| Changes of growth and development, leaf anatomy, photosynthetic characters, chloroplast pigment content, chlorophyll fluorescence parameters and enzyme activity in leaf of Chionanthus retusus and Acer davidii were searched with four different shading treatments (0%,15%, 35%, 50% and 70% shading). The activities of enzyme, the relative electrolyte leakage percentage and relative leakage of K~+of C. retusus, A. davidii's sticks under low temperature treatments were studied in this paper. Purpose of the research is to investigate the shading tolerance and freezing resistance mechanisms of C. retusus and A. davidii, and provide evidences to promote the application and cultivation of them. The main findings are summarized as follows:(1)There was little effect of growth on C. retusus under shanding treatments, but there was significant effect of growth on A. davidii under shanding treatments: the higher growth of shooting and stem diameter of C. retusus was 32.1cm and 0.289cm, respectively, under 15% shading treatment;A. davidii were 138.8cm and 0.878cm, respectively, under 50% shading treatment;But the min growth of shooting of C. retusus and A. davidii was 28.7cm and 68.0cm, respectively, under 0% shading treatment;at 70% shading treatment, there was max growth of shooting in C. retusus and A. davidii, it was 35.2cm and 155.5cm, respectively.(2) The max depth of leaves, the depth of palisade tissue of C. retusus under 15% shading treatment, was 137.4μm and 40.7μm, respectively, the min was 120.6μm and 30.0μm;the max depth of sponge tissue was 88.3μm under 50% shading treatment, the min was 79.3μm under 0%. The max depth of leaves, the depth of sponge tissue of A. davidii under 50%, was 97.0μm and 55.3μm, respectively;the max depth of palisade tissue was 37.3μm under 15%, the min depth of leaves, depth of palisade tissue was 85.5μm and 25.3μm;The ratio of palisade tissue/sponge tissue in leaves decreased with the increasing of shading,(3) The max content of chlorophyll showed on July, and the min on October from May to October. With the increasing of shading, the content of chlorophyll was increased, at July;there was max content at 50% shading treatment, and the min at 70%.(4)The curves diurnal variation of net photosynthetic rate of C. retusus and A. davidii with 0% to 15% shading treatments presented two peaks, while there was only one peak from 35% to 70% shading treatments. The net photosynthetic rate was higher in May and September, but it was lower in July and June. The max net photosynthetic rate and average photosynthetic rate of C. retusus presented at 15% shading treatments, but A. davidii presented 50% shading treatments. The light compensate point, light saturation point were decreased with the increasing of shading. (5) With the increasing of shading, the chlorophyll fluorescence parameters such as Fv/Fmand Fo of C. retusus and A.r davidii increased, there were the max Fv/Fm and Fo at 70%, and the min at 0%. The diurnal variations of Fv/Fm showed decrease-increase curves, and the max of Fv/Fm presented at 6:00 O'clock. The diurnal variations curves of Fo presented one peaks.(6) The activity of enzyme (SOD and POD)in leaf of C. retusus and A. davidii decreased with the increasing of shading;from May to October, the SOD activity of C. retusus's leaves showed decrease-increase curve, the max SOD activity presented on May, the POD activity showed increase-decrease-increase-decrease curve, and max presented September;while SOD and POD activity of A. davidWs leaves showed increase-decrease curves;and the content of MDA in C. retusus''s leaves showed increase -decrease-increase curve, in A. davidii showed decrease-increase curve,the max content of MDA presented on October.(7) The activities of SOD and POD in membrane increased early and decreased later;the content of MDA increased, and the relative electric conductivity and relative leakage of K+ increased as S-curves with the temperature decreased. According to the Logistic equation, we could calculate the semi-lethal temperature (LT50) for C. retusus"'s and A. davidiVs one-year sticks, it was in agreement with the recover test result. In general, A. davidii showed stronger shading-tolerance and freezing-resistance. |
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