选取入侵植物三裂叶蟛蜞菊(Wedelia trilobata)及其本地近缘种蟛蜞菊(W. chinensis)为实验材料,比较干旱和复水后二者叶片的叶绿素荧光特性和抗氧化酶活性等生理指标的变化规律,探讨入侵种三裂叶蟛蜞菊对干旱的响应和生态适应性.结果发现,在自然干旱处理过程中,入侵种三裂叶蟛蜞菊与本地种蟛蜞菊相比土壤含水量下降较快,对它们叶片气孔形态的比较发现,干旱胁迫11d后三裂叶蟛蜞菊叶片气孔开度明显大于蟛蜞菊,这可能是导致其失水较快的原因之一.干旱胁迫11d后三裂叶蟛蜞菊的PSⅡ最大光能转化效率(Fv/Fm)降低了43.8%,而蟛蜞菊只降低了3.7%;同时,与蟛蜞菊相比,三裂叶蟛蜞菊的PSⅡ实际光化学量子产量(Yield)、表观光合电子传递速率(ETR)和光化学猝灭系数(qP)也表现出较大幅度的降低,说明三裂叶蟛蜞菊对干旱胁迫较敏感;但复水后,三裂叶蟛蜞菊能够较快地恢复到正常水平,且与本地种不存在显著差异.这主要是由于入侵种在遭受干旱胁迫时提高了对其过量激发能的热耗散能力以及超氧化物歧化酶(SOD)和抗坏血酸还原酶(APX)的活性,保护光合机构少受不可逆的损伤,使其在干旱胁迫解除后光合功能得以迅速恢复.研究结果初步表明三裂叶蟛蜞菊容易受到水分条件的限制,它向干旱地区扩散的可能性较小.
Wedelia trilobata (L.) Hitchc., a creeping herb that originated from Central and South America, is listed as one of the world's 100 worst invasive alien species. After its introduction to south China, it has become a common invasive plant in cropland, plantations and natural forests. Wedelia chinensis is the native congener of W. trilobata in China, but has not been found harmful to native plants or habitats. The aims of this study were to investigate the effects of drought stress and rehydration on chlorophyll fluorescence, antioxidative activity and some other ecophysiological parameters in leaves of the alien invasive W. trilobata and its native congener W. chinensis, and explore the response and ecological adaptability of this invasive species to drought stress. Soil water content during the course of natural drought treatment of W. trilobata plants decreased faster than in the case of W. chinensis plants. A comparison of stomatal morphology revealed that the opening of stomata was remarkably greater in leaves of W. trilobata than that of W. chinensis after 11d of drought stress, which may partly explain the faster water loss in W. trilobata. After 11d of drought stress, W. trilobata showed a significant decrease of 43.8% in maximum quantum efficiency of photosystem Ⅱ photochemistry (Fv/Fm), compared with a much smaller decrease of 3.7% in W. chinensis. In comparison with W. chinensis, greater decreases of the effective PSⅡ quantum yield (Yield), apparent electron transport rate (ETR) and coefficient of photochemical quenching (qP) were also found in W. trilobata by the end of drought treatment. These observations indicate that this invasive species is susceptible to drought stress. However, the alterations in W. trilobata could rapidly recover after rehydration. Increased heat dissipation of excess excitation energy and enhanced the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) for scavenging oxygen radicals alleviated irreversible damage of the photosynthetic apparatus during drought stress and promoted recovery when the drought stress was released. In conclusion, W. trilobata is susceptible to drought stress and its spread to arid regions is likely to be limited.