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Based on the remote sensing and meteorological data collected from the 1981–2004 period, we calculated the alpine grassland Net Primary Productivity (NPP) in Northern Tibet using the Carnegie–Ames–Stanford Approach (CASA), and subsequently analyzed the trend of grassland NPP changes and its response to climate change from 1981 to 2004. The results show that alpine grassland NPP in Northern Tibet was very low in the last 24 years with a relatively large yearly variation. Most of the grassland area (88.61%) in Northern Tibet did not show a significant annual NPP change. The area with a significant decrease of annual NPP variation accounted for only 11.30% of the total grasslands surface, whereas that with a significant increase accounted for 0.09%. In recent years, the precipitation variation in Northern Tibet resulted in an increase of grassland NPP, though solar radiation resulted in decreased grassland NPP. During the 1981–2004 period, total solar radiation, precipitation and temperature, with a decreasing impact magnitude factor, have impacted the grassland NPP in Northern Tibet. The impact of regional climate change on grassland NPP was overall more detrimental than positive. [ABSTRACT FROM AUTHOR]

Rare species can switch between abundant and rare, respond to various external disturbances, enhance community resilience, and reduce the lag in ecosystem recovery. However, the impact of N enrichment on microbial community dynamic changes in rare species during the growing season is still poorly understood. To clarify which taxa contribute most to the community variation under N enrichment and whether the responses of these taxa vary at different periods of the growing season, we set up a 6-years multi-level field N addition experiment in an alpine meadow on the Tibetan Plateau. The variation in soil bacterial community diversity, composition, species interactions, and assembly process of different abundance profiles were investigated in the early, mid, and late-growing seasons. Approximately 80% of bacteria were classified as rare taxa (including permanently and conditionally rare taxa). The influence of N enrichment on the bacterial community was seasonally dependent. Bacterial community diversity and composition dissimilarity significantly increased only in the early growing season, especially in permanently rare taxa and conditionally rare taxa, but remained stable in the mid-and late-growing seasons. Seasonal fluctuations led to a shift in community composition, and conditionally rare taxa were the primary component of seasonal variation in community composition. Simultaneously, microbial network complexity and stability gradually increased over time, as evidenced by decreased modularity and vulnerability and increased robustness, clustering coefficient, connectivity, and keystone nodes. The assembly of conditionally rare taxa showed a significant difference under N addition, presented as decreased drift and increased dispersal limitation, which are closely related to the composition of the entire bacterial community. Our findings emphasize that the conditionally rare taxa decisive contribute to changes in the bacterial community under N enrichment, but seasonal fluctuations can make bacterial communities resistant to the influence of N enrichment. [ABSTRACT FROM AUTHOR]

To understand effects of soil microbes on soil biochemistry in alpine grassland ecosystems under environmental changes, we explored relationships between soil microbial diversity and soil total nitrogen, organic carbon, available nitrogen and phosphorus, soil microbial biomass and soil enzyme activities in alpine meadow, alpine steppe and cultivated grassland on the Qinghai-Tibetan plateau under three-year warming, enhanced precipitation and yak overgrazing. Soil total nitrogen, organic carbon and NH4-N were little affected by overgrazing, warming or enhanced precipitation in three types of alpine grasslands. Soil microbial biomass carbon and phosphorus along with the sucrase and phosphatase activities were generally stable under different treatments. Soil NO3-N, available phosphorus, urease activity and microbial biomass nitrogen were increased by overgrazing in the cultivated grassland. Soil bacterial diversity was positively correlated with, while soil fungal diversity negatively with soil microbial biomass and enzyme activities. Soil bacterial diversity was negatively correlated with, while soil fungal diversity positively with soil available nutrients. Our findings indicated soil bacteria and fungi played different roles in affecting soil nutrients and microbiological activities that might provide an important implication to understand why soil biochemistry was generally stable under environmental changes in alpine grassland ecosystems. [ABSTRACT FROM AUTHOR]

This study addresses the role of climate variability in the livelihoods of agricultural communities in Ningxia, Northwest China. Data sources comprise meteorological observations and official reports, complemented by questionnaires and focus group discussions designed around a livelihoods framework. Sample villages were located in three different agricultural systems: irrigated, mixed irrigated/grazing, and rainfed. Much of Ningxia is perennially dry and this is a significant limiting factor to agricultural production in the region, exacerbated by drought and buffered by irrigation mainly supplied from the Yellow River. Climate observations show stable temperatures from the 1950s to the 1980s followed by a positive trend (0.38°C/decade 1961-2010). Precipitation shows very modest trends and low decadal variability. Recent climate variability, particularly a drought from 2004-2006, was perceived to have had a significant effect on agricultural production and access to water, but it was not the only challenge respondents had faced. Susceptibility to drought was higher in the mixed irrigated and grazing and rainfed areas, due to farmers' greater exposure to climatic hazards and because a higher proportion of their income originated from farming activities. Respondents were using a wide range of measures to retain and enhance soil moisture and maintain agricultural production. The discussion examines challenges in disentangling the role of climate within rapidly changing livelihood systems. [ABSTRACT FROM AUTHOR]