Changes of anaerobic to aerobic conditions but not of crop type induced bulk soil microbial community variation in the initial conversion of paddy soils to drained soils

•Land use conversion changed soil properties and microbial communities.•Crop type conversed had no significant effects on microbial communities during the initial of conversion.•Soil pH drove the variations in microbial communities.

Soil microorganisms are the main drivers of all of the biochemical processes that occur in soils. Land-use conversion, a common occurrence driven by market economy, changes plant species and the associated management strategies, thus significantly influences soil microbial communities. However, few studies have been conducted to disentangle the effect of the alteration of plant species from that of soil environment during the initial years of conversion. In this study, the effect of land-use conversion from double rice cropping (RR) to maize-maize (MM) and soybean-peanut (SP) double cropping systems on soil physical and chemical properties and microbial communities was studied two years after the conversion in southern China. The results showed that land use conversion significantly changed the soil properties, microbial communities and microbial biomass. The soil water content decreased significantly by 26.3%, and the pH decreased by 0.50 and 0.52 for MM and SP, respectively, compared with RR. Soil inorganic N also decreased significantly by 55% after the conversion to drained fields. The total phospholipid fatty acids (PLFAs), and bacterial, G +, G − and actinomycetic PLFAs decreased significantly after the conversion. No significant differences were found in the soil properties, microbial communities and microbial biomass between the converted MM and SP. Our results indicated that the changes of anaerobic to aerobic conditions, rather than of crop type, induced the variations in the soil properties and microbial communities during the initial years after conversion from paddy soils to drained soils. In particular, soil pH was the key factor that regulated the variations in the soil microbial communities after conversion.