Effects of nitrogen addition and increased precipitation on soil hydrolytic enzyme activities in a temperate meadow steppe

摘要

Soil extracellular enzymes are the proximal drivers of organic matter decomposition via mineralizing organic matter and releasing carbon and nutrients in forms that can be assimilated.This process can be greatly affected by the change of temperature, precipitation, and other environmental factors.However, few experiments have been conducted to study the responses of hydrolase activities to the interaction of nitrogen (N) deposition and precipitation.The main purpose of this study was to investigate the change of soil hydrolytic enzyme activities in a Stipa baicalensis meadow steppe with a complete randomized block factorial experimental design with the N addition, the increased precipitation and a combination of N and precipitation increase in northeastern China.These hydrolases included carbon-acquisition enzymes (α-glucosidase, αG;β-glucosidase, βG;β-xylosidase, βX;Cellobiohydrolase, CBH), nitrogen-acquisition enzymes (N-acetylglucosaminidase, NAG;Leucine aminopeptidase, LAP), and phosphorus-acquisition enzymes (acid phosphatases, aP).The results showed that N addition just significantly increased the activity of NAG and increased precipitation had no significant effect on all hydrolase activities, N addition and increased precipitation had significantly interactive effects on the activity of βX and CBH.However, single N addition resulted in an increase in the activity of NAG, βG, βX and CBH, as well as the content of soil organic carbon (SOC), soil total N (TN), soil available N (AN) and soil moisture (SM).But, all the significant effects disappeared when precipitation synchronously increased.On the other side, single increased precipitation led to the obvious increase of SOC, TN and AN, and the change of precipitation had no significant effects on hydrolytic enzyme activities in all plots.Correlation analysis demonstrated that soil properties enormously influenced NAG but had relatively weak effects on the activity of other enzymes.Redundancy analysis indicated that the patterns of hydrolase activities were mainly driven by soil pH, SOC and TN.Overall, our results suggested that the variation of carbon-acquisition and nitrogen-acquisition hydrolase activities caused by N addition was offset by the effects of increased precipitation.Furthermore, the differential responses of hydrolases to N addition and increased precipitation may have important implications for carbon and nutrient cycling under the conditions of global change in the future.