[Effects of vegetation restoration on nutrient and microbial properties of soil aggregates with different particle sizes in the loess hilly regions of Ningxia, Northwest China].

We explored the effects of vegetation restoration on the soil nutrients and microbial pro-perties of soil aggregates with different particle size by comparing soils in a natural grassland which had been restored for nearly 30 years and in cropland in the loess hilly regions of Ningxia. We analyzed the soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), soil basal respiration (CO-C) and respiratory quotient (qCO) of different particle size soil aggregates collected from cropland and natural grassland. The results showed that soil aggregates of natural grassland had more micro-aggregates (particle size <0.25 mm), higher nutrient concentrations (SOC, TN and available K) and C/N than that of cropland. The highest concentrations of SOC and TN in 1-2 mm aggregates and higher C/N in natural grassland and cropland suggested that vegetation restoration could improve the capacity of soil aggregates to reduce nutrient loss and accumulate organic matter, with the highest nutrient accumulation in 1-2 mm aggregates. Microbial biomass (MBC, MBN) and CO-C in natural grassland were higher than in cropland, but the qCO was significantly lower, suggesting that vegetation restoration could effectively improve soil microbial biomass and activity, and make soil habitats more stable. The magnitude of responses of the microbial characteristics of different particle aggregates to vegetation restoration varied due to the differences in nutrient characteristics. The MBC of 1-2 mm aggregates, the MBN of <0.25 mm, 0.25-1 mm and 1-2 mm aggregates, the microbial activity of 1-2 mm and >5 mm aggregates were more sensitive than the rest of the particle aggregates of vegetation restoration. In conclusion, vegetation restoration could effectively improve the fertility and structural characteristics of soil aggregates, and the most prominent improvement was in 1-2 mm particle size aggregates.