Response of soil aggregate-associated fertility and microbial communities to afforestation in the degraded ecosystem of the Danjiangkou Reservoir, China.

Aims: Afforestation is considered as an effective method to restore degraded ecosystem. The effects of afforestation on soil fertility, microbial communities assembly have been broadly studied in the whole soil, yet gaps still exist at the aggregate scale. Methods: In the Danjiangkou Reservoir area, we set up 3 quadrats (20 m × 20 m) for bareland, farmland and woodland, respectively, and separated the collected soil into four aggregate size fractions (<0.25 mm, 0.25–1 mm 1–3 mm and > 3 mm). Soil fertility, enzyme activities, microbial communities composition were determined for all aggregate fractions. Results: Afforestation promoted soil fertility, enzyme activities and their aggregational differentiation. E.g., invertase activity in woodland was 3.6 times higher than in bareland. Interestingly, the aggregational differentiation of bacterial alpha-diversity (P < 0.05) was more sensitive to afforestation than fungal alpha-diversity (P > 0.05). Conversely, afforestation caused that more fungal taxa (16 Ascomycota and 3 Basidiomycota taxa) were susceptible to aggregates than bacterial taxa (5 Proteobacteria taxa). In bareland, deterministic process (83.3%) was the decisive factor for bacterial communities, while fungal communities was determined by stochastic (48.5%) and deterministic (51.5%) processes. Afforestation transformed assembly processes, with dispersal limitation (53%) occurring in bacterial communities and variable selection (68.2%) in fungal communities. Conclusions: Overall, afforestation enhanced soil fertility, enzyme activities and their variation with aggregate. Moreover, responses of fungal and bacterial assembly to afforestation vary at the soil aggregate level. This study demonstrated the importance of soil aggregates in predicting and quantifying the impact of afforestation on soil fertility and microbial communities. [ABSTRACT FROM AUTHOR]