2023 Volume 53 Pages 43-54
Castanopsis sieboldii (Makino) Hatus. is one of the most popular evergreen broad-leaved species, distributing from Okinawa Pref. to the area beyond Kanto region, Japan. However, there are limited estimations of transpiration amounts with sap flow measurements, thereby very few knowledge of its characteristics of water use. Here we evaluated transpiration amounts of three trees of C. sieboldii based on the thermal dissipation method for 12 months from October 2020 to September 2021 within Forestry and Forest Products Research Institute, Ibaraki Pref., Japan. The minimum and maximum of transpiration amounts were found in mid-winter (January 2021) and early summer (June–July), respectively. The crown conductance, which indicates the degree of stomatal openness for whole leaves of a tree, was saturated when daytime mean of solar radiation was more than 200 W m−2. The crown conductance showed a decreasing trend with increasing daytime mean vapor pressure deficit. The daily mean value of soil water content to the depth of 40 cm was about 0.3 to 0.5 during the observation period, resulting in its less effect on the conductance. The optimum value of daytime mean air temperature for the conductance was found for the range of 10–20°C. The three trees showed isohydric behaviors, revealed by the analysis for the response of the conductance to vapor pressure deficit. Therefore, these test trees would avoid hydraulic failure with maintaining steady midday leaf water potential by closing stomata under extremely drought conditions.
