Functional Trait Diversity in Overstorey and Understorey Enhances Microbial Carbon Use Efficiency in Forest Plantation Soils

Abstract

Soil microbial carbon (C) use efficiency (CUE) is a critical parameter in C cycling process, but its relationship with aboveground plant community attributes remains largely unexplored.  This study examines how functional diversity and vegetation composition influence microbial CUE in soils across four subtropical plantation types. The hypotheses tested include: (i) the effects of overstorey tree and understorey plant diversity on microbial CUE are shaped by multiple community- and ecosystem-level functional dimensions (dispersions, means, variances, skewness, and kurtosis); and (ii) microbial CUE is influenced by resource limitations in soil. The results indicate that while soil microorganisms in all four plantations experience co-limitation by C and phosphorus (P), plantations with higher plant diversity exhibit much lower C and P limitations for soil microorganisms compared to those with lower plant diversity. Across all plantations, plant community attributes, functional traits, and soil physico-chemical and microbial properties account for a substantial proportion of microbial CUE variation. Specifically, greater functional diversity in overstorey trees and understorey plants effectively reduces microbial C and P limitations and increases microbial CUE. The community-weighted moments of leaf nitrogen (N) and P contents explain a larger proportion of microbial CUE variation compared to other measures of multifunctionality traits alone. These findings indicate that plant community composition and function play a critical role in regulating microbial CUE and resource limitations. The results highlight that maintaining a functionally diverse overstorey and understorey plant layer is essential for enhancing soil C storage in forest ecosystems.

Keywords: Biodiversity-ecosystem functioning, Community-weighted moments, Microbial resource limitations, Plant functional traits, Understorey plants