Plant above-ground biomass and litter quality drive soil microbial metabolic limitations during vegetation restoration of subtropical forests

Abstract

Changes in litter quality (carbon:nitrogen, C:N) and above-ground biomass (AGB) following vegetation restoration significantly impact soil physicochemical properties, yet their effects on soil microbial metabolic limitations remain unclear. We measured litter quality, AGB, soil physicochemical properties, and extracellular enzyme activity (EEA) along a vegetation restoration gradient (7, 14, 49, 70 years, and nearly climax evergreen broadleaved forests) in southern China. We also evaluated soil microbial metabolic limitations by a vector analysis of the EEA. Results revealed the soil microbial metabolisms were co-limited by C and phosphorus (P). The microbial C limitation initially decreased (before 14 years) and then increased, while the microbial P limitation initially increased (before 49 years) and then decreased. Partial least squares path modeling (PLS-PM) showed that the microbial C limitation was mainly attributed to microbial C use efficiency induced by litter quality, suggesting that microorganisms may transfer cellular energy between microbial growth and C-acquiring enzyme production. The microbial P limitation was primarily correlated with AGB-driven change in soil elements and their stoichiometry, highlighting the importance of nutrient stoichiometry and balance in microbial metabolism. The shifts between microbial C and P limitations and the strong connections of plant-soil-microbe processes during vegetation restoration revealed here will provide us with helpful information for optimal management to achieve forest restoration success.