Forest type mediates biodiversity and abiotic controls on ecosystem multifunctionality in subtropical forests

Ecosystem multifunctionality (EMF) characterizes the capacity of ecosystems to sustain multiple functions simultaneously, including productivity, nutrient cycling, carbon storage, and decomposition. Although mixed-species forests are widely promoted for restoration, it remains unclear how multidimensional biodiversity (taxonomic, functional, and structural) interacts with abiotic conditions (soil properties, climate, and topography) to regulate EMF across contrasting subtropical forest types. We quantified EMF using four ecosystem functions—aboveground biomass, soil carbon storage, nutrient cycling, and litter quality—across 54 permanent plots (n = 18 per forest type) representing coniferous, broadleaved, and mixed forests in Chongqing, China. Potential drivers and specified direct and indirect statistical associations were evaluated using multiple regression, hierarchical partitioning, and piecewise structural equation modeling. EMF differed markedly among forest types, with mixed forests showing lower EMF than coniferous and broadleaved forests. This pattern was inconsistent with the expectation that species mixtures enhance EMF through functional complementarity, but it does not contradict biodiversity–function theory generally. Forest-type-specific analyses identified distinct associations: microbial nutrient status, particularly microbial biomass nitrogen, was positively associated with EMF in coniferous forests; topographic slope was negatively associated with EMF in broadleaved forests; and Rao’s quadratic entropy, representing functional diversity, was negatively associated with EMF in mixed forests. Overall, these results indicate that biodiversity–environment relationships are context-dependent, with the importance and direction of potential drivers varying among forest types.