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

• Effects of N and/or P addition on soil enzyme activity in two forest types.
• Adding N increased acid phosphatase activity in old soils.
• Adding N increased β-glucosidase activity in young soils.
• Adding P alleviated the stimulation of N on acid phosphatase activity in old soils.
• Adding P alleviated the stimulation of N on β-glucosidase activity in young soils.

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 N ha−1 yr−1), P addition (150 kg P ha−1 yr−1) and NP addition (150 kg N ha−1 yr−1 plus 150 kg P ha−1 yr−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.