C_3与C_4植物的环境调控

Environmental regulations of C_3 and C_4 plants

环境条件决定着不同光合类型植物的地理分布范围和区域 ,一般来说 ,C4 植物分布于高温、强光的环境而 C3植物分布于阴凉、湿润的环境 ,且 C4 比 C3植物光合速率高。但环境条件影响着不同光合类型植物的光合潜能的发挥 ,C4 植物在高温、强光、干旱条件下所表现出来的优势在其它环境条件下未必就显现出来。环境条件甚至可以引起 C3、C4 光合途径间的相互转化 ,这使得目前几种鉴别植物光合类型的方法出现不一致的结果。因此 ,在判断植物的光合类型时 ,要注意多种手段的综合利用 ,同时注意植物所处环境条件的影响。

It is well known that there are three photosynthetic types in the world which are structurally, biochemically and physiologically diversified. However, environmental conditions play significant roles in the distribution and ecophysiological features of different photosynthetic types and even change the photosynthetic pathways. In this review, we have summarized the environmental effects on photosynthesis with different pathways, with the main points being as follows:Firstly, environmental factors may influence the geological distributions of different photosynthetic types, C_3, C_4 and CAM. Plants with different photosynthetic pathways are found in different areas of the world. For example, C_4 plants mainly inhabit in areas from 45°S to 60°N. In such a scope, the higher in latitude, the lower in proportion of C_4 species in plant communities. While there are few C_4 plants beyond this scope. As for the distribution and proportion of C_3 plant along latitude, it is contrary to that of C_4 plants. In general, C_4 plants always distribute in the hot, high irradiation and relatively arid habitats while C_3 plants exist in the cool and shade areas with higher soil water availabilities.Secondly, the photosynthetic character is also of environment-dependence. It is generally considered that C_4 plants always possess higher net photosynthetic rate than C_3 plants. However, this is not always true. Some advantages such as higher carboxylation ability and resource use efficiency could not be found when C_4 plants living in the adverse conditions, e.g., low temperature and weak light conditions. Thirdly, ecological factors could even change the photosynthetic pathways. Some C_3-C_4 intermediate plants were observed gradually in the past decades. One typical example (Eleocharis vivipara) is discussed in detail in this review. This species distributes in the flexible conditions from terrestrial to aquatic. The displaying of C_3 or C_4 pathways is totally depended on the environmental conditions. The finding of numerous C_3-C_4 intermediate plants indicates that C_4 photosynthesis pathways could be educible.Form the above description; we now understand that photosynthetic pathways and their characters are largely environment-regulated. It seems difficult to improve the photosynthetic rates by introducing C_4 pathway into C_3 crops. When we assess the photosynthetic characters of certain species, it is suggested that various measurements should be taken and the environmental conditions should be taken into account.