Kenichi Yazaki: Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan.
Mayumi Y Ogasa: Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan.
Makoto Shirai: Graduate School of Bioresource Sciences, Nihon University, Fujisawa, Kanagawa 252-0880, Japan.
Takashi Nakano: Mount Fuji Research Institute, Yamanashi Prefectural Government. Fuji-Yoshida, Yamanashi 403-0005, Japan.
Jin Yoshimura: Department of Mathematical and Systems Engineering, Graduate School of Science and Technology, Shizuoka University, Hamamatsu, Shizuoka 432-8561, Japan.
Climate-induced forest die-off is widespread in multiple biomes, strongly affecting the species composition, function and primary production in forest ecosystems. Hydraulic failure and carbon starvation in xylem sapwood are major hypotheses to explain drought-induced tree mortality. Because it is difficult to obtain enough field observations on drought-induced mortality in adult trees, the current understanding of the physiological mechanisms for tree die-offs is still controversial. However, the simultaneous examination of water and carbon uses throughout dehydration and rehydration processes in adult trees will contribute to clarify the roles of hydraulic failure and carbon starvation in tree wilting. Here we show the processes of the percent loss of hydraulic conductivity (PLC) and the content of nonstructural carbohydrates (NSCs) of distal branches in woody plants with contrasting water use strategy. Starch was converted to soluble sugar during PLC progression under drought, and the hydraulic conductivity recovered following water supply. The conversion of NSCs is strongly associated with PLC variations during dehydration and rehydration processes, indicating that stored carbon contributes to tree survival under drought; further carbon starvation can advance hydraulic failure. We predict that even slow-progressing drought degrades forest ecosystems via carbon starvation, causing more frequent catastrophic forest die-offs than the present projection.
