水分處理對無患子苗木形態、葉部生理及光合作用的影響

Abstract

野外觀察無患子(Sapindus mukorossi)在水分缺乏的情況下仍能生長良好，為了解其適應機制，本研究對三年生無患子苗木做不同水分處理，並針對其形態、生理及內部調節進行探討。 本研究以土壤含水率為依據對無患子苗木做三種水分處理，結果顯示無患子苗木在充分供水下有最大生長量，但卻可在對很多植物已是永久凋萎點的極低土壤含水率(RWC 4.96%)下生存。苗木外觀除葉片角度變化極顯著外，生物量分配差異不大，葉片外部形態亦無顯著變化。在細胞組織層級上具高比例的質外固著水、低的細胞壁彈性係數與高濃度的可溶性物質，及相當低的氣孔導度減少蒸散，顯示無患子苗木具相當強的防止水分散失能力，有助於缺水逆境中生存。 無患子的光合作用能力在充分供水時最佳，而嚴重缺水時光合作用速率顯著變差，但經葉綠素螢光的測定得知光合系統並未因缺水受到傷害，推測類囊體膜脂質的調控能在缺水環境下維持光合路徑穩定性，有利其在乾燥環境的生存。經試驗結果無患子具多種對缺水環境的耐受因子，有相當強的抗旱能力，但也相對限制最大光合潛力，在水分充足環境下光合能力低於其他生活型態相近之植物而不利於競爭。

From field observations, we found that Sapindus mukorossi has good performance in water deficit habitat. In order to understand the adaptation mechanism of S. mukorossi, we planted three-year-old seedlings under various water treatments and measured the responses on phenology, physiology and internal adjustment of the seedlings. In this study we applied three water treatments based on soil relative water content. The results indicate that S. mukorossi had the best performance under sufficient water supply, but can survive on dry soil, which represent permanent wilting point for some other plants (RWC 4.96%). There’s no obvious difference in the biomass allocation and leaf morphological response among treatment, except the leaf angle. S. mukorossi shows strong avoidance function to avoid the loss of body water, such as low stomatal conductance, high apoplastic water content in tissue, dense cytoplasm and low elasticity coefficient of cell wall, which can help S. mukorossi to survive in drought environment. S. mukorossi grown under sufficient water supply had the best photosynthetic performance and the lowest which under drought treatment. However, the result of the analysis of leaf plasma membrane and chlorophyll fluorescence show that there’s no damage of photosystem under water deficit condition and plant can maintain photosynthetic capacity in drought environment. High level protection of the photosystem might contribute to the maintenance of photosynthetic capacity during water deficit. However, high tolerance of drought stress of S. mukorossi could inhibit photosynthetic potential, thus, under sufficient water supply condition, it would not be beneficial to compete with other similiar lifestyle plants.