Elevational gradients represent model systems for understanding the relationships between soil microbial communities and environmental factors, but the multiple influences of plant-soil linkages and climate conditions on elevational diversity gradients (EDGs) of soil microbes have never been explored. Here, we examined how climate conditions, plant diversity and soil properties affect EDGs of soil bacteria at different soil depths. Bacterial communities were investigated at four soil depths in 60 vegetation survey plots along elevational gradients in central Japan. In this study, elevational gradients reflected climate conditions, including mean annual temperature and seasonality of temperature and precipitation. Bacterial diversity decreased with elevation in the surface soil, but showed no relationship with elevation in deep soils. The structural equation modeling showed that soil bacterial diversity was directly affected by plant functional diversity, where leaf C:N ratio diversity had stronger effects than soil properties. We found that EDGs of soil bacteria were determined by the degree of indirect effects of climate conditions, via plant functional diversity and soil properties, against the direct effect of climate conditions on bacterial diversity. These findings demonstrate that community assembly of soil microbes is causally linked with climate conditions, plant functional diversity and soil properties, which determine EDGs.

Summary: Unraveling the mechanisms of home‐field advantage (HFA) is essential to gain a complete understanding of litter decomposition processes. However, knowledge of the relationships between HFA effects and microbial communities is lacking. To examine HFA effects on litter decomposition, we identified the microbial communities and conducted a reciprocal transplant experiment, including all possible combinations of soil and litter, between sites at two elevations in cool‐temperate forests. Soil origin, rather than HFA, was an important factor in controlling litter decomposition processes. Microbiome‐wide association analyses identified litter fungi and bacteria specific to the source soil, which completely differed at a low taxonomic level between litter types. The relative abundance of these microbes specific to source soil was positively correlated with litter mass loss. The results indicated that the unique relationships between plant litter and soil microbes through plant–soil linkages drive litter decomposition processes. In the short term, soil disturbances resulting from land‐use changes have the potential to disrupt the effect of soil origin and hinder the advancement of litter decomposition. These findings contribute to an understanding of HFA mechanisms and the impacts of land‐use change on decomposition processes in forest ecosystems.

We analyzed basal area (BA) growth using growth data obtained from permanent plots over 4 years for five major tree species in Anhui Province, eastern China. The studied species were dominant conifers (Pinus massoniana and Cunninghamia lanceolata) and co-dominant broad-leaved species (Castanopsis eyrei, Castanopsis sclerophylla, and Loropetalum chinense). A hierarchical Bayesian approach was used to estimate species-specific parameters and to quantify a spatially autocorrelated random effect. We selected a model that included only the following relevant predictor variables: initial size, asymmetric competition, spatially autocorrelated random effect, and random effect associated with plots. For all species analyzed, the model accounted for significant proportions of the variation (R² = 70–98 %) in BA growth rates. The initial slope of the relationship between BA growth rate and the initial BA tended to be steeper for P. massoniana than for C. lanceolata. The BA growth rate increased from an initial low value and then leveled off, with a lower maximum BA growth rate for C. lanceolata than for P. massoniana. The BA growth rate of P. massoniana was significantly affected by asymmetric competition with neighbors. The results of our analyses were used to predict to what extent thinning neighboring trees at different intensities would reduce competition impacts on BA growth of P. massoniana and C. lanceolata. Our results also helped to clarify the ecological characteristics of the species analyzed, as well as the spatial distribution of unknown factors influencing tree growth.