Effect Of Low Light Stress On Some Physiological Metabolisms Of Chamaecrista Rotundifolia

Chamaecrista rotundifolia interplanted in orchards can prevent soil erosion, improve soil fertility and the ecological environment, enhance and improve fruit trees growth and fruit quality. Low light stress caused by the shading of fruit trees inhibited Chamaecrista rotundifolia's growth seriously. Up to date, report about the mechanism of low light stress on Chamaecrista rotundifolia's growth is not found. In order to illustrate the physiological mechanisms of low light stress on Chamaecrista rotundifolia's growth, photosynthesis, chlorophyll fluorescence parameters, nitrogen metabolism, reactive oxygen metabolism were studied.The main conclusions are as follows:1 50%LI(50% light intensity),30%LI(30% light intensity) and 10%LI(10% light intensity) treatments decreased Chamaecrista rotundifolia's height,stem diameter,leaf number and leaf area comparing with CK(natural light) treatment, indicating that low light stress could inhibit the growth of Chamaecrista rotundifolia, and the inhibition increased with the deeper degree of low light stress.2 Under low light stress, not only the contents of Chla, Chlb and the rate of Chla/Chlb were reduced, but also the content of Carotenoid(Car) was reduced. Comparing with upper leaves, the effect of low light stress on photosynthetic pigment content was more serious.3 Low light stress had markedly effects on chloroplast ultrastructure of Chamaecrista rotundifolia. Mesophyll cell deformated, cell membrane ruptured, the number of chloroplast in unit cells decreased and the individuals became smaller under low light stress. With the low light stress increased, grana lamellae expansed and disintegrated, stromal lamellae fractured, the number of starch grains in chloroplast decreased.4 Net photosynthetic rate, stomatal conductance and stomatal limitation value decreased significantly under low light stress while intercellular CO2 concentration increased significantly. Low light stress also decreased dark respiration rate, light compensation point, light saturation point, the apparent quantum yield, the carboxylation efficiency, CO2 saturation point, and little change in CO2 compensation point was found under low light stress. The results showed that both stomatal and non-stomatal factors affected the photosynthesis of Chamaecrista rotundifolia.5 The photosynthetic apparatus of Chamaecrista rotundifolia leaves were damaged under low light stress, and the number of PSâ…¡active reaction center decreased with the closure level increased. Under low light stress, the minimal fluorescence production increased, while the maximal fluorescence production, variable fluorescence, maximal photochemical efficiency decreased. QA restored remarkably causing the mass accumulation of QA-. At the same time, the electronic transmission reduced, leading to the inhibition of electron transfer from QA- to QB, and the decrease of electron transfer rate. In addition, energy dissipation increased while energy in electron transfer and performance index of PSâ…¡decreased significantly.6 Low light stress reduced nitrate reductase activity and enhanced NO3-_N content in Chamaecrista rotundifolia leaves. Nitrate reductase activity and NO3-_N content had highly significant negative correlation. Under low light stress, the content of soluted protein delined.7 SOD and POD activities of Chamaecrista rotundifolia leaves increased while CAT activity decreased significantly under low light stress which resulted in the increase of O2.- producing rate, H2O2 and MDA content, and membrane permeability, eventually caused membrane lipid peroxidation and membrane system damage.