The border row crop in strip intercropped maize is often exposed to heterogeneous light conditions, resulting in increased photosynthesis and yield decreased. Previous studies have focused on photosynthetic productivity, whereas carbon allocation could also be one of the major causes of decreased yield. However, carbon distribution remains unclear in partially shaded conditions. In the present study, we applied heterogeneous light conditions (T), and one side of plants was shaded (T-30%), keeping the other side fully exposed to light (T-100%), as compared to control plants that were exposed entirely to full-light (CK). Dry weight, carbon assimilation, ¹³C abundance, and transport tissue structure were analyzed to clarify the carbon distribution in partial shading of plants. T caused a marked decline in dry weight and harvest index (HI), whereas dry weight in unshaded and shaded leaves did not differ. Net photosynthesis rate (Pn), the activity of sucrose phosphate synthase enzymes (SPS), and sucrose concentration increased in unshaded leaves. Appropriately, 5.7% of the ¹³C from unshaded leaves was transferred to shaded leaves. Furthermore, plasmodesma density in the unshaded (T-100%) and shaded (T-30%) leaves in T was not significantly different but was lower than that of CK. Similarly, the vascular bundle total area of T was decreased. ¹³C transfer from unshaded leaves to ear in T was decreased by 18.0% compared with that in CK. Moreover, ¹³C and sucrose concentration of stem in T were higher than those in CK. Our results suggested that, under heterogeneous light, shaded leaves as a sink imported the carbohydrates from the unshaded leaves. Ear and shaded leaf competed for carbohydrates, and were not conducive to tissue structure of sucrose transport, resulting in a decrease in the carbon proportion in the ear, harvest index, and ear weight.

中文翻译：

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异质光照条件减少了向玉米穗的同化易位。

间作间作玉米的边界行作物经常暴露于异质光照条件下，导致光合作用增加，单产下降。先前的研究集中在光合生产力上，而碳分配也可能是产量下降的主要原因之一。但是，在部分阴影条件下碳分布仍然不清楚。在本研究中，我们采用了异质光照条件（T），与对照植物相比，植物的一侧被遮蔽（T-30％），另一侧完全暴露在光线下（T-100％）。完全暴露在全光（CK）下。干重，碳同化，¹³分析了碳的丰度和运输组织的结构，以阐明植物部分遮荫下的碳分布。T引起干重和收成指数（HI）的显着下降，而无阴影和阴影的叶片的干重没有差异。在未遮荫的叶片中，净光合作用速率（Pn），蔗糖磷酸合酶活性（SPS）和蔗糖浓度增加。适当地，未遮盖的叶片中¹³ C的5.7％转移到了遮盖的叶片上。此外，T中未遮蔽（T-100％）和遮蔽（T-30％）叶片的胞浆密度没有显着差异，但低于CK。类似地，T的血管束总面积减少。¹³与CK相比，T中未遮蔽的叶向耳朵的碳转移降低了18.0％。此外，T中茎的¹³ C和蔗糖浓度高于CK。我们的结果表明，在异质光照下，阴影叶片作为水槽从未阴影叶片中导入了碳水化合物。耳朵和遮荫的叶子竞争碳水化合物，并且不利于蔗糖运输的组织结构，从而导致耳朵中碳含量，收割指数和耳朵重量的降低。