Phenology of leaf morphological, photosynthetic, and nitrogen use characteristics of canopy trees in a cool-temperate deciduous broadleaf forest at Takayama, central Japan

We studied interannual variations in single-leaf phenology, i.e., temporal changes in leaf ecophysiological parameters that are responsible for forest canopy function, in a cool-temperate deciduous broadleaf forest at Takayama, central Japan. We conducted long-term in situ research from 2003 to 2010 (excluding 2008). We measured leaf mass per unit area (LMA), leaf chlorophyll and nitrogen contents, and leaf photosynthetic and respiratory characteristics [dark respiration, light-saturated photosynthetic rate (A_max), maximum carboxylation rate (V_cmax), and electron transport rate (J_max)] of leaves of mature canopy trees of Betula ermanii Cham. and Quercus crispula Blume, from leaf expansion to senescence. All leaf characteristics changed markedly from leaf expansion (late May) through senescence (mid–late October). The photosynthetic capacity of B. ermanii leaves rapidly increased during leaf expansion and decreased during senescence, while that of Q. crispula leaves changed gradually. The relationships among LMA, photosynthetic capacity, and nitrogen content changed throughout the season. The timings (calendar dates) of leaf expansion, maturity, and senescence differed among the 7 years, indicating that interannual variations in micrometeorological conditions strongly affected leaf phenological events. We examined the seasonal changes as a function of the date or cumulative air temperatures. From leaf expansion to maturity, the increases in chlorophyll content, A_max, V_cmax, J_max, and LMA were explained well by the growing-degree days, and their decreases in autumn were explained well by chilling-degree days. Our findings will be useful for predicting the effects of current variations in climatic conditions and future climate change on forest canopy structure and function.