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 t o increase production of these enzymes to enhance the supply of inorganic n itrogen (N) and phosphorus (P). Regulation of enzyme production may be a po int where N and P cycles interact. We measured acid phosphatase and chitina se (N-acetyl ss-D-glucosaminide) activity in soil across a chronosequence i n Hawaii where N and P availability varies substantially among sites and lo ng term fertilizer plots had been maintained for over 4 years. Phosphatase activity was high at all sites. Chitinase activity decreased si gnificantly as age and N availability increased across the chronosequence. Phosphorus addition suppressed phosphatase activity at all sites, while N a ddition increased phosphatase activity at the young, N-limited site. In con trast, N addition repressed chitinase activity only at the N limited young site, and P additions had no effect on chitinase activity. These results su ggest 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.