Effects of exogenous abscisic acid(ABA) on the photosynthesis and chlorophyll fluorescence parameters of Tripterygium wilfordii seedlings exposed to low temperature.

Taking one year-old Tripterygium wilfordii cutting seedlings as test materials,this paper studied the effects of foliar spraying 0,5,10,15,20,and 25 mg·L-1 of abscisic acid(ABA) on the leaf photosynthesis and chlorophyll fluorescence characteristics of the seedlings under low temperature stress.Spraying 20 mg·L-1 of ABA increased the cold-resistance of the seedlings significantly,manifesting in the slowing down of the decrease amplitudes of leaf net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(gs),and intercellular CO2 concentration(Ci) and the increase of photosynthetic capacity.After 6 days exposure to low temperature,the initial fluorescence(Fo) decreased with increasing concentration of applied ABA,the maximum fluorescence(Fm) and maximal photochemical yield(Fv/Fm) increased,the actual photochemical efficiency of system Ⅱ(ΦPSⅡ) and photochemical quenching coefficient(qP) increased after an initial decrease,and the non-photochemical quenching coefficient(qN) showed a 'decreasing-increasing-decreasing' trend.The Pn,gs,qP,Fm,and Fv/Fm reached their peak values at 20 mg·L-1 of ABA.In all treatments,with the increase of photosynthetically active radiation(PAR),the relative electron transport rate(rETR) increased first and decreased then,reached the peak when the PAR was 395 μmol·m-2·s-1,and the peak value of the rETR in treatments 25 and 20 mg·L-1of ABA was 17.1% and 5.2% higher than that of the control,respectively.The light response curves of the ΦPSⅡ decreased with increasing PAR,whereas those of qN performed in adverse.