Soil microbial activity varies seasonally in frozen alpine soils during cold seasons and plays a crucial role in available N pool accumulation in soil. The intra- and interannual patterns of microbial and nutrient dynamics reflect the influences of changing weather factors, and thus provide important insights into the biogeochemical cycles and ecological functions of ecosystems. We documented the seasonal and interannual dynamics of soil microbial and available N in an alpine meadow in the eastern part of Qinghai–Tibet Plateau, China, between April 2011 and October 2013. Soil was collected in the middle of each month and analyzed for water content, microbial biomass C (MBC) and N (MBN), dissolved organic C and N, and inorganic N. Soil microbial community composition was measured by the dilution-plate method. Fungi and actinomycetes dominated the microbial community during the nongrowing seasons, and the proportion of bacteria increased considerably during the early growing seasons. Trends of consistently increasing MBC and available N pools were observed during the nongrowing seasons. MBC sharply declined during soil thaw and was accompanied by a peak in available N pool. Induced by changes in soil temperatures, significant shifts in the structures and functions of microbial communities were observed during the winter–spring transition and largely contributed to microbial reduction. The divergent seasonal dynamics of different N forms showed a complementary nutrient supply pattern during the growing season. Similarities between the interannual dynamics of microbial biomass and available N pools were observed, and soil temperature and water conditions were the primary environmental factors driving interannual fluctuations. Owing to the changes in climate, seasonal soil microbial activities and nutrient supply patterns are expected to change further, and these changes may have crucial implications for the productivity and biodiversity of alpine ecosystems.

Litters of reproductive organs have rarely been studied despite their role in allocating nutrients for offspring reproduction. This study determines the mechanism through which flower litters efficiently increase the available soil nutrient pool. Field experiments were conducted to collect plant litters and calculate biomass production in an alpine meadow of the eastern Tibetan Plateau. C, N, P, lignin, cellulose content, and their relevant ratios of litters were analyzed to identify their decomposition features. A pot experiment was performed to determine the effects of litter addition on the soil nutrition pool by comparing the treated and control samples. The litter-bag method was used to verify decomposition rates. The flower litters of phanerophyte plants were comparable with non-flower litters. Biomass partitioning of other herbaceous species accounted for 10–40 % of the aboveground biomass. Flower litter possessed significantly higher N and P levels but less C ∕ N, N ∕ P, lignin ∕ N, and lignin and cellulose concentrations than leaf litter. The litter-bag experiment confirmed that the flower litters of Rhododendron przewalskii and Meconopsis integrifolia decompose approximately 3 times faster than mixed litters within 50 days. Pot experiment findings indicated that flower litter addition significantly increased the available nutrient pool and soil microbial productivity. The time of litter fall significantly influenced soil available N and P, and soil microbial biomass. Flower litters fed the soil nutrition pool and influenced nutrition cycling in alpine ecosystems more efficiently because of their non-ignorable production, faster decomposition rate, and higher nutrient contents compared with non-flower litters. The underlying mechanism can enrich nutrients, which return to the soil, and non-structural carbohydrates, which feed and enhance the transitions of soil microorganisms.

Root-rot disease has lead to serious reduction in yields and jeopardized the survival of the economically and ecologically important Zanthoxylum bungeanum trees cultured in Sichuan Province. In order to investigate the interaction between the microbiome and the root-rot disease, a metagenomic analysis was performed to characterize the microbial communities and functions in Z. bungeanum root endosphere, rhizosphere and bulk soil with/without root-rot disease. Soil physicochemical properties, microbial population size and enzyme activities were also analyzed for finding their interactions with the root-rot disease. As results, lower total nitrogen (TN) and available phosphorus (AP) contents but higher pH in rhizosphere and bulk soil, as well as lower substrate-induced respiration (SIR) and higher protease activity in bulk soil of diseased trees were found, in comparison with that of healthy trees. Microbial diversity and community composition were changed by root-rot disease in the endosphere, but not in rhizosphere and bulk soils. The endophytic microbiome of diseased trees presented higher Proteobacteria abundance and lower abundances of Bacteroidetes, Firmicutes and dominant fungal phyla. The relative abundances of nitrogen cycle- and carbon cycle-related genes in endophytic microbiomes were different between the diseased and healthy trees. Based on ANOSIM and PCoA, functional profiles (KEGG and CAZy) of microbiomes in rhizosphere and bulk soil shifted significantly between the diseased and healthy trees. In addition, soil pH, TN, AP, SIR, invertase and protease were estimated as the main factors influencing the shifts of taxonomic and functional groups in microbiomes of rhizosphere and bulk soil. Conclusively, the imbalance of root and soil microbial function groups might lead to shifts in the root endosphere-rhizosphere microenvironment, which in turn resulted in Z. bungeanum root-rot.