| Light and water are important factors affecting crop growth,yield,and quality.Global extreme weather events have become more frequent in recent years due to anthropogenic activity and industrial development.Drought and the uneven spatial and temporal distribution of light resources have created additional challenges for sustainable crop production,especially in the dry farming area of the Loess Plateau in Northwest China.It does not meet the needs for crop growth and development,which negatively impacts crop growth and yield improvement,particularly during the critical growth stage of crops.Insufficient light and water deficit will cause serious crop yield reduction.In this study,aiming at the problem of continuous improvement of light and water use efficiency of crop production in the arid area of the Loess Plateau,the effects of shade and drought on the photosynthetic characteristics and yield formation of maize and wheat were studied by setting different light and water gradients during the grain-filling period in the second ripening area of wheat maize cropping system in Shaanxi Province.The physiological properties of summer maize(Zea mays L.)and winter wheat(Triticum aestivum L.),as well as the potential relationship and mutual feedback mechanism between yield,are studied in order to explore the coupling of "light water" under different irrigation levels and light conditions.This will help improve the wheat and maize cropping system’s ability to prevent natural disasters,optimize the allocation of optical water resources,and achieve stable and high crop yields to provide a theoretical basis.A two-year(2020-2022)experiment was carried out using movable rain shelters in the Northwest A&F University in Yangling District,the Institute of Water-saving Agriculture in Arid Areas.Five shading treatments: 15 days shading(SD15);12 days shading(SD12);9days shading(SD9);6 days shading(SD6),and 3 days shading(SD3),and four irrigation treatments: full irrigation(I100);75% of full irrigation(I75);50% of full irrigation(I50)and25% of full irrigation(I25)were applied.The effects of different shade and irrigation conditions on the physiological response mechanism,yield and quality traits of winter wheat and summer maize were studied.The main results are as follows:1.Different degrees of shade during the grain-filling period reduced the grain yield,1000-grain weight,and grain protein content of winter wheat but increased the grain starch content.Plant height increased with a decrease in shading duration to favor the efficient capturing of light.However,with the increase of drought,the photosynthetic rate of winter wheat gradually decreased.The combined stress of long-term shade(SD15,SD12,and SD9)and drought(I25)during the grain-filling period significantly reduced the yield and quality of winter wheat.In the case of sufficient moisture(I100),proper shading(SD3,SD6,and SD9)improves plant height and photosynthetic performance,and increases the distribution of dry matter from the vegetative organs to the grains.2.The combined stress of shade and drought helped improve summer maize’s antioxidant capacity.However,it still caused oxidative damage to summer maize leaves,significantly reducing photosynthetic efficiency,yield,and quality.The combination of SD12 and I25 resulted in a 24% decrease in photosynthetic performance and grain yield in summer maize compared to the control.It was noticed that the grain yield was inhibited with the prolongation of the shading period.Under fully irrigated conditions,the plants under SD3,SD6,SD9,and SD12 displayed a reduction of 21.35,26.67,34.26.90,and 41.61% in grain yield when compared with SD0,respectively.For drought stress,a maximum reduction in grain yield was observed under 25% irrigation.Moreover,as an individual effect,75,50,and 25% irrigation decreased grain yield by 15.37,25.36,and 22.44%,respectively,over control.The combination of proper shade and irrigation was beneficial to improve grain quality,and the combination of SD12 with I25,I50,and I75 increased the protein content of maize grain by 3.94%,8.06%,and 6.70%,respectively.3.The combined stress of shade and drought significantly reduced the fluorescence quantum yield and PSII of wheat flag leaf,which in turn reduced grain yield.With the increase of irrigation level and shade duration,the fluorescence quantum yield,photochemical quenching(q P),non-photochemical quenching(NPQ),and chlorophyll fluorescence parameters(Fv/Fm)of winter wheat showed decreasing changes.In summary,shade exacerbated the negative effects of water scarcity on winter wheat and summer maize plants.The combined stress of continuous shade for 15 days and the irrigation level of 25% forced the yield of winter wheat and summer maize to decrease by 78%and 54.06%,respectively.Although different degrees of combined stress increased the antioxidant enzyme activity of plants,it was insufficient to counteract the oxidative damage caused by stress.The main reasons for the decrease in maize yield were the oxidative damage of malondialdehyde(MDA)expression and the decrease of photosynthetic properties in the late stage of summer maize.The results provide a theoretical basis for the sustainable wheat maize cropping system and effective irrigation measures in the Loess Plateau area under the future climate background from crop growth,physiological characteristics,and yield response mechanism. |
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