101 research outputs found

    Plant functional trait diversity regulates the nonlinear response of productivity to regional climate change in Tibetan alpine grasslands

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    The biodiversity-productivity relationship is still under debate for alpine grasslands on the Tibetan Plateau. We know little about direct and indirect effects of biotic and abiotic drivers on this relationship, especially in regard to plant functional trait diversity. Here, we examine how aboveground net primary productivity (ANPP) and precipitation use efficiency (PUE) respond to climate, soil and community structure across alpine grasslands on the Northern Tibetan Plateau. We found that both ANPP and PUE showed nonlinear patterns along water availability and site altitude variation, which together accounted for 80.3% and 68.8% of variation in ANPP and PUE, respectively, by optimal generalized additive models. Functional trait divergence (FTD) and community weighted mean (CWM) of plant functional traits were as important as plant species diversity (PSD) for explaining the nonlinear productivity- climate relationship. These findings were confirmed by results from principal component analyses and structural equation models. We also found that FTD was negatively correlated with PSD across different alpine grasslands. Our results implicate: first, the combinatorial influences of temperature and precipitation gradients are important for predicting alpine grassland dynamics; second, the convergence and divergence of plant functional traits may have the potential to elucidate the effect of plant diversity on ecosystem functionality

    Changes in plant species richness distribution in Tibetan alpine grasslands under different precipitation scenarios

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    Species richness is the core of biodiversity-ecosystem functioning (BEF) research. Nevertheless, it is difficult to accurately predict changes in plant species richness under different climate scenarios, especially in alpine biomes. In this study, we surveyed plant species richness from 2009 to 2017 in 75 alpine meadows (AM), 199 alpine steppes (AS), and 71 desert steppes (DS) in the Tibetan Autonomous Region, China. Along with 20 environmental factors relevant to species settlement, development, and survival, we first simulated the spatial pattern of plant species richness under current climate conditions using random forest modelling. Our results showed that simulated species richness matched well with observed values in the field, showing an evident decrease from meadows to steppes and then to deserts. Summer precipitation, which ranked first among the 20 environmental factors, was further confirmed to be the most critical driver of species richness distribution. Next, we simulated and compared species richness patterns under four different precipitation scenarios, increasing and decreasing summer precipitation by 20% and 10%, relative to the current species richness pattern. Our findings showed that species richness in response to altered precipitation was grassland-type specific, with meadows being sensitive to decreasing precipitation, steppes being sensitive to increasing precipitation, and deserts remaining resistant. In addition, species richness at low elevations was more sensitive to decreasing precipitation than to increasing precipitation, implying that droughts might have stronger influences than wetting on species composition. In contrast, species richness at high elevations (also in deserts) changed slightly under different precipitation scenarios, likely due to harsh physical conditions and small species pools for plant recruitment and survival. Finally, we suggest that policymakers and herdsmen pay more attention to alpine grasslands in central Tibet and at low elevations where species richness is sensitive to precipitation changes

    Identifying the Relative Contributions of Climate and Grazing to Both Direction and Magnitude of Alpine Grassland Productivity Dynamics from 1993 to 2011 on the Northern Tibetan Plateau

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    Alpine grasslands on the Tibetan Plateau are claimed to be sensitive and vulnerable to climate change and human disturbance. The mechanism, direction and magnitude of climatic and anthropogenic influences on net primary productivity (NPP) of various alpine pastures remain under debate. Here, we simulated the potential productivity (with only climate variables being considered as drivers; NPPP) and actual productivity (based on remote sensing dataset including both climate and anthropogenic drivers; NPPA) from 1993 to 2011. We denoted the difference between NPPP and NPPA as NPPpc to quantify how much forage can be potentially consumed by livestock. The actually consumed productivity (NPPac) by livestock were estimated based on meat production and daily forage consumption per standardized sheep unit. We hypothesized that the gap between NPPpc and NPPac (NPPgap) indicates the direction of vegetation dynamics, restoration or degradation. Our results show that growing season precipitation rather than temperature significantly relates with NPPgap, although warming was significant for the entire study region while precipitation only significantly increased in the northeastern places. On the Northern Tibetan Plateau, 69.05% of available alpine pastures showed a restoration trend with positive NPPgap, and for 58.74% of alpine pastures, stocking rate is suggested to increase in the future because of the positive mean NPPgap and its increasing trend. This study provides a potential framework for regionally regulating grazing management with aims to restore the degraded pastures and sustainable management of the healthy pastures on the Tibetan Plateau. View Full-Tex

    Effect of Land Cultivation on Soil Nutrient Sedimentation in Water at Southern China

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    Soil erosion associated with land cultivation exerts a great impact on ecological environment. Such an impact is specific of land, crop, tillage, management and so on. This study aimed to investigate the effects of crop cultivation on water quality by comparing nutrient distribution in the sediment at Southern China. Two sedimentation sites adjacent to the uncultivated (S1) and cultivated upland (S2) were selected and samples were analyzed. Results showed that soil pH decreased with the increasing depth above 20 cm and then kept relatively stable of the both sediments. Soil organic matter, nitrogen and phosphorus contents decreased with the increasing depth. There was no significant difference between two sediments in organic matter and nitrogen contents, but the total phosphorus and extractable phosphorus contents in S2 were much higher than that in S1. The data indicated that soil eroded from S2 could possess much high potential to deteriorate water quality. Nutrient sedimentation can reflect the history of soil erosion and provide useful information for sustainable soil management and water conservation through improving cultivation and tillage measures

    Climate Variability Rather Than Livestock Grazing Dominates Changes in Alpine Grassland Productivity Across Tibet

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    Alpine grasslands on the Tibetan Plateau, being vulnerable to environmental and anthropogenic changes, have experienced dramatic climate change and intensive livestock grazing during the last half-century. Climate change, coupled with grazing activities, has profoundly altered alpine grassland function and structure and resulted in vast grassland degradation. To restore degraded grasslands, the Central Government of China has implemented the Ecological Security Barrier Protection and Construction Project since 2008 across the Tibetan Autonomous Region. However, the relative effect of climate change and grazing activities on the variation in alpine grassland productivity is still under debate. In this study, we quantified how aboveground net primary production (ANPP) varied before (2000-2008) and after (2009-2017) starting the project across different alpine grasslands and how much variance in ANPP could be attributed to climate change and grazing disturbance, in terms of temperature, precipitation, solar radiation, and grazing intensity. Our results revealed that Tibet's climate got warmer and wetter, and grazing intensity decreased after starting the project. Mean ANPP increased at approximately 81% of the sites, on average from 27.0 g C m(-2) during 2000-2008 to 28.4 g C m(-2) during 2009-2017. The ANPP positively correlated with annual temperature and precipitation, but negatively with grazing intensity for both periods. Random forest modeling indicated that grazing intensity (14.5%) had a much lower influence in controlling the dynamics of grassland ANPP than precipitation (29.0%), suggesting that precipitation variability was the key factor for alpine grassland ANPP increase across Tibet

    Grazing Exclusion to Recover Degraded Alpine Pastures Needs Scientific Assessments across the Northern Tibetan Plateau

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    The northern Tibetan Plateau is the most traditional and important semi- nomadic region in Tibet. The alpine vegetation is sensitive and vulnerable to climate change and human activities, and is also important as an ecological security in protecting the headwaters of major rivers in Asia. Therefore, the Tibetan alpine grasslands have fundamental significance to both Mainland China and South Asia. The pasture degradation, however, likely threatens the livelihood of residents and the habitats of wildlife on this plateau. Since 2004, the government has launched a series of ecological restoration projects and economic compensatory payment polices. Many fences were additionally built on degraded pastures to prevent new degradation, to promote functionality recovery, and to balance the stocking rate with forage productivity. The grazed vs. fenced paired pastures across different zonal grassland communities along evident environmental gradients provide us with a natural comparative experiment platform to test the relative contributions of natural and anthropogenic factors. This study critically reviews the background, significance of and debates on short-term grazing exclusion with fences in this region. We also aim to figure out scientific and standardized workflows for assessing the effectiveness of grazing exclusion and compensatory payments in the future. View Full-Tex

    Two new species of Diphya Nicolet, 1849 (Araneae, Tetragnathidae) from Southwest China

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    Two new species of tetragnathid spiders from Guizhou and Sichuang provinces of China are described: Diphya guiyang J. Zhang & H. Yu, sp. nov. (♂♀) and Diphya weimiani J. Zhang & H. Yu, sp. nov. (♀). Detailed descriptions, diagnoses, and photographs are provided for these two species, as well as a key and a distribution map for Chinese Diphya species. DNA barcodes (a partial fragment of the mitochondrial cytochrome oxidase subunit I gene, COI) of both new species were obtained for species delimitation, matching of different sexes, and future use in molecular studies

    A review of the spider genus Sinoalaria (Araneae, Theridiosomatidae), with the descriptions of four new species and two new combinations

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    The spider genus Sinoalaria Zhao & Li, 2014 is redefined and reviewed. A total of ten species are studied, including four new species: S. chi Yu & Lin, sp. nov. (♂♀), S. shenhei Yu & Lin, sp. nov. (♀), S. shuidi Yu & Lin, sp. nov. (♀), S. xiaotu Yu & Lin, sp. nov. (♂♀). Two new combinations are proposed: Sinoalaria nitida (Zhao & Li, 2012), comb. nov. and S. prolata (Zhao & Li, 2012), comb. nov., both transferred from Karstia Chen, 2010. The material of six known species were re-examined and photographed, including the type species, S. chengguanensis (Zhao & Li, 2012). A key is provided for all species of the genus, as well as diagnoses, illustrations, and a distribution map
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