curve, with the average annual values being 24.64 and 18.42 t·hm^-2, respectively. The average annual evapotranspirations of Luochuan and Mizhi were 623.82 and 458.97 mm, the average annual drought stress days of Luochuan and Mizhi were 20.4 and 52.73 days, and the water overconsumption were 167.94 and 121.15 mm, respectively. The available soil water contents in Luochuan and Mizhi showed a sharp decline from 1 to 25 years old and from 1 to 23 years old, respectively, with average annual soil desiccation rates being 64.6 and 68.03 mm·a^-1, respectively. The dry layer of deep soil for the orchards of Luochuan and Mizhi appeared at the 13th and 7th years, and would be stable after 23 and 22 years, respectively. The formation and stability time of the soil dry layer in the area with high precipita-tion was later than that with low precipitation. Long-term soil moisture deficit would result in irreversible soil dry layer. Water footprint of apple production in Luochuan and Mizhi were low in the early stage and high in the later stage, with the average annual values being 0.187 and 0.194 m³·kg^-1, respectively. Both apple yield and production water footprint were affected by precipitation. To ensure the sustainable and healthy development of apple industry, it was recommended that the optimal planting age of apple trees is about 23 years on the Loess Plateau where water sources is limited, and the maximum should not exceed 25 years.

Constructing biomass models for natural Quercus mongolica based on Bayesian seemingly unrelated regression

XIE Long-fei, LI Feng-ri, DONG Li-hu

2022, 33(7):  1937-1947.  doi:10.13287/j.1001-9332.202207.019

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In this study, the biomass models for natural Quercus mongolica in Heilongjiang Province were constructed based on the predictors of diameter at breast height (D) and tree height (H) by several methods including multivariate likelihood analysis and seemingly unrelated regression. The results showed that the H could significantly improve the stem biomass model, with the coefficient of determination (R²) being increased from 0.953 to 0.988 and the root mean square error (RMSE) being reduced by 14 kg, but it had no significant improvement for the biomass model of branch, foliage, and root. The error structures of both biomass model systems (only D and D-H) were multiplicative, indicating that the linear models after logarithmic transformation were more appropriate. The R² for the biomass models of stem, branch, foliage and root were 0.953-0.988, 0.982-0.983, 0.916-0.917, and 0.951-0.952, while the RMSE were 13.42-27.03, 6.84-7.00, 1.95-1.97 and 9.71-9.84 kg. Compared with the feasible generalized least squares (FGLS) approach, Bayesian estimation had similar fitting performance and provided parameter estimates with different variations. The standard errors of parameters for FGLS were 0.054-0.211. There were similar variations (standard deviations of 0.055-0.221) for the two Bayesian estimation with no prior information (DMC and Gibbs1). The Gibbs sampler with a multivariate normal distribution with a mean vector of 0, variances of 1000 and covariances of 0 (Gibbs2) or the prior information from the historical researches summary for Quercus trees biomass models (Gibbs3) produced greater variation than those of FGLS, DMC, and Gibbs1 (stan-dard deviations were 0.080-0.278), while Gibbs sampler with the prior information obtained from own data (Gibbs4) provided the lower variations than others (standard deviations were 0.004-0.013). The Gibbs4 approach provided the narrowest 95% prediction interval and produced the smaller prediction biases, with the average absolute error percentage (MAPE) for stem, branch, foliage, root and total of the only-D biomass model being 19.8%, 24.7%, 24.6%, 29.0% and 13.1%, while MAPE for the corresponding components of D-H biomass model kept same except for stem and total decreased to 10.5% and 9.8%, which indicated that Gibbs4 could provide more accurate biomass predictions. Compared with classical statistics, accurate prior information made Bayesian seemingly unrelated regression an advantage in estimation stability and uncertainty reduction.

Identification of forest vegetation types in southern China based on spatio-temporal fusion of GF-1 WFV and MODIS data

XU Li, OUYANG Xun-zhi, PAN Ping, ZANG Hao, LIU Jun, YANG Kai

2022, 33(7):  1948-1956.  doi:10.13287/j.1001-9332.202207.022

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It is difficult to obtain long time series of high spatial resolution remote sensing images in southern China because of the complex terrain and frequent cloudy and rainy weather. In contrast, the spatio-temporal fusion can sychonorously obtain remote sensing data with high spatial-temporal resolution, which is beneficial to extract forest vegetation type information. With Xingguo County of Jiangxi Province as the study area, we fused the Landsat8 OLI and GF-1 WFV images with high spatial resolution with high temporal resolution of MODIS09 A1 image on the basis of enhanced spatial and temporal adaptive reflectance fusion model (ESTARFM), reconstructed the time series data of ESTARFM_Landsat8 EVI and ESTARFM_GF-1 EVI with 8 d step of enhanced vegetation index (EVI), obtained the phenology (PH) characteristics, and identified the forest vegetation types by using random forest classification model. The results showed that the correlation coefficients between the fusion data of ESTARFM_Landsat8 EVI and ESTARFM_GF-1 EVI and the real images were all greater than 0.7, and had good consistency in spatial distribution, which could be used to supplement the missing data with high spatial resolution. The extraction accuracy of random forest classification with different combination modes was EVI+PH>EVI>PH and the classification accuracy of fusion data GF-1 was higher than that of Landsat8. A total of 43 variables were selected as the optimal feature variables for classification. The overall accuracy and Kappa coefficient were 95.6% and 94.9%, respectively, including 37 sequential EVI values and 6 phenological feature information. The sequential EVI data contributed more to the identification of forest vegetation types, while the phenological feature information was beneficial to improve the classification accuracy. The ESTARFM fusion algorithm was suitable for GF-1 and MODIS data, which could solve the problem of insufficient long-term sequence of high spatial resolution images. The GF-1 temporal fusion images had high accuracy in the identification of forest vegetation types in southern China under complex terrain and frequent cloudy and rainy weather.

Variation characteristics of normalized difference vegetation index in Northwestern Sichuan Plateau and its response to extreme climate during 2001-2020

WANG Xin, WANG Ming-tian, FENG Yong, ZOU Yu-jia, GUO Bin

2022, 33(7):  1957-1965.  doi:10.13287/j.1001-9332.202207.020

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The northwestern Sichuan Plateau is a typical eco-climate sensitive area, where vegetation condition is closely related to climate change. We used the MODIS-NDVI and the meteorological data during 2001-2020 to investigate the change trend of normalized difference vegetation index (NDVI) and the mechanism underlying its responses to climate factors in the growing season of northwestern Sichuan Plateau by using the methods of maximum value composite, geodetector model, trend analysis, and correlation analysis. The results showed that vegetation coverage in northwestern Sichuan Plateau was overall good during the study period. 86.8% of the regional vegetation was stable, 12.6% of the regional NDVI was weakly and continuously increasing, and 0.6% of the regional NDVI was decreasing. The ecological environment of the whole region exhibited a steady and good development trend. The vegetation coverage in the study area exhibited apparent spatial variation with a general tendency of increase from southwest to northeast, as well as obvious variation with elevation. The NDVI rose with elevation below 1350 m, varied slightly from 1350 to 3650 m, dropped from 3650 to 5900 m, with a rapid drop between 4750 to 5900 m. There was almost no vegetation above 5900 m. The NDVI of northwestern Sichuan Plateau was affected by the interactions of natural factors. Thermal factors were the dominant climate factors, including monthly maximum value of daily maximum temperature, monthly minimum value of daily minimum temperature, growing season length, annual mean temperature, mean temperature over the growing season. All these factors were positively correlated with NDVI excepted for monthly maximum value of daily maximum temperature. The response of NDVI to temperature index was higher than that of precipitation index. Under the background of climate warming, extreme temperature warming index played a major role in promoting the growth and improvement of vegetation in northwestern Sichuan Plateau, especially in high-altitude areas.

Evaluation of climate regulation service at prefecture-level city: A case study of Fuzhou City, China

BING Long-fei, WANG Jiao-yue, YIN Yan, XI Feng-ming, ZHANG Wen-feng, MA Ming-jing, NIU Le

2022, 33(7):  1966-1974.  doi:10.13287/j.1001-9332.202207.021

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Ecosystem services are the bridge between ecosystem functions and human welfare. Climate regulation service (CRS) has an extremely important role in ecosystem services. It is important to conduct a comprehensive assessment based on the whole process of CRS occurrence for scientific assessment of ecosystem services. With Fuzhou City as a case, we carried out the assessment of CRS at the local and municipal scales, and analyzed the spatial and temporal variations of CRS at the administrative unit and land use and land cover scales. The results showed that the aggregated physical capacity of CRS in Fuzhou City was 4.01×10¹² MJ (monetary value 613.944 billion yuan, GDP 561.808 billion yuan) and 4.66×10¹² MJ (monetary value 714.002 billion yuan, GDP 785.681 billion yuan) in 2015 and 2018, respectively, and that the monetary value of CRS was roughly equivalent to the GDP of that year. The main land use/cover (LULC) type was woodland, cultivated land, and water area, which accounted for 57%, 15%, and 9% of Fuzhou’s land area, respectively. Water area contributed the most to Fuzhou’s CRS, with a contribution of over 60% in 2018, higher than woodland (12%), and cultivated land (13%). The CRS was lower in built-up areas and eastern farming areas. Between 2015 and 2018, the area of LULC change in Fuzhou was 1805.5 km². The largest changes were cultivated land and wood land. The main land use transfer direction was between cultivated land and woodland, woodland and garden land, cultivated land and residential and industrial and mining land. The aggregated physical capacity of CRS changed by 6.74×10¹¹ MJ, while the corresponding monetary value of 103.58 billion yuan. The CRS changes were concentrated in the central and western regions such as Minhou, Minqing, and Yongtai, and the western mountainous regions such as Luoyuan and Fuqing. The most drastic change of CRS was found in water area. The conversion of water areas produced extremely strong changes in CRS, much stronger than the effects of conversion of other LULC types.

Characteristics of extreme temperature variation in the Loess Plateau and its correlation with average temperature

LIU Pan, ZHAO Xi-ning, GAO Xiao-dong, YU Liu-yang, REN Min

2022, 33(7):  1975-1982.  doi:10.13287/j.1001-9332.202207.024

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In recent decades, extreme climate occurred frequently on the Loess Plateau. It is thus particularly important to study and predict the occurrence of extreme climate. Available researches on extreme climate mainly focus on the changing characteristics of the event itself, but ignore the correlation between average temperature and its changing trend. We used linear trend estimation, Mann-Kendall test, sliding t test and Pearson correlation analy-sis to study the variation trend of extreme temperature and its correlation with average temperature on the Loess Plateau based on the daily maximum temperature, minimum temperature and average temperature data of 79 meteo-rological stations from 1986 to 2019. The results showed that the extreme warmth index in the Loess Plateau region showed a significant upward trend, the extreme cold index showed a significant downward trend, and the frequency of extreme high temperature events increased. Most of the extreme temperature indices had abrupt changes in the middle and late 1990s and in 2012, and the extreme temperature showed a downward trend from 1998 to 2012, which better responded to the phenomenon of global warming hiatus. The increasing trend of mean temperature in the gully region, the rocky mountain region and the valley plain region was more obvious than that in other regions. The stations with large trend of extreme temperature index almost all occurred in the region with large increases of mean temperature. The increases of average temperature in small increments increased the frequency of extreme high temperature event, with the change range of extreme low temperature and its rate being greater than the extreme high temperature. Climate warming on extreme temperature index had a different effect, small changes in the average temperature in the Loess Plateau made the climate transfer towards the direction of more frequent heat.

Optimization of urban ecological spatial structure based on network analysis: A case study of Changzhou City, China

WU Qian-lian, LI Fei-xue, ZHANG Qi-shun, LI Man-chun

2022, 33(7):  1983-1992.  doi:10.13287/j.1001-9332.202207.023

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The rapid development of economy and society leads to the rapid expansion of cities, resulting in the atrophy of urban ecological space and the decline of ecological function, as well as a serious threat to urban ecological security. It is of great significance for the sustainable development of a city to systematically analyze the structure of urban ecological space and put forward targeted protection and optimization measures. Taking Changzhou City as the research area and considering the natural ecological function and social service function of urban ecological space, we constructed two ecological networks, the “source-corridor” ecological network based on natural ecology and the “supply-demand” ecological network based on human ecology. For the “source-corridor” ecological network, quantitative analysis was mainly carried out from the importance of nodes, network connectivity and stability. For the “supply-demand” ecological network, quantitative analysis was mainly carried out from the importance of nodes, supply-demand equilibrium and stability. The results showed that the levels of connectivity and stability of the “source-corridor” ecological network in the main urban area of Changzhou were not high, the stability level of the “supply-demand” ecological network was general, and there was spatial mismatch between service supply and demands. From the perspective of connectivity and stability improvement, an optimization scheme of “source-corridor” ecological network with 12 additional source nodes and 57 corridors was proposed. From the perspective of supply-demand balance and stability improvement, an optimization scheme of “supply-demand” ecological network with 22 new supply nodes was proposed. Compared with the original “source-corridor” ecological network, the connectivity level of the optimized network was improved by 10%, and the network stability was improved by 0.05. Compared with the initial “supply-demand” ecological network, the service level of the optimized network was improved by 4%, and the network stability was improved by 0.10. Finally, we integrated the two ecological networks, and formulated the implementation plan of protection and management for both the current protected patches and the new ecological nodes.

Spatiotemporal charactersitics of decoupling between land surface thermal environment and ecosystem ser-vice value in Pearl River Delta Urban Agglomeration, China

HUANG Zhuo-nan, CHEN Ying-biao, WU Zhi-feng

2022, 33(7):  1993-2000.  doi:10.13287/j.1001-9332.202207.025

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The Pearl River Delta Urban Agglomeration (PRDUA) is a highly urbanized region in China. The urbanized climate, especially the heat island effect, has a significant impact on urban ecosystems and habitats. Based on MODIS land surface temperature (LST) data and land cover data in 2000, 2005, 2010, 2015, and 2019, we quantified the land surface thermal environment and ecosystem service value (ESV), analyzed the decoupling between LST and ESV in the PRDUA from 2000 to 2019 using the decoupling analysis model, revealed the trade-off between them, and analyzed the spatiotemporal variation of the synergistic state between LST and ESV in PRDUA. The results showed that, from 2000 to 2019, the spatial pattern of land surface thermal environment in the PRDUA was relatively stable in time series but showed spatial variation with high fluctuation in the core area and low fluctuation in the peripheral area. The ESV of the PRDUA showed a trend of stable spatial distribution and decreasing in time series. The ESV of all the nine cities in PRDUA decreased by more than 9%. The decoupling between land surface thermal environment and the overall ESV of the PRDUA, as well as with the values of provisioning, regulating and support services, was dominated by weak negative decoupling and strong negative decoupling, showing a more significant trade-off, which indicated that the ecosystems of the PRDUA were still significantly influenced by the environmental characteristics of urbanization, and that the spatiotemporal variation of the decoupling states was related to the spatial variation of urbanization levels in PRDUA. The formulation of future ecological policies in the PRDUA must consider the differences in urbanization levels and the differences in the trade-offs between urbanized environments and ecosystems to precisely formulate ecological control and restoration plans and improve the efficiency and implementation effects of ecological planning.

Relationship between economy and ecology of Pearl River Delta Urban Agglomeration based on ecological footprint of net primary productivity

AO Yong, ZHANG Meng-na, ZHAO Yong-hua, WANG Xiao-feng, BAI Zhao-di, JIANG Ling-feng

2022, 33(7):  2001-2008.  doi:10.13287/j.1001-9332.202207.027

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With the acceleration of regional economic integration, human activities have played an increasingly crucial role in regional sustainable development. In this study, MODIS remote sensing data and ecological footprint of net primary productivity (EF-NPP) were leveraged to calculate the equivalence factor and yield factor of the six major biologically productive land areas in the Pearl River Delta Urban Agglomeration. We analyzed the changes in per capita ecological footprint, per capita ecological carrying capacity, natural resource utilization efficiency and ecological moderate population from 2000 to 2020. Results showed that the per capita ecological footprint in the Pearl River Delta Urban Agglomeration continued to rise from 2000 to 2020. The ecological occupation of energy land was the highest. The ecological footprint was high in west, low in middle, and higher in northwest of the study area. The per capita ecological carrying capacity was relatively high in Zhaoqing and Jiangmen and low in Shenzhen, Dongguan, Foshan and Zhongshan. The gap between the ecological moderate population and the regional actual population widened over time, reaching 30.62 million in 2020. The regional actual population was much larger than the ecological moderate population, indicating huge population pressure. The natural resource utilization efficiency of the three main industries was high. The economic benefits created by the per capita ecological footprint increased by 36800 yuan·hm^-2 during the research period, with an average annual growth rate of 1800 yuan·hm^-2. The growth rate of the tertiary industry was the highest. Therefore, the results could provide reference for the study on natural resource utilization efficiency in medium and small-scale regions.

Temporal and spatial characteristics and correlation of the coordinated development of economy, society and ecological environment in the Yangtze River Delta, China

KONG Fan-bin, YUAN Ru-xue, XU Cai-yao

2022, 33(7):  2009-2016.  doi:10.13287/j.1001-9332.202207.026

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The imbalance of regional development is one of the important obstacles for the implementation of regio-nal coordinated development strategy. Based on the panel data of 41 cities in the Yangtze River Delta from 2010 to 2019, the regional coordinated development index system with five subsystems was constructed, including economic development, science and education, infrastructure, people’s life, and resource and environment. With the help of GeoDa and ArcGIS software, we used measurement model of regional coordinated development and method of exploratory spatial data analysis to analyze the temporal and spatial variations and internal correlation of various elements of regional coordinated development in the Yangtze River Delta. The results showed that, from the perspective of regional development, the coordination of regional development in the Yangtze River Delta had increased annually from 2010 to 2019. The level of economic development and science and education in Shanghai and Suzhou was ahead of other cities, while the development coordination of Northwest Anhui, Zhoushan and Huangshan was weaker than other cities. The order of average autocorrelation degree of each subsystem from high to low in the Yangtze River Delta from 2010 to 2019 was people’s life, economic development, resource and environment, science and education, and infrastructure. Among them, the global Moran’s index (Moran I) of economic development and science and education subsystem showed a downward trend, while science and education subsystem showed no significant correlation. Moran I of infrastructure subsystem was mostly at the low level with a great fluctuation in different years. People’s life had obvious spatial characteristics of high-high and low-low agglomeration. The global Moran I of resources and environment showed a pattern of “V” distribution. Economic development and science and education were the two factors most closely related to regional coordinated development.