Study On Physiological Mechanisms Of Plasticity Generated By Citrus Unshiu Cv. Guoqing No.1 Under Low Light Condition

With the rapid development of modern agriculture,the protected culture plays more and more important roles.Low light is one of the most important factors that affecting yield and quality of the crops cultivated in protected condition.The present study is aimed to better know the effects of low light on the photosynthesis of Sutsuma mandarin under protected condition.3 years old Sutsma mandarin(Citrus unshiu cv.Guoqing No.1) potted seedlings that grafted trifoliate orange,were used as materials.Seedlings grown under low light condition for about one month.The changes of organizational structure,nitrogen metabolism,absorption and distribution of light,PSâ…¡photosynthetic performance,and other aspects of photosynthesis characters were measured.The main results were as follows:1.Under low-light stress,the photosynthetic pigment content of plants were reduced, the distribution of excitation energy became imbalance between PSâ… and PSâ…¡,and the overall photochemical capacity ofφPSâ…¡was enhanced.Two regular performances were presented when the plants were exposed 37%and 12%light intensities for two months and then they were tumed to normal light intensity.The first is the irreversible physical persecution were not occurred under the intensity of this stress in respect of the content of chlorophyll.The second is a similar degree of performance presented on the the return processes in summer or autumn shoots regardless of the two treatments under 37%and 12%light stress,there was no significant difference between the two plants aspect of the physiological state.2.Plants grown under normal light condition suffered more photoinhibition than plants grown under low light condition,and so the photochemical reaction ability.3.Low-light stress reduced the sensitivity of water use efficiency to the changes of light.4.Photosynthate analysis:Except for sucrose,reducing sugar,starch and total non-structural carbohydrates all decreased.Photosynthate of summer shoots under low-light had the same lever. Low light increased the content of nitrate and the activity of the three types of NO₃^--assimilation,but the two kinds of nitrate played different kinds of roles.However the stress were still exist until autumn season.5.Under low light treatment,C/N increasing obviously shows that the hindered phenomenon of nitrogen synthesis is stronger than the carbohydrates synthesis.With the dim light stess finishing,the restoration of C/N is the most enormous and rapid.6.The changes of leaves' organizational structure proofed that the light have played a so important roles in the early development of the leaves.