Microbes are the unseen majority in soil and comprise a large portion of life’s genetic diversity. Subsoil (below 20 cm), with low nutrient content and large volume, often possesses large numbers of microbes, and these soil microbes are strongly influenced by soil physical and chemical properties. However, there are few of studies regarding the effects of soil properties on soil microbes in subsoil.    

To determine the relationship between soil microbial communities and soil properties and the effects of long-term fertilizer applications on soil microbial communities in different soil depths, LI Chenhua et al. conducted an experiment in the southern edge of the Gurbantonggut Desert. Two typical fertilizer treatments (i.e. inorganic fertilizer alone (CF) and inorganic fertilizer combined with wheat straw (CF/OM)) were applied to compare with no fertilizer treatment (CK) in the experimental design. 

Soil depth had a highly significant effect on the soil microbial communities, with Actinobacteria and Proteobacteria dominated in topsoil (0–0.2 m) while Proteobacteria overwhelmingly dominated in subsoil (0.2–3 m). With soil depths increasing, the relative abundance of Actinobacteria and Deltaproteobacteria decreased while that of Gammaproteobacteria increased.  Long-term fertilizer application changed the bacterial community within the soil profile. For example, in CF/OM treatment, the order Methylococcales, order Enterobacteriales, order Pseudomonadales and Nitrospirae were more abundant; while in the CF treatment, the order Xanthomonadales, order Nitrosomonadales, Gemmatimonadetes and Crenarchaeota were more abundant.  

Soil properies in dfferent soil depths had distinct effects on soil microbial communities. In topsoil, total nitrogen content had the greatest effect on microbial community, following by total phosphorus, soil organic carbon, electrical conductivity and pH. However, in subsoil, soil organic carbon and electrical conductivity had significant influences on microbial community structure, following by total nitrogen, total phosphorus and pH. 

The study was published in Soil Biology & Biochemistry in August 2014.