哀牢山和猫儿山中山常绿和落叶阔叶树光合特性对季节温度变化的响应

研究调查了云南哀牢山中山常绿阔叶林和广西猫儿山中山落叶水青冈林中共生的常绿和落叶阔叶树光合特性在2005年的季节变化,探讨了两地温度气候差异对植物优势度的影响。在夏季,同一生境下的常绿植物和落叶植物之间以及两个生境树种之间的光合速率没有显著差别。当温度下降时,两个生境内的常绿和落叶植物的光合速率都下降,这与气孔的部分关闭和光系统Ⅱ活性的下降有显著的关系。气孔的部分关闭有利于减少水分蒸腾损失,但落叶树气孔关闭程度明显高于常绿植物而且无法避免严重的光抑制。常绿植物通过气孔调节来提高光合水分利用效率和通过光系统Ⅱ活性调节来降低光合机构的损伤来维持叶片四季常绿,但是猫儿山中山森林冬季低温严重损害气孔和光系统Ⅱ的功能而使常绿植物生长受到严重制约并限制其在群落中成为优势种,与之相反,哀牢山中山森林冬季相对暖和导致常绿植物能积累更多的光合产物并促进其在群落中形成优势。

Photosynthetic response to seasonal temperature changes in evergreen and deciduous broad-leaved trees in montane forests of Ailao Mountain and Mao'er Mountain

The present study investigated the seasonal changes in photosynthetic charateristics of co-occurring evergreen and deciduous broad-leaved trees in a montane evegreen broad-leaved forest in Yunnan Ailao Mountain and a montane decidous beech forest in Guangxi Mao' er Mountain in 2005, and tried to explore the effects of temperature climate differences between the two habiitas on species dominance. In summer, light-saturated photosynthetic rates per leaf area (A_(max_a) exhibited no differences either between evegreen and deciodus species in each habitat or between the two habitats. However, as air temperature decreased, A_(max_a) of evegreen and deciodus species dropped in both habitats, resulting from partly stomatal closures and decreases of photosytem Ⅱ activities. Stomatal closures could decrease water losses, but decidous spicies had higher degree of stomatal closures than evergreen species and were unavoidable to suffer heavier photoinhibition. Evergreen species could maintain green leaves by promoting photosynthetic water use efficiency through stomatal control and enhancing the ability of photosynthetic apparaturs via photosytem Ⅱ adjustments. However, low tempertures in winter led to heavy malfunction of stomata and photosytem Ⅱ and consequent low dominance of evergreen species in montane decidous beech forest in Mao'er Mountain. By contrast, relative warmness in winter helped evegreen species of montane evegreen broad-leaved forest in Ailao Mountain to acculmate more photosynthetic biomass and facilated them to dominate in the communities.