Soil abundant and rare microbes and their contributions to nutrient cycling in the upland and paddy stages: Insights from oilseed rape-rice and wheat-rice rotations

Abstract

Microorganisms can be divided into abundant and rare microbial taxa, which play a vital role in soil nutrient cycling. However, it remains unclear how paddy-upland rotation patterns and stages affect soil abundant and rare microbial taxa and their roles in soil multi-nutrient cycling. In this study, we investigated the differences in abundant and rare microbial taxa between oilseed rape-rice (OR) and wheat-rice (WR) rotations in upland and paddy stages through an 8-year field experiment, and their roles in soil nutrient cycling were also explored. The results showed that crop rotation patterns significantly altered the composition of both abundant and rare microbial communities in paddy-upland rotation systems. Bacterial taxa were more affected by crop rotation patterns than fungal taxa. Compared with the WR rotation, the OR rotation increased the relative abundance of rare bacterial taxa but decreased that of rare fungal taxa, particularly in the paddy stage. Additionally, the OR rotation significantly increased the Chao1 index of rare bacterial taxa, but decreased the Shannon index of rare fungal taxa. PLFA analysis showed higher soil viable microbial biomass in the upland than in the paddy stage. Compared with the WR rotation, the viable microbial biomass in the soil of the OR rotation decreased by 17.7 % during the upland stage, but increased by 22.3 % during the paddy stage. In the upland stage, rare bacterial taxa were primarily influenced by viable microbial biomass (including bacterial PLFAs, gram-positive bacteria and gram-negative bacteria). The composition of rare fungal taxa was affected by viable microbial biomass, as well as nitrate nitrogen, potentially mineralizable nitrogen, and dissolved organic nitrogen (DON). In the paddy stage, both abundant and rare bacterial and fungal taxa were mainly influenced by DON and free amino acids. Compared with the WR rotation, the OR rotation improved the soil multi-nutrient cycling index, increased by 44.6 % and 143.3 % in the upland and paddy stages, respectively. Crop rotation regulated soil multi-nutrient cycling mainly by influencing rare bacterial taxa and viable microbial biomass in both upland and paddy stages. Therefore, this study highlights the critical role of rare bacterial taxa in soil multi-nutrient cycling within paddy-upland rotation systems.