Abstract:To understand the factors influencing seasonal variation in leaf respiration (RL), the leaf gas exchange characteristics and related leaf traits were examined for three tree species in northeastern China. The species were Korean pine (Pinus koraiensis), Mongolian pine (P. sylvestris var. mongolica) and white birch (Betula platyphylla). The RL, net photosynthetic rate, and air temperature (Tair) were measured in situ with an infrared gas exchange analyzer (LI-6400 IRGA) twice per month throughout the growing season in 2011 (from April to October for the pines; from June to September for the birch). Specific leaf area (SLA) was calculated from oven-dried leaf weight and projected leaf area; nonstructural carbohydrates (NSC) concentrations were determined by a modified phenol-sulfuric acid method; and leaf nitrogen concentrations were measured by the Kjeldahl method. A stepwise multiple regression procedure was applied to explore the relationships between RL and leaf traits. The area-based RL (RL-area) of Korean pine and Mongolian pine peaked in early and late growing seasons, while the RL-area of white birch declined gradually with the growing season proceeding. The ratio of RL-area to total photosynthesis and leaf trait parameters (i.e., soluble sugar concentration, starch concentration, SLA, leaf nitrogen concentration) also exhibited seasonal variations for the three species. The RL-area of pines were positively correlated with Tair, while that of the birch was not. The mass-based RL (RL-mass) of the three tree species, however, were all positively related with Tair in an exponential function. The leaf trait parameters affecting the RL varied with species, and the soluble sugars concentration significantly influenced the RL for all the species. These results suggest that seasonal variation in RL jointly controlled by growth rhythm, temperature and leaf traits.
