不同施N水平纽荷尔脐橙叶绿素含量的季节变化

以1年生盆栽枳砧纽荷尔脐橙为试材，研究不同施N水平对叶片N含量，春梢、夏梢和秋梢落叶率，以及春梢、夏梢和秋梢叶绿素含量季节变化的影响。结果显示，施N植株前期落叶率略高于未施N植株，后期无显著差异；叶片N含量与施N量存在极显著正相关关系（r=0.97）；施N处理显著提高了不同枝梢叶片的叶绿素含量，并且在整个测定时期内使叶绿素含量维持在较为稳定的水平；单株施N量高于6.5 g时叶绿素含量不再显著增加，但更有利于维持叶绿素含量的周年稳定；对照（不施N）的不同枝梢叶片叶绿素含量从当年9月开始明显下降，翌年3月出现锐降，而施N植株仅略微下降。由此可见，N不仅可提高叶绿素含量且可减少其季节性变化幅度。

The Seasonal Variation of Chlorophyll Content in Newhall Navel Orange Seedlings Applied with Different N levels

One year old potted Newhall navel orange (Citrus sinensis Osbeck cv Newhall) budlings on trifoliata orange (Poncirus trifoliata (L.) Raf.) rootstocks, applied with different nitrogen(N) levels, were used to study the effects of N application levels on leaf-falling ratios, leaf N contents and the seasonal changes of chlorophyll contents in leaves of spring, summer and autumn shoots. Results showed that leaf-falling ratios of all shoots in the plants applied with N were slightly higher than those in the plants without N in November, but there was no significant difference in the following May and November. There were most significantly positive correlation between N contents in leaves and amounts of N application (r=0.97). The significant increase in chlorophyll contents in leaves of spring, summer and autumn shoots could result from the application of N, and chlorophyll contents in leaves of plants with N application were relative steady in the whole measurement period. With the increase of N application rate, the chlorophyll contents no longer increased significantly as a plant was applied with more than 6.5 g N. However, high rate of N application was beneficial for the stability of chlorophyll contents. The chlorophyll contents in leaves of all shoots of control plants decreased obviously in September and reduced sharply in the following March, while slightly decrease occured in N treated plants. These results suggested that N application could raise chlorophyll contents in leaves of Newhall navel orange and made the chlorophyll contents be steady.