Studies On Yield Formation And Physiological Characteristics Of Summer Maize Vaireties With Different Plant Height And The Regulation Of Plant Density

The experiment was carried out in Shandong Agricultural University experimentalfarm, and the State Key Laboratory of Crop Biology from2009to2011.Denghai661（DH661）, Chaoshi3（CS3）, Ludan981（LD981）and Xianyu335（XY335） wereused for experimental materials, and planted by three different densities which were4.50×10⁴,6.75×10⁴and9.00×104plant·ha^-1. To study colony structural, yield formation andphysiological characteristics of summer maize varieties with different plant height, and theregulation of plant density. The main results as followed:1. Summer maize varieties with different plant height all can achieve high yieldThree types of summer maize varieties were used in this study, low-plant height varietyDenghai661（DH661）, medium-plant height variety Chaoshi3（CS3）, high-plant heightvarieties Ludan981（LD981） and Xianyu335（XY335）. Three kinds of maize varieties,which were significant difference in the stem height, could get the higher yields, which weremore than10000kg·ha^-1. With the increase of plant density, the yield of low-plant heightvariety showed the biggest increase, while the1000grains mass and grains number per earof high-plant height variety showed lower decrease.2. Dry matter accumulation and distribution characteristics of summer maize varietieswith different plant heightThe results showed that the difference of dry matter accumulation for different plantheight maize varieties was mainly manifested after the flowering stage. Along with theincrease of the plant height, dry matter accumulation after the flowering stage reduced. Thecarbon distribution rate in lower part of stem in low-plant height variety was lower than thehigh-plant height varieties. The carbon assimilation transition and distribution characteristics of the different parts of plant （top, middle and bottom） were studied throughthe tracer of isotope¹³C. The results indicated that the leaves in different part of differentplant height maize varieties have different contribution to grain yield. With the decrease ofthe plant height, the dry matter transition of middle and bottom leaves were increased, thatof top leaves was contrary. The relative contribution of top leaves of high-plant heightvarieties to grains was higher than that of low-plant height variety, which of lower leaves ofhigh-plant height varieties was contrary. There were differences in the contribution to grainof different parts leaves before or after flowering. For the dry matter transition, the topleaves of LD981and XY335were the highest; the middle leaves of DH661were thehighest.3. Grain filling characteristics of summer maize varieties with different plant heightThe time reaching the maximum grain-filling rate （Tmax） of low-plant height varietywas3±days later than that of high-height variety. The maximum grain-filling rate （Wmax）of4.50×10⁴plant·ha^-1was significantly higher than that of6.75×10⁴plant·ha^-1, there wereno significant different between6.75×10⁴plant·ha^-1and9.00×10⁴plant·ha^-1. With theincrease of plant density, maximum grain-filling rate （Gmax） of low-plant height varietyhad no significant different, but that of high-height variety was gradually reduced. With theincrease of plant density, the time reaching the maximum grain-filling rate of summer maizevarieties with different plant height in advanced, and, the active grain-filling period wasreduced.4. Photosynthetic characteristics of summer maize varieties with different plant heightWith the increase of plant density, the grain yield increase of DH661was maximum,while the leaf area index （LAI）, photosynthetic pigment content and net photosynthetic rateof functional leaves were decreased. Before flowering, the net photosynthetic of leaves justenter the function were higher; however, after flowering, the net photosynthetic of top andmiddle leaves mainly higher than that of other leaves, the different plant height summermaize varieties were inconsistent. The difference of net photosynthetic rate between thethree parts of plant （top, middle and bottom） of low-plant height variety was less than that ofhigh-plant height varieties, and the same as the effect of plant density. The netphotosynthetic rate of top leaves had no significantly difference between low-plant heightand high-plant height varieties, while the net photosynthetic rate of middle and bottomlevies of low-plant height variety were significantly higher than that of high-plant heightvarieties. 5. Effect of endogenous hormone content of summer maize varieties with differentplant heightIn the process of seed growth, the higher content of GA, IAA and ZR of low-plantheight variety which played a driving role in yield formation, had closely related with grainfilling rate, while the higher content of ABA did just opposite.6. Endogenous protective enzyme activities of summer maize varieties with differentplant heightWith the increase of planting density, the activity of SOD, POD, CAT, APX and thesoluble protein content of summer maize varieties with different plant height were graduallydecreased, while the content of MDA was gradually increased. The endogenous protectiveenzyme activities in latter growing period of high-plant height varieties were reduced, andthe content of MDA was increased, which had no effect to slowing down aging.7. The stem lodging resistance of summer maize varieties with different plant heightWith the increase of plant density, vascular bundle in the unit area increased, especiallythe increase in small vascular bundles was the key to improve stalk puncture strength. Stemrind thickness, vascular bundle number, the area of the central vascular bundle, xylem andphloem of high-plant height varieties reduced significantly, Lodging property in fieldsincreased significantly. Strong lodging-resistance ability of low-plant height help laid thefoundations for a high yield by closing density.8. Root morphology of summer maize varieties with different plant heightWith the growth process, root surface area, root volume, root length and number ofroot tips increased first and then decreased, and the highest was in the flowering stage. Withthe increase of plant density, root surface area, root volume, root length and number of roottips were gradually reduced, and the low-plant height variety had the least differencesbetween the three densities. The root system distribution in shallow soil zone of low-plantheight variety was higher than that of high-plant height varieties, and the differences of rootsystem distribution in different soil layers of low-plant height variety was higher than that ofhigh-plant height varieties, too.