Regulation of soil phosphatase and chitinase activity by N and P availability

Soil microorganisms and plants produce enzymes that mineralize organically bound nutrients. When nutrient availability is low, the biota may be able to increase production of these enzymes to enhance the supply of inorganic nitrogen (N) and phosphorus (P). Regulation of enzyme production may be a point where N and P cycles interact. We measured acid phosphatase and chitinase (N-acetyl ss-D-glucosaminide) activity in soil across a chronosequence in Hawaii where N and P availability varies substantially among sites and long term fertilizer plots had been maintained for over 4 years. Phosphatase activity was high at all sites. Chitinase activity decreased significantly as age and N availability increased across the chronosequence. Phosphorus addition suppressed phosphatase activity at all sites, while N addition increased phosphatase activity at the young, N-limited site. In contrast, N addition repressed chitinase activity only at the N limited young site, and P additions had no effect on chitinase activity. These results suggest that the regulatory relationship between nutrient supply and nutrient mineralization are asymmetric for N and P, and that the differences could help to explain differences observed in patterns of N and P availability.