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Ecological intensification (EI) is the enhancement of ecosystem services to complement or substitute for the role of anthropogenic inputs in maintaining or increasing yields. EI has potential to increase farming's environmental sustainability, e.g. reducing environmentally harmful management activities while sustaining yields. EI is based upon ecological processes which in turn are influenced by biodiversity. We review how biodiversity, particularly vascular plant diversity, can regulate ecosystem processes relevant to EI at multiple spatial scales. At an individual plant genotype level, complementarity in functional traits has a direct impact on productivity. At in-field, population level, mixtures of crop types confer resilience to minimize the risk of pest and disease incidence and spread. Scaling up to the field level, a diversity of non-crop plants (i.e. weeds) provides resources necessary for in-field functional processes, both below ground (carbon inputs, decomposition) and above ground (resource continuity for pollinators and natural enemies). At the landscape scale, mosaics of semi-natural and managed vegetation provide buffers against extreme events through flood and drought risk mitigation, climate amelioration and pest population regulation. Overall this emphasizes the importance of heterogeneity across scales in maintaining ecosystem functions in farmland. Major research challenges highlighted by our review include the need: to better integrate plant functional diversity (from traits to habitat scales) into cropping system design; to quantify the (likely interactive) contribution of plant diversity for effective EI relative to other management options; and to optimize through targeted management the system function benefits of biodiversity for resilient, efficient and productive agroecosystems. [ABSTRACT FROM AUTHOR]

Aphids are important herbivorous insects that can cause significant crop damage, leading to yield reduction and economic loss. One avenue being explored to reduce aphid impacts is the development of aphid-resistant plants. Under projected climate scenarios, it is expected that plants will be exposed to greater biotic and abiotic stress, including increased herbivorous insect infestation and exposure to prolonged periods of environmental stress, particularly drought. In response to these projections, plant–aphid interactions under drought conditions have been a subject of growing interest; however, few studies have looked at the impact of drought stress on plant resistance to aphids despite the potential importance for plant breeding. Here, we examine the latest scientific advances regarding variation in plant resistance to aphids under drought, emphasizing underlying mechanisms and functional trade-offs and propose a conceptual model relating plant tolerance to drought with plant resistance to aphids. [ABSTRACT FROM AUTHOR]

Crops are exposed to myriad abiotic and biotic stressors with negative consequences. Two stressors that are expected to increase under climate change are drought and infestation with herbivorous insects, including important aphid species. Expanding our understanding of the impact drought has on the plant–aphid relationship will become increasingly important under future climate scenarios. Here we use a previously characterized plant–aphid system comprising a susceptible variety of barley, a wild relative of barley with partial aphid resistance, and the bird cherry-oat aphid to examine the drought–plant–aphid relationship. We show that drought has a negative effect on plant physiology and aphid fitness, and provide evidence to suggest that plant resistance influences aphid responses to drought stress. Furthermore, we show that the expression of thionin genes, plant defensive compounds that contribute to aphid resistance, increase in susceptible plants exposed to drought stress but remain at constant levels in the partially resistant plant, suggesting that they play an important role in determining the success of aphid populations. This study highlights the role of plant defensive processes in mediating the interactions between the environment, plants, and herbivorous insects. [ABSTRACT FROM AUTHOR]

Aphids, including the bird cherry-oat aphid (Rhopalosiphum padi), are significant agricultural pests. The wild relative of barley, Hordeum spontaneum 5 (Hsp5), has been described to be partially resistant to R. padi , with this resistance proposed to involve higher thionin and lipoxygenase gene expression. However, the specificity of this resistance to aphids and its underlying mechanistic processes are unknown. In this study, we assessed the specificity of Hsp5 resistance to aphids and analysed differences in aphid probing and feeding behaviour on Hsp5 and a susceptible barley cultivar (Concerto). We found that partial resistance in Hsp5 to R. padi extends to two other aphid pests of grasses. Using the electrical penetration graph technique, we show that partial resistance is mediated by phloem- and mesophyll-based resistance factors that limit aphid phloem ingestion. To gain insight into plant traits responsible for partial resistance, we compared non-glandular trichome density, defence gene expression, and phloem composition of Hsp5 with those of the susceptible barley cultivar Concerto. We show that Hsp5 partial resistance involves elevated basal expression of thionin and phytohormone signalling genes, and a reduction in phloem quality. This study highlights plant traits that may contribute to broad-spectrum partial resistance to aphids in barley. [ABSTRACT FROM AUTHOR]