Responses of soil acid phosphatase and beta-glucosidase to nitrogen and phosphorus addition in two subtropical forests in southern China

Abstract

Elevated nitrogen (N) deposition has dramatically altered soil phosphorus (P) and carbon (C) cycles in forests and altered extracellular enzyme activity. However, the effects of N addition and the interactive effects of combined N and P additions on soil enzyme (e.g. phosphatase and glucosidase) activity in different types of forests (young vs. old-growth) remain unclear. To better understand this, a long-term N–P fertilization experiment was initiated in January 2007 in two subtropical forests (an old-growth monsoon evergreen broadleaf forest (MEBF) and a young Masson pine forest (MPF)) in southern China. Four treatments were established, including control (no nutrient addition), N addition (150 kg Nha−1yr−1), P addition (150 kg Pha−1yr−1) and NP addition (150 kg Nha−1yr−1 plus 150 kg Pha−1yr−1). Soil physicochemical properties, acid phosphatase (APA-s) and β-glucosidase (BGA-s) activity per soil were measured in July 2012 and July 2013. Both APA-s and BGA-s were higher in MEBF than in MPF. N addition significantly stimulated APA-s in MEBF and BGA-s in MPF. P addition significantly suppressed APA-s in both forests and BGA-s in MEBF. Moreover, P addition decreased the stimulating effect of N addition on APA-s in MEBF and on BGA-s in MPF. Our results suggest that (1) N addition may exacerbate soil P limitation in old-growth forests and result in the deficiency of easily available C in young forests and (2) P addition may mitigate these negative effects of N addition in both forest types. Our findings suggest that P fertilization may be an effective practice to improve soil P availability in old-growth forests and soil C availability in young forests under N deposition condition.