棉花产量因主茎不同叶位叶绿素含量变化对播期和密度的响应

Cotton Yield Is Affected by the Distribution of Chlorophyll Content Response to Sowing Date and Planting Density

叶绿素含量是田间诊断氮素营养供应状况指标之一,与氮代谢密切相关。【目的】为探讨播期和密度对迟直播棉花主茎不同叶位氮代谢与产量的影响。【方法】采用裂区试验设计,以播期(月-日)(S1,05-30;S2,06-14)为主区,密度(株·m-2)为副区(D1,7.5;D2,9.0;D3,10.5),在大田试验条件下研究了不同生育时期棉花主茎不同叶位叶绿素含量的动态变化。【结果】1)棉花叶绿素a、b、(a+b)含量盛花期>初花期>现蕾期,且随叶位由上而下先升高(倒3~5叶最高)后降低,随密度增加而降低,播期间(现蕾期、初花期、盛花期)S2显著高于S1(现蕾期叶绿素b无显著差异),播期、密度均不改变这些指标在叶位间的变化趋势,播期与密度交互作用存在差异(应作相应的统计分析);2)棉花叶绿素a/b现蕾期>初花期(盛花期),不同叶位间现蕾期随叶位由上而下先升高(倒3~4叶最高)后降低,但初花期和盛花期变化平缓,播期、密度不影响叶位间的变化趋势;3)通过逐步回归分析法,得到单叶叶绿素含量(叶绿素(a+b)、叶绿素a、叶绿素b、叶绿素a/b)能够显著代表整株平均水平的叶位,即为棉花叶绿素含量典型叶,现蕾期为倒5叶,初花期为倒4叶,而盛花期随叶绿素指标不同而异。【结论】S1D2产量最高,叶绿素含量、a/b值比较合理。

Chlorophyll content, which is related to nitrogen metabolism, is a commonly used diagnostic index of supplied nitro- gen nutrition conditions in the field. [Objective] In this study, we examined the effect of sowing date and planting density oneot- ton nitrogen metabolism under late and direct seeding conditions. [Method] A split-field design, with sowing date （S1, May 30; S2, June 14） as the main plot and density （plants.m-2） （D1, 7.5; D2, 9.0; D3, 10.5） as the subplot, was used to measure the dy- namics of chlorophyll contentamong nitrogen metabolism that was discussed in this paper. [Result] We found that cotton chloro- phyll a, b and （a＋b） contents were highest at peak bloom, followed by first bloom and then squaring; the contents of leaves, which increased moving downwards from the top of the plant to the 3^rd to 5^th leaves and then dropped, decreased with increased planting density. Except for chlorophyll b during squaring, planting date S2 resulted in higher chlorophyll contents during squar- ing, first bloom and peak bloom than S1; however, differences among leaf positions were not altered by either sowing date or density. Cotton chlorophyll afo values were highest at squaring, followed by first bloom （peak bloom）. In regard to leaf position, this ratio increased moving downwards from the top of the plant to the 3^rd to 4^th leaves; values then decreased at squaring but only changed gradually at both first bloom and peak bloom. Neither sowing date nor density had an effect on differences among leaf positions. We used stepwise regression analysis to choose an individual leaf position with a chlorophyll content corresponding to the average for the entire plant. The typical cotton leaf representing chlorophyll status was identified as the 5^th leaf during squar-ing and the 4^th leaf during first bloom, but varied during peak bloom. [Conclusion] In short, S 1D2 gave the highest yield with the optimum chlorophyll （a＋b） content and chlorophyll a/b value.