压砂西瓜叶片SPAD值变化规律及其对氮素的响应

The dynamic change of SPAD value of different watermelon leaves and its responses to nitrogen rates

通过田间试验,研究压砂西瓜生长期基部、中部和顶部叶片SPAD值的变化规律及不同施氮水平对叶片SPAD值的影响.结果表明:压砂西瓜叶片SPAD值随生育期的变化而变化,并因叶片部位的不同而异.苗期以基部叶SPAD值最高,伸蔓期至收获期以中部叶和顶部叶的较高.从苗期至成熟期,基部和中部叶SPAD值动态变化规律基本一致,即苗期与成熟期较低,而伸蔓期至膨瓜期较高且保持相对稳定,分别为56.2和60.6.顶部叶SPAD值在苗期至膨瓜期逐渐增加,而收获期迅速下降.总体而言,中部叶SPAD值变化比较平稳且变异系数较小.施氮水平与不同部位叶片SPAD值有密切关系,且因生育时期不同而异.苗期,基部、中部和顶部叶片SPAD值均随施氮水平提高,呈倒S型变化;伸蔓期至膨瓜期呈典型的报酬递减抛物线变化趋势,且相关性均达到显著或极显著水平;收获期,基部叶和中部叶SPAD值仍保持抛物线式变化,但相关系数有所降低.说明伸蔓期至膨瓜期叶片SPAD值水平较高,此时期适量施氮有助于不同部位叶片叶绿素的累积,而过量则使叶片SPAD值降低;同时,整个生育期中部叶片SPAD值保持较高和较稳定水平,并且与施氮水平之间呈稳定的报酬递减关系,因此可以作为压砂西瓜氮素营养诊断的指示器官.

Field-plot experiment was carried out to study the dynamic change and the respond on nitrogen rates of SPAD value in base, middle, and forehead spot leaves of watermelon on gravel-sand field. The results showed that the SPAD value changed with the growth stage and was varied in different spot leaves. The SPAD value of base leaves was biggest in seedling stage, but the SPAD value in middle and forehead leaves were higher from stretching stage period to maturing stage. The dynamic change of SPAD value in base and middle leaves was almost the same, it was lower in seedling stage and har- vest time. From stretching stage to expanding stage it was kept higher and relatively stable which are 56.2 and 60.6 respec- tively. As for the forehead leaves, the SPAD value was gradually increased from seedling stage to expanding stage and was dropped rapidly in the mature stage. In a word, the SPAD value of middle leaves was relatively stable and its variable coeffi- cient was lower. The SPAD value of different spot leaves were closely related to nitrogen level and it is different from growth period. In seedling stage, the SPAD value of base, middle and forehead leaves was ＂S＂ shape change with the increase of ni- trogen rates. However, it followed the law of diminishing returns and changed by ＂parabolic＂ curve from stretching stage to ex- panding stage, and the correlation between SPAD Value and nitrogen rates got significant level or very significant level. In maturing stage, the SPAD value of base and middle leaved was parabolic but the correlation decreased. The results indicated that the SPAD value was higher from stretching stage to expanding stage, and the suitable nitrogen application can enhance chlorophyll, but excess nitrogen makes the SPAD lower. Meanwhile, during the whole growing period of watermelon, the SPAD in middle leaves is higher and stable and the changes with the increase of nitrogen follows the law of diminishing returns, so the middle leaves can be as the diagnosis organ of nitrogen.