To better understand the photosynthetic regulation between lower leaves and top leaves, leaf gas exchange and chlorophyll fluorescence were examined in field and climate chamber grown cotton (Gossypium hirsutum L. cv. Xinluzao 45). Two planting density treatments were used in the field: low planting density (LD) and high planting density (HD), and two artificial shade treatments were used in the climate chamber: no shade (NS) and lower leaves shaded (LS). Our results show that the maximum net photosynthetic rate (P_max), light saturation point (LSP) and light compensation point (LCP) of top leaves were decreased, but the apparent quantum efficiency of net carbon assimilation (AQE) of top leaves was increased in HD and LS, which had a similar trend to the lower leaves. Although top and lower leaves improved the utilization of light, the fractions of light absorbed by the PSII antenna that is utilized in PSII photochemistry Y(II) and photochemical quenching coefficient (qP) of top leaves and lower leaves were decreased in HD and LS. Furthermore, the fraction of absorbed light that is dissipated thermally via ΔpH and xanthophylls regulated processes Y(NPQ) and non-photochemical quenching (NPQ) of top leaves were increased in HD and LS. In summary, these results suggest that the light energy utilization and photochemical efficiency of the top leaves in cotton are regulated by the light environment of the lower leaves, and the activation of thermal dissipation confers photoprotection of top leaves despite systemic regulation from lower leaves in cotton. Therefore, considering that cotton is cultivated in high density in most cotton areas of the world, the systemic regulation of photosynthetic capacity in top leaves affected by light environment of lower leaves caused by high-density cultivation needs to be considered comprehensively in practical production. Then, the optimal photosynthetic capacity of the population can be obtained.

中文翻译：

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尽管从棉花的下部叶片进行系统调节，但增强的散热功能仍可在上部叶片中提供光保护作用

为了更好地了解下叶和上叶之间的光合作用，在田间和气候室内种植的棉花（棉（Gossypium hirsutum L. cv。Xinluzao 45））中检测了叶片气体交换和叶绿素荧光。在该领域中使用了两种种植密度处理方法：低种植密度（LD）和高种植密度（HD），并且在气候箱中使用了两种人工遮荫处理方法：无遮荫（NS）和下部遮阴阴影（LS）。我们的结果表明最大净光合速率（P _max），顶叶的光饱和点（LSP）和光补偿点（LCP）降低，但HD和LS顶叶的净碳同化（AQE）的表观量子效率增加，与降低叶子。尽管上下叶片提高了光的利用率，但是PSII天线吸收的光在PSII光化学Y（II）和光化学猝灭系数（qPHD和LS降低了顶叶和下叶的）。此外，HD和LS中，通过αpH和叶黄素调节过程Y（NPQ）和非光化学淬灭（NPQ）顶叶的热耗散的吸收光的比例增加。总之，这些结果表明，棉花下部叶片的光环境调节着棉花顶叶的光能利用和光化学效率，尽管棉花下部叶片的系统调节作用，但热耗散的激活仍能赋予上部叶片光保护作用。 。因此，考虑到世界上大多数棉花地区都以高密度种植棉花，在实际生产中，需要综合考虑高密度栽培引起的下部叶片光照环境对上部叶片光合能力的系统调节。然后，可以获得种群的最佳光合能力。