The responses of carbon- and nitrogen-acquiring enzymes to nitrogen and phosphorus additions in two plantations in southern China

In tropical plantations, nutrients such as nitrogen (N) or phosphorus (P) are often applied as management practices. However, the effects of such nutrient additions on topsoil C- and N-acquiring enzymes activities are unclear. In this study, the impacts of fertilization on β-1,4-glucosidase (BG), β-D-cellobiosidase (CBH), β-1,4-xylosidase (BX), β-1,4-N-acetyl-glucosaminidase (NAG), and leucine amino peptidase (LAP) enzymes activities from topsoil and litter layer of two tropical plantations (Acacia auriculiformis and Eucalyptus urophylla) were measured. The results showed that N addition had neutral impact on topsoil enzymes, while significantly elevating the activities of BG, CBH, BX, and NAG in the litter layer. P fertilization had no impacts except for an elevation of NAG in litter sample. There was no interactions found between N and P additions on these enzyme activities. The clearer impacts of N over P fertilization were unexpected because that the study site receives a high rate of atmospheric N deposition, and has low soil P availability. The impact of P fertilization on hydrolytic enzyme activities may be less important compared with that of N.