Thermotolerance Of Photosynthesis In Shade-adapted Plants

Shade environment is universal in gardens.Few of researches focus on the response of plants grown under shade to high temperature stress.The thermotolerance of photosynthesis in two shade-adapted plants (H.'Honey Bells', Clematis heracleifolia) were evaluated in this study and their possible mechanisms were analyzed.The effects of different light intensity (CK100%,Tl 50%,T2 25%,T310%) on plants growth were different,The primary index including changes of leaf characters,photosynthetic characters and ornamental feature of plants were measured,The result showed:1. Shading treatments have an obvious effect on the leaf characters of plants. With the increasing of sun-shading,the leaf area,the specific leaf weigh and the stoma density were different changed,the leaf area compares CK to be up first and then down.The specific leaf weigh and the stoma density had been still decreased.The chlorophyll content increase as shading increase,and the rations of chlorophyll a/b were induced.2. Photosynthetic gas exchange and PSâ…¡photochemistry were analyzed in shade tolerance plants.Compared with the light contrast, the net photosynthetic rate(Pn)of shade plants was decreased. But their maximum photochemical efficiency (FV/FM) and electron transport per excited cross-section (ETo/CS)were higher compare with the plant fully exposed to light. While the internal CO2 concentration (Ci) of plants was increased, the lower Pn may caused by their lower CO2 assimilation by shade is not due to inactivity PSâ…¡.3. Ornamental features: After shading for two months,a few of plant leaves with CK treatment turned yellow.These plants are adapted to live with lower light intensity and can maintain ornamental character better.Trough the above analysis,the order of ability to shade-tolerance of ground cover plant is three groups: (1) Five kinds of plants have strong shade-tolerance; (2) Four kinds of plants have half shade-tolerance; (3) Three kinds of plants have weak shade-tolerance.4. Higher thermo-stability of photosynthesis was found in shade-adapted leaves than that of in control plants of the two plants exposed to three kinds of shading environment.At high temperature, Pn in control plants decreased quickly,but the shade-adapted plants still slowly decreased.The response of PSâ…¡photochemistry to heat stress was modified by shading treatment.The declines in FV/FM, PI,ETo/Cs were smaller in shade-adapted leaves than in control leaves.These results suggest that some protective effects on photosynthesis in shade-adapted plants not only against shade-stress but also high temperature stress.