It is important to explore and propose a potential source for further improvements in drought tolerance in spring wheat (Triticum aestivum L.). The present study aimed to evaluate the significance of ear as a post-anthesis carbon source under drought conditions in wheat genotypes with different sink–source balances. Field trials were conducted in 2017 and 2018 for four spring wheat genotypes (T. aestivum L.) with different sink–source balances in two different soil water conditions, irrigated and drought. The relative importance of a post-anthesis carbon gain and dry matter remobilization as source functions for grain filling was evaluated in both environments. Digital infrared thermal imagery analysis was undertaken to analyse the contribution of the photosynthetic source to the leaf canopy and ear parts. In irrigated conditions, carbon assimilation was the major source for grain filling in all genotypes, whereas the contribution of dry matter remobilization was up to 20%. This was supported by a larger leaf area index (LAI) with a lower canopy temperature as the soil water stress alleviated. The ear temperature was always maintained below the canopy temperature, irrespective of irrigation treatment. When the drought intensity became more severe, very small leaf area was insufficient as the photosynthetic source organ for grain filling. Under severe drought condition, especially for genotypes with a larger sink capacity, carbon supply from ear itself appeared to play a significant role in grain filling. This study suggested that enhancing ear photosynthesis could be potential target for improving drought tolerance for high-yielding modern wheat genotypes with larger sink and smaller biomass.

中文翻译：

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穗作为花后碳源提高春小麦（Triticum aestivum L.）耐旱性的潜在重要性

探索和提出进一步提高春小麦 ( Triticum aestivum L.)耐旱性的潜在来源非常重要。本研究旨在评估穗作为干旱条件下具有不同库源平衡的小麦基因型的开花后碳源的重要性。2017 年和 2018 年对四种春小麦基因型（T. aestivumL.) 在灌溉和干旱这两种不同的土壤水分条件下具有不同的汇源平衡。在这两种环境中评估了作为籽粒灌浆源函数的花后碳增加和干物质再动员的相对重要性。进行数字红外热成像分析以分析光合源对叶冠和穗部的贡献。在灌溉条件下，碳同化是所有基因型籽粒灌浆的主要来源，而干物质再动员的贡献高达 20%。随着土壤水分胁迫的减轻，较大的叶面积指数 (LAI) 和较低的冠层温度支持了这一点。无论灌溉处理如何，耳朵温度始终保持在冠层温度以下。当旱情变得更加严重时，非常小的叶面积不足以作为灌浆的光合源器官。在严重干旱条件下，特别是对于库容量较大的基因型，穗本身的碳供应似乎对籽粒灌浆起着重要作用。该研究表明，增强穗光合作用可能是提高具有较大汇和较小生物量的高产现代小麦基因型的耐旱性的潜在目标。