| Light is absorbed and dispersed by the suspended substances when it transmits in water, which causes the attenuation of light,changes its intensity and forms the different spectrums.In the euphotic lakes,red and blue light were greatly absorbed and dispersed by the suspended substances such as DOC and Phytoplankton.Because blue and red light were the photosynthetically available light,the attenuation of blue and red light in water,must have a significant effect on the growth and distribution of submerged aquatic plants.The study is using color films to determine the effect of light quality on Potamogeton crispus and Vallisneria natans.The germination of Potamogeton crispus' turions,the growth of their seedlings,the chlorophyll contents of leaves and some chlorophyll fluorescence parameters were measured.The result shows:(1)The germination ratio of turions on day 7 were significantly varied due to exposing under different light quality.The turions exposing under red light germinated fast while those under blue light germinated slowly.However,all turions could germinate on day 21.The highest seedling height appeared in seedlings under red light,which was respectively 2.24 times and 2.06 times to those under blue light and white light.Also,the length of roots developed under blue light was only 34.2%and 64.7%of those under red light and white light,indicating that blue light could strongly inhibite the growth of seedling's roots.(2)Light quality has obvious effect on the chlorophyll contents and fluorescence parameters of leaves.After 20 days,there was significant difference in the chlorophyll contents in Potamogeton crispus'leaves due to distinct light quality:the chlorophyll contents of leaves exposing under red light were higher than those under blue and white light.A significant difference in some chlorophyll fluorescence parameters(qP,Yield and rETR)was also observed under different light quality,which suggested that red light could promote the photosynthesis process.All of these indicated that there might have a red light effect in the process of the turion germination and seedling growth.(3)Light quality has an obvious effect on the length and width of leaves of Vallisneria natans.For the value of leaf length,it was reduced with the decreasing light intensity under blue and white light,while uder red light it was increased firstly and then decreased:the longest leaf length occurred under 10%light intensity.For the value of leaf width,under white and blue light it was increased firstly and then decreased with the reduced light intensity,while under red light it was increased with the decreasing light intensity.The effect of light intensity on leaf width was not significant under red and white light(p＞0.05),but the effect reached significant level under blue light(p＜0.05).Besides,under same light intensity,leaf width significantly varied with different light intensity(p＜0.05).(4)There was an obvious difference in chlorophyll contents under various treatments.The chlorophyll contents of leaves were reduced with the decrease of the light intensity under same light quality.Also,under same light intensity,light quality could obviously affect chlorophyll contents.The chlorophyll contents of leaves in blue light was highest while those in white light was lowest when exposing under 30%and 10%light intensity.But when exposing under 5%light intensity,the chlorophyll contents of leaves in red light was highest while it was lowest in white light.(5)There was a significant difference in chlorophyll fluorescence parameters under various treatments.Under 30%light intensity,photosynthetic rate of leaves in white light was higher than that in other treatments.Under 10%light intensity,the chlorophyll fluorescence parameters,such as F_v/F_m,Yield and qP,of leaves in red light were higher than those in other treatments,which indicates that plants have a highest photosynthetic capacity in red light.
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