Abstract The objective of this work was to study the effect of the decrease in incident solar radiation on leaf senescence, its consequence on the fraction of radiation intercepted by the leaves and on the grain and oil yield in sunflower. Five field experiments were conducted in Balcarce, with three hybrids, maintaining non limiting soil water conditions and nutritional status, and controlling weeds and insects. Treatments of different shading levels (50 or 80% of radiation interception) were applied during different periods of crop development (around flowering, during a window within the grain filling period or during the complete grain filling period). Shading levels were more intense than those expected by cloudiness in field conditions. The number, weight and oil concentration of grains, leaf area, incident radiation (I0) and the transmitted to incident radiation ratio (the fraction of radiation intercepted by leaves, I/I0) by different leaves strata were measured. Intercepted radiation (iPAR) was calculated as the product between I0 and I/I0. Shading treatments reduced grain and oil yield between 23 and 51%. No differences among periods or levels of shading were observed on grain and oil yield. Both the number and weight of grains decreased by shadings. Oil concentration decreased (between 5 and 21%) only when shading was applied during the window within the grain filling period or during the complete grain filling period. Shading accelerated leaf senescence but it did not affect the ratio I/I0. Intercepted PAR accumulated during the grain filling period was not related to the ratio I/I0. Incident radiation (I0) accounted for differences in grain and oil yield observed among treatments and experiments. It is concluded that the higher leaf senescence by decrease in I0 did not affect grain and oil yield through a decrease in the ratio I/I0.

中文翻译：

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叶片衰老并未解释在辐射限制条件下在向日葵中观察到的谷物和油产量的变化

摘要 这项工作的目的是研究入射太阳辐射减少对叶片衰老的影响，其对叶片截获的辐射分数和向日葵籽粒和油产量的影响。在 Balcarce 进行了五次田间试验，使用三个杂交种，保持非限制性的土壤水分条件和营养状况，并控制杂草和昆虫。在作物发育的不同时期（开花前后、灌浆期的一个窗口期或整个灌浆期）应用不同遮荫水平（50%或80%的辐射拦截）的处理。阴影水平比现场条件下的多云所预期的更强烈。籽粒的数量、重量和含油量、叶面积、测量了不同叶片层的入射辐射（I0）和透射入射辐射比（叶片截获的辐射分数，I/I0）。截获辐射 (iPAR) 计算为 I0 和 I/I0 之间的乘积。遮荫处理使谷物和油产量降低了 23% 到 51%。在谷物和油产量方面没有观察到遮荫时期或水平之间的差异。谷物的数量和重量都因阴影而减少。仅当在籽粒灌浆期间的窗口期间或在籽粒完全灌浆期间施加遮荫时，油浓度降低（在 5% 和 21% 之间）。遮荫加速叶片衰老，但不影响 I/I0 比值。籽粒灌浆期截获的PAR与I/I0比值无关。入射辐射 (I0) 解释了处理和实验之间观察到的谷物和油产量差异。得出的结论是，通过降低 I0 导致的更高的叶片衰老不会通过降低 I/I0 比率来影响谷物和油产量。