Effects Of Different Light Intensity On Photosynthetic Characteristic In Leaves Of High Yield Winter Wheat

In order to explore the mechanisms of acclimation to changes of environmental light intensity, effects of shade on photosynthetic rate, characteristic of chlorophyll a fluorescence, photosystemⅡ(PSⅡ) functions, heat dissipation, transfer and distribution of photosynthetic assimilation products and effects of high light on the photosynthetic apparatus after shade treatment were investigated in high yield winter wheat cultivar 01-35 and Lumai14(L-14) by measuring the parameters of chlorophyll fluorescence, gas exchange, content of water soluble carbohydrate, starch in flag leaves and dry weight in different organs. The main results are as follows:1. Photosynthetic rate decreased obviously in both 01-35 and L-14 when they were in low light condition, the decrease of LCP, LSP, AQY and CE indicating that the photosynthetic capacity declined. Pn of 01-35 in both shade and full sunlight was higher than that of L-14, which suggested that the photosynthetic capacity of 01-35 was higher in shade conditions.2. Enhancement of chlorophyll content, especially Chl b content in flag leaves was increased in shade, and the ratio of chlorophyll a/b decreased, indicating that the ability to absorb week light was enhanced. The extent of enhancement of chlorophyll content was higher in 01-35 than in L-14, indicating that 01-35 was more tolerant to shade condition.3. The content of water soluble carbohydrate in flag leaves, the rate of grain filling and grain weight of 01-35 and L-14 decreased after shading, but the content of water soluble carbohydrate and starch in flag leaves of 01-35 were lower than L-14 before and after shading, and the output rate of assimilation products in haulm of 01-35 increased significantly after shading, indicating higher ability of photosynthetic assimilation transfer in 01-35.4. Upon sudden exposure from low to high light, the Pn, Gs, rETR and NPQ in full light leaves increased to maximal levels in a short period, whereas it took a much longer time for those of shaded leaves. Lower NPQ induced higher excess photons in shade leaves. LowerΦPSⅡand NPQ were found in shaded leaves at higher irradiance, which induced higher excess photons at higher irradiance,5. Compared with leaves grown in full sunlight, higher initial slope (α), decline slope (β), maximum relative electron transport rate (rETRmax) and minimum saturating irradiance (Ek) of rapid light curves were found in shaded leaves when adapted in low light, but there were no significant difference between them.β, rETRmax, Ek and NPQ were significantly lower in shaded leaves than that in leaves grown in full sunlight, indicating that the ability of light utilization and thermal energy dissipation were lower in shaded leaves.6. Under high light stress, the decline extent of Fv/Fm and PIabs were lower in shaded leaves of 01-35 than that of L-14, which suggested that shaded leaves of 01-35 could maintain higher photosynthetic activity under high light. The damage of reaction centers, donor and acceptor sides in shaded leaves of 01-35 were less than that of L-14. Compared with L-14, more trapping energy were used for electron transport and lower injury of photosynthetic performance was found in shaded leaves of 01-35. Therefore, the photosynthetic apparatus in 01-35 was more tolerant to light stress after shading.