Effect of high light and desiccation on photosystem II in the seedlings and mature plants of tropical seagrass Enhalus acoroides during low tide

During low tide, the intertidal seagrass Enhalus acoroides is often exposed to high light and desiccation, which can seriously threaten its survival, at least partly by inhibiting photosystem II (PSII) activity. The response of leaves of E. acoroides to high light and desiccation was compared for seedlings and mature plants. Results show that the resistance of seedling and mature leaves to high light was quite similar, but to desiccation was very different. Seedling leaves were more sensitive to desiccation than the mature plant leaves, but had better water retention. The damage of desiccation to seedling leaves was mainly caused by dehydration, whereas that to mature plant leaves was caused by hypersaline toxicity. The recovery rate of PSII of seedling leaves was significantly slower than that of the mature plants after the stresses disappeared, which may at least partly contribute to seedling mortality in the wild. In addition, compared to high light, desiccation seriously inhibited the recovery rate of PSII activities even if the leaves became fully rehydrated to their normal relative water content (RWC) in the following re-immersion. Desiccation inhibited the recovery rate of RC/CS M (reaction center per cross section (at t = t F m )) to decrease the production of assimilatory power, which maybe the cause of the slower PSII recovery in desiccation treatments. This study demonstrates that desiccation particularly coupling with high light have a very negative effect on the PSII of E. acoroides during low tide and the sensitivity of seedlings and mature plants to desiccation is significantly different, which have important reference significance to choose an appropriate transplanting depth where seedlings and mature plants of E. acoroides not only receive sufficient light for growth, but also that minimize desiccation stress during low tide.