Yoshimura Kenichi, Saiki Shin-Taro, Yazaki Kenichi, Ogasa Mayumi Y, Shirai Makoto, Nakano Takashi, Yoshimura Jin, Ishida Atsushi
Kansai Research Center, Forestry and Forest Products Research Institute, Fushimi, Kyoto 612-0855, Japan.
for Ecological Research, Kyoto University, Otsu, Shiga 520-2113, Japan.
Sci Rep. 2016 Apr 15;6:24513. doi: 10.1038/srep24513.
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.
气候引发的森林死亡现象在多个生物群落中广泛存在，对森林生态系统的物种组成、功能及初级生产力产生了强烈影响。木质部边材中的水力衰竭和碳饥饿是解释干旱导致树木死亡的主要假说。由于难以获取足够多关于成年树木干旱致死的实地观测数据，目前对于树木死亡生理机制的理解仍存在争议。然而，同时考察成年树木在脱水和再水化过程中的水分与碳利用情况，将有助于阐明水力衰竭和碳饥饿在树木枯萎中的作用。在此，我们展示了具有不同水分利用策略的木本植物远端枝条的导水率损失百分比（PLC）和非结构性碳水化合物（NSC）含量的变化过程。在干旱条件下，随着PLC的发展，淀粉转化为可溶性糖，供水后导水率得以恢复。在脱水和再水化过程中，NSC的转化与PLC变化密切相关，这表明储存的碳有助于树木在干旱条件下存活；进一步的碳饥饿会加速水力衰竭。我们预测，即使是进展缓慢的干旱也会通过碳饥饿使森林生态系统退化，导致比目前预测更为频繁的灾难性森林死亡。
