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Climate change and human activities such as overgrazing and rapid development of tourism simultaneously affected the vegetation of the Zoige Plateau. However, the spatiotemporal variations of vegetation and the relative contributions of climate change and human activities to these vegetation dynamics remain unclear. Therefore, clarifying how and why the vegetation on the Zoige Plateau changed can provide a scientific basis for the sustainable development of the region. Here, we investigate NDVI trends using the Normalized Difference Vegetation Index (NDVI) as an indicator of vegetation greenness and distinguish the relative effects of climate changes and human activities on vegetation changes by utilizing residual trend analysis and the Geodetector. We find a tendency of vegetation greening from 2001 to 2020, with significant greening accounting for 21.44% of the entire region. However, browning area expanded rapidly after 2011. Warmer temperatures are the primary driver of vegetation changes in the Zoige Plateau. Climatic variations and human activities were responsible for 65.57% and 34.43% of vegetation greening, and 39.14% and 60.86% of vegetation browning, respectively, with browning concentrated along the Yellow, Black and White Rivers. Compared to 2001–2010, the inhibitory effect of human activity and climate fluctuations on vegetation grew dramatically between 2011 and 2020. [ABSTRACT FROM AUTHOR]

Abstract Background Dissolved organic matter (DOM) plays a significant role in the biogeochemical cycle of crucial elements in aquatic ecosystem. However, it is still not clear on the spectral characteristics of water DOM in different types of alpine wetlands, which have less anthropogenic influences and intensive ultraviolet radiation. Here, we collected 107 water samples from marsh, lake, and river wetlands in the Zoige plateau, China, and analyzed the chemical characteristics, compositions, and potential sources of chromophoric DOM by combining UV–vis spectroscopy and excitation–emission matrix fluorescence spectroscopy coupled with parallel factor analysis (EEMs-PARAFAC). Results UVC and UVA fulvic-like substances were the prevailing fluorescence components in water DOM, which accounted for 23.74–71.59% and 16.76–30.01% of the total fluorescence intensity, respectively. Compared with the lake and river wetlands, fluoresce intensities of UVC and UVA fulvic-like substances in DOM were higher in marsh wetland. Marsh wetlands possessed the highest SUVA254, E2/E3, E2/E4, and E4/E6 of DOM, suggesting higher humification degree, higher relative molecular nominal size, and higher aromaticity. And the E2/E4 ratios in most water samples were higher than 12, indicating water DOM was mainly derived from autochthonous sources in alpine wetlands. Conclusions Wetland types strongly affected the spectral characteristics of water DOM in Zoige plateau. These findings may be beneficial for sustainable management of alpine wetlands. Graphical Abstract

Background: Dissolved organic matter (DOM) plays a significant role in the biogeochemical cycle of crucial elements in aquatic ecosystem. However, it is still not clear on the spectral characteristics of water DOM in different types of alpine wetlands, which have less anthropogenic influences and intensive ultraviolet radiation. Here, we collected 107 water samples from marsh, lake, and river wetlands in the Zoige plateau, China, and analyzed the chemical characteristics, compositions, and potential sources of chromophoric DOM by combining UV–vis spectroscopy and excitation–emission matrix fluorescence spectroscopy coupled with parallel factor analysis (EEMs-PARAFAC). Results: UVC and UVA fulvic-like substances were the prevailing fluorescence components in water DOM, which accounted for 23.74–71.59% and 16.76–30.01% of the total fluorescence intensity, respectively. Compared with the lake and river wetlands, fluoresce intensities of UVC and UVA fulvic-like substances in DOM were higher in marsh wetland. Marsh wetlands possessed the highest SUVA254, E2/E3, E2/E4, and E4/E6 of DOM, suggesting higher humification degree, higher relative molecular nominal size, and higher aromaticity. And the E2/E4 ratios in most water samples were higher than 12, indicating water DOM was mainly derived from autochthonous sources in alpine wetlands. Conclusions: Wetland types strongly affected the spectral characteristics of water DOM in Zoige plateau. These findings may be beneficial for sustainable management of alpine wetlands. [ABSTRACT FROM AUTHOR]

Grasslands play a vital role in the global ecosystem. Efficient and reproducible methods for estimating the grassland aboveground biomass (AGB) are crucial for understanding grassland growth, promoting sustainable development, and assessing the carbon cycle. Currently, the available methods are limited by their computational inefficiency, model transfer, and sampling scale. Therefore, in this study, the estimation of grassland AGB over a large area was achieved by coupling the PROSAIL model with the support vector machine regression (SVR) method. The ill-posed inverse problem of the PROSAIL model was mitigated through kernel-based regularization using the SVR model. The Zoigê Plateau was used as the case study area, and the results demonstrated that the estimated biomass accurately reproduced the reference AGB map generated by zooming in on on-site measurements (R2 = 0.64, RMSE = 43.52 g/m2, RRMSE = 15.13%). The estimated AGB map also maintained a high fitting accuracy with field sampling data (R2 = 0.69, RMSE = 44.07 g/m2, RRMSE = 14.21%). Further, the generated time-series profiles of grass AGB for 2022 were consistent with the trends in local grass growth dynamics. The proposed method combines the advantages of the PROSAIL model and the regression algorithm, reduces the dependence on field sampling data, improves the universality and repeatability of grassland AGB estimation, and provides an efficient approach for grassland ecosystem construction and planning. [ABSTRACT FROM AUTHOR]

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Soil phosphorus (P) is a vital nutrient that controls wetland productivity and ecological functions. However, the effects of soil P forms on P availability during wetland degradation are relatively unknown. We selected differently degraded marshes, including non‐degraded marsh (NDM), lightly degraded marsh (LDM), moderately degraded marsh (MDM), and heavily degraded marsh (HDM), to research the changes in soil P forms by sequential chemical extraction and its regulation on P availability in the Zoige Plateau, China. The results showed that compared with the 0–30 cm soil layers of NDM, the main changes in total P concentration were a significant increase of 31.6%–44.2% in LDM and MDM, and the available P concentration increased by 28.7%–76.2% in LDM and MDM but decreased by 4.0%–47.5% in HDM with a lower P activation coefficient. Marsh degradation increased the concentration of soil dicalcium phosphates, P occluded in iron hydroxides, and organic P from the entire profile by 46.7%–137.7%, 31.7%–49.3%, and 78.1%–82.1%, respectively, while it decreased that of iron oxide surface adsorbed P and apatite P by 17.2%–32.2% and 15.3%–27.8%, respectively. Soil available P was mainly related to organic P and P non‐occluded in iron oxide minerals, which might also be a non‐negligible direct source of available P. The transformation from apatite P to organic P was an important regulatory mechanism of P availability in soils during marsh degradation. This study revealed the transformation trajectory of soil P forms owing to soil desiccation accompanied by plant community changes and overgrazing during alpine marsh degradation, and the risk of P limitation in HDMs with low soil available P. For degraded marsh restoration, some measures for improving P availability should be implemented in the future, such as grazing exclusion and the application of organic fertilizer. [ABSTRACT FROM AUTHOR]

Introduction: Soil quality plays an irreplaceable role in plant growth for restored grassland. However, few studies investigate the comprehensive effects considering soil and vegetation properties during the restoration of desertified grassland, which restrict the virtuous circle of restored grassland ecosystem. Methods: By setting three restoration patterns of enclosure plus grass (EG), enclosure intercropping shrub-grass (ESG), and enclosure plus sand-barrier and shrub-grass (ESSG) with three different restoration years (≤5, 7-9, and ≥15 years), we selected 28 physicochemical and microbial indicators, and constructed a minimum data set (MDS) to analyze the influences of restoration measurements on soil quality and ecological benefits in alpine desertified grassland. Results: The results showed that the MDS comprised seven soil quality indicators: silt, total nitrogen (TN), carbon-nitrogen ratio (C/N), total potassium(TK), microbial biomass carbon (MBC), microbial biomass phosphorus (MBP), and fungi. Soil quality index (SQI) and ecological restoration effect index (EREI) in restored grasslands significantly increased by 144.83-561.24% and 87.21-422.12%, respectively, compared with unrestored grassland, and their positive effects increased with extending restoration years. The increasing effects of SQI and EREI were the highest in ESSG, followed by EG and ESG. The increasing rate of SQI began to decrease after 5 years in EG and ESG, while it decreased after 7-9 years in ESSG, and that of EREI in EG was lower than ESSG in each restoration year. Our work revealed that ESSG was the optimum restoration pattern for desertified grassland, and anthropogenic monitoring and management measurements such as applying organic fertilization and mowing return reasonably should be carried out at the beginning of 5 years in EG and ESG as well as 7 years in ESSG tomaintain sustainable ecological benefits. Discussion: The study highlights that soil quality, including microbial properties, is a key factor to evaluate the restoration effects of desertified grassland. [ABSTRACT FROM AUTHOR]

Copyright of Acta Prataculturae Sinica is the property of Acta Prataculturae Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Grasslands play a vital role in the global ecosystem. Efficient and reproducible methods for estimating the grassland aboveground biomass (AGB) are crucial for understanding grassland growth, promoting sustainable development, and assessing the carbon cycle. Currently, the available methods are limited by their computational inefficiency, model transfer, and sampling scale. Therefore, in this study, the estimation of grassland AGB over a large area was achieved by coupling the PROSAIL model with the support vector machine regression (SVR) method. The ill-posed inverse problem of the PROSAIL model was mitigated through kernel-based regularization using the SVR model. The Zoigê Plateau was used as the case study area, and the results demonstrated that the estimated biomass accurately reproduced the reference AGB map generated by zooming in on on-site measurements (R2 = 0.64, RMSE = 43.52 g/m2, RRMSE = 15.13%). The estimated AGB map also maintained a high fitting accuracy with field sampling data (R2 = 0.69, RMSE = 44.07 g/m2, RRMSE = 14.21%). Further, the generated time-series profiles of grass AGB for 2022 were consistent with the trends in local grass growth dynamics. The proposed method combines the advantages of the PROSAIL model and the regression algorithm, reduces the dependence on field sampling data, improves the universality and repeatability of grassland AGB estimation, and provides an efficient approach for grassland ecosystem construction and planning.

Ecological environment is the essential material basis of human survival and connects regional economy with socially sustainable development. However, climate changes characterized by global climate warming have caused a series of ecological environmental problems in recent years. Few studies have discussed various climate factors affecting the ecological environment, and the spatial non-stationary effects of different climate factors on the ecological environment are still unclear. Dynamically monitoring ecological environment changes in fragile areas and identifying its climate-driving mechanism are essential for ecological protection and environmental repair. Taking Zoige Plateau as a case, this paper simulated the eco-environmental quality during 1987–2020 using remote sensing data, utilized Geodetector method to identify the contributions of various climate drivers to ecological environment quality, and then adopted the Geographically Weighted Regression model to explore the spatial non-stationary impacts of climate factors on ecological environment quality. The results showed that the ecological quality in the middle regions of the Zoige Plateau was slightly better than in the surrounding marginal areas. For the whole area of Zoige Plateau, the average ecological environment quality index was 54.92, 53.99, 56.17, 57.88, 63.44, 56.93, 59.43, and 59.76 in 1987, 1992, 1997, 2001, 2006, 2013, 2016 and 2020, respectively, which indicated that eco-environmental quality witnessed several fluctuations during the study period but showed a generally increasing trend. Among five climate factors, the temperature was the dominant climate factor affecting the ecological environment quality (q value: 0.11–0.19), sunshine duration (0.03–0.17), wind speed (0.03–0.11), and precipitation (0.03–0.08) were the main climate drivers, while the explanatory power of relative humidity to ecological environment quality was relatively small. Such various climate factors impacting the ecological environment quality demonstrated distinct spatial non-stationary and the range of driving impact varied with time. Temperature, sunshine duration, wind speed, and relative humidity promoted ecological environment quality in most regions (regression coefficients > 0), while precipitation mainly had a negative inhibitory impact (regression coefficients < 0). Meanwhile, the greater impacts of these five climate factors were concentrated in high-elevation regions of the south and west or the northern areas. The appropriate enhancement of climate warming and air humidity was beneficial to the improvement of the ecological environment, but the excessive precipitation would result in landslides and exhibit inhibition of vegetation growth. Therefore, selecting cold-tolerant herbs and shrubs, and strengthening climate monitoring and early warning systems (such as drought and excessive precipitation) are essential for ecological restoration. [ABSTRACT FROM AUTHOR]

Mountainous peatlands are one of the most important terrestrial ecosystems for carbon storage and play an important role in the global carbon cycle. An insight into the carbon cycle of peat swamps located in mountainous regions can be obtained by studying the distribution of soil organic carbon (SOC) and its relationships with environmental factors. This study focused on the development conditions of peat swamps in the Gahai wetlands, located on the Zoigê Plateau, China, with four different altitudinal gradients as experimental sample sites. The distribution of SOC and its relationship with environmental factors were analysed through vegetation surveys and a generalized additive model (GAM). The results show that with increasing altitude, soil temperature decreased while the soil pH and bulk density initially decreased then increased. On the contrary, the topographic wetness index (TWI), SOC content, above‐ground biomass and litter count initially increased then decreased. The SOC content of the 0–30 cm soil layer was in the range 226–330 g·kg−1 (coefficient of variation (CV) = 21.4%), and the 30–60 cm layer was 178–257 g·kg−1 (CV = 17.5%) and was significantly correlated (p <.05) with above‐ground biomass and litter count. Meanwhile, the SOC content in the 60–90 cm soil layer was in the range 132–167 g·kg−1 (CV = 9.2%) with a significant correlation (p <.05) with soil temperature, pH, bulk density and topographic moisture index. The study showed that the SOC content exhibited more pronounced spatial patterns with increasing altitude, with the peak value in the shallow soil layer appearing in lower elevation areas compared with the deep soil layer. The level of variation changed from medium to low, reflecting the stable mechanism for maintaining SOC within the heterogeneous peat swamp environment. [ABSTRACT FROM AUTHOR]

The artificial drainage and climate drying induced water table decline has resulted in large peat carbon and nitrogen (C&N) loss in peatlands, however, the effects of water table decline on C&N and microbe dynamics at different peat depths are not clear, as well as the effects of plant change and the restoration effects of rewetting. Here we selected a series of sites from undrained (NP), moderate-drained (MDP), deep-drained (DDP) to rewetted (RP) peatlands to study the variations in plants, C&N sequestration, stable isotopic abundances (δ13C and δ15N) and microbial communities at different depths. We found peatland drainage caused moderate degradation in the plant community, and litter greatly preserved the C&N in the 0–10/20 cm peat. Changes in C&N contents, δ13C and δ15N showed MDP had serious C&N loss in both the surface and part of subsurface peat (0-50 cm), and DDP caused more significant C&N loss in the subsurface peat (30-70 cm) than the surface peat (0-30 cm). Drainage changed the bacterial composition: oligotrophs (Acidobacteria) mostly increased, while copiotrophs (Proteobacteria and Bacteroidetes) mostly decreased. The stronger drainage the severer microbe changes, with serious changes in the subsurface peat rather than the surface peat; bacterial metabolic pathways exhibited similar patterns, and the changed pathways were mostly related to C&N metabolism. Long-term rewetting restored the surface C&N contents, δ13C and δ15N to the NP level with plant and litter recovery, whereas, the C&N contents and most of δ13C and δ15N in the subsurface peat were still significantly different from NP. RP had similar bacterial composition, diversity and metabolic pathways as NP in the surface peat, but the similarities between the subsurface microbes were very low. In addition, the taxonomic change, Shannon and Simpson indices of bacterial communities were significantly correlated with peat C&N dynamics during drainage and rewetting, and there were nine phyla dominantly relating to the peat C&N dynamics. Thus, the drainage caused C&N loss and microbial degradation were closely related, which were hard to be restored in the subsurface peat by the long-term rewetting. These indicated the peatlands with severe drainage or drying may consequently lose the stably restored subsurface C&N for a long-term and may have important implications with respect to climate change. [ABSTRACT FROM AUTHOR]

The alpine meadow ecosystems of the Zoige Plateau play important roles in the energy and water cycle of the Qinghai-Tibet Plateau, but observation data of this region regarding to surface energy and water fluxes are very scarce. In this study, annual flux measurements were conducted based on the eddy covariance technique at a typical alpine meadow on the Zoige Plateau by using a three-dimensional sonic anemometer and an infrared open-path carbon dioxide and water vapor analyzer. The surface energy and evapotranspiration (ET) fluxes were calculated at the basis of half-hour. The purpose of this study is to reveal the characteristics and influencing factors of surface energy exchanges and ET. The results are as follows. All energy flux components showed clear diurnal and seasonal variation patterns. The annual mean net radiation, sensible heat, latent heat, and soil heat fluxes were 94.5, 21.0, 51.8 and 1.2Wm-2, respectively. The energy fluxes showed a "single peak" diurnal variation pattern both in the growing season and the non-growing season, despite different peak times for different energy components. During the non-growing season, the sensible heat fluxes were slight larger than the latent heat fluxes, while the latter absolutely dominated during the growing season. The annual mean Bowen ratio and energy closure rate were 0.70 and 0.77, respectively. Radiation was the most important environmental factor that influenced the sensible heat fluxes, while temperature, radiation and water vapor pressure deficit for the latent heat fluxes. The ET fluxes during the growing season were significantly larger than those during the non-growing season. The daily ET fluxes ranged from 0.12 to 5.09mmd-1, and the annual mean value was 1.82mmd-1. Evapotranspiration during the non-growing season is controlled by the surface conductivity; during the growing season it is dominated by the radiation, rather than the surface conductivity of soil and vegetation. On a seasonal scale, the dynamics of ET depended on the seasonal variation of precipitation. The annual accumulated precipitation and ET were 682.7mm and 673.6mm, respectively, of which the growing season accounted for 84% and 82%. The lack of precipitation from June to July constrained the ET fluxes. During this period, soil water storage became the main source of ET. All precipitation finally returned to the atmosphere through ET. In this study, the seasonal variation patterns of the surface energy fluxes and ET were similar to those reported by other measurement studies on the Qinghai-Tibet Plateau. However, the annual mean Bowen ratio and annual accumulated ET were the largest among these studies. Such results were jointly attributed to the effects of temperature, precipitation, surface vegetation and other factors. Data of this study could be used for the parameterization optimization of the land surface models and for the validation of satellite and remote sensing data in the Zoige region. [ABSTRACT FROM AUTHOR]

Purpose: Phytoliths are microscopic particles of amorphous silica produced by plants that have vital importance for environmental change and carbon sequestration. This study investigated phytoliths and their morphotype assemblages, and phytolith-occluded carbon (PhytOC) along a marsh degradation gradient to clarify the significance of phytoliths for evaluating carbon sequestration dynamics during marsh degradation on the Zoige Plateau, China. Materials and methods: Soil samples from non-degraded marsh (NDM), lightly degraded marsh (LDM), moderately degraded marsh (MDM), and seriously degraded marsh (SDM) were collected. Soil phytolith shape and PhytOC were determined using heavy liquid suspension, microscope observations, and alkali-solution spectrophotometry. Results and discussion: The dominant phytolith morphotypes among the 15 identified in the soils from the differently degraded marshes were lanceolate, rectangular, and elongate, which originated from Poaceae and Cyperaceae. Soil phytolith morphotype assemblages show potential for studying past vegetation and climatic succession in alpine wetlands. The soil phytolith and PhytOC content exhibited no significant differences between the NDM and LDM samples. Compared with the NDM soil, phytolith content was significantly lower in the MDM (33.8–58.8%) and SDM (52.7–65.4%) soils, respectively, and PhytOC content was also significantly lower (by 31.0–57.1% and 47.5–74.4%, respectively). The soil phytolith and PhytOC content decreased significantly with soil depth, especially once the marsh has become moderately degraded. Conclusions: Alpine marsh degradation reduced the accumulation of soil PhytOC by decreasing the PhytOC input flux, thereby altering the long-term carbon sequestration mechanism of phytoliths in this alpine-marsh wetland ecosystem. [ABSTRACT FROM AUTHOR]

Zoigê Plateau, China’s largest plateau marsh wetland, has experienced large-scale degradation of the marsh wetland and evolution of the wetland landscape pattern over the past 40 years due to climate warming and human activities. How exactly do the wetland landscape pattern characteristics change? How do climatic change and human activities affect the wetland evolution? These questions are yet to be systematically investigated. In order to investigate changes to the marsh wetland on the Zoigê Plateau, field investigations, spatial and statistical analysis were undertaken. Findings from our study indicate that from 1977–2016, the area of marsh wetland on the Plateau reduced by 56.54%, approximately 66,700 hm2 of marsh wetland has been lost. The centroids of both marsh and marshy meadow migrated and the landscape centroid migration behaviors were also correlated with the distribution and variation of the marsh wetland on different slopes. In addition, the number of marsh landscape patches initially increased before decreasing; the number of marshy meadow landscape patches also recorded an initial increase, followed by a decline before a final increase. As the effects of human activities weakened, the aggregation degrees of both marsh and marshy meadow increased. Overall, the fragmentation degree, diversity and fractal dimension of the marsh wetland all declined. An investigation into the driving factors affecting the Plateau area shows that the increase of annual average temperature was the natural factor while trenching and overgrazing were the main human factors resulting in wetland degradation. Results from this study provide basic data and theoretical foundation for the protection and restoration of marsh wetland in alpine regions.

Alpine grassland of the Tibetan Plateau has undergone severe degradation, even desertification. However, several questions remain to be answered, especially the response mechanisms of vegetation biomass to soil properties. In this study, an experiment on degradation gradients was conducted in an alpine meadow at the Zoige Plateau in 2017. Both vegetation characteristics and soil properties were observed during the peak season of plant growth. The classification and regression tree model (CART) and structural equation modelling (SEM) were applied to screen the main factors that govern the vegetation dynamics and explore the interaction of these screened factors. Both aboveground biomass (AGB) and belowground biomass (BGB) experienced a remarkable decrease along the degradation gradients. All soil properties experienced significant variations along the degradation gradients at the 0.05 significance level. Soil physical and chemical properties explained 54.78% of the variation in vegetation biomass along the degradation gradients. AGB was mainly influenced by soil water content (SWC), soil bulk density (SBD), soil organic carbon (SOC), soil total nitrogen (STN), and pH. Soil available nitrogen (SAN), SOC and pH, had significant influence on BGB. Most soil properties had positive effects on AGB and BGB, while SBD and pH had a slightly negative effect on AGB and BGB. The correlations of SWC with AGB and BGB were relatively less significant than those of other soil properties. Our results highlighted that the soil properties played important roles in regulating vegetation dynamics along the degradation gradients and that SWC is not the main factor limiting plant growth in the humid Zoige region. Our results can provide guidance for the restoration and improvement of degraded alpine grasslands on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ecology & Rural Environment is the property of Journal of Ecology & Rural Environment Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Warming greatly reshapes carbon cycle of peatlands where soil is water saturated with anaerobic condition prevailing all the year round. However, little is known about the response of anaerobic mineralization of peatlands carbon to global warming, especially when considering the difference of soil from above water table (AWT) and below water table (BWT). This study measured variations in soil carbon anaerobic mineralization as a function of warming and depth by sampling 100-cm soil columns in Zoige plateau. Warming enhanced carbon anaerobic mineralization significantly with different increments among the whole depths. The response of CO 2 -C and CH 4 -C to warming varied with depth: at surface soil, both CO 2 -C and CH 4 -C emission increased with higher increment; at deep soil, CO 2 -C emission increased with small increment and CH 4 -C emission decreased. Substrate availability influenced carbon anaerobic mineralization rate and pathway. Substantial resistant carbon at deep soil lowered CO 2 increment and varied CH 4 production pathway. The temperature sensitivity of peat carbon anaerobic mineralization varied with depth, suggesting the heterogeneous distribution of soil substrate among the whole depths. AWT soil was higher in temperature sensitivity than BWT soil for the substantial simple carbon and higher microbial/enzyme activity at AWT. BWT soil was a major contributor of the amount of carbon emission and the total increased carbon caused by warming. Further, for the management of peatlands, we should conduct advanced research by focusing more towards the soil of whole depth, especially on the temperature sensitivity of AWT soil and the contribution to total carbon emission of BWT soil. [ABSTRACT FROM AUTHOR]

As an important part of the wetland ecosystem, alpine wetland is not only one of the most important ecological water conservation areas in the Qinghai–Tibet Plateau region, but is also an effective regulator of the local climate. In this study, using three machine learning algorithms to extract wetland, we employ the landscape ecological index to quantitatively analyze the evolution of landscape patterns and grey correlation to analyze the driving factors of Zoige wetland landscape pattern change from 1995 to 2020. The following results were obtained. (1) The random forest algorithm (RF) performs best when dealing with high-dimensional data, and the accuracy of the decision tree algorithm (DT) is better. The performance of the RF and DT is better than that of the support vector machine algorithm. (2) The alpine wetland in the study area was degraded from 1995 to 2015, whereas wetland area began to increase after 2015. (3) The results of landscape analysis show the decrease in wetland area from 1995 to 2005 was mainly due to the fragmentation of larger patches into many small patches and loss of the original small patches, while the 2005 to 2015 decrease was caused by the loss of many middle patches and the decrease in large patches from the edge to the middle. The 2015 to 2020 increase is due to an increase in the number of smaller patches and recovery of original wetland area. (4) The grey correlation degree further shows that precipitation and evaporation are the main factors leading to the change in the landscape pattern of Zoige alpine wetland. The results are of great significance to the long-term monitoring of the Zoige wetland ecosystem.

Time series remote sensing products with both fine spatial and dense temporal resolutions are urgently needed for many earth system studies. The development of small satellite constellations with identical sensors affords novel opportunities to provide such kind of earth observations. In this paper, a new dense time series 30-m image product was proposed respectively based on an 8-day, 16-day and monthly composition. The products were composited by the Charge Coupled Device (CCD) images from the 2-day revisit small satellite constellation for environmental monitoring and disaster mitigation of China (HJ-1A/B). Taking the Zoige plateau in China as a case area where it is covered by highly heterogeneous vegetation landscapes, a detailed methodology was introduced on how to use 183 scenes of CCD images in 2010 to create composite products. The quality of the HJ CCD composites was evaluated by inter-comparison with the monthly 30-m global Web-Enabled Landsat Data (WELD), 16-day 500-m MODIS NDVI, and 8-day 500-m MODIS surface reflectance products. Results showed that the radiometric consistency between HJ and WELD composited Top Of Atmosphere (TOA) reflectance was in good agreement except for May, June, July and August when more clouds and invalid data gaps appeared in WELD. Visual assessment and temporal profile analysis also revealed that HJ possessed better visual effects and temporal coherence than that of WELD. The comparison between HJ and MODIS products indicated that HJ composites were radiometrically consistent with MODIS products over areas consisting of large patches of homogeneous surface types, but can better reflect the detailed spatial differences in regions with heterogeneous landscapes. This paper highlights the potential of compositing HJ-1A/B CCD images, allowing for providing a cloud free, time-space consistent, 30-m spatial resolution, and dense in time series image product. Meanwhile, the proposed products could also be treated as a reference to generate regional or even global composited products for the on-going satellite constellations and even for the forthcoming satellite missions such as Sentinel-2A/B.

The Zoige Plateau is typical of alpine wetland ecosystems worldwide, which play a key role in regulating global climate and ecological balance. Due to the influence of global climate change and intense human activities, the stability and sustainability of the ecosystems associated with the alpine marsh wetlands are facing enormous threats. It is important to establish a precise risk assessment method to evaluate the risks to alpine wetlands ecosystems, and then to understand the influencing factors of ecological risk. However, the multi-index evaluation method of ecological risk in the Zoige region is overly focused on marsh wetlands, and the smallest units of assessment are relatively large. Although recently developed landscape ecological risk assessment (ERA) methods can address the above limitations, the final directionality of the evaluation results is not clear. In this work, we used the landscape ERA method based on land use and land cover changes (LUCC) to evaluate the ecological risks to an alpine wetland ecosystem from a spatial pixel scale (5 km × 5 km). Furthermore, the boosted regression tree (BRT) model was adopted to quantitatively analyze the impact factors of ecological risk. The results show the following: (1) From 1990 to 2016, the land use and land cover (LULC) types in the study area changed markedly. In particular, the deep marshes and aeolian sediments, and whereas construction land areas changed dramatically, the alpine grassland changed relatively slowly. (2) The ecological risk in the study area increased and was dominated by regions with higher and moderate risk levels. Meanwhile, these areas showed notable spatio-temporal changes, significant spatial correlation, and a high degree of spatial aggregation. (3) The topographic distribution, climate changes and human activities influenced the stability of the study area. Elevation (23.4%) was the most important factor for ecological risk, followed by temperature (16.2%). Precipitation and GDP were also seen to be adverse factors affecting ecological risk, at levels of 13.0% and 12.1%, respectively. The aim of this study was to provide more precise and specific support for defining conservation objectives, and ecological management in alpine wetland ecosystems.

Introduction: Soil quality plays an irreplaceable role in plant growth for restored grassland. However, few studies investigate the comprehensive effects considering soil and vegetation properties during the restoration of desertified grassland, which restrict the virtuous circle of restored grassland ecosystem., Methods: By setting three restoration patterns of enclosure plus grass (EG), enclosure intercropping shrub-grass (ESG), and enclosure plus sand-barrier and shrub-grass (ESSG) with three different restoration years (≤5, 7-9, and ≥15 years), we selected 28 physicochemical and microbial indicators, and constructed a minimum data set (MDS) to analyze the influences of restoration measurements on soil quality and ecological benefits in alpine desertified grassland., Results: The results showed that the MDS comprised seven soil quality indicators: silt, total nitrogen (TN), carbon-nitrogen ratio (C/N), total potassium (TK), microbial biomass carbon (MBC), microbial biomass phosphorus (MBP), and fungi. Soil quality index (SQI) and ecological restoration effect index (EREI) in restored grasslands significantly increased by 144.83-561.24% and 87.21-422.12%, respectively, compared with unrestored grassland, and their positive effects increased with extending restoration years. The increasing effects of SQI and EREI were the highest in ESSG, followed by EG and ESG. The increasing rate of SQI began to decrease after 5 years in EG and ESG, while it decreased after 7-9 years in ESSG, and that of EREI in EG was lower than ESSG in each restoration year. Our work revealed that ESSG was the optimum restoration pattern for desertified grassland, and anthropogenic monitoring and management measurements such as applying organic fertilization and mowing return reasonably should be carried out at the beginning of 5 years in EG and ESG as well as 7 years in ESSG to maintain sustainable ecological benefits., Discussion: The study highlights that soil quality, including microbial properties, is a key factor to evaluate the restoration effects of desertified grassland., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Li, Hu, Lang, Pu, Zhang, Li, Xu, Jia, Wang, Yuan and Li.)

Warming and human activities have caused peatland degradation and water table drawdown, which greatly influence the physicochemical characteristics of soil at different depths. How water table drawdown affects soil physicochemical characteristics is not well understood for the Tibetan Plateau, especially the Zoige peatlands. This study measured variations in C/N ratio, ash content, δ 13 C, and humification index (HI) as a function of water table drawdown and depth by sampling 100-cm soil columns from three sites with different water tables in the Zoige peatlands. C/N ratio decreased while ash content and HI increased with water table drawdown, suggesting greater decomposition of soil organic matter at sites with a lower water table. The response of soil physicochemical characteristics to water table drawdown varied with depth: in the layer above the water table, C/N ratio did not vary, ash content decreased and HI increased; in the layer below the water table, C/N ratio and HI decreased, while ash content increased. The physicochemical characteristics above the water table were influenced mainly by new carbon input, while the characteristics below the water table were influenced mainly by decomposition. The depth profile of C/N ratio, ash content and HI aligned well with peat formation and decomposition and may be indicators of peat degradation. δ 13 C did not vary with water table drawdown, depth, or decomposition process. These insights into the variation of soil physicochemical characteristics with depths and water table may help elucidate the processes behind peatland degradation. [ABSTRACT FROM AUTHOR]

Accurate wetland delineation is the basis of wetland definition and mapping, and is of great importance for wetland management and research. The Zoigê Plateau on the Qinghai-Tibet Plateau was used as a research site for research on alpine wetland delineation. Several studies have analyzed the spatiotemporal pattern and dynamics of these alpine wetlands, but none have addressed the issues of wetland boundaries. The objective of this work was to discriminate the upper boundaries of alpine wetlands by coupling ecological methods and satellite observations. The combination of Landsat 8 images and supervised classification was an effective method for rapid identification of alpine wetlands in the Zoigê Plateau. Wet meadow was relatively stable compared with hydric soils and wetland hydrology and could be used as a primary indicator for discriminating the upper boundaries of alpine wetlands. A slope of less than 4.5° could be used as the threshold value for wetland delineation. The normalized difference vegetation index (NDVI) in 434 field sites showed that a threshold value of 0.3 could distinguish grasslands from emergent marsh and wet meadow in September. The median normalized difference water index (NDWI) of emergent marsh remained more stable than that of wet meadow and grasslands during the period from September until July of the following year. The index of mean density in wet meadow zones was higher than the emergent and upland zones. Over twice the number of species occurred in the wet meadow zone compared with the emergent zone, and close to the value of upland zone. Alpine wetlands in the three reserves in 2014 covered 1175.19 km with a classification accuracy of 75.6%. The combination of ecological methods and remote sensing technology will play an important role in wetland delineation at medium and small scales. The correct differentiation between wet meadow and grasslands is the key to improving the accuracy of future wetland delineation. [ABSTRACT FROM AUTHOR]

Peatlands are one of the major natural sources of methane (CH), but the level of CH efflux is uncertain, especially in alpine peatlands. In this study, CH emission fluxes from natural and drained peatlands on the Qinghai-Tibet Plateau, southwest China, were measured from June to October in 2013 using the opaque static chamber technique and the Fast Greenhouse Gas Analyzer (DLT-100, Los Gatos Research Corp.). CH emission fluxes ranged from 2.07 to 56.33 mg m h in natural peatlands and from 0.02 to 0.42 mg m h in drained peatlands. Mean CH emission flux was 19.13 mg m h in natural peatlands and 0.14 mg m h in drained peatlands. These results showed that drainage led to a significant decrease in CH emissions. CH emission fluxes for all sampling plots were significantly correlated with variation in water table depth for linear ( R = 0.453, P < 0.01) and exponential functions ( R = 0.429, P < 0.01). [ABSTRACT FROM AUTHOR]

Wetland inundation is crucial to the survival and prosperity of fauna and flora communities in wetland ecosystems. Even small changes in surface inundation may result in a substantial impact on the wetland ecosystem characteristics and function. This study presented a novel method for wetland inundation mapping at a subpixel scale in a typical wetland region on the Zoige Plateau, northeast Tibetan Plateau, China, by combining use of an unmanned aerial vehicle (UAV) and Landsat-8 Operational Land Imager (OLI) data. A reference subpixel inundation percentage (SIP) map at a Landsat-8 OLI 30 m pixel scale was first generated using high resolution UAV data (0.16 m). The reference SIP map and Landsat-8 OLI imagery were then used to develop SIP estimation models using three different retrieval methods (Linear spectral unmixing (LSU), Artificial neural networks (ANN), and Regression tree (RT)). Based on observations from 2014, the estimation results indicated that the estimation model developed with RT method could provide the best fitting results for the mapping wetland SIP (R² = 0.933, RMSE = 8.73%) compared to the other two methods. The proposed model with RT method was validated with observations from 2013, and the estimated SIP was highly correlated with the reference SIP, with an R² of 0.986 and an RMSE of 9.84%. This study highlighted the value of high resolution UAV data and globally and freely available Landsat data in combination with the developed approach for monitoring finely gradual inundation change patterns in wetland ecosystems. [ABSTRACT FROM AUTHOR]

The wetlands on the Zoige Plateau have experienced serious degradation, with most of the original marsh being converted to marsh meadow or meadow. Based on the 3 wetland degradation stages, we determined the effects of wetland degradation on the structure and relative abundance of nitrogen-cycling (nitrogen-fixing, ammonia-oxidizing, and denitrifying) microbial communities in 3 soil types (intact wetland: marsh soil; early degrading wetland: marsh meadow soil; and degraded wetland: meadow soil) using 454-pyrosequencing. The structure and relative abundance of nitrogen-cycling microbial communities differed in the 3 soil types. Proteobacteria was the predominant phylum in most soil samples but the most abundant soil nitrogen-fixing and denitrifying microbial bacteria differed at the class, order, family, and genus levels among the 3 soil types. At the genus level, the majority of nitrogen-fixing bacterium sequences related to Bradyrhizobium were from marsh and marsh meadow soils; whereas those related to Geobacter originated from meadow soil. The majority of ammonia-oxidizing bacterium sequences related to Nitrosospira were from marsh (except for the 40-60 cm layer), marsh meadow and meadow soils; whereas those related to Candidatus Solibacter originated from 40-60 cm layer of marsh soil. The majority of denitrifying bacterium sequences related to Candidatus Solibacter and Anaeromyxobacter were from marsh and meadow soils; whereas those related to Herbaspirillum originated from meadow soil. The distribution of operational taxonomic units (OTUs) and species were correlated with soil type based upon Venn and Principal Coordinates Analysis (PCoA). Changes in soil type, caused by different water regimes were the most important factors influencing compositional changes in the nitrogen-fixing, ammonia-oxidizing, and denitrifying microbial communities. [ABSTRACT FROM AUTHOR]

Although mathematical models (e.g., DeNitrification and DeComposition (DNDC) provide a powerful tool to study regional carbon budget, it is still difficult to obtain accurate simulation results because there exists large uncertainties in modeling regional carbon budget. Through the investigation on the sensitivity of model output parameters to the input parameters, sensitivity analysis (SA) has been proved to be able to identify the key sources of uncertainties and be helpful to reduce the model uncertainties. However, some input parameters with discrete values (e.g., land use type and soil type) and the regional effect of the sensitive parameters were rarely examined in SA. In this paper, taking the Zoige Plateau as a case area, we combined the one-factor-at-a-time (OAT) with Extended Fourier Amplitude Sensitivity Test (EFAST) to conduct a SA of DNDC for simulating the regional carbon budget, including Gross Primary Productivity (GPP), Net Primary Productivity (NPP), Net Ecosystem Productivity (NEP), autotrophic respiration (Ra), soil microbial heterotrophic respiration (Rh) and ecosystem respiration (Re). The result showed that the combination of OAT and EFAST could test the contribution of the input parameters with discrete values to the output parameters. In DNDC model, land use type and soil type had a significant impact on the regional carbon budget of the Zoige Plateau, and daily temperature was also confirmed to be one of the most important parameters for carbon budget. For the other input parameters, with the change of land use type or soil type at regional scale, the sensitive parameters of carbon budget would vary accordingly. The SA results would provide scientific evidence to optimize DNDC model and they suggested that we should pay attention to the spatial/temporal effect of SA and try to use the appropriate data in simulation of the regional carbon budget. [ABSTRACT FROM AUTHOR]

Warming and water table drawdown greatly reshape peatland carbon cycle, especially when considering the old carbon stored under the peatland subsurface. However, little is known about the effects of warming, oxidizing by drying or their combination on carbon decomposition at different depths (0–100 cm) of peat. In this research, soil of different depths from Zoige Plateau was incubated in four scenarios (8 °C-anaerobic, 8 °C-aerobic, 18 °C-anaerobic and 18 °C-aerobic) to detect the exported carbon. Our result showed that soil respiration (Rs) increased obviously with enhanced temperature and oxygen. The total CO 2 fluxes of 2400.22 ± 57.69 mg m -2 d -1 under 8 °C-anaerobic condition increased by 73.6%, 40.7% and 176.5% with warming, oxidizing and their combined effect, respectively. The average dissolved organic carbon (DOC) concentration was 74.90 ± 8.09 mg kg -1 under 8 °C-anaerobic condition, but increased by 53.5%, 44% and 159.4%, respectively under the condition of warming, oxidizing and their combination. Rs and its variation under warming and oxidization differed significantly among different depths, probably caused by the differences of soil substrate, especially the variation in distribution of soil microbes and enzymes among depths of peatlands. By classifying the source of Rs as young soil (YS: 0–20 cm) and old soil (OS: 21–100 cm), this reseaerch found that OS accounted for a huge part of total Rs under 8 °C-anaerobic condition (CO 2 : 74.2%; DOC: 60.7%). Such relative contribution of OS to total Rs did not change obviously with warming or oxidizing. Though YS and OS responded equally to warming and oxidizing, OS was responsible for a larger proportion of total increase in Rs. Compared with other studies, we concluded that peatlands soil in our field of mid-latitude and high altitude is less sensitive to warming and oxidizing than peatlands of higher latitude, but that OS of this peatlands is more critical in predicting regional carbon cycle. [ABSTRACT FROM AUTHOR]

Measuring the impact of livestock grazing on grassland above-ground net primary production (ANPP) is essential for grass yield estimation and pasture management. However, since there is a lack of accurate and repeatable techniques to obtain the details of grazing locations and stocking rates at the regional scale, it is an extremely challenging task to study the influence of regional grazing on the grassland ANPP. Taking Zoige County as a case, this paper proposes an approach to quantify the spatial and temporal variation of grazing intensity and grazing period through time-series remote sensing data, simulated grassland ANPP through the denitrification and decomposition (DNDC) model, and then explores the impact of grazing on grassland ANPP. The result showed that the model-estimated ANPP while considering grazing had a significant relationship with the field-observed ANPP, with the coefficient of determination (R²) of 0.75, root mean square error (RMSE) of 122.86 kgC/ha, and average relative error (RE) of 8.77%. On the contrary, if grazing activity was not considered in simulation, a large uncertainty was found when the model-estimated ANPP was compared with the field observation, showing R² of 0.4, RMSE of 211.51 kgC/ha, and average RE of 32.5%. For the whole area of Zoige County in 2012, the statistics of the estimation showed that the total regional ANPP was up to 3.815 × 105 tC, while the total regional ANPP, without considering grazing, would be overestimated by 44.4%, up to 5.51 × 105 tC. This indicates that the grazing parameters derived in this study could effectively improve the accuracy of ANPP simulation results. Therefore, it is feasible to combine time-series remote sensing data with the process model to simulate the grazing effects on grassland ANPP. However, some issues, such as selecting proper remote sensing data, improving the quality of model input parameters, collecting more field data, and exploring the data assimilation approaches, still should be considered in the future work. [ABSTRACT FROM AUTHOR]

Time series remote sensing products with both fine spatial and dense temporal resolutions are urgently needed for many earth system studies. The development of small satellite constellations with identical sensors affords novel opportunities to provide such kind of earth observations. In this paper, a new dense time series 30-m image product was proposed respectively based on an 8-day, 16-day and monthly composition. The products were composited by the Charge Coupled Device (CCD) images from the 2-day revisit small satellite constellation for environmental monitoring and disaster mitigation of China (HJ-1A/B). Taking the Zoige plateau in China as a case area where it is covered by highly heterogeneous vegetation landscapes, a detailed methodology was introduced on how to use 183 scenes of CCD images in 2010 to create composite products. The quality of the HJ CCD composites was evaluated by inter-comparison with the monthly 30-m global Web-Enabled Landsat Data (WELD), 16-day 500-m MODIS NDVI, and 8-day 500-m MODIS surface reflectance products. Results showed that the radiometric consistency between HJ and WELD composited Top Of Atmosphere (TOA) reflectance was in good agreement except for May, June, July and August when more clouds and invalid data gaps appeared in WELD. Visual assessment and temporal profile analysis also revealed that HJ possessed better visual effects and temporal coherence than that of WELD. The comparison between HJ and MODIS products indicated that HJ composites were radiometrically consistent with MODIS products over areas consisting of large patches of homogeneous surface types, but can better reflect the detailed spatial differences in regions with heterogeneous landscapes. This paper highlights the potential of compositing HJ-1A/B CCD images, allowing for providing a cloud free, time-space consistent, 30-m spatial resolution, and dense in time series image product. Meanwhile, the proposed products could also be treated as a reference to generate regional or even global composited products for the on-going satellite constellations and even for the forthcoming satellite missions such as Sentinel-2A/B. [ABSTRACT FROM AUTHOR]

Exploring the suitable ecological niche environment for endangered species is essential to maintaining biodiversity and protecting endangered species. The Black-necked Cranes is considered as the environmental indicator and flagship species of the alpine wetland ecosystem, and has been listed as a vulnerable species by the IUCN (International Union for Conservation of Nature) several times. Nearly one-third of the world's Black-necked Cranes breed on the Zoige Plateau. However, no systematic studies have been conducted on the land cover patterns and habitat suitability of their breeding sites. In this study, the fine remote sensing land cover data from 2000 to 2015 and GIS technology were applied to establish habitat suitability index of Black-necked Cranes. Besides, the spatial autocorrelation analysis, geographical detector model and random forest algorithm were used to analyze and discuss the spatial distribution characteristics of habitat suitability and their main climatic drivers on breeding sites. The main results show the following: 1) Marsh wetlands, the dominant land cover types for Black-necked Cranes breeding, which showed a decreasing trend from 2000 to 2005 and an increasing trend from 2005 to 2015, with mainly converting to grassland; the reverse conversion rate of grassland, marsh wetlands, and water body was greater than the positive conversion rate for all three periods; the landscape pattern of most land types increased in fragmentation and decreased in agglomeration and connectivity from 2000 to 2015. 2) Suitable regions (highly-suitable and sub-suitable) accounted for between 11.62 and 13.84% of the total, with a gradual increase in the area of highly suitable regions over the three periods; the Moran's I indices were all greater than 0.80 from 2000 to 2015, indicating high positive spatial autocorrelation of habitat suitability and significant spatial clustering characteristics. 3) Climate influences the breeding habitat of Black-necked Cranes, with the main factors ranked as follows (power of determinant, PD > 0.165): precipitation from May to September > mean temperature from October to November > minimum temperature in November > annual precipitation > annual mean temperature; the interaction effects of climate factors include mutual and non-linear enhancement, with the largest PD value reaching 0.358 for the interaction between precipitation from May to September and November maximum temperature. The research aims to provide scientific evidence for the safe local breeding of Black-necked Cranes and biodiversity conservation in alpine wetland ecosystems. • The driving mechanisms of climatic factors on habitat suitability were analyzed using geographical detector and random forest algorithm. • By 2015, the water conditions had improved, with the area of marsh wetlands returning to 2000 levels. • There has been a gradual increase in the area of highly suitable region from 2000 to 2015. [ABSTRACT FROM AUTHOR]

As an important part of the wetland ecosystem, alpine wetland is not only one of the most important ecological water conservation areas in the Qinghai–Tibet Plateau region, but is also an effective regulator of the local climate. In this study, using three machine learning algorithms to extract wetland, we employ the landscape ecological index to quantitatively analyze the evolution of landscape patterns and grey correlation to analyze the driving factors of Zoige wetland landscape pattern change from 1995 to 2020. The following results were obtained. (1) The random forest algorithm (RF) performs best when dealing with high-dimensional data, and the accuracy of the decision tree algorithm (DT) is better. The performance of the RF and DT is better than that of the support vector machine algorithm. (2) The alpine wetland in the study area was degraded from 1995 to 2015, whereas wetland area began to increase after 2015. (3) The results of landscape analysis show the decrease in wetland area from 1995 to 2005 was mainly due to the fragmentation of larger patches into many small patches and loss of the original small patches, while the 2005 to 2015 decrease was caused by the loss of many middle patches and the decrease in large patches from the edge to the middle. The 2015 to 2020 increase is due to an increase in the number of smaller patches and recovery of original wetland area. (4) The grey correlation degree further shows that precipitation and evaporation are the main factors leading to the change in the landscape pattern of Zoige alpine wetland. The results are of great significance to the long-term monitoring of the Zoige wetland ecosystem. [ABSTRACT FROM AUTHOR]

Soil biological nitrogen fixation (BNF) represents a major pathway through which nitrogen enters pristine peatlands. Many peatlands have been undergoing human-induced changes in environmental factors, while environmental changes dramatically affect the community composition and activity of nitrogen-fixing prokaryotes (i.e., diazotrophs). However, the impact of peatland degradation on soil BNF remains unclear. By carrying out a field campaign, we examined how soil BNF varies along a natural gradient from pristine marshes to moderately-degraded meadows and sandy meadows on the Zoige Plateau. Plant and topsoil samples from four pristine marshes, three moderately-degraded meadows, and three sandy meadows were collected to determine the potential rate of nitrogen fixation (R Nfix), abundance of the nifH gene, diazotrophic community composition, and soil and plant characteristics. Our results showed that topsoil R Nfix varied in the range 0.018–3.00 μmol N g d.w.−1 day−1 (i.e. 21.74–1632.37 mg N m−2 day−1) across the ten sites, being lowest in sandy meadows and highest in pristine marshes. Topsoil R Nfix and diazotrophic abundance were positively correlated with soil water content, sedge cover, plant biomass, soil organic carbon content, and total nitrogen and phosphorus contents. Soil water content, which affected most plant and soil characteristics, had dominant influences on the abundance and community structure of diazotrophs. The R Nfix was closely correlated with the abundance of dominant diazotroph groups. The community composition of diazotrophs differed markedly among sites of different degradation levels. Proteobacteria was the most abundant diazotrophic phylum across the ten sites. Heterotrophic diazotrophs acted as the major contributor to BNF, especially in pristine marshes and moderately-degraded meadows. We conclude that soil water content was the main factor driving the depressed soil BNF during peatland degradation in Zoige, due to soil water effects on plant cover and biomass, soil organic carbon and total phosphorus, and the abundance and community structure of diazotrophs. Unlabelled Image • Peatland degradation depressed biological N 2 fixation in topsoil in Zoige. • Decreased soil water content was mainly responsible for depressed N 2 fixation. • Plants, soil nutrients and diazotrophs jointly regulated the N 2 fixation rate. • Heterotrophs were the main N 2 fixer at pristine and moderately-degraded sites. [ABSTRACT FROM AUTHOR]

• Soil and plant characteristics fist abruptly changed and then become relatively stable along the degradation gradients. • The turning points were observed in the third or fourth gradients of the degraded alpine meadow. • Soil water content is a sensitive indicator of alpine meadow degradation at Zoige. • Short-term grazing exclusion (GE) can effectively restore grasslands at Zoige. • The restoring efficiency of GE is highest at light shifting to moderate degradation stage. Grassland degradation has profound negative impacts on ecological functions, local economic development, and social stability. Although there are many studies on the alpine grassland degradation in the Tibetan Plateau, the variation in the response of alpine meadows to degradation and restoration processes, and the underlying mechanisms remain poorly understood. To explore these issues, we selected nine grassland degradation levels along an increasing gradient at Zoige in the Tibetan Plateau, and collected vegetation and soil samples in August 2017 and 2018 to assess the state of the grassland before and after grazing exclusion (GE), respectively. The results showed that above-ground biomass (AGB), below-ground biomass (BGB), Shannon–Wiener index, soil water content (SWC), soil organic carbon (SOC), total nitrogen (STN), and total phosphorus decreased gradually with severe degrees of degradation, whereas soil bulk density and pH increased. SWC in the topsoil presented the sharpest change in slope along the degradation gradient, indicating that SWC was a sensitive indicator of alpine meadow degradation in this area. One-year GE evidently increased SWC, SOC, STN, AGB, and BGB in lightly and moderately degraded grasslands. The restoration efficiency of GE first increased and then decreased along the degradation gradient, with the turning point appearing at the third or fourth degradation level. Based on these results, we can conclude that short-term GE is an effective method for grassland restoration in this humid area, and should be performed at the shift from light to moderate degradation stages when the efficiency of recovery is the highest. These findings could facilitate a better approach for the restoration of degraded alpine meadow ecosystems. [ABSTRACT FROM AUTHOR]

The Zoige Plateau is typical of alpine wetland ecosystems worldwide, which play a key role in regulating global climate and ecological balance. Due to the influence of global climate change and intense human activities, the stability and sustainability of the ecosystems associated with the alpine marsh wetlands are facing enormous threats. It is important to establish a precise risk assessment method to evaluate the risks to alpine wetlands ecosystems, and then to understand the influencing factors of ecological risk. However, the multi-index evaluation method of ecological risk in the Zoige region is overly focused on marsh wetlands, and the smallest units of assessment are relatively large. Although recently developed landscape ecological risk assessment (ERA) methods can address the above limitations, the final directionality of the evaluation results is not clear. In this work, we used the landscape ERA method based on land use and land cover changes (LUCC) to evaluate the ecological risks to an alpine wetland ecosystem from a spatial pixel scale (5 km × 5 km). Furthermore, the boosted regression tree (BRT) model was adopted to quantitatively analyze the impact factors of ecological risk. The results show the following: (1) From 1990 to 2016, the land use and land cover (LULC) types in the study area changed markedly. In particular, the deep marshes and aeolian sediments, and whereas construction land areas changed dramatically, the alpine grassland changed relatively slowly. (2) The ecological risk in the study area increased and was dominated by regions with higher and moderate risk levels. Meanwhile, these areas showed notable spatio-temporal changes, significant spatial correlation, and a high degree of spatial aggregation. (3) The topographic distribution, climate changes and human activities influenced the stability of the study area. Elevation (23.4%) was the most important factor for ecological risk, followed by temperature (16.2%). Precipitation and GDP were also seen to be adverse factors affecting ecological risk, at levels of 13.0% and 12.1%, respectively. The aim of this study was to provide more precise and specific support for defining conservation objectives, and ecological management in alpine wetland ecosystems. [ABSTRACT FROM AUTHOR]

Land use/land cover change (LUCC) is the most direct driving force of landscape pattern change. The Zoige Plateau is a natural ecosystem with the largest high-altitude swamp wetland in China and its land use pattern has undergone great changes in recent years, but how the changes of each land use type affect the landscape pattern is uncertain. Here, we used the object-oriented method to extract land use information in 2015. Then, combined with land use data, the land use change characteristics from 2000 to 2015 were analyzed. We used the correlation analysis method to analyze the effects of land use changes on landscape pattern systematically. Three key conclusions were reached. (1) Land use information for the Zoige Plateau could be extracted with high accuracy by combining the object-oriented method and support vector machine (SVM). The overall accuracy was 93.2% and the Kappa coefficient was 0.889. (2) The comprehensive dynamic degree of land use was the highest from 2010 to 2015. From 2000 to 2015, the wetland area decreased the fastest because 57.05% of the wetlands were transferred out. Construction land increased the fastest, and the transferred in area from grassland and farmland were the main reason. (3) The effects of unused land, farmland, and construction land on the overall landscape pattern were stronger than that of the other types, among which farmland had the most significant impact (with a correlation coefficient of 0.959, p < 0.001). The change of unused land was the most highly significant factor associated with the landscape area pattern, and both the water body and unused land showed strong correlations with landscape shape pattern change. This suggested that the effects of land use types occupying a relatively small area on the landscape pattern were intensified. This study will provide guidance for the environmental management of local land resources and other natural ecosystem areas. [ABSTRACT FROM AUTHOR]

The belowground bud bank plays an important role in plant communities succession and maintenance. In order to understand the response of the bud bank to the sod layer moisture, we investigated the bud bank distribution, size, and composition of six different water gradient alpine meadows through excavating in the Zoige Plateau. The results showed: (1) The alpine meadow plant belowground buds were mainly distributed in the 0–10 cm sod layer, accounting for 74.2%–100% of the total. The total bud density of the swamp wetland and degraded meadow was the highest (16567.9 bud/m3) and the lowest (4839.5 bud/m3). (2) A decrease of the moisture plant diversity showed a trend of increasing first and then decreasing. Among six alpine meadows the swamp meadow plant diversity was the highest, and species richness, Simpson, Shannon–Wiener, and Pielou were 10.333, 0.871, 0.944, and 0.931, respectively. (3) The moisture was significantly positively correlated with the total belowground buds and short rhizome bud density. There were significant positive correlations with sod layer moisture and tiller bulb bud density. This study indicates that the moisture affected bud bank distribution and composition in the plant community, and the results provide important information for predicting plant community succession in the alpine meadow with future changes in precipitation patterns. [ABSTRACT FROM AUTHOR]