Grain Yield In Response To Shading After Anthesis In Winter Wheat And Its Physiological Basis

Shading after anthesis as a result of cloudy or rainy days and big population density oftenoccurs in the the Huang-Huai-Hai plain of China, and has negative influence on wheat grainyield and quality. In the present study, different spike-types cultivars were used to evaluate theeffect of shading at different shading intensities and different grain filling stages in wheatgrain yield, senescence process, and N-fertilizer use. The main results were as follows:1Photosynthetic characteristics and antioxidative metabolism of flag leaves in responsesto shading during grain filling in winter wheat cultivarsThe chlorophyll content, net photosynthetic rate (Pn), contents of soluble protein and sugar,activities of antioxidative enzymes, and malondialdehyde (MDA) content were measuredfrom0to28d post flowering. Compared to S0treatment, the chlorophyll content andmaximal efficiency of photosystem II (PSII) photochemistry (Fv/Fm) of flag leaves wereenhanced in treatments S1and S2. From0to6d post flowering, the chlorophyll content andFv/Fmin S3were also higher than those in S0, but significantly lower than these in controls,thereafter. With the increase of shading intensity, the effective quantum yield of PSII (ΦPSⅡ)was promoted; whereas, the ratio of Chl a/b was declined. Compared to S0, treatments S2andS3significantly suppressed the activities of superoxide dismutase (SOD) and peroxidase(POD), Pn, and contents of soluble protein and total soluble sugar, but S1treatment showedpositive effects on above parameters.2Effect of shading on nitrogen accumulation and translocation of winter wheatThe results indicate that the shading at different grain-filling stages decreases the uptakeand translocation of N of the two cultivars which are in the order: T0>T3>T2>T1. Theamounts of nitrogen derived from soil range from68.0-71.39%and the percentages ofnitrogen derived from the basal fertilizer in the vegetative organs are lower than those derived from the topdressing fertilizer. The shading at different grain-filling stages increases theabsorption amount and proportion of soil N in the vegetative organs, and inhibits translocationof those to the grain. The grain yield, N uptake from fertilizer, fertilizer N use efficiency andpartial factor productivity from fertilizer N at different grain-filling stages are also in order:T0>T3>T2>T1. In conclusion, the shading at different filling stages decreases the uptake andtranslocation of N and grain yield, and the uptake and translocation are highest under theshading at the early filling stage and the lowest at the later filling stage.3Responses to post-anthesis shading in winter wheat with different spike typesUnder the same shading condition, Jinan17had larger chlorophyll content and higheractivities of PSII and antioxidative enzymes, but lower MDA content than Tainong18. Thisresult indicated that multiple-spike cultivar was more suitable than large-spike cultivar in theHuang-Huai-Hai Plain with shading problem at late growth period, because there were lessdamage of flag leaf and better photosynthetic function in multiple-spike cultivar. Wheat plantsunder S1shading condition had relatively high activities of antioxidative enzymes and lowdegree of membrane lipid peroxidation, which was in favor of stress resistance, maintaininghigh Pnduration, and accumulation of photosynthate in wheat plants.