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

Abstract

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. globulus_field saplings. In both experiments, N_area was generally positively correlated with levels of applied N but A_max was not.

There was generally no relationship between A_max and N_area in either E. nitens_glasshouse cuttings or E. globulus_field 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.