季节性干旱对白皮乌口树(Tarenna depauperata Hutchins)水分状况、叶片光谱特征和荧光参数的影响

Effects of Seasonal Drought on Water Status,Leaf Spectral Traits and Fluorescence Parameters in Tarennadepauperata Hutchins,a Chinese Savanna Evergreen Species

干热河谷稀树灌丛常绿植物能够忍受长达半年以上的季节性干旱胁迫,但对这些常绿植物响应干旱胁迫的生理生态机制研究很少。本研究以干热河谷稀树灌丛优势常绿植物白皮乌口树(Tarenna depauperata Hutchins)为研究对象,分别在雨季和干季测定其叶片的水势、压力-体积曲线、气体交换参数、叶片光谱特征以及叶绿素荧光和P700的光能分配。结果显示:受严重季节性干旱胁迫的影响,与雨季相比,干季的凌晨叶片水势(Ψpd)下降至-4.5 MPa,水分传导的叶比导率(KL)下降了49.5%,叶绿素反射指数(NDVI)下降了40.6%,花青素反射指数(ARI)上升至0.074(约为雨季的12.3倍),并且雨季和干季的叶片水势、水分传导效率、叶绿素含量和花青素含量均差异显著(P<0.05)。与雨季相比,干旱导致光系统Ⅱ(PSⅡ)最大光化学量子效率(Fv/Fm)显著下降至0.72(P<0.05),即PSⅡ发生光抑制,而光系统Ⅰ(PSⅠ)的活性(Pm)未发生明显变化;干季叶片的最大非光化学淬灭(NPQ)增加了31%,而激发的最大环式电子传递速率(CEF)下降了66%。表明长期干旱胁迫使CEF的激发受到强烈抑制,即光能捕获效率的降低和NPQ的增强促进了白皮乌口树在长期干旱胁迫下的光保护。

Chinese savanna evergreen plants can tolerate prolonged drought stress for more than half a year, but the mechanisms underlying the eco-physiological responses of these evergreen plants to drought stress are poorly understood. We selected a dominant evergreen species, Tarenna depauperata Hutchins, in this study and measured predawn leaf water potential, pressure-volume curves, leaf gas exchange, leaf spectral traits, chlorophyll fluorescence and P700 in the rainy and dry seasons, respectively. Results showed that predawn leaf water potential （pd） decreased to -4.5 MPa in the dry season. Compared with the values in the rainy season, leaf specific hydraulic conductivity （KL） decreased by 49.5%, the chlorophyll reflectance index （NDVI） decreased by 40.6%, and the anthocyanin reflectance index （ARI） increased to 0.074 in the dry season, which was 12.3 times as much as the value of the rainy season. The seasonal differences in pd, KL, NDVI and ARI were significant （P 〈 0.05）. The maximum quantum yield of PS II （Fv/Fm） decreased from 0.8 in the rainy season to 0.72 in the dry season （ P 〈 0.05）, indicating photoinhibition in PS 11 however, the activity of PSI （Pm） remained stable during peak drought. In addition, maximum non-photochemical quenching （NPQ） increased by 31% and the maximum cyclic electron flow （CEF） decreased by 66% in the dry season compared with those in the rainy season. These results suggested that CEF was significantly inhibited by prolonged seasonal drought. The downregulation of light harvesting efficiency and the enhancement of NPQ played important roles in the photoprotection of this Chinese savanna evergreen woody species.