• Energy Research

AbstractIntroductionA wide range of arbuscular mycorrhizal fungi (AMF) can be applied to agricultural soils as biofertilizers for increasing crop growth and yield. Current research also shows that AMF can stimulate plant defences against a range of herbivores and pathogens. However, to date, the efficient use of AMF in agriculture is largely impaired by our inability to predict the performance of different AMF‐plant complexes in variable environments. For instance, AMFs by increasing plant foraging capacity might alleviate allocation constraints in relation to growth versus defences. However, whether this effect occurs might depend on the in situ conditions. The main goal of this study was to investigate the context‐dependency of the ability of AMF to modulate plant growth and resistance against herbivores under variable soil water availability.Materials and MethodsTo address our goal, we performed a greenhouse experiment for measuring the effect of different AMF inocula (Funneliformis mosseae, Rhizophagus irregularis, or both) on tomato plants (Solanum lycopersicum) growth and defences against an insect herbivore under two conditions: a normal watering regime or drought conditions. We measured the functional, physiological and chemical traits of the plants.ResultsWe found that AMF presence generally decreased plant growth, but increased chemical defences and resistance against generalist caterpillars. Such growth‐defence trade‐off was nonetheless dependent on the identity of the mycorrhizal inoculum and on soil water content. Under drought, inoculated tomato plants lowered their investment to defence and noninoculated plants lowered their growth.ConclusionThis study highlights the influence of abiotic factors and fungal identity on plant–AMF–herbivore interactions. In a broader sense, our results point to the necessity of finding AMF species that have reduced context‐dependency to climatic factors, for more widespread use in organic agriculture.

AbstractIntroductionA wide range of arbuscular mycorrhizal fungi (AMF) can be applied to agricultural soils as biofertilizers for increasing crop growth and yield. Current research also shows that AMF can stimulate plant defences against a range of herbivores and pathogens. However, to date, the efficient use of AMF in agriculture is largely impaired by our inability to predict the performance of different AMF‐plant complexes in variable environments. For instance, AMFs by increasing plant foraging capacity might alleviate allocation constraints in relation to growth versus defences. However, whether this effect occurs might depend on the in situ conditions. The main goal of this study was to investigate the context‐dependency of the ability of AMF to modulate plant growth and resistance against herbivores under variable soil water availability.Materials and MethodsTo address our goal, we performed a greenhouse experiment for measuring the effect of different AMF inocula (Funneliformis mosseae, Rhizophagus irregularis, or both) on tomato plants (Solanum lycopersicum) growth and defences against an insect herbivore under two conditions: a normal watering regime or drought conditions. We measured the functional, physiological and chemical traits of the plants.ResultsWe found that AMF presence generally decreased plant growth, but increased chemical defences and resistance against generalist caterpillars. Such growth‐defence trade‐off was nonetheless dependent on the identity of the mycorrhizal inoculum and on soil water content. Under drought, inoculated tomato plants lowered their investment to defence and noninoculated plants lowered their growth.ConclusionThis study highlights the influence of abiotic factors and fungal identity on plant–AMF–herbivore interactions. In a broader sense, our results point to the necessity of finding AMF species that have reduced context‐dependency to climatic factors, for more widespread use in organic agriculture.

Summary Given the dual role of many plant traits to tolerate both herbivore attack and abiotic stress, the climatic niche of a species should be integrated into the study of plant defense strategies. Here we investigate the impact of plant reproductive strategy and components of species' climatic niche on the rate of chemical defense evolution in the milkweeds using a common garden experiment of 49 species. We found that across Asclepias species, clonal reproduction repeatedly evolved in lower temperature conditions, in species generally producing low concentrations of a toxic defense (cardenolides). Additionally, we found that rates of cardenolide evolution were lower for clonal than for nonclonal species. We thus conclude that because the clonal strategy is based on survival, long generation times, and is associated with tolerance of herbivory, it may be an alternative to toxicity in colder ecosystems. Taken together, these results indicate that the rate of chemical defense evolution is influenced by the intersection of life‐history strategy and climatic niches into which plants radiate.

Summary Given the dual role of many plant traits to tolerate both herbivore attack and abiotic stress, the climatic niche of a species should be integrated into the study of plant defense strategies. Here we investigate the impact of plant reproductive strategy and components of species' climatic niche on the rate of chemical defense evolution in the milkweeds using a common garden experiment of 49 species. We found that across Asclepias species, clonal reproduction repeatedly evolved in lower temperature conditions, in species generally producing low concentrations of a toxic defense (cardenolides). Additionally, we found that rates of cardenolide evolution were lower for clonal than for nonclonal species. We thus conclude that because the clonal strategy is based on survival, long generation times, and is associated with tolerance of herbivory, it may be an alternative to toxicity in colder ecosystems. Taken together, these results indicate that the rate of chemical defense evolution is influenced by the intersection of life‐history strategy and climatic niches into which plants radiate.

Climate change has various and complex effects on crop pests worldwide. In this review, we detail the role of the main climatic parameters related to temperature and precipitation changes that might have direct or indirect impacts on pest species. Changes in these parameters are likely to favour or to limit pest species, depending on their ecological context. On a global scale, crop pests are expected to benefit from current and future climate change. However, substantial differences appear across biomes and species. Temperate regions are generally more likely to face an increase in pest attacks compared with tropical regions. Therefore, climate change effects should be studied in the context of local climate and local ecological interactions across biomes.

Climate change has various and complex effects on crop pests worldwide. In this review, we detail the role of the main climatic parameters related to temperature and precipitation changes that might have direct or indirect impacts on pest species. Changes in these parameters are likely to favour or to limit pest species, depending on their ecological context. On a global scale, crop pests are expected to benefit from current and future climate change. However, substantial differences appear across biomes and species. Temperate regions are generally more likely to face an increase in pest attacks compared with tropical regions. Therefore, climate change effects should be studied in the context of local climate and local ecological interactions across biomes.

Climate change may promote the decoupling of the different above-ground and below-ground compartments of high elevation ecosystems. Along elevation gradients, a trade-off between species tolerance to cold climates and metabolic rates dictates that cold adapted organisms display a lower efficiency in decomposition, growth or herbivory. As a consequence, if dispersal or evolution under climate change is systematically faster for agents of one compartment (e.g. insect herbivores, or soil microbes, respectively) compared to others, novel and more efficient functions will arise in the alpine systems and increase fluxes of elements to and through this compartment. We illustrate this potential decoupling using a mechanistic model, where the efficiency of agents in the compartments follows the metabolic theory. To detect and forecast ecosystem decoupling under climate change, we argue that the current efficiency of agents should be measured systematically along elevation gradients. In addition, future research should investigate the impact of dispersal and evolution in response to climate change on ecosystem processes.

Climate change may promote the decoupling of the different above-ground and below-ground compartments of high elevation ecosystems. Along elevation gradients, a trade-off between species tolerance to cold climates and metabolic rates dictates that cold adapted organisms display a lower efficiency in decomposition, growth or herbivory. As a consequence, if dispersal or evolution under climate change is systematically faster for agents of one compartment (e.g. insect herbivores, or soil microbes, respectively) compared to others, novel and more efficient functions will arise in the alpine systems and increase fluxes of elements to and through this compartment. We illustrate this potential decoupling using a mechanistic model, where the efficiency of agents in the compartments follows the metabolic theory. To detect and forecast ecosystem decoupling under climate change, we argue that the current efficiency of agents should be measured systematically along elevation gradients. In addition, future research should investigate the impact of dispersal and evolution in response to climate change on ecosystem processes.