Effects of shades on the photosynthetic characteristics and chlorophyll fluorescence parameters of Urtica dioica
遮荫对异株荨麻光合特性和荧光参数的影响

The effects of the full daylight and the different degrees(43%,58%,73%,87% and 97%)of the shades on the photosynthetic characters and on the chlorophyll fluorescence parameters of Urtica dioica L.subsp.dioica 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 Uritica dioca 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 daylight and all shade conditions,the daily maximum and average of net photosynthetic rate decreased significantly with increasing of shade degree,and thereby efficiency of the solar energy utilization increased.The diurnal variations of transpiration rate and stomata conductance in leaves were similar to that of net photosynthetic rate,the values of transpiration rate and stomata conductance also decreased as increasing of the shade degree.The transpiration rate and stomata conductance under full daylight and all shade conditions showed a positive correlation but did not between the transpiration rate and net photosynthetic rate under full shade condition.The stomata conductance and net photosynthetic rate also did not show a positive correlation under full daylight and all shade conditions.The content of total chlorophyll,chlorophyll a and chlorophyll b in leaves grown under all shades conditions were significant higher than those under full daylight,and increased with increasing of shade degrees,meanwhile the chlorophyll a/b decreased.Fv/Fm and Fv/Fo were significantly higher than those under full daylight 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 total chlorophyll,chlorophyll a and chlorophyll b,and the value Fv/Fm and Fv/Fo under the shade conditions.