Climatic Variability Determines the Biological Diversity and Function of a Mixed Forest in Northeastern China at the Local-Scale

The adaptation to climatic variability and spatiotemporal distinctions in floristic and microbial assembly is important in forest ecology, especially in the context of biological diversity and functional traits. We investigated climatic variables, plant traits, edaphic properties, and microbial dimensions from various plots with an elevation gradient in a broad-leaved-Korean pine mixed forest. With increasing elevation, isothermality significantly increased; however, temperature and precipitation seasonality, as well as the mean temperature of the warmest quarter, significantly declined. Furthermore, high elevation sites were characterized by increased stand basal areas (Ba) and ectomycorrhizal (EM) tree abundance but featured decreases in the abundance of arbuscular mycorrhizal (AM) trees and the values of community-weighted mean (CWM) foliar traits (e.g., leaf area, leaf nitrogen content and leaf phosphorus content). Moreover, soil nutrient status, fungal and bacterial diversity indices, fungal saprotrophs, and bacterial function groups related to nitrite oxidation, ammonia oxidation, and nitrate denitrification were all negatively correlated to the elevation increment. In contrast, high elevation sites were characterized by enhanced EM growth and bacterial nitrogen fixation groups. Correlation analysis showed that the microbial diversity and relative abundances of microbial functional groups in soil were significantly influenced by climatic variability, CWM foliar traits and soil nutrient status. These findings demonstrate that the forces driving biological processes along climatic gradients are predictably in tandem with, but related to different extents, to the spatial compartmentalization of climatic variability in forest ecosystems at local scales.