濒危植物长叶榧的光合生理生态特性

Photosynthetic traits of the endangered plant species Torreya jackii

利用Li-6400 XT便携式光合作用仪对林窗、林缘、林下3种生境中的长叶榧(Torreya ackii)在春、夏、秋、冬4个季节里的光合生理生态指标进行测定,探讨3种生境中长叶榧光合能力的季节变化及其对不同光环境的响应,分析其濒危机制,为长叶榧的迁地保护和种群的繁衍复壮提供理论依据。结果显示:(1)林窗、林缘的长叶榧净光合速率(Pn)日变化在夏季呈"双峰"曲线,其它3个季节均呈"单峰"曲线;林下的Pn日变化在4个季节均呈"单峰"曲线。(2)3种生境中最大净光合速率(Pnmax)、光饱和点(LSP)、表观量子效率(AQY)、最大羧化速率(Vcmax)、最大电子传递速率(Jmax)、磷酸丙糖利用率(TPU)均为夏季最高,使得夏季有较强的光合作用能力,但夏季林窗、林缘的长叶榧出现光合"午休"现象,光补偿点(LCP)、暗呼吸速率(Rd)也较高,使得夏季林窗生境的长叶榧日均Pn明显低于于秋季,林缘的日均Pn与秋季差异不显著。(3)4个季节的日均Pn、Pnmax、LSP、Vcmax、Jma、TPU均为林窗最高,林窗与林下差异显著,表明长叶榧具有阳性植物的特点,适宜生长在光照较强的林窗生境。(4)在生长旺盛的夏、秋季,长叶榧的LSP比伴生物种低,LCP比伴生物种高,对光适应的生态幅度较窄;与伴生物种相比,长叶榧的Pn较低,光合能力较弱,在激烈的种间竞争中处于不利地位,可能成为其濒危的一个重要原因。

A portable Li-6400 XT photosynthesis measuring system （LI-COR Biosciences, Lincoln, NE, USA） was used to explore how Torreya jackii, an endangered species endemic to China, adapts to the environment and to illustrate and determine various photosynthetic characteristics of T. jackii in three natural habitats with different light conditions, specifically gap, edge and understory habitats. Also, the physiological mechanisms that have resulted in the endangered status of this species were explored to provide baseline reference data in support of off-site conservation and population rejuvenation of T. jackii. The results for T. jackii growing in forest gap and edge habitats show that when the diurnal variation in the photosynthetic rates in the summer is graphed, typical curves with double peaks appear; in addition, photosynthetic rates in the other seasons show curves with a single peak as do photosynthetic rates in understory habitat based on data in all four seasons. The net photosynthetic rate （Pnmax）, light saturation point （LSP）, apparent quantum yield （AQY）, maximum rate of carboxylation （Vcmax）, maximum rate of electron transport （Jmax）, and triose phosphate use rate （TPU） were highest in summer in all habitats; this indicates the photosynthetic capacity of T. jackii is significantly higher in summer than in other seasons. The graphs indicate a midday depression of photosynthesis occurs in summer in gap and edge habitats when the dark respiration rate （Rd） and light compensation point （LCP） are also higher. As a result, the daily mean values of Pn in gap habitat are significantly lower than in autumn while those of Pn in edge habitat are similar to the daily mean values observed in autumn. In all four seasons the daily mean values of Pn, Pnmax, LSP, Vcmax, Jma, and TPU in gap habitat are the highest with significant differences between those in gap and understory habitat. These findings indicate that the photosynthetic characteristics of T. jackii are typical for a plant growing in sunny habitats, meaning T. jackii grows more vigorously in gap habitat with adequate light. In summer and autumn, the LSP of T. jackii is lower than those of other plants typically associated with its habitats, while the LCP is higher than those of the associated plants, which indicates that T. jackii has a narrow ecological range of adaptability to light conditions. The Pn of T. jackii is lower than those of the associated plants in the community, indicating that T. jackii is at a disadvantage during interspecific competition with its poor ability to adapt photosynthetically to a wide variety of light conditions; this might be an important factor contributing to the endangered status of T. jackii.