Effects Of Nitrogen Supply On Photosynthetic Traits And Yield Under Different Shading Conditions In Winter Wheat

A field experiment was conducted to study the effects of low-light stress and nitrogen supply on photosynthetic characteristics and yield of winter wheat during jointing and filling stages.Three shading treatments were designed: S0(no shading),S1(75% of full radiation),S2(50% of full radiation),produced by black polypropylene fabric with 75% and 50% light transmittance and three N fertilizer rates were used: N0(0 kg?hm-2),N1(120 kg?hm-2)and N2(240 kg?hm-2).Each treatment had three replicates.1.Shading during jointing and filling stages significantly increased chlorophyll content and PSⅡ fluorescence photochemical quenching coefficient(q P).However,it significantly decreased chlorophyll a/b ratio and fluorescence non-photochemical quenching coefficient(q N).Thus shading treatment increased light use efficiency and reduced heat dissipation of flag leaves,which was helpful for better utilization of light energy in low light condition.Due to energy shortage,net photosynthetic rate(Pn)in shading treatments was lower than that in no shading treatment during jointing and midfilling stages.Because of higher chlorophyll content and efficiency of light energy conversion in shading treatments,Pn in S1 and S2 was higher than that in S0 at latefilling stage.With increase in N application rate,Pn,chlorophyll content,q P and ΦPSII increased significantly,which was advantageous to make full use of light energy and improve photosynthetic rate.High nitrogen fertilizer could improve chlorophyll content and efficiency of light energy conversion,which was helpful to alleviate adverse effects caused by weak light stress on photosynthesis in low light condition.2.Weak light stress increased leaf area,decreased specific leaf weight.It was in favor of absorption and utilization of light energy.Weak light stress decreased photosynthetic nitrogen use efficiency(PNUE),which was against absorption and utilization of nitrogen nutrient.More nitrogen application increased leaf area and decreased specific leaf weight,and it relieved adverse impacts caused by weak light stress on photosynthesis and absorption and utilization of nitrogen nutrient.3.Shading during jointing and filling stages significantly decreased the activity of key enzymes(nitrate reductase,glutamine synthetase,rubscio)in carbon and nitrogen metabolism.It impacted absorption and utilization of nitrogen nutrient and accumulation of photosynthate in winter wheat.But the activity of NR,GS and Rubscio at late-filling stage changed due to the delay of growth period in low light condition,and the highest activity appeared in S1.High nitrogen fertilizer could improve the activity of NR,GS and Rubscio,which promoted the carbon and nitrogen metabolism,so that the plants could get more assimilation product.It was beneficial for grain filling and improving yield.4.The reduction of photosynthetic rate and shortage of assimilate supply in low light condition decreased spike number,kernel number per spike,1000-grain weight,biomass and harvest index inordinately,and eventually led to the decrease of yield significantly.It had the largest effect on kernel number per spike,and the minimum effect on 1000-grain weight.More nitrogen application increased spike number,biomass,harvest index and yield,and decreased 1000-grain weight.The impact of nitrogen application on kernel number per spike varied with the diffident light condition.