Photosynthetic and Physiological Characteristics of Camellia petelotii Seedlings under Drought Stress

A pot experiment was conducted to study the effects of different water treatments[CK(with soil water content 85%~90% of field capacity),T1(with soil water content 65%~70% of field capacity),T2(with soil water content 50%~55% of field capacity),T3(with soil water content 35%~40% of field capacity)]on the photosynthetic and physiological characteristics of Camellia petelotii seedlings.The results showed that:(1)All plants were dead in T3 treatment,indicating that soil water content 50%~55%of field capacity is the threshold to water stress.(2)When increasing drought stress,the net photosynthetic rate(Pn),stomata conductance(Gs),transpiration rate(Tr),stomatal limitation values(Ls)and actual photosynthetic efficiency of PSⅡ(ΦPSⅡ)all significantly decreased,while the intercellular CO2concentration(Ci)and water use efficiency(WUE)kept invariable.The decrease of Pnin drought stress of C.petelotii was mainly caused by non-stomatal inhibition.(3)Compared with CK,the minimal fluorescence(F0),maximal fluorescence(Fm),maximum quantum yield of PSⅡ(Fv/Fm)and malondialdehyde(MDA)content of leaves in T1 treatment did not change significantly,while in T2 treatment,Fmand Fv/Fmdecreased significantly,F0 and MDA content enhanced significantly,which indicated that the reaction center of PSⅡ of C.petelotii was not injured in T1 treatment,while the photosynthetic apparatus was destroyed irreversible in T2 treatment.(4)The contents of total chlorophyll(Chl),chlorophyll a(Chl a),chlorophyll b(Chl b),carotenoid(Car)in leaves,Chl a/Chl b,Car/Chl,relative leaf water content(RWC)all decreased with increasing drought stress,while the proline(Pro)content increased under T1 treatment and decreased under T2 treatment.The results proved that C.petelotii was extremely sensitive to drought stress,the water deficit would restrain its photosynthesis.Intolerance to drought for C.petelotii may be an important reason to limit the spread of its population.