Objectives Many microbial communities exist in soils and play dominant roles during straw decomposition process. Understanding the succession pattern in bacterial community during crop straw decomposition is imperative in regulating and improving straw decomposition.
Methods The research was conducted at the Yuanyang Experimental Station of Henan Academy of Agricultural Sciences from October 2014 to October 2015. Dry maize straws (stalks and leaves) were shredded into 1‒2 cm long and 0.3‒1 cm wide, and 12 g of the straw samples were loaded into non-biodegradable nylon mesh bags (15 cm × 10 cm with pore diameter of 0.04 mm), and then buried 12 cm deep in the middle of two rows of winter wheat in October 5, 2014. Straw bags and soil samples were retrieved at 0, 1, 2, 4, 7, 10 and 12 months after burial for the determination of dry matter mass, C/N ratio of straw samples, and the bacterial abundance and diversity in straw and soil samples.
Results The rate of straw decomposition was greatest in the first two months after burial in soil, and there after decreased gradually. Reduction in straw masses was 19.2%, 32.9%, 44.2%, 52.2%, 66.8% and 73.8% of the total mass at 1, 2, 4, 7, 10 and 12 months after burial, respectively. The bacterial abundance in residual straw and soil increased significantly after burial, attaining its peak at 4 and 7 months, respectively. The bacteria richness index OTUs, ACE, Chao1 and Shannon in residual straws increased gradually with the extension of the experimental duration, while Simpson index gradually decreased. However, these indexes in soils did not change significantly during the study period. Compared with the initial sampling period (0 month), the relative abundance of phylum Bacteroidetes in straws increased significantly after 2 months. The bacterial communities dominated were Bacteroidetes and Proteobacteria at the early stage, afterwards, their abundances gradually decreased. The abundance of Proteobacteria remained high across the decomposition process while that of Actinobacteria was significantly low at 2 months but gradually increased; the abundances of Chloroflexi, Saccharibacteria, Acidobacteria, Verrucomicrobia, Planctomycetes and Gemmatimonadetes were low initially but also increased with time. Bacterial class composition was dominated by Sphingobacteriia, Flavobacteriia, Gammaproteobacteria and Alphaproteobacteria in the early stage, and the abundance of Actinobacteria, Anaerolineae and Bacilli gradually increased at the later stage. The rate of straw decomposition was mainly affected by its carbon content. Straw bacterial community was correlated with straw carbon and straw nitrogen in the early and later stages of decomposition, respectively. The bacterial community composition in straw tended to be similar to those in soils.
Conclusions Decomposition of maize straw is fast during the first 2 months of burial but gradually decreases afterwards. The dominating bacterial communities during the early stage are phylum Bacteroidetes and Proteobacteria, and class Sphingobacteriia, Gammaproteobacteria, Flavobacteriia and Alphaproteobacteria. However, they are succeeded by phylum Actinobacteria, Saccharibacteria, Acidobacteria, Chloroflexi, and class Deltaproteobacteria and Actinobacteria at the later stage of decomposition. The change in the carbon and nitrogen contents of straw is found to be mainly responsible for straw decomposition and the succession in bacterial community structure during straw decomposition process.
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