Differences in transpiration characteristics of Japanese beech trees, Fagus crenata, in Japan

Japanese beech (Fagus crenata Blume) is widely distributed across the Japan archipelago. This species requires morphological and physiological plasticity to cope with the diverse environmental conditions across its geographical range. In this study, we monitored transpiration (E) to examine plasticity mechanisms as an example of geographical variation in whole-tree water use. We determined E by measuring the sap flux of Japanese beech trees in three stands: Kuromatsunai (KR), Kawatabi (KW) and Shiiba (SH), which were located in different areas in Japan. We conducted biometric measurements to characterize leaf and crown morphology and evaluated geographical variations in E characteristics, such as canopy aerodynamic conductance, canopy stomatal conductance (G(S)) and decoupling coefficient (Omega). Leaf morphology and crown shape showed clear geographical clines. Individual leaf areas decreased in the order KR > KW > SH. The crown shape in the KR and KW stands was cylindrical but planar in the SH stand. We evaluated the effects of leaf and crown morphology on E characteristics. The Omega values showed that, while E in the KW and SH stands was highly sensitive to G(S) and atmospheric evaporative demand, E in the KR stand was sensitive to radiative energy. To maximize carbon gain without further water loss, trees maintain a high G(S) in a moist habitat. For example, the KR trees may decrease E by reducing their absorbed radiation energy by adjusting the individual leaf size and crown structure. Our results indicate that the geographical variation in the water use pattern of Japanese beech is determined by the interaction between its physiological and morphological status.