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Microorganisms play a crucial role in biogeochemical cycles and ecosystem processes, but the key factors driving microbial community structure are poorly understood, particularly in alpine environments. In this study, we aim to disentangle the relative contribution of abiotic and biotic factors shaping bacterial and fungal community structure at large and small spatial and integration scales in an alpine system dominated by a stress-tolerant cushion species Thylacospermum ceaspitosum. These effects were assessed in two mountain ranges of northwest China and for two contrasting phenotypes of the cushion species inhabiting two different microtopographic positions. The large-and small-scale abiotic effects include the site and microhabitat effects, respectively, while the large-and small-scale biotic effects include the effects of cushion presence and cushion phenotype, respectively. Soil microbial communities were characterized by Illumina Miseq sequencing. Uni-and multivariate statistics were used to test the effects of abiotic and biotic factors at both scales. Results indicated that the site effect representing the soil pH and abiotic hydrothermal conditions mainly affected bacterial community structure, whereas fungal community structure was mainly affected by biotic factors with an equal contribution of cushion presence and cushion phenotype effects. Future studies should analyze the direct factors contributing to shaping microbial community structure in particular of the cushion phenotypes.

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Question: Graminoid/shrubland communities include groups of forbs (herbaceous dicots) that differ in their traits, and in their direct and indirect responses to dominant neighbours. Although we have a growing knowledge of which traits might influence species' direct responses to dominant neighbours, and in particular the crucial importance of plant stature over foliage traits, less is known about the relationship between species' traits and direct responses to dominant neighbours.Location: An alpine graminoid/shrubland co-dominated by the shrub Dasiphora fruticosa and graminoids such as the sedge Kobresia capillifolia on the Tibetan plateau (China). Methods:The above-and below-ground effects of the shrub in the absence or presence of graminoids were manipulated to quantify direct and indirect responses of forb species, which were grouped with a PCA. For the forbs, six traits characterizing both plant stature and foliage properties were measured and a redundancy analysis was used to assess their patterns of direct and indirect responses to the dominant neighbours. Results:We found contrasting direct and indirect responses of forb species to the graminoids, and the above-and below-ground effects of the shrubs, separating the forbs into four species-groups. A significant positive indirect net effect of the shrubs was observed at the community-level. Traits of forb species were more tightly related to direct than indirect responses to dominant neighbours, while plant stature had a primary influence over foliage traits, which was only very weakly related to indirect responses. Conclusions: Although plant traits, in particular plant stature, have strong influences on species' direct responses to dominant neighbours, relationships to indirect interactions are more subtle and variable. This inhibits our prediction of the influence of species' traits on species composition of the community through indirect interactions. K E Y W O R D S alpine meadow, canopy effect, Dasiphora fruticosa, facilitation, functional traits, indirect effects, root effect, Tibetan plateau 404 |