| With the increase of planting density,the condition of ventilation and penetrating light became worse. Therefore, in high-density conditions, it becomes a key that how to improve the corn canopy structure, increased air and light conditions in maize cultivation. During 2008-2009 growing season, it was in the technical innovation center of maize in Huang-Huai-Hai region and state key laboratory of crop biology that the field experiment was conducted. The study used Denghai 701(a super-high yielding maize variety) as the experimental material, and there are three different planting densities, which were 67500 plants/hm2(D1), 90000 plants/hm2(D2) and 112500 plants/hm2(D3) respectively, and four row spacing forms (60+60,70+50,80+40,90+30). In the super-high yielding condition, effects of different planting densities and row spacing forms on the maize yield and canopy apparently photosynthesis characteristics were explored. The main results as followed:1.Effects of planting densities and row spacing forms on plant characters, yield, as well as its components of maizeThe maize yield, plant height and ear height were all increased with the density increasing, however, kernels numbers per ear, kernels numbers per row and weight per 1000 kernels reduced significantly, although the rows per ear decreased unobvious. As for plant height and ear height, D2 and D3 were 4.9cm and 9.3cm, 7.6cm and 11.4cm higher, in comparison of D1.Under the low density, the yields of the"80+40"and uniform row spacing forms were distinctly higher than those of the other ones; while compared with the other ones, the yield, kernels per row and weight per 1000 kernels of the"80+40"form were remarkably higher under the mediate and high densities. There were no noticeable treatment effects on plant height and ear height among four row spacing forms under D1 density but under higher densities(D2 and D3) the"80+40"form was the lowest one in terms of plant height and ear height and the difference became more and more big with the increase of the density. 2. Effects of planting densities and row spacing forms on the dynamics of dry matter accumulation of maizeThe increase of dry matter accumulation of maize population was accompanied by the increase of density. Under high density, the dry matter accumulation of the"80+40"form were the highest, especially at late development stage. However, the dry matter accumulation per plant had an opposite trend and D1 was almost 1/3 higher than D3, and the phenomenon mainly was present in middle and lower parts (below 150cm), but there were a little difference in upper part. The leaves and stems weight in middle-lower part decreased gradually; while the leaf dry weight above 210cm increased slightly with the increase of density. Under the same density, the leaf, stem and total dry matter accumulation of the"80+40"form in middle-lower part were higher than those of the others, contrary to it, the data showed lower in upper part.3.Effects of planting densities and row spacing forms on the ear leaf photosynthetic characters of maizeThe chlorophyll content, net photosynthesis rate (Pn), photochemical efficiency of PSII (Fv/Fm) and the actual quantum yield of PSII linear electron (ΦPSⅡ) were negatively correlated with the density, especially in the late growth stage. The activities of photosynthesis key enzymes (PEPCase and RUBPCase) performed consistent with them. The results indicated that the high density was unfavorable to photosynthesis of the ear leaf.Under low density, the chlorophyll content, Pn, Fv/Fm,ΦPSⅡand the activities of PEPCase and RUBPCase had no significant differences among all row spacing forms; while under middle-high densities, these values of the"80+40"form were the greatest, particularly at late development stages. So, the photosynthetic capacity of ear leaves was raised by the optimum row spacing form. 4.Effects of planting densities and row spacing forms on canopy light distribution and apparently photosynthesis characteristics of maizeWith the increase of density, the canopy photosynthetically active radiation (PAR) total capture ratio and the capture ratio in upper layer both raised simultaneously and yet that in ear leaf and lower layers represented decreasing. Whichever one the density was, the total capture ratio and capture ratio in ear leaf and lower layers of the"80+40"form was the biggest and the capture ratio of"60+60"form in upper layer was the highest, and it decreased following by the increase of the wide row spacing.The leaf area index (LAI) was positively correlated with the density at some extent but the time of the maximal LAI under three densities was different, which were at the grain filling stage under D1 and at flowering stage in high density respectively. In comparison of LAI in high density, the reducing extents in medium and low densities were smaller. At low density, the LAI of uniform form was higher than the others. The LAI in higher densities was significantly higher than those of the other density treatments. From all above, the conclusion that the"80+40"form under high density attributes to improve LAI, consequently, to enlarge the photosynthetic resource.The canopy apparently photosynthesis rate (CAP) after anthesis increased corresponding to the density increase. At the same density, the sequence of CAP among all forms was"80+40">"70+50">"60+60">"90+30"and the difference became larger with the density raising. The canopy respiration (CR) decreased first and increased latter after anthesis. At each growth stage the CR value and ratio of CR/TCAP increased with the density increase. Under the same density, the ratio of CR/TCAP of"80+40"form was obvious lower than the other ones and the trend performed very conspicuous under higher densities.5.Effects of planting densities and row spacing forms on seed-setting rate and the endogenous hormone contents in the upper ear part of maizeThe seed-setting rate decreased with the increase of the density. Under D1, it reduced as the wide row augmented; under D2 and D3, that of"80+40"form was the highest. Under D2, the contents of IAA, GA3, ZR and DHZR in upper ear part of"80+40"form were the highest before 25 days after pollination; while there were no significant differences among all forms. As for the content of ABA, that of"80+40"form was slightly higher than the others before 20 days after pollination and the data was lower later, particularly on the 40th day after anthesis.The results indicated that for obtaining high yield, we should choose higher density at first because the high density is the basis of improving maize yield. Secondly, the rational row spacing form can bring individual developmental potential to full play, coordinating the population and individual development and guaranteeing higher yield. Considering obtaining the high and stable yields, the optimal configuration for Denghai 701 was 90000 plants per hm~2 and"80+40"row spacing form in the conditions of this experiment.
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