[Effects of Farmland Abandonment on Soil Enzymatic Activity and Enzymatic Stoichiometry in the Loess Hilly Region, China].

Abstract

Clarifying the characteristic of soil enzymatic activity and stoichiometry variations as well as their influencing factors following farmland abandonment have important implications for understanding soil nutrient availability after revegetation and for illuminating the underlying mechanisms of soil nutrient cycling in ecosystems. To determine microbial nutrient limitations after farmland abandonment and to explore the driving factors of the variations in soil enzymatic activity and stoichiometry along a chronosequence of abandoned farmlands (0-, 10-, 20-, and 30-year-old) in the Loess Hilly Region, China, the potential activities of carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring enzymes, soil physicochemical properties, and plant diversity and family composition were measured. The results showed that the activities of β-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP), and alkaline phosphatase (ALP) increased significantly with the increasing years of land abandonment, whereas the activity of β-1,4-glucosidase (BG) showed the opposite change trend. Additionally, the ratios of BG:(NAG+LAP) and BG:ALP had the same variation trend with BG activity, which decreased significantly with increasing time, but the ratio of (NAG+LAP):ALP showed an increasing trend and then decreased, with the highest values observed in the 20-year sites. Moreover, the vector length of soil enzymatic stoichiometry decreased significantly as the years of land abandonment inceased, suggesting a reduced microbial C limitation after farmland abandonment. The vector angles <45°were observed at farmlands (0-year sites) and 10-year sites, whereas angles >45°were detected at 20-and 30-year sites, indicating that soil microbial communities were N-limited in the first 10 years of land abandonment and thereafter were P-limited. The redundancy analysis (RDA) reveled that soil organic C content, total N content, the C:N and C:P ratios, soil pH values, and plant diversity had significant effects on soil enzymatic activity and stoichiometry. A variation partitioning analysis (VPA) further demonstrated that edaphic and vegetation factors explained 62.0% of the total variance of soil enzymatic activity and stoichiometry. It should be noted that the interaction between vegetation characteristics and soil physicochemical properties was the major factor affecting soil enzymatic activity and stoichiometry, which explained 37.1% of the variance of the soil enzyme characteristics. Collectively, the application of P fertilizer should be considered to mitigate the deficiency of available P in the ecosystem during farmland abandonment, and these findings may provide a theoretical basis for understanding the mechanisms underlying microbe-mediated biogeochemical cycles as well as guiding soil nutrient management and the sustainable development of the ecological environment.