南亚热带常绿阔叶林林冠不同部位藤本植物的光合生理特征及其对环境因子的适应

Photosynthetic characteristics of canopy-dwelling vines in lower subtropical evergreen broad-leaved forest and response to environmental factors

对南亚热带常绿阔叶林中着生在林冠层不同部位的4种藤本植物(白背瓜馥木(Fissistigma glaucescens)、瓜子金(Dischidia chinensis)、蔓九节(Psychotria serpens)和山蒌(Piper hancei))的光合生理生态特性进行比较,探讨着生在林冠不同部位的藤本植物的光合生理特性随光照、温度、湿度等变化的规律。结果表明,鼎湖山南亚热带常绿阔叶林微生境由上至下发生了较大变化,相对于林内,冠层顶部具有高温、高光强、低湿度的特征。受这些变化的环境因子的影响,着生在林冠不同部位的藤本植物之间的光合生理特征存在着较大差异:着生于林冠层中上部的瓜子金和蔓九节的最大净光合速率分别为(2.9±0.6)和(6.3±1.3)μmolCO2·m-2·s-1,光饱和点为(168.5±83.4)和(231.4±147.8)μmol·m-2·s-1,显著小于位于冠层下部的白背瓜馥木和山蒌的最大净光合速率值(8.9±2.9)和(8.6±2.3)μmolCO2·m-2·s-1以及光饱和点值(491.6±230.8)和(402.3±112.8)μmol·m-2·s-1。瓜子金和蔓九节的光补偿点值为(16.1±5.9)和(10.1±5.7)μmol·m-2·s-1,水分利用效率值为(11.5±3.9)和(8.7±1.6)μmolCO2·mmol-1H2O,显著大于林内的白背瓜馥木和山蒌的光补偿点值(5.6±1.9)和(5.4±1.7)μmol·m-2·s-1以及水分利用效率值(6.7±1.8)和(6.8±1.3)μmolCO2·mmol-1H2O。这些光合生理指标的变化显示出植物对不同的温度、光照、湿度的适应,是植物适应环境条件的重要表现。

Vines are important floristic and ecological elements in forests of tropical and subtropical areas; however,few studies have provided information on the photosynthetic characteristics of vines. Our purpose is to characterize the photosynthetic traits of major canopy-dwelling vines in the lower subtropical evergreen broad-leaved forest in southern China.Methods We compared the photosynthetic characteristics of two upper-canopy vines （Dischidia chinensis and Psychotria serpens） and two lower-canopy vines （Fissistigma glaucescens and Piper hancei） in Dinghushan Nature Reserve. We measured maximum photosynthetic rate （Amax）, light saturation point （Lsp）, light compensation point （Lcp）, respiration in light （Rday）, convexity （K）, apparent quantum yield （Ф）, transpiration rate （Tr） and water utilization efficiency （WUE） using a LI-6400 system. We also determined environmental factors inside and outside the canopy.Important findings Differences of photosynthetic characteristics between the upper and lower canopy-dwelling vines can be largely explained by differences in environmental factors such as photosynthetic active radiation （PAR）, temperature and humidity within the forest canopy. Vines located in the upper canopy have lower annual mean Amax and LSP compared with those located in the lower canopy. Amax values of the upper canopy vines D. chinensis and Psychotria serpens are （2.9 ± 0.6） and （6.3 ± 1.3） μmol CO2·m2·s^-1, respectively, and their LSP values are （168.5 ± 83.4） and （231.4 ± 147.8） μmol CO2·m2·s^-1, respectively. The Amax values ofF. glaucescens and Piper hancei are （8.9 ± 2.9） and （8.6 ± 2.3） μmol CO2·m2·s^-1, respectively, and the LSP values are （491.6± 230.8） and （402.3 ± 112.8） μmol CO2·m2·s^-1, respectively. The lower canopy vines have lower LCP compared with the upper canopy vines. The LCP values are （5.6 ± 1.9） and （5.4 ± 1.7） μmol CO2·m2·s^-1 for E glaucescens and Piper hancei, respectively and （16.1 ± 5.9） and （10.1 ± 5.7） μmol CO2·m2·s^-1 for D. chinensis and Psychotria serpens, respectively. WUE values showed the same pattern, with values of （6.7 ± 1.8） and （6.8 ± 1.3） μmol CO2·mmol^-1H2O for F. glaucescens and Piper hancei, respectively, and （11.5 ± 3.9） and （8.7 ± 1.6） μmol CO2·mmol^-1H2O for D. chinensis and Psychotria serpens, respectively.