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Aims Climate change is predicted to cause both increased temperatures and changes in precipitation, leading to more severe droughts in some areas. How these changes will affect plant growth may depend in part on biotic context. Most vascular plants form symbiotic relationships with arbuscular mycorrhizal fungi (AMF), root symbionts that provide soil nutrients to plants in exchange for carbohydrates, which may reduce the effects of environmental stresses on plants. We investigated if AMF modified temperature and drought effects on plant growth, fitness and defenses against herbivory. Methods We manipulated AMF presence, temperature and water availability on bell pepper plants (Capsicum annuum L.) in a field setting to measure plant growth and fitness responses. In a growth chamber experiment, we also investigated if AMF influenced insect herbivores feeding on plants at elevated temperatures. Important findings Drought consistently reduced plant growth, and AMF did not change drought impacts. However, with sufficient water, AMF tended to benefit plant growth and flower production (but not fruit production) compared to non-mycorrhizal plants. In the growth chamber, temperature and AMF influenced plant protein and phosphorus contents, but not defensive chemistry or herbivore performance. Thus, AMF may ameliorate the effects of temperature stress due to climate change on plants by increasing growth and nutrient content, but these effects do not extend to the constitutive herbivory defenses examined here. [ABSTRACT FROM AUTHOR]

Aims The majority of angiosperms are pollinated by animals, and this interaction is of enormous importance in both agricultural and natural systems. Pollinator behavior is influenced by plants’ floral traits, and these traits may be modified by interactions with other community members. In recent years, knowledge of ecological linkages between above- and belowground organisms has grown tremendously. Soil communities are extremely diverse, and when their interactions with plants influence floral characteristics, they have the potential to alter pollinator attraction and visitation, but plant–pollinator interactions have been neglected in studies of the direct and indirect effects of soil organism–root interactions. Here, we review these belowground interactions, focusing on the effects of nitrogen-fixing bacteria, arbuscular mycorrhizal fungi and root-feeding herbivores, and their effects on floral traits and pollinators. Further, we identify gaps in our knowledge of these indirect effects and recommend promising directions and topics that should be addressed by future research. Important Findings Belowground organisms can influence a wide variety of floral traits that are important mediators of pollinator attraction, including the number and size of flowers and nectar and pollen production. Other traits that are known to influence pollinators in some plant species, such as floral volatiles, color and nectar composition, have rarely or never been examined in the context of belowground plant interactions. Despite clear effects on flowers, relatively few studies have measured pollinator responses to belowground interactions. When these indirect effects have been studied, both arbuscular mycorrhizal fungi and root herbivores were found to shift pollinator visitation patterns. Depending on the interaction, these changes may either increase or decrease pollinator attraction. Finally, we discuss future directions for ecological studies that will more fully integrate belowground ecology with pollination biology. We advocate a multilevel approach to these questions to not only document indirect effect pathways between soil interactions and pollination but also identify the mechanisms driving changes in pollinator impacts and the resultant effects on plant fitness. A more thorough understanding of these indirect interactions will advance ecological theory and may inform management strategies in agriculture and conservation biology. [ABSTRACT FROM AUTHOR]

Aims Although ecological interactions are often conceptualized and studied in a pairwise framework, ecologists recognize that the outcomes of these interactions are influenced by other members of the community. Interactions (i) between plants and insect herbivores and (ii) between plants and mycorrhizal fungi are ubiquitous in terrestrial ecosystems and may be linked via common host plants. Previous studies suggest that colonization by arbuscular mycorrhizal fungi (AMF) can modify plants’ induced responses to herbivore attack, but these indirect effects of fungal symbionts are poorly understood. I investigated the role of AMF in induced plant response to a generalist herbivore. Methods I manipulated AMF status and herbivory in Cucumis sativus L. (cucumber, Cucurbitaceae) in a greenhouse to investigate induced responses in the presence and absence of the mycorrhizal fungus Glomus intraradices (Glomeraceae). Spodoptera exigua Hübner (Noctuidae) were used to manipulate prior damage and later as assay caterpillars. I also measured G. intraradices and herbivory effects on plant N and effects on plant growth. Important Findings AMF status affected the induced response of C. sativus, underscoring the importance of incorporating the roles of plant symbionts into plant defense theory. Assay caterpillars ate significantly more leaf tissue only on mycorrhizal plants that had experienced prior damage. Despite more consumption, biomass change in these caterpillars did not differ from those feeding on plants with other treatment combinations. Leaf N content was reduced by G. intraradices but unaffected by herbivory treatments, suggesting that the observed differences in assay caterpillar feeding were due to changes in defensive chemistry that depended on AMF. [ABSTRACT FROM AUTHOR]