Regulation of crop rotation patterns on soil labile organic carbon, carbon-degrading microorganisms and their roles in organic carbon mineralization

Crop rotation is a vital practice in sustainable agricultural management. This study aimed to investigate soil labile organic carbon, carbon-degrading microorganisms, and soil organic carbon (SOC) mineralization in oilseed rape-rice (OR), wheat-rice (WR), oilseed rape-maize (OM), and wheat–maize (WM) rotations without (CK) and with the application of chemical fertilizers (NPK).

A 7-year field experiment involving different crop rotations was conducted in Shayang County, China. Fluorescence excitation—emission matrix (EEM) was used in analyzing dissolved organic carbon (DOC) structure, metagenomics was employed to investigate the specific glycoside hydrolase (GH) and auxiliary activity (AA) families. The mineralization of SOC was investigated through an incubation experiment.

The paddy-upland (OR, WR) rotations showed higher soil labile organic carbon content and simpler DOC structure than their corresponding continuous upland (OM, WM) rotations. Oilseed rape contained (OR, OM) rotations showed higher soil labile carbon content than the corresponding wheat contained (WR, WM) rotations. The abundance of soil GH family genes was higher in paddy-upland rotations than those in continuous upland rotations. Furthermore, both the abundance of soil GH family genes and β-glucosidase activity were higher in OM rotation than in WM rotation after fertilization. The SOC mineralization was higher in oilseed rape contained rotations than in wheat contained rotations and higher in paddy-upland rotations than in continuous rotations without fertilization. Fertilization increased SOC mineralization, but reduced the difference among crop rotation patterns.

Oilseed rape contained rotations had higher SOC mineralization than wheat contained rotations, rotations affected SOC mineralization mainly by regulating DOC content, abundance of GH gene families and β-glucosidase activity.