不同种植密度对施氮条件下玉米灌浆期叶片光合特性的影响

明确不同种植密度对施氮条件下玉米灌浆期叶片光合特征的影响，对通过种植密度调控玉米个体光合作用与群体产量关系，实现玉米稳产丰产具有理论和实践指导意义。在甘肃河西走廊，通过3 a田间试验，以施氮360 kg/hm²(N360)和不施氮(N0)为主区，玉米种植密度75 000株/hm²(D1)、87 000株/hm²(D2)和99 000株/hm²(D3)为副区，研究施氮条件下玉米灌浆期叶片光合特征对不同种植密度的响应。结果表明，试区玉米灌浆期光合有效辐射和大气温度最大值出现在14:00，最小值出现在6:00，而空气相对湿度最大值出现在6:00，最小值出现在14:00。施氮能够显著增加玉米灌浆期叶片净光合速率(P_{n)、叶片蒸腾速率(Tr)和气孔导度(Gs)，N360较N0在8:00-18:00的Pn平均增加19.5%~41.7%、Tr平均增加27.4%~44.1%、Gs平均增加27.4%~44.1%，但叶片胞间CO2浓度（Ci）显著降低；随着种植密度的增大，玉米灌浆期8:00―18:00的Pn、Tr、Gs呈降低趋势；N360D2与N360D1玉米灌浆期Pn差异不显著，显著大于其他处理。施氮水平和种植密度对玉米灌浆期8:00―16:00的叶片水分利用效率均无显著影响。N360较N0同时增加玉米籽粒产量和生物产量，但使玉米收获指数降低3.5%~5.3%；在N0中D2玉米籽粒产量大于D1和D3，而在N360中D2玉米籽粒产量与D3无显著差异，均显著大于D1；N360D2与N360D1的玉米籽粒产量无显著差异，均大于其他处理。总之，在施氮360 kg/hm²条件下，种植密度从75 000株/hm²增加到87 000株/hm²，能够使玉米灌浆期叶片光合速率保持在较高水平，提高收获指数，促进生物产量向籽粒产量的转化效率，获得最大籽粒产量。}

Effects of Different Planting Densities on Leaf Photosynthetic Characteristics under Nitrogen Fertilizationat at Filling Stage of Maize

This study aimed to investigate the effects of different planting densities of maize with nitrogen application on the photosynthetic characteristics of maize leaves at the filling stage.In this study, a 3-year field experiment was conducted in Hexi Corridor in Gansu province.With nitrogen application (N360) and no nitrogen application (N0) as main plots and three maize planting densities of 75 000 plants/hm(D1), 87 000 plants/hm(D2) and 99 000 plants/hm(D3) as split plots, the responses of photosynthetic characteristics of nitrogen application in maize leaves to different planting densities at filling stage were investigated.The results showed that the maximum value of photosynthetically active radiation and atmospheric temperature was at 14:00 and the minimum value was at 6:00, meanwhile, the maximum and minimum value of air relative humidity respectively were at 6:00 and 14:00.The nitrogen application significantly increased the net photosynthetic rate (P_{n), transpiration rate (Tr) and stomatal conductance (Gs) of N360 maize during filling stage, Pn, increased by 19.5%-41.7%,Tr increased by 27.4%-44.1% and Gs increased by 27.4%-44.1% from 8:00 am to 18:00 pm compared with N0.However, the intercellular CO2 concentration of N360 leaves significantly decreased compared with N0.With the increase of planting density, the Pn, Tr and Gs had a decreasing trend from 8:00 to 18:00 during filling stage of the maize.There was no significant difference in Pn of maize at filling stage between N360D2 and N360D1, which was significantly greater than that of other treatments.Nitrogen application rate and planting density had no significant effect on leaf water use efficiency from 8:00 am to 16:00 pm during maize filling stage.The grain yield and biological yield of maize under treatment of N360 was respectively increased compared with N0.However, the harvest index of maize with N360 was decreased by 3.5% to 5.3% compared with that of N0.The grain yield of D2 maize under treatment of N0 was greater than that of D1 and D3.However, the grain yield of D2 maize with N360 was not significantly different from that of D3 and was greater than that of D1.There was no significant difference in grain yield of maize between N360D2 and N360D1, both of which were higher than other treatments.In conclusion, with the increase of planting density from 75 000 plants/hm to 87 000 plants/hm, the leaf net photosynthetic rate of maize under 360 kg/hm² nitrogen application is at greater level, meanwhile, the harvest index is improved and the conversion efficiency of biological yield to grain yield is promoted, finally,the maximum grain yield is obtained.These findings provide theoretical and practical guidance for optimizing planting density and nitrogen application to achieve stable and high maize yield.}