Inter-specific Variations And Relationships In Leaf Traits Of Six Temperate Species In Northeastern China

Exploring temperal variations in leaf respiration (RL) and influencing factors may improve our understanding of physiological mechanisms regulating RL, which is critical for essessing carbon sink capacity of forests in Northeastern China. In this study, the leaf gas exchange characteristics and related leaf tarits were examined for six temperate tree species for two years. During the growing season in2011(from April to October for the pines; from June to September for the birch), the RL, net photosynthesis rate and air temperature (Tair) were measured in situ with an infrared gas exchange analyzer (LI-6400IRGA) twice per month for Korean pine(Pinus koraiensis), Mongolian pine (P. sylvestris var. mongolica) and white birch (Betula platyphylla). Leaf was sampled immediately after the measurement. Each month during July and September of2012, the diel course of RL and Tair was measured every two hours with a LI-840infrared gas exchange analyzer for Sibiria elm (Ulmus propinqua), white birch (Betula platyphylla), Manchurian walnut (Juglans mandshurica), Manchurian Ash (Fraxinus mandshurica). In July, leaf was also sampled every two hours to measure the diel course of nonstructural carbohydrates (NSC) concentrations. Specific leaf area (SLA) was calculated from oven-dried leaf weight and projected leaf area; NSC concentrations were determined by a modified phenol-sulfuric acid method; and leaf nitrogen concentrations were measured by Kjeldahl method. A stepwise multiple regression procedure was applied to explore the relationships between RL and leaf traits.The seasonal course of the area-based R1(RL-area) for Korean pine, Mongolian pine and white birch varied with tree species. Korean pine and Mongolian pine were peaked in early and late growing season, while the RL-area of white birch declined gradually with the growing season proceeding. The grand means of RL-area during the measuring period was:Korean pine (0.66μmol CO2·m-2·s-1)<white birch (0.84μmol CO2·m-2·s-1)<Mongolian pine (1.18μmol CO2·m-2·s-1). 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 rrelated with Tair in an exponential function. The temperature coefficients (Q10) of RL-area across the seasonl time scale for Mongolian pine, white birch and Korean pine was1.25,1.42and1.42, respectively; The Q10values of RL-mass for Mongolian pine, white birch and Korean pine was1.33,1.78,1.88, respectivey. The leaf trait parameters affecting the RL varied with species, and the soluble sugars concentration significantly influenced the RL for all the species. The diel courses of RL for Sibiria elm, white birch, Manchurian ash and Manchurian walnut were simililar to those of the Tair, and displayed a unimodal pattern. While the occuring time of peak RL varied with species and months. The grand means of RL during the daytime (6:00—18:00) were higher than those during the night. Throught the measuring period, the grand means of RL declined gradually for Sibiria elm, white birch, Manchurian ash and Manchurian walnut. The seasonal courses of RL normalized to10℃(R10) were different between the four species. The diel variations in NSC concentrations were minimal, especially when compared to seasonal variations. Except for Manchurian walnut, soluble sugar and starch concentrations of the other three species displayed a unimodal pattern. The nitrogen concentrations increased during the measuring perion. Across both diel and seasonal time scales, RL was related to Tair in an exponential function for Sibiria elm, white birch, Manchurian ash and Manchurian walnut, but the relationship fited better across the diel time scale than the seasonal time scale. The Q10values across the diel time scale for Sibiria elm, white birch, Manchurian ash and Manchurian walnut displayed a similar seasonal pattern, and increased gradually during the measuring period. The Q10values at the seasonal time scale for Sibiria elm, white birch, Manchurian ash and Manchurian walnut were1.99,2.03,1.95,1.97, respectively and were smaller than the Q10values across the diel time scale by1%,11%,14%,9%, respectively. In this study, the degree of RL acclimation to temperature was quantified by means of two indexes. Both indexes indicated that leaves acclimated to the seasonal changes in temperature, but in both cases thermal acclimation of RL was significantly different between species. Overall, RL of the compound leaf species acclimate to seasonal temperatures to a greater degree than single leaf species.Overall, across both diel and seasonal time scales, RL displayed certain temperal dynamics. While across the diel time scale, RL were controlled mainly by temperature,while across seasonal time scale, RL was jointly controlled by growth rhythm, temperature and leaf traits.