Addressing the challenge of combined heat and drought stress for cereal production

干旱目前限制了全球谷物产量的约10%，并预计随着气候变化而恶化1。研究人员最近发现了可以通过改变植物生理来减少干旱影响的农用化学化合物2。这些化合物，通常是抗蒸腾剂，促进气孔关闭，减少植物叶片的水分损失，提高水分利用效率-实现“每滴更多的作物”。我们的CASE合作伙伴，先正达，一家领先的科学农业技术公司，希望通过筛选c. 200种候选化合物。现有的“气孔关闭避免干旱”方法的一个缺点是干旱经常与热浪同时发生。有足够水分的植物通常可以保持凉爽;当空气温度高于最佳温度时，它们会释放水分，水分蒸发，植物内部温度降低到环境温度以下（图1，曲线左侧）。没有足够水分的植物，或气孔功能受损的植物，不能自我冷却，对产量产生负面影响（图1，右侧，也见4）。在我们迅速变暖的世界里，作物生产者不能依赖气孔关闭或其他牺牲冷却能力的耐旱机制。我们提出的项目有两个主要目标：从广义上讲，我们希望增加理解，并最终预测干旱和高温对作物产量的影响。第二，我们希望利用这种生物学上的理解来确定新的化合物，这些化合物可以赋予耐旱性，同时避免对热应激的敏感性增加。假设1）干旱增加了植物对热胁迫的敏感性，2）气孔关闭化合物，抗蒸腾剂，在减少干旱胁迫的同时，增加了热胁迫的风险如何我们的博士生将使用我们开发的一种方法来量化热和干旱单独和组合的影响（图1）。他们将能够利用阅读、阿伯里斯特威斯和先正达先进的植物表型基础设施。我们在不同的时间内保留水分，让土壤干燥到特定的湿度水平，然后将植物暴露在受控环境中的温度制度下。植物的反应是使用三个关键变量来测量的：通过多光谱3D扫描的植物生长速率，以提供对压力和不同化合物对发育的影响的详细了解;蒸腾速率，以了解压力和化合物对气孔关闭的影响;以及叶片温度（特别是植物和周围空气之间的温差），以量化压力。通过这种方法，学生将能够稳健地量化不同化合物对植物胁迫耐受性的影响。博士生将进行他们的大部分工作对作物幼苗。所涉及的短时间尺度允许对先正达的大量候选化合物进行多次试验和快速筛选。我们将对植物进行两种微妙不同类型的干旱处理; i）脱水，以了解胁迫体验的真实的世界差异（和化合物的真实的世界益处），ii）将植物保持在恒定的土壤水分水平（例如通过重新浇水），以了解在相同水平的干旱和高温下化合物处理之间的生理差异。一旦我们确定了有前景的化合物，我们将在生殖发育期间对植物进行试验，这代表了该化合物在田间的实际使用情况，并使我们更接近农场。

Drought currently restricts global cereal production by c.10% and is projected to worsen with climate change1. Researchers have recently identified agrochemical compounds that can reduce the impacts of drought by modifying plant physiology2. These compounds, typically anti-transpirants, encourage stomatal closure which reduces water loss from plant leaves and increases the efficiency of water use - enabling "more crop per drop". Our CASE partner, Syngenta, a leading science-based agricultural technology company, wants to advance this research by screening c. 200 candidate compounds. A downside of existing 'drought avoidance by stomatal closure' approaches is that drought often co-occurs with heat waves3. Plants with enough water can normally keep themselves cool; they release water when air temperature is above optimal, the water evaporates, and plant internal temperature is reduced below ambient (Fig 1, left side of curves). Plants without adequate water, or plants with disrupted stomatal functioning, cannot cool themselves, with negative consequences for yield (Fig 1, right side, also see 4). In our rapidly warming world, crop producers cannot rely on stomatal closure or other drought tolerance mechanisms that sacrifice cooling ability. Our proposed project has two main objectives: in broad terms we want to increase understanding, and eventually predict, the effects of combined drought and high temperature on crop yield. Second, we want to use this biological understanding to identify novel compounds that confer drought tolerance while avoiding increased susceptibility to heat stress. Hypotheses1) Drought increases plant susceptibility to heat stress and vice-versa2) Stomatal closure compounds, antitranspirants, while reducing drought stress, increase risk of heat stressHowOur PhD student will use a method we have developed for quantifying effects of heat and drought separately and in combination (Fig. 1). They will be able to take advantage of advanced plant phenotyping infrastructure at Reading, Aberystwyth and Syngenta. We withhold water for different durations, allowing the soil to dry to specific moisture levels before exposing plants to temperature regimes in controlled environments. Plant responses are measured using three key variables: plant growth rate via multispectral 3D scans to provide detailed insights into effects of stress and different compounds on development; transpiration rate to understand effects of stress and compounds on stomatal closure; and leaf temperature (particularly the temperature difference between plants and surrounding air) to quantify stress. By following this approach the student will be able to robustly quantify the effect of different compounds on plant stress tolerance. The PhD student will conduct most of their work on crop seedlings. The short timescales involved allow multiple trials and rapid screening across Syngenta's large number of candidate compounds. We will subject plants to two subtly different types of drought treatment; i) withdrawal of water, to understand real world differences in stress experience (and real world benefits of compounds), ii) plants held at constant levels of soil moisture (e.g. via re-watering) to understand differences in physiology between compound treatments under equal levels of drought and heat. Once we have identified promising compounds we will conduct a trial on plants during reproductive development, which represents a realistic use case of the compounds in the field and brings us closer to the farm.