飞机草和兰花菊三七光合作用对生长光强的适应

Acclimation of Photosynthesis to Growth Light Intensity in Chromolaena odorata L. and Gynura sp.

测定了干季不同光强下生长的飞机草和兰花菊三七叶片最大净光合速率 (Pmax)、荧光动力学参数、叶绿素含量和比叶重 (LMA) ,研究了两种植物适应光环境的策略 ,探讨了其与入侵性的关系。 1 0 0 %光强下 ,两种植物主要通过降低捕光色素复合体Ⅱ的含量减少光能吸收 ,提高Pmax增加光能利用维持叶片能量平衡 ,而它们的热耗散能力并不强 ,均显著低于其它光强下的值。 1 0 0 %光强下 ,提高类胡萝卜素含量是飞机草耗散过剩能量的有效策略 ,而兰花菊三七可能有其它耗散途径。4.5 %光强下仅飞机草能够存活 ,它通过降低LMA、维持很低的日间热耗散和较高的光合系统Ⅱ非环式电子传递效率适应了弱光环境。推测对强光环境较强的适应能力是入侵植物的共性之一 ,但这种能力强不一定入侵性大。

Biological invasion is a focus of ecological research. Studies of invasiveness ask: which traits enable a species to become an invader? The high potential for acclimation to environment factors, such as light intensity, is thought to be a critical characteristic of invasive plant, but this hypothesis has not been tested at physiological level. In this paper fluorescence kinetics parameters, the maximum photosynthetic rate (P max ), chlorophyll content and lamina mass per unit area (LMA) were measured in seedlings of Chromolaena odorata L. King & Robinson (Compositae) and Gynura sp.(Compositae) grown under different relative irradiance (RI 100%, 50%,12.5% and 4.5%). We want to know (1) the ability and the way they keep leaf energy balance under different light regimes and (2) does this ability associated with their invasiveness? And how? For both C.odorata and Gynura sp. grown under RI 100%, chlorophyll a/b ratio was higher(Fig.5) and the minimum fluorescence was lower in direct proportion to the maximum fluorescence(Fig.2), while keeping the maximum efficiency of PSⅡ photochemistry at a high level(Fig.1). All these phenomena indicated a down regulation of light harvesting complex Ⅱ content, which resulted in a decrease of light absorbance. Under RI 100%, the P max of C.odorata and Gynura sp. reached 19 and 22 μmol m -2 s -1 respectively(Fig.6), while their potentials of non-photochemical quenching efficiency only reached about 1.5 and 1.0, respectively under 1 500 μmol m -2 s -1 (Fig.4). These facts mean that, for both species, it is the high photosynthetic ability rather than thermal dissipations which plays a major role in high light acclimation. It seemed that this strategy is widely adopted by light-demanding plant. Unlike many other published results, we found that both the species grown under RI 100% exhibit a smaller thermal dissipation potential than those grown under low light regimes(Fig.4). The enhanced carotenoid content of C. odorata grown under RI 100%(Fig.5) was correlated with the scavenging of active oxygen induced by excess light energy. Gynura sp. perhaps needed other ways, such as Mehler reaction or photorespiration, to protect its photosynthetic apparatus from photodamage caused by active oxygen. Gynura sp. perished soon after being placed in RI 4.5%. For the first time, we found that C.odorata, a typical light-demanding species, could survive and keep growing under this low light regime. Several characteristics, including lower LMA(Fig.6)and level of thermal dissipation(Fig.3), and higher quantum yield of PSⅡnon-cycle electron transport(Fig.3), explained its success under extreme low light condition. It was consistent with the result we got from Eupatorium adenophorum, another famous invasive species, that both C.odorata and Gynura sp. could dissipate the excess energy efficiently and keep high P max under RI 100%. As all these invaders could acclimate to high light perfectly, we consider this trait to be a common property of invasive plants. But, the ability seemed not related to the potential of invasiveness. Compared with Gynura sp., C. odorata exhibited a lower ability of high light acclimation but a greater invasiveness in the habitats studied in this work.