Land use change from upland to paddy field in Mollisols drives soil aggregation and associated microbial communities

Irrigated rice fields in northeast China are established on soils characterized as upland soils, and in this process, oxic upland conditions are converted into anoxic wetland conditions. However, the consequences of such land use changes for soil aggregation and associated microbial communities are poorly understood. Therefore, the objective was to study the activity and structure of the microbial communities of soils from a permanent upland as well as paddy soils converted from upland fields, soil microbial communities were determined using Biolog EcoPlates (TM) and HiSeq. The results showed that the conversion of upland to paddy soil resulted in increased soil organic carbon (SOC) contents and decreased urease, beta-glucosidase, and cellulose activities, while SOC and total nitrogen (TN) contents decreased with decreasing aggregate size for both land use types. Following land use change, microbial diversity was increased and microbial community activity and composition were changed. When upland fields were converted into paddy systems, the relative abundances of Bacteroidetes, Chloroflexi, and Nitrospirae increased, whereas those of Acidobacteria, Gemmatimonadetes, and Planctomycetes decreased significantly. Most importantly our results indicated that the microbial community is modulated by soil aggregate sizes and land use change, and latter is a stronger determinant in shaping soil microbial communities.