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The aim of this study was to evaluate the relationships among changes in the soil microstructure, soil physicochemical traits and microbial communities during desertification. Soil samples were collected from grasslands at different stages of desertification, from an area of the Tibetan Plateau. Soil aggregate fractionation and soil physicochemical properties were analysed using standard methods, and the abundance and diversity of bacteria associated with different aggregate fractions were estimated by quantitative PCR and Illumina Miseq amplicon sequencing. Sequential changes in response to desertification stages were detected in the analysed features. For instance, soil nutrients, microbial biomass C and N, water content and pH initially changed during the light desertification stage; then, the soil aggregation decreased during the intermediate stages; and finally, bacterial abundance and diversity decreased during heavy and severe desertification stages. During grassland desertification, vegetation coverage positively influenced soil aggregation by affecting soil properties (e.g., pH and SOC), whereas bacterial communities in FMi (free microaggregates) and FSC (free silt and clay) were negatively related to soil aggregation. This study reports novel information concerning the desertification process and the sequential modification of soil traits and interactions among soil physical properties (aggregate composition), soil nutrients and the soil microbial community in the grasslands of the Tibetan Plateau. Highlights: Bacterial community was more sensitive in macroaggregates than in microaggregates.Composition of small macroaggregates and associated bacteria changed during desertification.Bacterial community in microaggregates, silt and clay negatively affected aggregation.Vegetation coverage affected aggregation by changing soil traits and bacterial community. [ABSTRACT FROM AUTHOR]

Aim: This study aimed at predicting how sub-alpine coniferous ecosystems respond to global changes in the Eastern Tibetan Plateau by understanding soil microbial communities and activities, as well as variation in the quality and quantity of soil organic matter. Methods: An experiment was conducted to examine soil microbial communities and their related soil processes in rhizospheric soil of two coniferous species that were exposed to two levels of temperature (unwarmed and infrared heater warming) and two levels of nitrogen (unfertilized and 25 g N m a) from April 2007. Results: Four-year night warming alone slightly affected the phospholipid fatty acid contents of the microbial community. However, the combination of nitrogen addition and soil warming significantly affected soil microbial composition while reducing the biomass of major microbial groups and the activities of most enzymes, especially in Abies faxoniana plots. The combination of warming and nitrogen addition increased soil labile C and N pools in Picea asperata plots and was beneficial for soil recalcitrant C, as well as for labile and total C and N pools in A. faxoniana plots. Conclusion: Results indicated that future warming will slightly affect soil microbial communities and their related soil processes. However, warming combined with high nitrogen deposition will significantly constrain soil microbial biomass and enzyme activities, consequently increasing soil C and N pools in sub-alpine coniferous forests of this region. [ABSTRACT FROM AUTHOR]

Plant senescence is a critical life history process accompanied by chlorophyll degradation and has large implications for nutrient resorption and carbohydrate storage. Although photoperiod governs much of seasonal leaf senescence in many plant species, temperature has also been shown to modulate this process. Therefore, we hypothesized that climate warming would significantly impact the length of the plant growing season and ultimate productivity. To test this assumption, we measured the effects of simulated autumn climate warming paradigms on four native herbaceous species that represent distinct life forms of alpine meadow plants on the Tibetan Plateau. Conditions were simulated in open-top chambers (OTCs) and the effects on the degradation of chlorophyll, nitrogen (N) concentration in leaves and culms, total non-structural carbohydrate (TNC) in roots, growth and phenology were assessed during one year following treatment. The results showed that climate warming in autumn changed the senescence process only for perennials by slowing chlorophyll degradation at the beginning of senescence and accelerating it in the following phases. Warming also increased root TNC storage as a result of higher N concentrations retained in leaves; however, this effect was species dependent and did not alter the growing and flowering phenology in the following seasons. Our results indicated that autumn warming increases carbohydrate accumulation, not only by enhancing activities of photosynthetic enzymes (a mechanism proposed in previous studies), but also by affecting chlorophyll degradation and preferential allocation of resources to different plant compartments. The different responses to warming can be explained by inherently different growth and phenology patterns observed among the studied species. The results implied that warming leads to changes in the competitive balance among life forms, an effect that can subsequently shift vegetation distribution and species composition in communities. [ABSTRACT FROM AUTHOR]