1. Stability is a useful indicator of the functioning and sustainability of an ecosystem, and much studies have explored the effects of anthropogenic disturbance on the inter-annual stability of plant community. However, the effects of multiple anthropogenic stressors on seasonal community stability have not been clearly elucidated, especially for vulnerable semi-arid grasslands.2. During the growing season in the 5th year of the experiment, we determined how nitrogen (N) addition, water addition and shrub removal altered seasonal community stability in a semi-arid grassland dominated by the shrub Caragana microphylla on the Mongolian Plateau.3. We found that shrub removal, N addition and water addition had different effects on the stability of community and plant functional groups (PFGs). Shrub removal increased seasonal community stability mostly via increases in the stability of perennial forbs and C 4 plants, and shrub removal did not alter the effects of N addition or water addition on seasonal community stability or PFG stability. 4. N addition decreased seasonal community stability mostly via decreases in the stability of perennial rhizome grasses and C 4 plants. Water addition increased seasonal community stability mostly via increases in the stability of annuals and biennials, perennial forbs, perennial rhizome grasses, dominant species and C 4 plants. Species asynchrony and PFG stability but not species richness or soil abiotic or biotic variables helped to maintain seasonal community stability under N addition or water addition. 5.Our findings indicate that future scenarios of increases in N deposition and shrub encroachment will strongly reduce community stability in drylands, and that future scenarios of increases in precipitation together with shrub removal might help to maintain the stability of this and other dryland ecosystems.

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Although habitat loss and subdivision are considered main causes of sharp declines in biodiversity, there is still great uncertainty concerning the response of soil microbial biomass, diversity, and assemblage to habitat subdivision at the regional scale. Here, we selected 61 subtropical land-bridge islands (with small, medium, and large land areas) with a 50-year history of habitat subdivision and 9 adjacent mainland sites to investigate how habitat subdivision-induced unequal-sized patches and isolation affects biomass, diversity, and assemblages of soil bacteria and fungi. We found that the soil bacterial and fungal biomass on all unequal-sized islands were higher than that on mainland, while soil bacterial and fungal richness on the medium-sized islands were higher than that on mainland and other-sized islands. The habitat subdivision-induced increases in microbial biomass or richness were mainly associated with the changes in subdivision-specified habitat heterogeneities, especial for soil pH and soil moisture. Habitat subdivision reduced soil bacterial dissimilarity on medium-sized islands but did not affect soil fungal dissimilarity on islands of any size. The habitat fragment-induced changes in soil microbial dissimilarity were mainly associated with microbial richness. In summary, our results based on the responses of soil microbial communities from subtropical land-bridge islands are not consistent with the island biogeographical hypotheses but are to some extent consistent with the tradeoff between competition and dispersal. These findings indicate that the response of soil microbial communities to habitat subdivision differed by degree of subdivision and strongly related to habitat heterogeneity, and the distribution of microbial diversity among islands is also affected by tradeoff between competition and dispersal.