沂蒙山区金银花光合效率响应极端干旱—复水的干旱阈值研究

As global climate change, regional severe soil drought occurs frequently, which seriously restricts photosynthetic physiological process of plants. The occurrence of severe drought could also reduce the photosynthetic efficiency which reflects both photosynthesis and transpiration, leading in increasing trends of risk in trees. Re-watering is an effective and adaptive measure to remit the damage of drought on trees. How to confirm the drought thresholds of rewatering based on photosynthetic physiological process is one of the scientific questions in establishing adaptive mesure system of high water use efficiency. This project will measure and analyze the response and mechanism of photosynthetic efficiency to severe drought and re-watering in Yimeng mountainous area, by choosing Lonicera japonica Thunb. as material, using the method of artificial water offering, natural plants consumption, and continuous moisture observation with simulated field test. The drought thresholds composed by soil water point and its lasting times, at which photosynthetic efficiency changes significantly, will be revealed, and the re-watering thresholds maintaining high photosynthetic productivity will be also determined. All the achievements in this project will be significant to decreasing risk of productivity and proving water government efficiency in Lonicera japonica under severe drought conditions. It can also provide scientific evidence for establishing systems of forest positively adapting to severe drought.

气候变化导致区域性土壤极端干旱频发，严重制约树木光合生理过程，降低光合效率。复水是缓解树木生产力损失的重要适应性措施。如何立足于植物光合生理过程确定复水的干旱阈值，是极端干旱频发区建立高效用水适应性措施体系亟待解决的科学问题之一。本项目以沂蒙山区灌木金银花（ Lonicera japonica Thunb.）为试验材料布设类大田试验，设计人工补充灌水、植物自然耗水和持续水分测定相结合的控水方法，分析金银花光合效率响应“极端干旱水分阈值—阈值持续—复水”的动态过程，阐明光合效率发生显著变化（降低、恢复）的生理学机理；确定金银花光合效率显著变化的干旱阈值和较高光合生产力的复水阈值（水分阈值及其持续时间）。研究结果对持续干旱背景下沂蒙山区金银花生产力损失降低与高效水分管理具有重要意义，为区域典型灌木积极应对极端干旱逆境的适应性措施体系构建供科学支撑。

土壤极端干旱严重制约沂蒙山区金银花光合作用。本研究探讨了土壤持续干旱下金银花光合生理过程的变化规律，阐明了金银花光合效率对不同极端干旱水分阈值—阈值持续—复水的响应过程与机理，确定了维持金银花较高光合生产力的复水阈值。研究发现：[1]金银花净光合速率（Pn）和水分利用效率（WUE）对持续降低的土壤含水量（RSWC）表现为显著的阈值响应。当42.38%≤RSWC≤96.05%时，金银花具有较高光合生产力和高效生理用水特性；当RSWC降低至29.71%时，非气孔限制导致Pn和WUE开始显著减小。[2]确定RSWC≤29.71%的低产低效水为金银花极端干旱水分范围，气孔机制转折点（29.71%）、叶片萎蔫点（11.44%）和Pn≈0点（11.44%）为极端干旱下特征水分阈值。[3]极端干旱下非气孔限制导致光合效率显著降低，非气孔限制因素与水分阈值、阈值持续时间有关。在阈值范围23.99%≤RSWC≤29.71%时，抗氧化酶活性降低、光合机构膜系统破坏是抑制光合作用的主要非气孔因素；当RSWC<23.99%时，PSⅡ破坏、抗氧化酶活性降低、光合机构膜系统破坏共同导致光合作用的非气孔限制。两个水分阈值胁迫持续期间，PSⅡ、酶活性和光合机构膜系统持续损伤，以持续前5-10d的损伤程度最大，当胁迫持续至一定时间后，PSⅡ、酶活性和光合机构膜系统发生严重损伤或不可逆性破坏。[4]不同极端干旱复水后光合效率的恢复速度和程度可分为4种类型：快速恢复至对照值、较快恢复至平均值、较慢恢复至平均值、较慢恢复至较低值，与复水前气孔和非气孔因素的损伤程度有关。复水前，气孔关闭、抗氧化酶活性降低、PSⅡ和光合机构膜系统损伤均是可逆的处理，Pn和WUE复水后5d内恢复至或超过对照值；若气孔和非气孔因素有其一的损伤是不可逆的，则复水后恢复速度较慢，且复水30d时仍不能完全恢复。[5]极端干旱下，基于两个水分阈值，确定了金银花维持较高光合生产力的复水阈值：RSWC29.71%（20）、RSWC11.44%（10），在水分阈值RSWC=29.71%、11.44%分别持续≤20d、≤10d 时复水，金银花能恢复至均值以上较高光合生产力水平。研究结果可为极端干旱下沂蒙山区金银花的合理水分管理和适应性措施体系构建提供参考。