Effect of low temperature at jointing stage on photosynthetic characteristics and yield in wheat cultivar Yangmai 16

Photosynthetic characteristics and yield changes of wheat(cv.Yangmai16)under low temperature treatments(-2,-4℃)at jointing stage were studied by means of artificial temperature-controlled phytotron.The contents of chlorophyll,chlorophyll a(chl a),and chlorophyll b(chl b)in leaves decreased significantly under lower temperatures and longer stress.The ratio of chlorophyll a to chlorophyll b decreased at the preliminary stage,and then increased.Under low temperature stress,net photosynthesis rate(Pn),stomatal conductance(Gs),transpiration rate(Ti)decreased,whereas intercelecullar CO2concentration(Ci)decreased firstly and then increased significantly.Under the stress of-2℃lasting for 12hand-4℃lasting for 6h,the decrease in photosynthetic rate was mainly caused by stomatal factors.Under the stress of-2℃lasting for more than 12hand-4℃lasting for more than 6h,the decrease in photosynthetic rate was primarily caused by non-stomatal factors.Therefore,stomatal effects,non-stomatal effects and chlorophyll content reduction mainly caused the decrease in net photosynthetic rate of wheat plants under cold stress.The longer and lower temperature was,the more yield declined.The yield of the treatments of-2℃and-4℃lasting for 48 h were significantly lower than that of the control,which decreased by 71.08%and 80.15%respectively.The number of spikes and grains per ear reduction were the main reasons of yield decrease under low temperature stress at jointing stage.