Within-canopy gradients of nitrogen and photosynthetic activity of Eucalyptus nitens and Eucalyptus globulus in response to nitrogen nutrition

Growth of plantation eucalypts responds strongly to applied nitrogen ( N). Above-ground biomass accumulation, gas exchange and foliar N per unit leaf area (N-area) along vertical and lateral gradients within a canopy were assessed in Eucalyptus nitens ( Deane & Maiden) Maiden cuttings in a glasshouse experiment (E. nitens(glasshouse) cuttings) and E. globulus Labill. saplings in a field trial (E. globulus(field) saplings) under varying levels of applied N. A large range of maximum net photosynthesis (A(max)) and N-area was observed among different leaf-age classes (apical, expanding, mature and old) within vertical and lateral gradients in both E. nitens(glasshouse) cuttings and E. globulusfield saplings. In both experiments, Narea was generally positively correlated with levels of applied N but Amax was not. There was generally no relationship between A(max) and N-area in either E. nitens(glasshouse) cuttings or E. globulusfield saplings, except in expanding and mature leaves within the vertical gradient of E. nitens(glasshouse) cuttings. These results contribute to the emerging consensus among workers that within species, poor correlation between A(max) and N-area is often observed. Biomass data indicate that increased N application significantly increased growth in both experiments. Overall, the results of these experiments provide information that will further resolve the predictive strength of process-based models that describe growth of E. nitens and E. globulus in plantations.