Land-use change from cropland to plantations affects the abundance of nitrogen cycle-related microorganisms and genes in the Loess Plateau of China

The “Grain for Green” project has been considered an effective avenue to control soil erosion, improve vegetation coverage and prevent ecosystem degradation in the Loess Plateau of China. However, the effect of the project on the underlying microbial mechanism of soil nitrogen cycling is not well understood. In the present study, the effect of land-use change from cropland to plantations on soil microbial community and functional genes involved in the nitrogen cycle was investigated via metagenomic sequencing analyses. The abundance rather than the composition of functional genes for nitrification, denitrification, assimilatory and dissimilatory nitrogen reduction significantly changed during the conversion of cropland to plantations. The abundance rather than the composition of microorganisms involved in the nitrogen cycle also changed significantly. The effect on the abundance of functional genes and microorganisms was mainly related to changes in soil properties, such as organic matter, total nitrogen, available phosphorus, available potassium and pH. The observed changes likely decrease the potential of nitrification, denitrification and assimilatory nitrogen reduction in the soil of plantations. Our results demonstrate that land-use change from cropland to plantations significantly affects soil nitrogen cycling in the Loess Plateau of China.