Response of heterotrophic respiration to vegetation restoration in a karst area of SW China

Abstract The Grain‐for‐Green Program in China aims to restore sloping karst cropland severely degraded by intensive agriculture to secondary forest. Heterotrophic respiration (Rh) is a major process of carbon release from soils and is associated with the sequestration of soil organic carbon (SOC). However, we still do not have a comprehensive understanding of Rh and what drives it along soil profile horizons during the natural vegetative recovery process in typical karst soils. We investigated the responses of Rh (C release per gram of soil) and specific Rh (C release per gram of SOC) in soil horizons from the soil surface to bedrock at the different vegetation recovery stages in a karst region. Coincident soil microbial properties (e.g., bacterial and fungal abundance, total microbial biomass, potential enzyme activities) and physicochemical properties were quantified. Vegetation restoration after cropland abandonment significantly increased Rh rates due to increased soil nutrients and microbial biomass, bacterial abundances, and hydrolase activities (all, p < 0.05). The rates of Rh enhanced in sloping cropland (SC) from the soil surface to bedrock but reduced in the recovering stages (ASC: abandoned sloping cropland and SF: secondary forest ) and primary forest (PF). The specific Rh between SF ( 1.34 mg CO 2 ‐C g −1 SOC d −1 ) and PF ( 1.32 mg CO 2 ‐C g −1 SOC d −1 ) were not significantly different but both of them were greater than those in SC ( 0.79 mg CO 2 ‐C g −1 SOC d −1 ) and ASC (0.8 mg CO 2 ‐C g −1 SOC d −1 ). Soil physicochemical properties and microbial properties explained approximately 48% and 22% of the variations in Rh along vegetation recovery , respectively . Nitrogen to phosphorus stoichiometry exerted the most direct and positive effects on Rh, suggesting the importance of managing soil nutrient status to regulate carbon decomposition during vegetation recovery in karst soils. The increased microbial biomass was the most important microbial factor regulating Rh in later vegetation recovery phases. Our results provide scientific insight into the impact of vegetation restoration on Rh in degraded ecosystems, which is important for reducing carbon loss in karst soils.