遮荫对连翘光合特性和叶绿素荧光参数的影响

本文系统研究了不同程度的遮荫(0%、43%、70%、97%)处理对连翘叶片光合特性和叶绿素a荧光参数的影响。结果表明：随着遮荫程度增加，最大净光合速率、光补偿点、光饱和点、暗呼吸速率降低；净光合速率日变化均呈单峰型，峰值和光能利用率增加；叶绿素a b、叶绿素a、叶绿素b含量增加，叶绿素a/b降低；叶绿素a荧光参数Fv/Fm和Fv/Fo日变化呈单谷曲线，值均高于全光照的，且随着遮荫程度的提高其值均依次增加。这说明，连翘是一种耐荫性很强的植物，遮荫可使其降低光补偿点、光饱和点、净光合速率、暗呼吸速率以及叶绿素a/b，增加总叶绿素、叶绿素a、叶绿素b含量、光能利用率以及PSⅡ原初光能转化效率和潜在活性，从而增强其在弱光条件下的生长发育能力。

Effects of shades on the photosynthetic characteristics and chlorophyll fluorescence parameters of Forsythia suspensa

The effects of the full day light and the different degrees (43%,70%,97%) of the shades on the photosynthetic characters and on the chlorophyll fluorescence parameters of Forsythia suspensa were examined in these observation. The results indicated that the light compensation point (LCP), light saturation point (LSP)and dark respiration rate (DP) of the F. suspensa plant were at a low level, the value of which decreased with the increasing of shade degree. The diurnal variation of net photosynthetic rate (Pn) presented only one peak under both full day light?and all shade conditions, the daily maxmium and average of net photosynthetic rate decreased significantly with increasing of shade degree, and there by efficiency of the solar energy utilization increased.The diurnal variations of transpiration rate and stomata conductance in leaves were smiilar to that of net photosynthetic rate, the values of transpiration rate and stomata conductance also decreased as increasing of the shade degree. The net photosynthetic rate, transpiration rate and stomata conductance under full day light and all shade conditions showed a positive correlation.The content of chlorophyll a b,chlorophyll a and chlorophyll b in leaves grown under all shades conditions were significant higher than those under full day light, and increased with increasing of shade degrees, mean while the chlorophyll a/b decreased. Fv/Fm and Fv/Fo were significantly higher than those under full day light and increased with increasing of shade degrees under all shade conditions. Results obtained from above showed that the shade tolerant of the stinging nettle plant was contributed by decreasing the light saturation point, light compensation point, dark respiration rate and chlorophyll a/b, through which it increased the efficiency of the solar energy utilization, the content of chlorophyll a b, chlorophyll a and chlorophyll b, and the value Fv/Fm and Fv/Fo under the shade conditions.