Study on the geochemical cycles of carbon and nitrogen in shrub encroachment soils

Shrub encroachment is one of most pressing ecological concerns within terrestrial ecosystems as it is an important process of grass soil carbon stocks. Shrub encroachment is the result of the combination of global climate change, rainfall, fire, and biological activities and has a significant impact on regional environments, climate, soil properties, and the carbon cycle. At present, the impacts of shrub encroachment on ecosystems are still unclear, and differences in soil organic carbon and nitrogen reserves, nutrient cycling, and soil greenhouse gas emissions have all been reported after shrub encroachment under different climates and rainfall gradients. This paper summarizes and reviews the effects of shrub encroachment on aggregate stability, enzyme activity, and soil carbon and nitrogen cycling. Shrub encroachment alters the stability and enzyme activities of soil aggregates, which affects soil respiration and the storage, decomposition, and recycling of soil-derived materials. This will significantly affect regional and global climate change. Therefore, this paper proposes strengthening the long-term localization of experimental observations of the shrub formation process to understand the controllable influencing factors underlying shrub encroachment. In addition, this paper recommends strengthening the stability of the soil organic carbon pool and soil aggregates within the carbon and nitrogen cycle after shrub encroachment.