Effects of nitrogen additions on soil extracellular enzyme activity: A meta-analysis
Anthropogenic nitrogen (N) deposition could affect the rate of forest litter decomposition and soil organic matter (SOM) storage by regulating extracellular enzyme activity (EEA). Effects of long-term N additions on microbial enzyme activities have been a research focus over decades, but few studies have synthesized the extant datasets to elucidate the mechanistic controls of N impact on EEA. Ten enzymes are studied in the meta analysis including labile carbon (C) acquired enzymes α-1,4-Gulcosidase (AG), β-1,4-Glucosidase (BG), β-D-Cellobiosidase (CBH) and β-1,4-Xylosidase (BX), N acquired enzymes β-1,4-N-Acetyl-Glucosaminidase (NAG), leucine aminopeptidase (LAP) and urease, phosphorus (P) acquired enzymes acid phosphatase (AP), refractory C acquisition enzymes phenol oxidase (POX) and peroxidase (PER). We hypothesized that adding N would significantly depress EEA associated with microbial N and recalcitrant C acquisitions, and increase EEA associated with labile C acquisitions across a wide range of environmental, edaphical and physiological conditions. The varying responses of each EEA to N additions were also further explored under different environmental, edaphical and physiological conditions.
In this meta-analysis, we synthesized responses of ten soil extracellular enzymes to N additions in more than 35 published field and laboratory studies. Our preliminary results showed that on average, the activity of BG increased by 10.1% and POX decreased consistently by 10.8% in response to N addition, and the elevated directional trends were consistent across different studies. On average, the activity of LAP increased by 3.4% and the activity of urease, AG, BX, CBH, NAG, PER and AP activities decreased by 9.2%, 5.7%, 3.2%, 2.5% 1.8%, 1.5% and 0.7%, respectively. Further analysis showed that the response of EEA to N addition varied significantly across different soil types. Our study can potentially help clarify the overall effect of N addition on EEA and elucidate the influences of environmental, edaphical and physiological situations in altering N effect on EEA. The information obtained in this study can be useful to simulate responses of nutrient release and cycling to N enrichment in enzyme-driven SOM decomposition models.