Photosynthesis and Chlorophyll-fluorescence of Magnolia grandiflora Seedlings under Low Temperature Stress

A research about effects of low temperature stress on Magnolia grandiflora L.seedlings photosynthesis and chlorophyll-fluorescence was performed and while the temperature conditions were designed to 0℃,-4℃,-8℃,-12℃,-16℃,respectively.The results showed that with the decrease of temperature,the net photosynthesis rate(Pn),the stomatal conductance(Gs),the transpiration rate(Tr),the intercellular CO2 concentration(Ci) and the leaf chlorophyll concentration all decreased and the variations indicated the stress of low temperature had caused damages to photosynthetic system,stomata and chlorophyll.Furthermore,the determination of chlorophyll-fluorescence parameters revealed the PSⅡ maximal photochemical efficiency(Fv/Fm),the PSⅡ potential photochemical efficiency(Fv/F0),the maximum quanta yield(Yield),the photosynthetic electron transport(ETR),the photochemical quenching coefficient(qP) decreased under the low temperature stress,while the primary fluorescence(F0) and the non-photochemical quenching coefficient(qN) increased.These results suggested that the low temperature stress had caused damage to the PSⅡ reaction center,with the exception of stomatal inhibition,of Magnolia grandiflora seedlings.Furthermore,the damage of PSⅡ brought to inactivation of photosynthesis center,decreases of both primary capture capacity and assimilation efficiency of light energy,increase of light energy consumption by means of heat and the final weakening of photosynthesis capacity of Magnolia grandiflora seedlings.