Effects Of Shade,waterlogging And Their Combined Stress On Yield And Growth Characteristics Of Summer Maize

This study was conducted from 2019 to 2020 in Huanghuaihai maize science and technology park and state key laboratory of crop biology.Denghai 605(DH605)was selected as experimental material.The experiment was to study the effects of waterlogging,shade and their combine stress on yeild and growth of summer maize at the third leaf stage(V3),the sixth leaf stage(V6),and the flowering stage(VT)in order to provide basis for stress resistance and stable yield of summer maize.The main findings are as follows:1.Effects of shade,waterlogging and their combined stress on yield and its components of summer maizeThe grain yield of summer maize was significantly decreased under the combined stress of shade and waterlogging.The yield of combined stress of waterlogging and shade in V3,V6and VT decreased by 39.4%,31.9%and 28.9%,respectively,and that of shading treatment in V3,V6 and VT decreased by 6.5%,10.3%and 27.2%,respectively the yields of waterlogging at V3,V6 and VT were treatments decreased by 39.4%,34.4%and 6.5%,respectively,compared with CK.It can be seen that shade,waterlogging and its combined stress had the greatest effect on the yield at V3,followed by V6 and VT stage,and the combined stress had a greater effect than the single stress.2.Effects of shade,waterlogging and their combined stress on the ear development characteristics of summer maizeShade,waterlogging and their combined stresses inhibited the growth of ear and tassel,reduced the panicle length,affected the total number and effectiveness of floret differentiation,interfered with fertilization and seed setting,and then affected the formation of grains.The total number of floret differentiation decreased by 8.1%and 15.3%respectively under shade and combined stress of waterlogging and shade in the early growth period,the total number of differentiated florets decreased by 9.9%and 10.0%,respectively,in contrast,the abortion rate of florets treated with shade and waterlogging at V3,V6 and VT increased by 18.3%,14.2%and 20.7%,respectively the abortion rates of florets treated with shading at V3,V6 and VT were 1.6%,4.7%and 21.1%higher than those of CK,and the abortion rates of florets treated with waterlogging at V3,V6 and VT were 15.9%,12.3%and 5%higher than those treated with CK.The growth of panicle was inhibited,the total number of floret differentiation decreased,the fertilization rate decreased,and the seed setting rate decreased,which led to the increase of the total abortion rate of floret and the decrease of the seed setting rate.3.Effects of shade,waterlogging and their combined stress on the photosynthetic characteristics of summer maizeThe Leaf Area Index(LAI)and SPAD of summer maize were decreased under the combined stress of shade and waterlogging,and then the photosynthetic performance of summer maize was damaged,and the net photosynthetic rate(P_n),transpiration rate(T_r)and stomatal conductance(G_s)were decreased significantly,the intercellular carbon dioxide concentration(C_i)increased slightly,in which the Pn of combined treatment of waterlogging and shade in V3,V6 and VT period decreased by 36.4%,33.4%and 29.3%,respectively.At the same time,there was a significant difference between combined treatment of waterlogging and shade and shade treatment in the early growth stage,but there was a little difference between them,compared with shading treatment,V3 and V6 composite treatment decreased by 33.7%and 28.3%respectively,while VT combined treatment of waterlogging and shade decreased by 24.8%compared with waterlogging treatment.4.Effects of shade,waterlogging and their combined stress on the leaf senescence characteristics of summer maizeThe activities of senescent enzymes such as SOD,POD and CAT were significantly decreased after shade,waterlogging and their combined stress were over.The activities of SOD were decreased by 44.2%,36.5%and 30.1%,and the activities of POD and CAT were similar in different treatments.In addition,shade,waterlogging and their combined stress also led to the increase of MDA content.The decrease of senescent enzyme activity and the increase of MDA content showed that the protective enzyme system was destroyed,the accumulation of active oxygen increased,the membrane lipid peroxidation increased,the chloroplast structure was destroyed,and the loss of chlorophyll intensified,the result was that photosynthesis of summer maize was inhibited.5.Effects of shade,waterlogging and their combined stress on the dry matter accumulation and distribution of summer maizeShade,waterlogging and their combined stress reduced the total dry matter accumulation.Compared with CK treatment,the total dry matter accumulation of V3,V6 and VT treatment decreased by 44.7%,35.1%and 20.3%,respectively,and the proportion of dry matter distribution to grains decreased by 23.9%,19.2%and 14.6%,respectively,the total amount of dry matter accumulation and the proportion of dry matter distribution to grains in the combined treatment were less than those in the shade treatment and waterlogging treatment.The decrease of the total dry matter accumulation and the decrease of the ratio of dry matter to grain were also the main reasons for the decrease of grain yield.6.Effects of shade,waterlogging and their combined stress on lodging resistance of summer maizeCombined stress of waterlogging and shade affected the growth of stem.Under shade,waterlogging and their combined stress,the stem length,stem diameter and puncture intensity of the third node in the aerial part of summer maize decreased,the puncture strength of the stems of combined stress of waterlogging and shade at V3,V6 and VT stage were decreased by 22.7%,11.5%and 9.9%respectively,while shade treatment at V3,V6 and VT stage decreased by 5.1%,3.4%and 6.8%respectively,waterlogging treatment decreased by 21%,15%and 9.6%,respectively.After combined treatment of waterlogging and shade,the microstructure of the stem changed,the thickness of the the thickness of the cortex and the thick-walled tissue inside the vascular bundle became thinner,and the number of vascular bundle decreased,which led to the decrease of the lodging resistance and the increase of lodging risk of stem.The combined treatments of waterlogging and shading at V3 and V6 had greater influence on the lodging resistance of culms than at VT.