Changes in microbial community structure and functioning with elevation are linked to local soil characteristics as well as climatic variables

Mountain forests are important carbon stocks but are threatened by increased insect outbreaks and climate driven forest conversion. Soil microorganisms play an eminent role in nutrient cycling in forests and form the basis of soil food webs. Uncovering the driving factors shaping microbial communities and functioning at mountainsides worldwide is of importance to better understand their dynamics at local and global scales. We investigated microbial communities and their drivers along an elevational gradient of primary forests at Changbai Mountain, China. We analysed substrate-induced respiration and phospholipid fatty acids (PLFA) in litter and two soil layers at seven sites. In the litter layer the increase in microbial biomass (Cmic) as well as in stress indicator ratios with elevation were negatively correlated with Ca concentrations indicating increased nutritional stress in high microbial biomass communities at sites with lower Ca availability. PLFA profiles in litter separated low and high elevations, this was less pronounced in soil, suggesting that leaflitter functions as buffer for soil microbial communities. Annual variations in temperature correlated with PLFA profiles in all layers, while annual variations in precipitation correlated with PLFA profiles in upper soil only. Furthermore, the availability of resources, soil moisture, Ca concentrations and pH structured the microbial communities. Pronounced changes in Cmic and stress indicator ratios in the litter layer between pine dominated (800 – 1100 m) and spruce dominated (1250 – 1700 m) forests indicated a shift in the structure and functioning of microbial communities between forest types. The study highlights strong changes in microbial community structure and functioning along elevational gradients, but also shows that these changes and their driving factors vary between layers. Besides annual variations in temperature and precipitation, carbon accumulation and nitrogen acquisition shape changes in microbial communities with elevation at Changbai Mountain.