The Effects Of Low Light Intensity On Photosynthetic Properties And Growth And Development Of Muskmelon (Cucumis Melo L.)

The light intensity is the main limitative factor of greenhouse production in muskmelon. Many photosynthetic characteristics of two muskmelon varieties under two levels of low light intensities stress( 45% and 68% of natural light intensity) were studied ,such as diurnal change in net photosynthetic rate( Pn), the effects of photon flux density ,CO2 concentration on photosynthesis of mature leaves et al. The membrane-lipid peroxidation, the contents of total soluble sugar, soluble protein and chlorophyll ,the leaves' growth and development in muskmelon, specific leaf weight (SLW) ,the density of pores ,the yield, the number of fruit per plant ,mean fruit wt., and the stable carbon isotope composition δ13C values in muskmelon under low light intensits stress were also studied. The results showed that:1. Under different light intensities, the responsive curves of photosynthesis in mature muskmelon leaves to the change of photon flux density and CO2 concentration can be described with quadratic equations,the specific shape of the curves varied with muskmelon varieties ,the ecological factor concened and the light intensities.2. For the muskmelon varieties researched, light compensation points(LCP) increased,and light saturation point (LSP),apparent quantum yield (AQY) and maximum assimilation rate at LSP decreased under two levels of low light intensities. The range of using light was narrower under low light stress than CK,the potentially photosynthetic ability decreased and the rate of using low light intensities became lower.3. Under low light intensities stress ,CO2 compensation point(CCP) increased,CO2 saturation point (CSP),carboxylation efficiency(CE) and regenerative rate of RuBP decreased; The rate of using low CO2 concentration became lower.4. Diurnal change in net photosynthetic rate (Pn) in muskmelon leaves was a typical "none-drop" bimodal curve. Although the environmental factors were very important to diurnal change in Pn,they did not change the type of the curve.5. MDA, the main product of membrane-lipid peroxidation ,peroxidation(POD) activity and catalase(CAT) activity of both cultivars increased under low light stress, and had significant difference at different stage. The activity of superoxida dismutase(SOD)also changed,but no regulation.6. With the decreasing of light intensity, the contents of total soluble sugar and chlorophyll decreased and the content of soluble protein increased. There was significant difference in different treatments.7. Single leaf area and LAI increased,the specific leaf weight were down under low light intensities, the leaves of two cultivars changed thinner,the single leaf area of them were bigger than that of natural light intensity ;The density of pores decreased and the pores changed longer and thicher under low light intensities. The yield, the number of fruit per plant and mean fruit wt. of two muskmelon varieties also decreased under low light intensities.8. Leaf δ13C values of muskmelon decreased with the declining of light intensity , there were different between cultivars and between stages.To sum up, low light-resistant cultivar of muskmelon should be selected and bred in the greenhouse production of muskmelon.