Afforestation impacts microbial biomass and its natural 13C and 15N abundance in soil aggregates in central China

Abstract

We investigated soil microbial biomass and its natural abundance of δ13C and δ15N in aggregates (>2000μm, 250–2000μm, 53–250μm and <53μm) of afforested (implementing woodland and shrubland plantations) soils, adjacent croplands and open area (i.e., control) in the Danjiangkou Reservoir area of central China. The afforested soils averaged higher microbial biomass carbon (MBC) and nitrogen (MBN) levels in all aggregates than in open area and cropland, with higher microbial biomass in micro-aggregates (<250μm) than in macro-aggregates (>2000μm). The δ13C of soil microbial biomass was more enriched in woodland soils than in other land use types, while δ15N of soil microbial biomass was more enriched compared with that of organic soil in all land use types. The δ13C and δ15N of microbial biomass were positively correlated with the δ13C and δ15N of organic soil across aggregates and land use types, whereas the 13C and 15N enrichment of microbial biomass exhibited linear decreases with the corresponding C:N ratio of organic soil. Our results suggest that shifts in the natural 13C and 15N abundance of microbial biomass reflect changes in the stabilization and turnover of soil organic matter (SOM) and thereby imply that afforestation can greatly impact SOM accumulation over the long-term.