Effects Of Different Light Intensity On Ecophysiological Characteristics Of The Endangered Plant Tetracentron Sinense Oliv.

In this paper,the characteristics of morphology,physiology and biochemistry,photosynthesis and the leaf ultrastructure of Tetracentron sinense 2-year-old young trees were investigated at different intensity simulated by artificial shading（L1:100%NS（natural sunlight）in open space;L2:50%NS in forest gap or edge;L3:10%NS in the understory）,and the influence mechanism of light intensity on the establishment of the young tree was analyzed,which can provide the scientific basis for the effective management and protection of T.sinense.The main results are as follows:（1）Effects of light intensity on morphological characteristics of the young treesWhen shading for 60 d,there was no significant difference in the height growth and root to shoot ratio（R/T）of T.sinense young trees under different light intensity.The growth of the stem under L3 treatment was significantly lower than that under L1and L2 treatment;the maximum of leaf number appeared under L2 treatment,and the leaf area also increased significantly;the specific leaf area（SLA）under L2 and L3treatment was significantly larger compared to L1.The results indicated that 50%NS was beneficial to capture more light energy and synthesize more organic matter for T.sinense young trees.（2）Effects of light intensity on physiological and biochemical characteristics of young treesWith the increase of treatment time,the SOD,CAT activity in L1 and L3 treatment was gradually lower than that in L2,and the difference reached a significant level when shading for 60 days.The MDA content was significantly higher than that in L2treatment,when shading for 40 d and 60 d.The activity of POD was significantly higher in L3 treatment than that in other treatments..The results showed that the young trees of T.sinense were better protected by antioxidant enzymes under 50%light intensity.There were significant differences in the soluble sugar content in the leaves of T.sinense young trees under different light intensities for each treatment time,and the trend was L1>L2>L3.The contents of soluble protein and free proline in L1 and L2treatments were significantly higher than those in L3 treatment.The results indicated that the photosynthesis of young trees will be blocked,and the accumulation of assimilation products will be reduced when the light intensity is too weak.（3）Effects of light intensity on photosynthetic characteristics of young treesShading significantly increased the content of Chla,Chlb and total chlorophyll in the leaves of T.sinense,and there was no significant difference in the Chla/b value of leaves under different light intensities when shading for 60 days.The light response curve showed that the moderate shading can increase the photosynthetic rate of the leaves,and the maximum leaf net photosynthetic rate(P_{n max})under L2 conditions is significantly higher than L1 and L3.The light compensation point（LCP）and dark respiration rate（Rd）of leaves in L2 and L3 treatments were significantly lower compared to L1 treatment,while light saturation point（LSP）was significantly higher compared to L1 treatment.Under different treatments,both Ci and Tr showed L3>L2>L1,while Gs showed L2>L3>L1,WUE showed L1>L2>L3,and LUE showed L2>L1>L3.The results showed that the leaves of T.sinense under 100%light intensity were inhibited by light,and its stomata were limited,while in 10%light intensity the leaves could not reach the maximum photosynthetic rate quickly,limited by nonstomatal restriction.（4）Effects of light intensity on ultrastructure of young tree leavesUnder L2 treatment,the chloroplast structure of the leaves was good,the Osmiophilic globule were few,the number of Grana lamella and Stroma lamella was more and the arrangement was tight.Under L1 and L3 treatment,the chloroplast ultrastructure was damaged to different degrees,and the damage degree increased gradually with the increase of treatment time.The results suggested that the photosynthetic components of T.sinense leaves under 50%light intensity are well structured compared to other light intensities,which was conducive to the efficient progress of photosynthesis.The comprehensive analysis showed that the environment in forest gap or edge was beneficial to the survival and growth of T.sinense young trees,while the environment in open space and the understory were not conducive to the survival and growth of the T.sinense young trees could regenerate well under forest gap or edge.For the natural population restoration of T.sinense,the light environment in forest gap or edge suitable for the growth of young trees should be created to promote the establishment of T.sinense young trees.