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

We investigated soil microbial biomass and its natural abundance of delta C-13 and delta N-15 in aggregates (>2000 mu m, 250-2000 mu m, 53-250 mu m and <53 mu m) 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 (<250 mu m) than in macro-aggregates (>2000 mu m). The delta C-13 of soil microbial biomass was more enriched in woodland soils than in other land use types, while delta N-15 of soil microbial biomass was more enriched compared with that of organic soil in all land use types. The delta C-13 and delta N-15 of microbial biomass were positively correlated with the delta C-13 and 6115N of organic soil across aggregates and land use types, whereas the C-13 and N-15 enrichment of microbial biomass exhibited linear decreases with the corresponding C:N ratio of organic soil. Our results suggest that shifts in the natural C-13 and N-15 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. (C) 2016 Elsevier B.V. All rights reserved.