[Relationships between stoichiometric characteristics of soil enzymatic activities and environmental factors in parallel valleys of western Yunnan, China.]

The valleyes of Hengduan Mountains contain the landscapes with high heterogeneity as well as high diversity of climate and vegetation types. To explore the soil cycling of four elements (C, N, P, S) across the parallel valleys of Nujiang River, Lancang River, Jinsha River and Yuanjiang River in western Yunnan, we collected top soils (0-10 cm) in forests, grasslands, and croplands. The activities of soil enzymes, including β-glucosidase (BG), β-N-acetylglucosaminidase (NAG), acid phosphatase (AP), and sulfatase (SU), which drive the soil C, N, P and S cycling, were determined. We analyzed the relationships of soil enzymatic activities and their stoichiometric characteristics with environmental factors. The activities of both AP and NAG had significant difference among different basins and different land types. The activities of AP, BG, NAG and SU were significantly positively related with each other. From southeast to northwest, the activities of BG, NAG, and SU increased with the altitude. Across all basins, the ecoenzymatic ratios of soils always ranked as AP:SU > BG:SU > NAG:SU > BG:NAG > BG:AP > NAG:AP. Compared with forest and grassland soil, cropland soils in each watershed had a higher BG:NAG and a lower NAG:AP (except Yuanjiang River basin). Moreover, AP:SU, BG:SU and NAG:SU of cropland soils were lower than those of forest and grassland in Yuanjiang River basin. However, they were higher than forest and lower than grassland in both Lancang River basin and Jinsha River basin. Soil enzyme activities and enzymatic stoichiometry were affected by physicochemical properties of soil, climate, and location, with the most contribution from soil physicochemical properties. Agricultural land use significantly affected the stoichiometry of C:N:P acquiring enzymes in soils by reducing the activity of N-degrading enzymes relative, resulting in the increases of BG:NAG and the decreases of NAG:AP. Agricultural activities had limited effects on other enzymatic stoichiometries.