The upper and middle reaches of Dongjiang watershed is the important water source protected area of Pearl River Delta and HongKong. Situation of water resources not only impact the economic development and people's life in Pearl River Delta, but also in HongKong. Guangdong Provincial has started water conservation forest construction project in the upper and middle reaches of Dongjiang watershed so as to construct an important ecological security system of water source protected area that are expected to protect water sources and purify water quality. While the problems of afforestation design, tree species selection, cultivation and management appeared in water conservation forest construction project by field investigation. By using Li-6400 portable photosynthesis system produced by Ll-COR company, six-year-old major broad-leaved tree species for afforestation, Schima superba,Castanopsis hystrix, Michelia macclurel, and Castanopsis sfissa, in the upper and middle reaches of Dongjiang watershed for comparative studies on their photosynthetic and physiological parameter characteristics, such as photosynthesis, transpiration, and water use efficiency, as well as the diurnal changes of photosynthetic characteristics and response to light intensity of the four tree species in natural habitats. The results showed that the diurnal change of net photosynthetic rate ( Pn ) of Schima superba and Castanopsis fissa displayed a two-peak pattern, while Michelia nacclurei and Castanopsis hystrix displayed a one-peak pattern, and values of Pn of all the four trees Pn occurred at 10:00, with 8.73, 6.00, 6.68, 7.91 rmol·m-1s-1 respectively. The daily average value of Pn of Schima superba was highest, followed by Michelia macclurei, Castanopsis hystrix, and Castanopsis fissa respectively, as for the order of magnitude, the transpiration rate ( Tr ) in a descending order of Castanopsis hystrix, Schima superba, Michelia macclurei,Castanopsis fissa, and the water use efficiency ( WUE ) in a descending rank of Schima superba, Castanopsis fissa, Michelia macclurei, and Castanopsis hystrix. Schima superba thus had higher photosynthetic ability, water use efficiency, and high adaptability to the environment. The photosynthesis-light response curves of the four species could be well simulated by the non-rectangular hyperbolic models (R2 ＞ 0.98) and the exponential curves (R2 ＞ 0.98). For each of the four species, the predicted values of maximum net photosynthetic rate (P max), dark respiration (Rd) and apparent quantum yield (a) by the non-rectangular hyperbolic model were greater than those by the exponential curve respectively, and moreover were closer to the corresponding observations, while the predicted light saturation point (Lsp) by each of the two models was far lower than the observed. The young and middle-aged the four trees were photophilic and shade-tolerant with high light saturation point, low light compensation point (Lcp)and low a, and thus had high adaptability to high light and high ability to use low light and high light. These physiological studies may be helpful to planting design, tree species selection, and tending of water source forest.%在东江中上游,以6年生造林树种木荷Schima superba、红锥 Castanopsis hystrix、火力楠 Michelia macclurei和藜蒴Castanopsis fissa为材料,利用Li-6400 光合作用测定系统,对东江中上游水源林主要造林树种木荷、红锥、火力楠和藜蒴叶片光合日变化和光响应进行了测定,探讨了4种树种在当地自然生境下的光合生理特征.结果表明:木荷和藜蒴净光合速率(Pn)日变化呈"单峰"曲线,火力楠和红锥净光合速率(Pn)日变化呈"双峰"曲线,4种树种净光合速率(Pn)最大值均出现在10:00左右,分别为8.73、6.00、6.68和7.91 μmol·m-4·s-1;4种树种净光合速率(Pn)日均值表现为木荷>火力楠>红锥>藜蒴,蒸腾速率(Tr)日均值表现为红锥>木荷>火力楠>藜蒴,水分利用效率(WUE)日均值表现为木荷>藜蒴>火力楠>红锥,木荷具有高光合、高水分利用效率的生理特性,对环境适应能力强.4种树种光响应曲线均符合非直角双曲线模型(R2>0.98)和指数模型(R2>0.98),采用非直角双曲线模型拟合的4种树种最大净光合速率(Pmax)、暗呼吸速率(Rd)和表观量子效率(a)基本高于指数模型相应拟合值,且接近实测值,但2种模型拟合的光饱和点低于实际观测值.在中幼龄阶段,木荷、红锥、火力楠和藜蒴表现出较高的光饱和点(LSP)、较低的光补偿点(LCP)和较低表观量子效率,具有较强的耐阴喜光特性,对光照强度表现出一定的适应性和可塑性,对弱光与强光的利用能力较高.这些研究结果为东江流域水源林造林设计、树种筛选和抚育提供理论参考.
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