Mulching practices decreased soil microbial carbon degradation potential under spring maize in the Loess Plateau of China

Abstract

Surface mulching with crop straw or plastic film has a great potential in soil carbon (C) sequestration. A 10-yr field experiment on spring maize was conducted in the Loess Plateau of China to compare the impacts of crop straw (SM) and plastic film (FM) mulching on soil microbial C-degradation genes using a metagenomic approach. Compared to those with no mulching (CK), soil C fractions significantly increased under SM while decreased under FM. However, the relative abundance of total microbial C-degradation genes did not change under SM, but was significantly lower by 3.9 % under FM. Specifically, the relative abundance of genes involved in stable C degradation did not vary with mulching, while those in labile C degradation decreased by 14.0 % (p < 0.05) under FM compared to CK. At the gene group level, FM decreased the relative abundances of genes involved in the degradation of monosaccharides, disaccharides, polysaccharides, hemicellulose, cellulose, and chitin by 5.9 %, 9.2 %, 3.3 %, 8.6 %, 8.1 %, and 25.4 % (p < 0.05), respectively, compared to CK. The random forest analysis indicated that the PYG was the predominant gene affecting microbial biomass C, followed by araB, K07046, E3.1.1.11; pectinesterase, and bglB. Genes involved in soil C-degradation were more abundant in Proteobacteria and Actinobacteria than in other phyla. Mantel test showed that soil pH and C:P ratio emerged as the key factors influencing microbial C-degradation genes. Therefore, soil C-degradation potential would be inhibited by long-term mulching practices, especially with plastic film. The combined application of crop straw and plastic film mulching may accomplish the dual objectives of enhancing soil C storage and lowering C-degradation potential in dryland cropping systems.