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 x four soil depths (0-10 cm, 10-20 cm, 20-40 cm and 40-60 cm) x three N treatment levels (control, 50 and 100 kg N ha(-1) year(-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 4-5 years of N addition had no significant effect on the activities and ratios of these enzymes inmost 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. (C) 2017 Elsevier B.V. All rights reserved.