Seasonal variation in the temperature response of leaf respiration in Quercus rubra: foliage respiration and leaf properties

Leaf respiratory temperature responses and general leaf properties of Quercus rubra were measured throughout the 2003 growing season in a deciduous forest in the northeastern USA. Measurements were made in the upper and lower portions of the canopy at two sites with different soil water availability. Correlations among respiration and various leaf properties were examined. At a set temperature (10 and 20°C), area-based leaf respiration rates were higher in both the early and late growing season than in the mid-growing season (0•50 vs 0•33µmol CO2 m2 s-1at 10°C, on average). Upper-canopy leaves generally had higher respiration rates than lower-canopy leaves (0•53 vs 0•30 µmol CO2 m-2 s-1 at 10°C, on average). At the drier site a more significant seasonal pattern in respiration was observed, while at the more mesic site a stronger canopy-position effect was detected. E0, a model variable related to the overall energy of activation of respiration, varied only slightly (52±5 kJ mol-1K-1), and was not influenced by season, site or canopy position. Leaf properties (specific leaf area, nitrogen, soluble sugars) also varied with season, site and canopy position. Leaf N and reducing monose were positively correlated with leaf respiration rates. After isolating single factors (season, site, canopy position), reducing monose could partially explain the seasonality in respiration (32- 79%), and leaf N (Narea) was well correlated with the canopy-position effect. Our results suggest that the temporal and spatial heterogeneities of respiration need to be considered in ecosystem models, but significant simplifications may be made in Q. rubra by assuming a constant temperature coefficient (E0, 52•5 kJ mol-1in this study) or predicting the base respiration rate (R0) from well understood leaf properties