玉米密植群体下部叶片衰老对植株碳氮分配与产量形成的影响

玉米密植会造成花后下部叶片早衰,为探明其对植株根系性能、碳氮积累分配及产量形成的影响,采用大田与土柱栽培相结合的方式,以登海661和郑单958为试材,分析了密植条件下两品种花后碳氮分配、根系性能和植株干物质积累量的变化。两年结果表明,玉米密植群体下部叶片早衰导致两品种花后穗位叶叶绿素含量和净光合速率显著降低,向根系转运的光合产物数量显著减少,成熟期(R6)的根系生物量、根长密度和根系表面积较CK显著减少。根系性能的下降导致花后氮素吸收量显著降低,叶片光合速率降低、整株叶片衰老进程加快,单株籽粒产量显著下降,登海661较CK低7.61%,郑单958较CK低8.35%。郑单958的花后叶片衰老要早于登海661,且叶面积和净光合速率比登海661低,导致花后干物质积累量和产量较登海661显著降低。可见玉米密植群体花后下部叶片衰老加速了根系衰老,降低了氮素吸收量,影响整株绿叶面积和光合持续期,最终导致花后干物质积累量和籽粒产量降低。

Effects of Lower Leaf Senescence on Carbon and Nitrogen Distribution and Yield Formation in Maize (Zea mays L.) with High Planting Density

Increasing the population density accelerates the senescence of lower leaves, affecting carbon (C) and nitrogen (N) partitioning in maize (Zea mays L.), and also influencing N uptake by roots after silking. We used the maize varieties Denghai 661 and Zhengdan 958 in field and soil column experiments to analyse of changed of C and N distribution, root system function and plant dry matter accumulation in high plant density at post-silking. The chlorophyll content and net photosynthetic rate of the ear leaf showed a significant decrease. Compared with CK, Denghai 661, and Zhengdan 958 decreased the photosynthetic translocation from at lower leaves to roots. Root biomass, root length density and root surface area were also negatively affected post-silking. The reduction of root function significantly reduced nitrogen uptake and leaf photosynthetic rate and leading to accelerate leaf senescence process at post-silking. Grain yield decreased 7.61% in Denghai 661 and 8.35% in Zhengdan 958. Zhengdan 958 had earlier leaf senescence, lower leaf area and net photosynthetic rate than Denghai 661, significantly decreasing dry matter accumulation and yield. In conclusion, lower leaf senescence accelerates root senescence, decreases nitrogen uptake, whole plant green leaves area and photosynthetic duration, eventually reduced dry matter accumulation and yield.