| Due to climate changes,the effects of high temperature stress on crops growth and yield formationare more and more serious.As a preferring warm and cool environment crop,wheat is very sensitive to high temperature stress,especially during grain filling stage,resulting in reduced grain filling rate and lower yield.Magnesium(Mg)is the fourth most important element of plant only next to nitrogen,phosphors and potassium.Exogenous Mg(either in soil or foliage)will significantly increase wheat yield.Therefore,it is very important to study the effect sand physiological mechanism of Mg on grain filling under high temperature stress during grain filling stage.In this study,the pot experiments were conducted,using winter wheat Yangmai16,to explore the response of grain filling and yield formation to different exogenous Mg concentrations(either 0 or 20kg.hm-2)at booting stage and high temperature tress at grain filling stage,respectively.High temperature tress(Day/night 32/22 C)treatment was applied from14 to 20 days at post-anthesis(Ti),21 to 27 days at post-anthesis(T2)in the different grain filling growth stage.The physiological mechanism of exogenous Mg on wheat grain filling and yield formation was investigated via photosynthetic characteristics,reactive oxygen metabolism,carbon and nitrogen metabolismto provide an theoretical basis for wheat stability yield under climate changes environment.The main results are as follows:1 Effects of Mg fertilization on grain filling and yield in winter wheat under high temperature stress during grain filling stage.High temperature tress significantly decreased the maximum grain filling rate and shortened the grain filling duration,leading to reduced 1000-grain weight and grain yield,especially in the T2 treatment.Mg application significantly increased 1000-grains weight and grain yield under high temperature stress by increasing maximum grain filling rate and prolonging the grain filling duration.Furthermore,heat stress reduced post-anthesis dry matter accumulation,nutrient organ dry matter translocation,translocation efficiency and harvest index,while magnesium application showed positive effects on those traits.Consequently,the application of magnesium at booting stage improved grain yield by enhancing the capacity of dry matter accumulation and translocation.2 Effects of Mg fertilization on photosynthetic characteristics and senescence in winter wheat under high temperature stress during filling stage.The high temperature stress significantly decreased Pn,Gs,Tr,photosynthetic pigments,PS Ⅱ,Fv/Fm and ΦPS Ⅱ,but increased Ci,which indicating that the decrease in Pn under high temperature stress was mainly caused by non-stomatal factors.Mg application with higher photosynthetic pigments content,Gs,Tr,Fv/Fm and ΦPS Ⅱ,and lower Ci can enhance the photosynthetic stability to alleviate the negative effectsof non-stomatal factors on photosynthesis.In addition,the content of soluble protein and Rubisco were reduced under heat stress,and the decreases was higher in T2 treatment.Mg application showed positive effects on soluble protein and Rubisco contents,showing that the application of magnesium could alleviate senility by enhancing the CO2 carboxylation efficiency and inhibiting the hydrolysis of protein.High temperature stress significantly increased the content of superoxideanion radical(O2·-)and malondialdehyde(MDA).While magnesium application increased the activity of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)to remove the adverse effects of O2· and MDA on cell membrane under heat stress.The above results showed that Mg application could maintain the stability of photosynthetic system and anti-aging to produce more photosynthetic matter,contributing to higher grain yield.3 Effects of Mg fertilization on carbon and nitrogen metabolism in winter wheat under high temperature stress during filling stage.The nitrogen content and nitrate reductase(NR),glutamine synthetase(GS)activities in flag leaf of wheat were significantly decreased by high temperature stress,while the better performance on leaf nitrogen content and NR,GS activities were found in Mg20 magnesium application than those in Mg0 under heat stress,indicating that magnesium application stimulated the capability of nitrogen assimilation and utilization.Heat stress reduced the content of soluble sugar and sucrose,and activity of sucrose phosphate synthase(SPS)in flag leaf.Magnesium application improved the ability of photosynthetic matter transforming into sugar by increasing the accumulation of soluble sugar and sucrose contentand SPS activity,thus increasing grain sucrose content for laying the foundation.High temperature stress had negative effects on grain sucrose content and sucrose synthase(SS)activity,but Mg application showed positive effects on those traits.The results showed that Mg application could improve grain translocation and assimilation ability under heat stress.Therefore,magnesium applied could coordinate the balance of source-sink carbon and nitrogen metabolism,which was conducive to increasegrain yield.In conclusion,magnesium application during booting stage decreased the damage of membrane lipid peroxidation under heat stress during filling stage to improve the photosynthetic capacity and stimulate the accumulation of photosynthetic product for maintain higher level of source and flow fromphotosynthetic products to grains.Furthermore,it improved the assimilation ability of sink by increasing the activity of nitrogen and carbon metabolic enzymes to promote grain filling for higher wheatgrain yield. |
