Potential functional differentiation from microbial perspective under dryland-paddy conversion in black soils

Improving soil carbon sequestration and reducing greenhouse gas emissions in farmland require understanding how the microbial communities that control the agroecosystem function. Here, we surveyed the soil microbial communities in neighboring pairs of dryland and paddy fields in the black soils of northeastern China. Soil moisture, mean weight diameter of aggregates, fluorescence index and biological index of dissolvable organic matter, total anion concentration, and prokaryotic community α-diversity were higher in paddy soils than in dryland soils, while soil saturated hydraulic conductivity (SHC), dissolvable total nitrogen, and fungal community α-diversity were lower in paddy soils than in dryland soils. Moreover, soil moisture (P < 0.01) and SHC (P < 0.05) had significantly positive correlations with the α-diversity of prokaryotic and fungal communities, respectively. The co-occurrence network complexity of microbial communities was lower in paddy fields than in dryland fields, while the co-occurrence network tightness and cooperation of microbial communities were higher in paddy fields than in dryland fields, which may help paddy microbiome resist environmental disturbances. Taken together, both dryland and paddy fields had their own advantages in evaluating soil biological health from microbial community diversity and network stability. Additionally, the differential groups of CH4 production, S cycle, and Fe cycle (e.g., Bathyarchaeota, Bacteroidetes, and Geobacter) increased, while those of environmental remediation and biological control (e.g., Blastococcus and Roseiflexus) decreased after the change from dryland to paddy fields. Further combined with metagenomic analysis, the functions of CH4 production, CO2 fixation, N fixation, and sulfur reduction were enhanced in paddy soils, while those of CH4 oxidation, nitrification, and N2O production were reduced. In conclusion, the ecological functioning of the differential groups may lead to the increase of CH4 emission and CO2 fixation, and the decrease of N2O emission in paddy fields of black soil, even in non-flooding period.