[AGRIFOOD] Trophic cascades in a changing climate - effects of elevated CO2 on breakdown of plant defences

预计到2050年，大气中的二氧化碳浓度将上升到550ppm，同时植物生产力也会随之提高。这样的预测很少考虑到植物-昆虫的相互作用，在气候变化下，这种相互作用可能会通过改变植物对草食的抗性来破坏初级生产的预期增长。这可能会对未来的粮食安全产生重大影响。气候变化有可能调节植物对草食的抵抗力。高二氧化碳浓度(Eco2)已经被证明损害了植物对昆虫食草动物的直接和间接防御，例如，通过下调植物抗性基因导致食草动物性能增强。在许多农业生态系统中，植物防御是通过选择性育种产生的，这意味着植物无法足够快地适应抗性机制，以抵消Eco2的危害效应。此外，目前尚不清楚，当植物防御系统受到损害时，较高的营养水平将如何应对食草动物丰度的增加。利用一个由红树莓(Rubus Idaeus)、大型树莓蚜虫(Amphorophora Idaei)、捕食性瓢虫(Coccinella Septempot Tata)和寄生蜂(Aphidus Ervi)组成的多营养系统，本博士将研究Eco2对多营养相互作用的影响，特别是对植物防御破坏的影响。红星天牛是欧洲树莓生产中最重要的害虫(病毒媒介)。树莓品种对蚜虫取食的抗性是由A1和A10基因支撑的，其中A10基因赋予更强的抗性，可能是通过改变叶蜡组成。初步研究结果表明，在Eco2环境下，由于基因表达的改变，蚜虫克服了树莓的抗性。该项目的目标是：(1)表征Eco2对植物对不同生物型蚜虫的抗性的影响，并确定哪些基因与此有关；(2)测量支持抗性分解的植物防御机制中的表型变化；以及(3)确定气候诱导的食草动物丰度变化如何影响较高营养水平的种群动态。该项目将利用受控环境设施中的实验微观世界，测试是否：假设1：Eco2加速抗性分解，部分适应的生物型对抗性基因下调的反应最快；假设2：Eco2改变与抗虫性相关的叶蜡的组成；假设3：在Eco2下，捕食者和寄生蜂种群将遵循与较大的蚜虫种群相对应的滞后增长，但相互干扰将阻碍在最高蚜虫密度下的觅食行为。这项博士建议与农业食品研究的NERC Open Case优先领域紧密结合，特别强调气候变化通过模式作物中的抗性分解对有害生物扩散的影响。这项研究的影响将是提供多营养相互作用在气候变化下可能如何改变的机械证据。这将使作物育种者能够针对特定的植物抗性特征和生物防治措施，对气候变化下的作物生产进行适应和“未来验证”。这直接有助于制定《国家气候研究中心战略计划》，使社会能够对全球气候变化作出紧急反应。该项目将通过调查气候变化将如何影响作物-草食动物-敌人的相互作用来实现LWEC的关键目标，并向负责适应和缓解气候变化的政策制定者提供及时的基于证据的建议。

Atmospheric carbon dioxide concentrations are predicted to rise to 550ppm by 2050 with concomitant increases in plant productivity. Such predictions seldom account for plant-insect interactions that under climate change may undermine projected increases in primary production by altering plant resistance to herbivory. This has potentially major implications for future food security. Climate change has the potential to modulate plant resistance to herbivory. Elevated CO2 concentrations (eCO2) have been shown to compromise both direct and indirect plant defences to insect herbivores, for example, by down regulation of plant resistance genes leading to enhanced herbivore performance. In many agro-ecosystems, plant defences arise through selective breeding which means plants are unable to adapt resistance mechanisms quickly enough to counteract the compromising effects of eCO2. Moreover, it remains unclear how higher trophic levels will respond to increases in herbivore abundance when plant defences are compromised. Using a multi-trophic system comprising red raspberry (Rubus idaeus), the large raspberry aphid (Amphorophora idaei), a predatory ladybird (Coccinella septempunctata) and an aphid parasitoid (Aphidus ervi), this PhD will investigate the effects of eCO2 on multi-trophic interactions, and specifically plant defence breakdown. Amphorophora idaei is the most significant pest (virus vector) of raspberry production in Europe. Plant resistance to aphid feeding in raspberry cultivars is underpinned by A1 and A10 genes, with A10 conferring stronger resistance, probably through altered leaf wax composition. Preliminary findings suggest aphids overcome resistance in raspberry under eCO2 because of altered gene expression. This project aims to: (1) characterise the effects of eCO2 on plant resistance to different aphid biotypes and identify which genes are implicated; (2) measure the phenotypic changes in plant defence mechanisms underpinning resistance breakdown; and (3) determine how population dynamics of higher trophic levels are affected by climate-induced changes in herbivore abundance. With experimental microcosms in controlled environment facilities, this project will test whether: Hypothesis 1: eCO2 accelerates resistance breakdown, with partially adapted aphid biotypes responding most rapidly to the down-regulation of resistance genes; Hypothesis 2: eCO2 alters composition of leaf waxes associated with aphid resistance; and Hypothesis 3: predator and parasitoid populations will follow a time-lagged increase corresponding to larger aphid populations under eCO2, but mutual interference will impede foraging behaviour at highest aphid densities. This PhD proposal is strongly aligned to the NERC Open Case Priority area of Agrifood research, with particular emphasis on the effects of climate change on proliferation of pests through resistance breakdown in a model crop. The impact of this study will be to provide mechanistic evidence of how multi-trophic interactions are likely to alter under climate change. This will enable crop breeders to target particular plant resistance traits and biocontrol measures for the adaptation and 'future proofing' of crop production under climate change. This contributes directly to the NERC Strategic Plan to enable society to respond urgently to global climate change. The project will meet key objectives of LWEC by investigating how climate change will affect crop-herbivore-enemy interactions and provide timely evidence-based recommendations to policy makers charged with climate change adaptation and mitigation.