Yazaki Kenichi, Kuroda Katsushi, Nakano Takashi, Kitao Mitsutoshi, Tobita Hiroyuki, Ogasa Mayumi Y, Ishida Atsushi
Department of Plant Ecology, Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki, 305-8687, Japan.
Department of Wood Properties, Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki, 305-8687, Japan.
PLoS One. 2015 Aug 20;10(8):e0135117. doi: 10.1371/journal.pone.0135117. eCollection 2015.
Partial leaf shedding induced by hydraulic failure under prolonged drought can prevent excess water consumption, resulting in delayed recovery of carbon productivity following rainfall. To understand the manner of water use of invasive species in oceanic island forests under a fluctuating water regime, leaf shedding, multiple physiological traits, and the progress of embolism in the stem xylem under repeated drought-irrigation cycles were examined in the potted saplings of an invasive species, Bischofia javanica Blume, and three endemic native species, Schima mertensiana (Sieb. Et Zucc,) Koitz., Hibiscus glaber Matsum, and Distylium lepidotum Nakai, from the Bonin Islands, Japan. The progress of xylem embolism was observed by cryo-scanning electron microscopy. The samples exhibited different processes of water saving and drought tolerance based on the different combinations of partial leaf shedding involved in embolized conduits following repeated de-rehydration. Predawn leaf water potential largely decreased with each successive drought-irrigation cycle for all tree species, except for B. javanica. B. javanica shed leaves conspicuously under drought and showed responsive stomatal conductance to VPD, which contributed to recover leaf gas exchange in the remaining leaves, following a restored water supply. In contrast, native tree species did not completely recover photosynthetic rates during the repeated drought-irrigation cycles. H. glaber and D. lepidotum preserved water in vessels and adjusted leaf osmotic rates but did not actively shed leaves. S. mertensiana exhibited partial leaf shedding during the first cycle with an osmotic adjustment, but they showed less responsive stomatal conductance to VPD. Our data indicate that invasive B. javanica saplings can effectively use water supplied suddenly under drought conditions. We predict that fluctuating precipitation in the future may change tree distributions even in mesic or moist sites in the Bonin Islands.
长期干旱下由水力衰竭引起的部分落叶可防止水分过度消耗，从而导致降雨后碳生产力的恢复延迟。为了解在波动水分条件下大洋岛屿森林中入侵物种的水分利用方式，我们对入侵物种重阳木（Bischofia javanica Blume）以及来自日本小笠原群岛的三种本地特有物种——日本紫茎（Schima mertensiana (Sieb. Et Zucc,) Koitz.）、光叶木槿（Hibiscus glaber Matsum）和鳞秕蚊母树（Distylium lepidotum Nakai）的盆栽幼树，在反复干旱-灌溉循环下的落叶情况、多种生理特征以及茎木质部栓塞进展进行了研究。通过低温扫描电子显微镜观察木质部栓塞的进展。根据反复脱水后栓塞导管中涉及的部分落叶的不同组合，样本呈现出不同的节水和耐旱过程。除重阳木外，所有树种的黎明前叶水势随着连续的干旱-灌溉循环而大幅下降。重阳木在干旱条件下显著落叶，并对水汽压亏缺表现出气孔导度响应，这有助于在恢复供水后，使剩余叶片的气体交换得以恢复。相比之下，本地树种在反复干旱-灌溉循环期间光合速率并未完全恢复。光叶木槿和鳞秕蚊母树在导管中保存水分并调节叶片渗透速率，但不主动落叶。日本紫茎在第一个循环中表现出部分落叶并伴有渗透调节，但其对水汽压亏缺的气孔导度响应较小。我们的数据表明，入侵的重阳木幼树能够在干旱条件下有效利用突然供应的水分。我们预测，未来降水的波动可能会改变小笠原群岛中即使是湿润或潮湿地区的树木分布。
