Nitrogen deposition has minor effect on soil extracellular enzyme activities in six Chinese forests

Soil extracellular enzymes play a key role in mediating a range of forest ecosystem functions (i.e., carbon and nutrients cycling and biological productivity), particularly in the face of atmospheric N deposition that has been increasing at an unprecedented rate globally. However, most studies have focused only on surface soils in a single ecosystem. In this study, we aimed to determine whether the effect of simulated N deposition on the activities and ratios of soil enzymes changes with soil depth across six forest ecosystems in eastern China. We collected soil samples from three blocks×four soil depths (0–10cm, 10–20cm, 20–40cm and 40–60cm)×three N treatment levels (control, 50 and 100kgNha−1year−1) at each of the six forest ecosystems. We measured the activities of seven soil enzymes involved in C-, N- and P-cycling. We found that 4–5years of N addition had no significant effect on the activities and ratios of these enzymes in most cases. The interactions among N addition, site and soil depth on soil enzyme activities were not significant, except that acid phosphatase activity showed site-specific responses to N addition. Our findings suggest that the activities of soil enzymes involved in C- and N-cycling generally do not track simulated N deposition in the six forest ecosystems. Further work on plant, soil and microbial characteristics is needed to better understand the mechanisms of soil enzyme activities in response to N deposition in forest ecosystems. [Display omitted] •The effect of N deposition on soil enzymes was studied across six Chinese forests.•N addition had no effect on the activities and ratios of soil enzymes in most cases.•N addition effect did not vary with site and soil depth except acid phosphatase.•Soil enzyme activities do not track N deposition in the six Chinese forests.