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Abstract Plants alter soil biotic and abiotic properties with consequences for plant community dynamics at local and global scales, but how plant–soil interactions are affected by other environmental and biotic interactions remains poorly understood. We performed a fully reciprocal plant–soil feedback (PSF) experiment between two herbaceous plants, Monarda fistulosa and Plantago lanceolata, and tested how PSFs were influenced by drought and foliar powdery mildew pathogen infection. We observed significant negative feedbacks between the two plant species, but only when plants were grown with live soil biota and infected with powdery mildew. The strongest feedback was observed under both foliar infection and drought. High-throughput sequencing of soil fungi and bacteria from the treatment groups with foliar infection and drought revealed that both fungal and bacterial community composition were influenced by soil condition (live versus sterile) and soil training (Monarda versus Plantago). Together, our results indicate that the observed negative PSF was driven by foliar pathogens and plant species-specific soil microbial communities and intensified by drought. Our study suggests that PSF can be sensitive to both aboveground plant–pathogen interactions and climatic factors, improving our understanding of microbial impacts on plant community dynamics. This article is part of the theme issue ‘Wild plant pathosystems’. 

Abstract Major goals of disease ecology are to understand how disease dynamics and host–pathogen evolution shift across contexts and to apply lessons from natural populations to human-managed systems. These goals are especially pressing under rapid environmental change. Wild plant–pathogen systems are ideal for studying the complex ecological and evolutionary dynamics within and between natural and human-managed environments. Here, we review important recent contributions on the ecology and evolution of wild plant pathogens and introduce the articles in this theme issue, emphasizing their relevance to agriculture and the broader field of disease ecology. The articles in this issue are centred around three core themes where research on wild plant pathogens has enhanced our understanding of disease: (i) plant–pathogen responses to environmental change, (ii) evolutionary dynamics of wild plant–pathogen systems, and (iii) disease interactions between wild and cultivated plants. The featured articles span within-host to ecosystem levels covering a wide range of taxa and approaches. Together, these articles advance our fundamental understanding of disease and contribute knowledge useful in developing more sustainable plant health management strategies. We conclude by highlighting key gaps and avenues for future research into the ecological and genetic drivers of disease in wild plants and at the agro-ecological interface. This article is part of the theme issue ‘Wild plant pathosystems’. 

Abstract Understanding how urbanization affects plant interactions with pathogens and herbivores is important for clarifying how changes in land use, climate and biodiversity affect ecological and evolutionary processes, and for managing urban plants to maximize ecosystem services. We performed a systematic literature review of relationships between urbanization and pathogens or pests of wild and cultivated plants. We identified k = 171 relationships from n = 54 studies in which pathogen or pest abundance was quantified in both urban and non-urban areas and summarized their distribution across taxa, geographic regions and directions and mechanisms of effects proposed by the authors. Most studies featured tree hosts and their arthropod pests or fungal pathogens. Grasses and forbs were the next most commonly studied hosts, followed by crops and shrubs. We then performed a meta-analysis limited to trees, which had the most studies with sufficient statistical information (k = 55 relationships, n = 14 studies). In that meta-analysis, we found no overall effect of urbanization on tree pest or pathogen abundance. However, there was a significant effect of pest/pathogen, with arthropod pests trending towards lower abundance in urban areas and fungal pathogens trending towards higher abundance. Drawing on literature from the broader fields of urban ecology, disease ecology and plant pathology, we synthesize our findings and offer insights into mechanisms by which urbanization influences disease and herbivory in wild and cultivated plants. We conclude by identifying research gaps, with the goal of informing management strategies that prioritize food security, environmental health and global biodiversity. This article is part of the theme issue ‘Wild plant pathosystems’. 

Abstract Most biodiversity dynamics and ecosystem processes on land take place in microclimates that are decoupled from the climate as measured by standardised weather stations in open, unshaded locations. As a result, microclimate monitoring is increasingly being integrated in many studies in ecology and evolution.Overviews of the protocols and measurement methods related to microclimate are needed, especially for those starting in the field and to achieve more generality and standardisation in microclimate studies.Here, we present 10 practical guidelines for ground‐based research of terrestrial microclimates, covering methods and best practices from initial conceptualisation of the study to data analyses.Our guidelines encompass the significance of microclimates; the specifics of what, where, when and how to measure them; the design of microclimate studies; and the optimal approaches for analysing and sharing data for future use and collaborations. The paper is structured as a chronological guide, leading the reader through each step necessary to conduct a comprehensive microclimate study. At the end, we also discuss further research avenues and development in this field.With these 10 guidelines for microclimate monitoring, we hope to stimulate and advance microclimate research in ecology and evolution, especially under the pressing need to account for buffering or amplifying abilities of contrasting microhabitats in the context of global climate change. 

Abstract Increased temperatures associated with urbanization (the “urban heat island” effect) have been shown to impact a wide range of traits across diverse taxa. At the same time, climatic conditions vary at fine spatial scales within habitats due to factors including shade from shrubs, trees, and built structures. Patches of shade may function as microclimate refugia that allow species to occur in habitats where high temperatures and/or exposure to ultraviolet radiation would otherwise be prohibitive. However, the importance of shaded microhabitats for interactions between species across urbanized landscapes remains poorly understood. Weedy plants and their foliar pathogens are a tractable system for studying how multiple scales of climatic variation influence infection prevalence. Powdery mildew pathogens are particularly well suited to this work, as these fungi can be visibly diagnosed on leaf surfaces. We studied the effects of shaded microclimates on rates of powdery mildew infection onPlantagohost species in (1) “pandemic pivot” surveys in which undergraduate students recorded shade and infection status of thousands of plants along road verges in urban and suburban residential neighborhoods, (2) monthly surveys of plant populations in 22 parks along an urbanization gradient, and (3) a manipulative field experiment directly testing the effects of shade on the growth and transmission of powdery mildew. Together, our field survey results show strong positive effects of shade on mildew infection in wildPlantagopopulations across urban, suburban, and rural habitats. Our experiment suggests that this relationship is causal, where microclimate conditions associated with shade promote pathogen growth. Overall, infection prevalence increased with urbanization despite a negative association between urbanization and tree cover at the landscape scale. These findings highlight the importance of taking microclimate heterogeneity into account when establishing links between macroclimate or land use context and prevalence of disease. 

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