Effects Of Leaf Removal On Yield And Physiological Characteristics Of Summer Maize Under High Density

The experiments were conducted in 2014 and 2015 at the Technological Innovation Center of Maize in Huang-Huai-Hai Region and the State Key Laboratory of Crop Biology of Shandong Agricultural University.Two large-area summer maize(Zea mays L.)cultivars,Zhengdan958 and Xianyu335,were planted at two different plant densities of 75000 plants hm–2 and 105,000 plants hm–2.Seven days after silking,we removed two(L2),four(L4)or six(L6)leaves from the top of plants,with no leaf removal as control(L0).The regulation effects of leaf removal on shoot and root growth,grain develop and yield of summer maize were studied to provide theoretical basis for further increasing grain yield through adjusting the plant architectures.The main results were as follows: 1.Effects of leaf removal on population structure and leaf area index of summer maizeLeaf removal the top leaves under different plant densities led to clear differences in LAI.At the density of 105000 plants hm-2,excising two leaves from the top of a plant increased LAI significantly since 35 days after silking.For Zhengdan958,excising two leaves led to an increase in LAI by 18.69% as compared with control,while it increased 28.56% for Xianyu335.Nevertheless,excising four or six leaves led to a reduction of LAI as compared with L0 treatment under high plant density.In addition,under different density,leaf removal markedly increased the light transmission rate during grain filling,improved the illumination in field,while excessive leaf removal caused light leakage losses in later period.At the density of 75000 plants hm-2,excising leaves decreased LAI significantly since 7 days after silking.2.Effects of leaf removal on dry matter and N accumulation of summer maizeAt the density of 105000 plants hm-2,excising two leaves from the top of a plant decreased dry weight in stem,which was transferred to grain,but increased dry matter accumulation since leaf-removal treatment application and increased shoot biomass at maturation.For Zhengdan958,relative to the control,plants in L2 obtained 4.12% higher shoot biomass at maturation under the higher density,while it increased 5.11% for Xianyu335.At the same density,excising four or six leaves increased the amount of dry matter transportation in stem and leaves and decreased the total shoot biomass significantly due to excessive leaf removal decreased the ratio of dry matter after 7DAS.Furthermore,effects of leaf removal on N accumulation and distribution were significant.7DAS,leaf removal significantly reduced N accumulation in remainder leaves.At the density of 105000 plants hm-2,excising two leaves significantly decreased N accumulation in stem,which was propitious to transfer N from stem to grain.What's more,at maturity,excising two leaves significantly increased total shoot N accumulation amount at the density of 105000 plants hm-2.Zhengdan958 and Xianyu335 plants in L2 exhibited a 7.16% and 7.07% increase,respectively,in total N accumulation compared with control.At the same density,excising four or six leaves decreased total N accumulation amount and grain N accumulation at maturity.At the density of 75000 plants hm-2,although leaf removal promoted transportation N from stem to grain,total N accumulation and the grain N accumulation significantly decreased because of a sharp reduction of N accumulation ratio after 7DAS.3.Effects of leaf removal on root growth of summer maizeLeaf removal led to significant effects on root growth and function of summer maize under two densities.At the density of 105000 plants hm-2,excising two leaves from the top of a plant had bigger root at 49 days after silking as compared with control,which exhibited a 5.75% increase in root dry weight and a 7.78% increase in root length density.And excising two leaves significantly increased root dry weight and root length density in deep soil,promoted plant N uptake,thereby maintained root TTC reducing capacity higher,retarded senescent speed,which was benefit to uptake N.But at the same density,excessive cutting four or six leaves led to roots dry weight and roots length density reduction and a decline in root activity.At the density of 75000 plants hm-2,leaf removal caused the decline in root dry weight and root length density at 49 days after silking significantly,while decreased root activity and the amount of N uptake.4.Effects of leaf removal on grain filling and yield of summer maizeGrain filling and yield of summer maize were significantly affected by leaf removal at different densities.At the density of 105000 plants hm-2,excising two leaves from the top of a plant significantly increased grain volume,Wmax and Gmax,leading to higher grain dry weight and yield.At the density of 105000 plants hm-2 in 2015,the grain yield in L2 treatment increased by 9.14% in Zhengdan958 and by 9.92% in Xianyu335 compared with L0 at the same density,while it in Zhengdan958 and Xianyu335 increased by 5.60% and 7.67%,respectively,compared with L0 at the density of 75000 plants hm-2.At the density of 105000 plants hm-2,excising four or six leaves causing the loss of leaf source,decreasing grain filling rate significantly,led to reductions of grain dry weight and yield.At the density of 75000 plants hm-2,Wmax and Gmax declined after removing leaf,and decreased grain dry weight and grain number at maturity,which led to a reduction of grain yield.