Biomass and Functional Traits of Plants and Soil Carbon‐to‐Nitrogen Ratio Jointly Control the Effect of Living Roots on Soil Carbon Decomposition

Plant functional traits and their comprehensive characterization, namely the plant economics space (PES), are increasingly recognized to play a key role in shaping ecosystem functioning. However, how plant functional traits regulate the effect of living roots on soil carbon decomposition (known as rhizosphere priming effect, RPE) across plants with diverse species, phylogenetic, and functional diversity remains unclear. By synthesizing 639 global RPE observations from 103 species planted in 120 mineral soils, we show that plant belowground biomass, plant functional traits along the PES collaboration gradient (from do-it-yourself to outsourcing), and soil C/N ratio jointly drive global variation in RPE magnitude, with the former two showing positive correlations and the latter showing a negative correlation with RPE. We thus propose a "biomass-nitrogen-traits" model of RPE, in which large-biomass plants with thick roots (outsourcing strategy) in low C/N soils promote soil C decomposition more strongly than small-biomass plants with thin roots (do-it-yourself strategy) in high C/N soils. These findings provide a new perspective that the PES collaboration gradient can affect microbial decomposition and biogeochemical cycles and can help better predict belowground ecosystem functioning due to changes in species composition and functional traits of plant community under global change.