Soil microbial diversity and network complexity sustain ecosystem multifunctionality following afforestation in a dry-hot valley savanna

Increasing aridity over the last six decades has resulted in severe degradation of ecosystem functioning and structure in the dry-hot valley savanna. It remains largely uncertain whether afforestation could recover the ecosystem multifunctionality (EMF) of the previous savanna in this region. Here, we discern key factors maintaining EMF and several specific ecosystem functions in a dry-hot valley in southwest China. We recorded plant traits, soil properties, enzymatic activity, and microbial community structure across 70 plots which included six plantations and one savanna. Afforestation could restore the EMF level of savanna by increasing individual ecosystem functions. However, not all plantations could attain the EMF level (5.29 on average) of the savanna and species identity was important for recovery in EMF and multiple ecosystem functions. Soil microbial diversity, but not plant species richness, drove improvements in EMF and multiple ecosystem functions following afforestation in the savanna. Soil fungal network complexity was the most important regulator of EMF (standardized total effect (STE) = -0.484, P < 0.01), plant biomass (STE = 0.34, P < 0.05) and soil organic carbon (SOC) stock (STE = -0.527, P < 0.01), and soil nutrients (STE = -0.7, P < 0.01), and soil fungal diversity was found to have an indirect effect on EMF (STE = 0.428, P < 0.01), SOC stock (STE = 0.355, P < 0.01), soil nutrients(STE = 0.315, P < 0.01), and decomposition (STE = 0.46, P < 0.01). Soil bacterial network complexity was related to carbon cycling and decomposition. Soil pH and soil water content played important roles in maintaining EMF and multiple ecosystem functions. Our study highlights that soil microbial diversity and network complexity are important predictors driving EMF and multiple ecosystem functions following afforestation in the dry-hot valley savanna.