Forest productivity and efficiency of resource use across a chronosequenceof tropical montane soils

We tested the hypothesis that plants adjust to nutrient availability by alt ering carbon allocation patterns and nutrient-use efficiency (NUE = net pri mary production NPP per unit nutrient uptake), but are constrained by a tra de-off between NUE and light-use efficiency (epsilon = NPP per unit interce pted light). NPP, NUE and E were measured in montane Metrosideros polymorph a forest across a 4.1 x 10(6) yr space for time substitution chronosequence in which available soil N and P pools change with site age. Although the r ange of N and P availability across sites was broad, there was little diffe rence in NPP between sites, and in contrast to theories of carbon allocatio n relative to limiting resources, we found no consistent relationships in p roduction allocation to leaves, fine roots or wood. However, canopy nutrien t pools and fluxes were correlated with the mass of fine roots per unit soi l volume and there was a weak but positive correlation of NPP with LAI. Pat terns of E and NUE across the soil developmental sequence were opposite to each other. E increased as nutrient availability and nutrient turnover incr eased, while NUE decreased in response to the same influences but reached i ts highest values where either N or P availability and turnover of both N a nd P were low. A negative correlation between E and NUE supports the hypoth esis that a trade-off exists between E and leaf characteristics affecting N UE.