Effects Of Late Sowing On Photosynthetic Capacity And Yield Of Wheat Under Heat Stress At Late Grain–filling Stage

Wheat is an important food crop in China,and heat stress is one of the important factors affecting the growth and development of wheat.The field experiment was carried out in2017–2018 and 2018–2019 for two wheat's consecutive season at Dawenkou town,Tai'an,Shandong province.Tainong 18 is a cultivar with bigger ears and lower tillering capacity.We set up two sowing date treatments,including conventional sowing?8 October?and late sowing?22 October?,and use open–type warming system.The responses of late sowing on flag leaf photosynthetic characteristics,grain–filling characteristics and yield of wheat under heat stress at late grain–filling stage were studied.The main findings are as follows:1 Effect of late sowing on grain yield under heat stress after floweringIn this experiment,the grain number per unit area and grain weight during the two sowing dates were not significantly different under natural temperature,so there was no significant difference in grain yield during the two sowing dates.Compared with the conventional sowing,the late sowing can increase the yield by increasing the grain weight and stabilizing grain number per unit area under heat stress,indicating that late sowing is an effective cultivation and management measure to deal with the heat stress at late grain–filling stage.2 Effect of late sowing on dry matter accumulation and transfer under heat stress after floweringAt the same sowing date,compared with the normal temperature,heat stress significantly increased the translocation amount,translocation rate and contribution rate of dry matter in the vegetative organs before anthesis and decreased the dry matter accumulation and contribution rate after flowering.Under heat stress,compared with the early sowing,late sowing decreased the dry matter translocation amount,translocation rate and contribution rate in the vegetative organs before flowering,and respectively increased the dry matter accumulation and contribution rate after flowering.It showed that late sowing can increased dry matter accumulation after flowering under heat stress,help to increase grain weight and grain yield.3 Effect of late sowing on photosynthetic capacity under heat stress after floweringIn this experiment,the sowing date significantly affected the photosynthetic rate,stomatal conductance,intercellular CO₂ concentration and chlorophyll content of winter wheat flag leaves.With the growth and development of wheat after flowering,the flag leaves photosynthetic rate,stomatal conductance and chlorophyll content all showed a decreasing trend,while the intercellular CO₂ concentration showed an increasing trend.Moreover,under normal temperature stress,the photosynthetic rate,stomatal conductance and chlorophyll content were higher,while the intercellular CO₂ concentration was opposite.Under normal temperature and high temperature,flag leaf photosynthetic rate,stomatal conductance,intercellular CO₂ concentration and chlorophyll content of late sowing wheat were significantly higher than that of conventional sowing,and the effect of late sowing on photosynthesis increased under heat stress.This indicates that late sowing can alleviate the inhibition effect of heat stress on wheat's photosynthesis.Under heat stress,late sowing ensured the relative stability of thylakoid membrane through improveing the unsaturated fatty acids index,and consequently retarded the damage of photosynthetic apparatus of flag leaves by high temperature.Late sowing ensured the energy transmission through enhancing the scavenging capacity of ROS in flag leaves,therefore increased the distribution of available energy in photochemistry and improved the assimilation capacity of photosynthetic system.The supply of substrate for the photosynthesis was also increased owing to the improved intercellular CO₂ concentration and stomatal conductance.4 Effect of late sowing on grain filling characteristics under heat stress after floweringIn this experiment,at normal temperature,grouting parameters of two sowing date were basic consistent.But Under heat stress,late sowing winter wheat mainly increases chlorophyll content by increasing leaf mass per area and specific leaf nitrogen content of wheat flag leaves,thus prolonging leaf function period;increases photosynthetic electron transport and ensures carbon assimilation,thereby improving photosynthetic rate.Late sowing wheat grain filling date prolonged 3.01 d,grain filling rate increased 8.64%and grain enlarged 10.34%under heat stress.