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

Aims 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 (Φ), 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·m–2·s–1, respectively, and their LSP values are (168.5 ± 83.4) and (231.4 ± 147.8) μmol·m–2·s–1, respectively. The Amax values of F. glaucescens and Piper hancei are (8.9 ± 2.9) and (8.6 ± 2.3) μmol CO2·m–2·s–1, respectively, and the LSP values are (491.6 ± 230.8) and (402.3 ± 112.8) μmol·m–2·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·m–2·s–1 for F. glaucescens and Piper hancei, respectively and (16.1 ± 5.9) and (10.1 ± 5.7) μmol·m–2·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·H2O for F. glaucescens and Piper hancei, respectively, and (11.5 ± 3.9) and (8.7 ± 1.6) μmol CO2·mmol–1 H2O for D. chinensis and Psychotria serpens, respectively.