Seasonal patterns of foliage respiration in dominant and suppressed Eucalyptus globulus canopies.

We examined spatial and temporal dynamics of foliage respiration in canopies of dominant and suppressed Eucalyptus globulus trees to better understand processes regulating foliage respiration in a young fast-growing stand. Temperature response functions and seasonal measures of respiration (measured at a reference temperature of 15 °C, R₁₅) were studied for approximately 1 year to (i) examine controls on respiration as a function of canopy position, foliar nitrogen and non-structural carbohydrate concentrations and (ii) assess the capacity for thermal acclimation within E. globulus canopies. The short-term temperature response of respiration varied both with canopy position and seasonally. Area-based R(15) measurements declined with increasing canopy depth and were strongly related to foliar N concentrations, especially in upper-canopy positions. R₁₅ was negatively correlated with the average temperature of the preceding 14 days, a pattern consistent with thermal acclimation. In suppressed canopies, R₁₅ was higher than that at similar canopy heights in dominant trees. Similarly, foliar concentrations of non-structural carbohydrates were also relatively higher in suppressed canopies than dominant canopies, providing support for a substrate-based model of leaf respiration. Our data highlight the dynamic nature of foliar respiration within E. globulus canopies, which contrasts with the generally simplistic representation of respiration within most process-based models.