Soil bacterial community composition and diversity response to land conversion is depth-dependent

Abstract

Background: Transitions from traditional cropping systems to afforestation and agroforestry practices are the most common patterns of land use change in China, but little is known about how soil properties and bacterial communities are altered. This study compared four afforestation and agroforestry practices that had been converted from corn and wheat rotation systems for several years with adjacent legacy corn and wheat rotation systems to test the impacts of these land conversions on soil properties and bacterial communities. Results: The results revealed that afforestation and agroforestry practices significantly increased soil organic carbon (SOC) and total nitrogen (TN) levels compared with those in the legacy cropping systems, and the ginkgo (Ginkgo biloba L.)-wheat (Triticum aestivum L.) system had the highest SOC and TN contents. Afforestation and agroforestry practices increased the number of unique bacterial operational taxonomic units (OTUs) in the topsoil and subsoil, and the metasequoia (Metasequoia glyptostroboides Hu et Cheng) system had the highest diversity and richness indices. Land conversion had a greater effect on the bacterial community beta diversity in the topsoil than in the subsoil. Redundancy analysis (RDA) showed that SOC, TN, and total phosphorus (TP) were the most important factors explaining variations in the bacterial community structure. The bacterial phyla Proteobacteria, Acidobacteria, Chloroflexi, Actinobacteria, and Nitrospirae dominated both the topsoil and the subsoil, and Proteobacteria was the most abundant. Alphaproteobacteria and Betaproteobacteria were the dominant classes. Only the relative abundance of Actinobacteria was significantly different among land use patterns in both the topsoil and the subsoil, and Nitrospirae was significantly different among land use patterns only in the topsoil, with higher relative abundance in the gingko and metasequoia systems, while other bacterial phyla were not markedly affected by land conversion. Conclusion: The results demonstrate that afforestation and agroforestry practices have significant impacts on the soil bacterial community and may be key factors influencing taxonomic shifts and functional variations in bacterial communities, especially in the topsoil.

Keywords

• Land conversion
• Soil bacterial community
• Soil properties
• High-throughput sequencing