Response of soil extracellular enzyme activity to experimental precipitation in a shrub-encroached grassland in Inner Mongolia

Abstract

Shrub encroachment has caused a vegetation shift in arid and semiarid grassland ecosystems around the world, leading to marked changes in ecosystem structures and functions. Soil extracellular enzyme activity (EEA) is an informative indicator of microbial decomposition and plays an important role in soil biogeochemical cycles, but it is unclear how shrub encroachment affects soil EEA, especially in the future precipitation pattern under climate change. In this study, we measured soil EEAs in a shrub-encroached grassland in Inner Mongolia, China, after four years of in situ experimental precipitation manipulation. Soil samples were collected from grass patches and shrub patches in four precipitation manipulation treatments (−30%, control, +30%, and +50%). Four soil enzymes involved in carbon cycling (α-glucosidase, AG; β-1,4-glucosidase, BG; β-D-cellobiosidase, CB; and β-xylosidase, XS), two nitrogen-acquiring enzymes (β-1,4-N-acetyl-glucosaminidase, NAG; and leucine amino peptidase, LAP), and one phosphorus-acquiring enzyme (acid phosphatase, AP) were investigated. The results showed that BG, XS, and LAP activities were significantly enhanced in shrub patches than grass patches (p < 0.05). BG, LAP, and AP were significantly different in precipitation treatments (p < 0.05) and were highest in +30% and shrub patches. Shrub encroachment and increased precipitation (+30%) interactively enhanced LAP (p < 0.05). Our study also showed that soil temperature and soil moisture were major factors for the variations in EEA under different precipitation treatments in the grass patches, while soil temperature, NH4+-N and NO3−-N were major causes for those in the shrub patches. Overall, our study highlights that shrub encroachment and altered precipitation can influence soil EEA, which in turn may have consequential effects on nutrients availability and biochemical cycling.