种植密度对烟草冠层辐射和群体光合作用的影响

烟草群体光合能力是烟叶产量和品质形成的基础,种植密度是调节烟草个体生长和群体发展的重要因素。以烤烟品种‘云烟85’为材料,设置3个种植密度(D1:16 529株·hm~(-2);D2:18 182株·hm~(-2);D3:20 202株·hm~(-2))处理,研究密度对烟草群体叶面积动态、冠层辐射、群体光合作用及经济性状的影响。结果表明,烤烟群体发展动态表现为圆顶期叶面积指数(LAI)最大,行间叶尖距和冠层透光率最低,以后随着叶片的成熟采收,LAI逐渐减小,行间叶尖距和冠层透光率逐步增大。与此相应,群体光合速率(RCP)也以圆顶期较高。同一时期不同处理间相比,随密度增加LAI增大,行间叶尖距和冠层透光率减小。群体光合速率随密度的变化表现为,在圆顶期从D1到D2群体光合速率增加,从D2到D3有所下降,中部叶片采收后3个密度间差异不显著。相关分析表明,LAI与叶尖距、透光率呈显著负相关,与群体光合速率呈正相关,但不显著。表明群体光合速率并非随密度增大而持续提高,密度过大时,反而导致群体光合速率下降。产量和产值从D1到D2显著增加,从D2到D3则有所下降,上等烟比例以D2最高。从群体发展的协调性、田间管理的方便性及生产成本等综合考虑,烤烟品种云烟85的种植密度以18 182株·hm~(-2)左右较为适宜。

Effect of Planting Density on Light Transmittance and Canopy Photosynthesis of Flue-cured Tobacco Plants

Canopy photosynthetic capacity determines the yield and quality,while planting density affects the growth and canopy development of a flue-cured tobacco plant.Varied planting densities (i.e.,D1at 16 529 plants per hm2,D2 at 18 182 plants per hm2,and D3 at 20 202 plants per hm2) were applied to study their effect on the leaf area index (LAI),light transmittance (LT),photosynthesis,and economy of the canopies on Yunyan 85tobacco plants.The results showed that,during the entire course of canopy development,LAI was at its highest level and the distance between leaf tips of adjacent lines (DLT) and LT at their lowest in the dome stage.As the leaves matured and upon harvest,LAI declined,while DLT and LT increased.Consequently,the canopy photosynthetic rate(RCP) peaked during the dome stage.In comparison,in the same period,an increased planting density would induce a heightened LAI but lowered DLT and LT.On the other hand,the changes of planting density or leaf-harvesting did not significantly affect RCP on the plants.LAI was found inversely correlated to DLT and LT.The correlation between RCP and planting density varied at the dome stage.RCP raised as the density increased from D1 to D2,but decreased from D2 to D3.And,RCP correlated to leaf-removal,but insignificant.RCP could not be continually risen with increasing planting density.In fact,it declined when the density exceeded a certain level.Yield and output on tobacco leaves increased significantly as the planting density increased from D1 to D2,but decreased from D2 to D3.The percentage of high-grade tobacco was maximized with D2 among the 3 treatments.Taking the canopy development,field management and production cost together into consideration,a planting density approximating 18 182 plants per hm2seemed optimal for Yunyan 85 cultivation.