Effect of land uses on soil microbial community structures among different soil depths in northeastern China

Changes in land use affect the cycling and supply of soil nutrients, directly leading to changes in soil properties and the structure of soil microbial communities and altering the structure and function of terrestrial ecosystems. Previous studies have focused only on the response of soil microbial communities to changes in land use; however, the main drivers of changes in soil microbial community structure and abundance under different land uses and soil depths are still obscure. In this study, four types of land use (natural secondary forest, SF; larch plantation, LP; farmland, FL; and abandoned land, AL) in northeastern China were selected, and soil from the 0-5 cm, 5-10 cm and 10-20 cm layers was collected to evaluate the microbial communities by means of phospholipid fatty acid (PLFA) analysis. Due to land use history and soil legacy, land use had significant effects on soil organic carbon (C), nitrogen, and phosphorus, as well as on pH, bulk density, moisture, and phenolic compounds. The C content in SF was 40.7% higher than that in AL, and the total phenol (T-Ph) in SF was 39.6% lower than that in LP. Land use had a significant effect on total PLFAs, bacterial, fungal, actinomycetal and Gram-positive PLFA biomarkers. In topsoil, the total PLFAs and fungal communities were 55.62% and 240.51% higher than in AL, respectively. The cyclopropyl:monoenoic precursor fatty acids (cy:pre) PLFA biomarkers were higher in LP. The correlation between phenolic compounds and soil microbial community structure at every soil depth was stronger than the correlations between these structures and C, N, C/N and pH. Total phenol content promoted and inhibited the growth of various groups of microorganisms in the 0-5 cm and 5-10 cm soil layers, respectively. In summary, land use changed soil physicochemical properties in the conversion from SF to LP, FL and AL. These abiotic factors, especially phenolic compounds, regulated soil microbial community structure and abundance.