Seasonal fluctuations and temperature dependence of leaf gas exchange parameters of co-occurring evergreen and deciduous trees in a temperate broad-leaved forest

摘要

Seasonal fluctuations in leaf gas exchange parameters were investigated in three evergreen (Quercus glauca Thunb., Cinnamomum camphora Sieb. and Castanopsis cuspidata Schottky) and one deciduous (Quercus serrata Thunb.) co-occurring, dominant tree species in a temperate broad-leaved forest. Dark respiration rate (R_n), maximum carboxylation rate (V_cmax) and stomatal coefficient (m), the ratio of stomatal conductance to net assimilation rate after adjustment to the vapor pressure deficit and internal carbon dioxide (CO₂) concentration, were derived inversely from instantaneous field gas exchange data (one-point method). The normalized values of R_n and V_cmax at the reference temperature of 25 °C (R_n25, V_cmax25) and their temperature dependencies (ΔH_a(R_n), ΔH_a(V_cmax)) were analyzed. Parameter V_cmax25 ranged from 24.0–40.3 μmol m−2 s−1 and ΔH_a(V_cmax) ranged from 29.1–67.0 kJ mol−1. Parameter R_n25 ranged from 0.6–1.4 μmol m−2 s−1 and ΔH_a(R_n) ranged from 47.4–95.4 kJ mol−1. The stomatal coefficient ranged from 7.2–8.2. For the three evergreen trees, a single set of V_cmax25 and R_n25 parameters and temperature dependence curves produced satisfactory estimates of carbon uptake throughout the year, except during the period of simultaneous leaf fall and leaf expansion, which occurs in April and May. In the deciduous oak, declines in V_cmax25 were observed after summer, along with changes in V_cmax25 and R_n25 during the leaf expansion period. In all species, variation in m during periods of leaf expansion and drought should be considered in modeling studies. We conclude that the changes in normalized gas exchange parameters during periods of leaf expansion and drought need to be considered when modeling carbon uptake of evergreen broad-leaved species.