Straw Returning Promote Carbon Storage by Changing Aggregate Bacterial Community and Enzymatic Activity: A 35-Year Field Experiment

Abstract

Soil bacterial community structure and carbon-fixation function gene are easily influenced by changes in field agronomic management measures (i.e. straw returning), while their effects on soil organic carbon (SOC) across different soil aggregates remains unclear. Here, soil samples were collected from the 35-year-old long-time rice-wheat rotation experiment with three treatments: no chemical fertilizer or straw (CK), chemical fertilizer only (NPK), and straw returning plus chemical fertilizer (NPKM) to explore the microbial regulation mechanism of soil aggregate size on SOC. Results showed that, 1) Compared with CK and NPK, the NPKM significantly increased the contents of SOC and MBC in 0.25–1 mm aggregate. Similarly, the higher cbbL abundance (6.26×108 copies g-1) and RubisCO activity (172.92 nmol h-1 g-1) in 0.25–1 mm aggregate were found in NPKM. 2) Diversity and richness of bacterial communities in various soil aggregate size fractions decreased in NPK but increased in NPKM. The relative abundance of Proteobacteria and Actinobacteria in 0.25–1 mm aggregate of NPKM were greatly detected compared to other soil samples, which indicated that there are sufficient nutrients in 0.25–1 mm aggregate and was beneficial to the growth of eutrophic bacteria. 3) Following RDA analysis, SOC and MBC were closely related to bacterial community structure in soil aggregate. Bacterial community diversity (Shannon index) promoted RubisCO activity by regulating cbbL gene abundance (path coefficient = 0.67, p < 0.001), and finally positively affected SOC content. In conclusion, the primary soil aggregate size class involved in carbon-fixation in a long-time rice-wheat rotation soil, and straw returning promoted carbon storage by changing aggregate bacterial community structure.

Keywords: straw returning, aggregate carbon-fixation potential, cbbL, RubisCO, bacterial community