Effects of gravel-sand mulching on soil bacterial community and metabolic capability in the semi-arid Loess Plateau, China

Gravel and sand mulching is an indigenous technology used for the crop yield for at least 300 years in the loess area of northwest China; however, little is known about the changes of soil bacterial community and metabolic capability under the mulching. In this study, we investigated the soil microbial community structure and metabolic functional diversity during mulching using Illumina MiSeq sequencing and Biolog ECO method. Totally, 9417 OTUs were classified at 97% similarity level for soil samples after 0 (control), 4, 7, and 10 years of mulching. Dendrogram result indicated that mulching affected the soil bacterial community; and the higher richness and diversity of bacterial community were detected in mulching samples. The average abundance of soil bacteria (such as Proteobacteria, Actinobacteria, Firmicutes and Nitrospirae) in mulching samples was higher than samples without mulching. Besides, some microbial communities (such as Rhodobacteraceae, Phenylobacterium, Pseudonocardia, Nonomuraea and Aeromicrobium) were only present in the mulched soil samples. However, the lower metabolic capability was observed in mulching samples based on Biolog method, which the main reason for the opposite result might be that the soil objects detected by the two methods are different. In conclusion, these results demonstrated that gravel and sand mulching affected the structure and metabolic capability of bacterial community and was one reason for crop yield.