Soil physicochemical properties and microorganisms jointly regulate the variations of soil carbon and nitrogen cycles along vegetation restoration on the Loess Plateau, China.

Background and aims: Vegetation restoration can effectively improve multiple soil functions by altering soil microorganisms and physicochemical properties. However, dynamic variations in soil physicochemical properties, microbial communities, and possible pathways to control soil C and N cycles with vegetation restoration are not fully understood. Methods: Therefore, soil physicochemical properties, enzymatic activities, microbial communities, and key C and N cycling processes were investigated in the vegetation sequence on the Chinese Loess Plateau. Results: The results indicated that vegetation restoration had significant positive effects on soil nutrients, C and N cycling rates, and enzymatic activities. Bacterial richness increased significantly along the chronosequence, while fungal richness decreased, but microbial diversity showed less variation. There were no clear covariant trends between soil properties, microorganisms, and nutrient cycles with vegetation restoration. Bacterial and fungal communities were sculptured by similar soil physicochemical indices, which exert more influence on bacteria than on fungi. C cycles were directly and significantly affected by soil physicochemical properties and bacterial composition/richness, but not by fungal communities. N cycles were directly and significantly affected by soil physicochemical properties and fungal composition/richness/diversity, but not by bacterial communities. Furthermore, enzymatic activities were significantly related to C and N cycles, determined mainly by soil physicochemical properties. Soil physicochemical properties, but not microorganism, were key regulators of C and N cycles. Conclusion: Soil physicochemical properties can regulate C and N cycles directly or indirectly by shaping microorganisms or regulating enzymatic activities. The complicated interplay between soil properties, microorganisms, and their regulation of soil nutrient cycleS prevent a clear-cut synergy between the three factors during vegetation restoration. [ABSTRACT FROM AUTHOR]