Effects of long-term straw retention on soil microorganisms under a rice-wheat cropping system

The objective of this study was to investigate how straw-incorporating practices affect bacterial communities and carbon source utilization capacity under a rice-wheat rotational farming practice in central China. To clarify the effect of long-term straw incorporation in microbial abundance and carbon metabolism, a long-term field experiment was initiated in May 2005 (rice-planting season). Soil bacterial communities were revealed by high-throughput sequencing technology. After ten cycles of annual rice-wheat rotation (2005-2015), 2 M (straw incorporation) and 2 M + NPK (high straw incorporation + chemical fertilizer) treatments had significantly more bacterial phyla compared with CK (non-fertilization) and NPK (chemical fertilizer) treatments. Taxonomic analysis revealed that 2 M and NPK + 2 M treatments had a significantly greater abundance of microbial communities, especially the Gemmatimonadetes, Acidobacteria, Firmicutes, and Actinobacteria. In the NPK versus 2 M, 2 M treatment had a significantly greater abundance of Rozellomycota (P < 0.05). In the NPK + 2 M versus NPK, NPK + 2 M treatment also had significantly greater abundance of Ascomycota (P < 0.05). Principal component analysis (PCA) analysis showed that 2 M treatment was separate from other treatments. Using biolog-ECO method, the metabolic diversity and functional characteristics of microbial communities were used to indicate the ability of microorganisms to utilize carbon source. The carbon utilization ability of soil microorganisms in 2 M + NPK treatment was significantly higher than that of CK treatment (P < 0.05). The utilization ability of carboxylic acids, polymers, and other mixtures of carbon sources in 2 M treatment was higher than those of other treatments. These findings suggest that long-term straw incorporation affects the abundance and carbon utilization ability of soil microorganisms within 0-20 cm soil depths, among which, Gemmatimonadetes, Firmicutes, and Actinobacteria may play crucial roles in bacterial communities and carbon source utilization capacity.