Helena Van De Velde's research while affiliated with University of Antwerp and other places

Biotic interactions shape community evolution, but we lack mechanistic insights on how metabolic and ecological processes under climate change are altered by biotic interactions. We used a two‐trophic model community consisting of the aphid Dysaphis plantaginea feeding on the forb Plantago lanceolata, and a grass competitor Lolium perenne that does not experience herbivory by the aphid. Monocultures and mixtures were exposed to the herbivory treatment and to three relevant simulated environmental changes as prevalent under current climate change (increased temperature, CO2, and increased temperature and CO2) Elevated CO2 reduced the nitrogen content of P. lanceolata, while simultaneous increases of CO2 and temperature modified the plant metabolic component and the magnitude of these responses in different directions. Elevated CO2 enhanced defence systems in P. lanceolata, but these effects were not altered by warming. Interspecific plant competition did, however, neutralize these responses. There were no indirect effects of climate change on aphid population growth despite changes in plant defence, nutritional quality and biomass induced by our environmental change scenarios. We thus demonstrate interactions between abiotic and biotic processes on plant metabolite profiles, but more importantly, that climate change effects on a selection of the metabolic pathways are altered by herbivory and competition. Our experiment under semi‐natural conditions thus demonstrates the non‐additive and often neutralizing effects of biotic interactions on plant metabolism and species performance under climate‐associated environmental change. A free Plain Language Summary can be found within the Supporting Information of this article.

Biotic interactions shape community evolution, but we lack mechanistic insights on how metabolic and ecological processes under climate change are altered by biotic interactions. We used a two-trophic model community consisting of the aphid Dysaphis plantaginea feeding on the forb Plantago lanceolata , and a grass competitor Lolium perenne that does not experience herbivory by the aphid. Monocultures and mixtures were exposed to the herbivory treatment and to three relevant simulated environmental changes as prevalent under current climate change (increased temperature, CO 2 , and increased temperature and CO 2 ) Elevated CO 2 reduced the nitrogen content of P. lanceolata , while simultaneous increases of CO 2 and temperature modified the plant metabolic component and the magnitude of these responses in different directions. Elevated CO 2 enhanced defence systems in P. lanceolata , but these effects were not altered by warming. Interspecific plant competition did, however, neutralise these responses. There were no indirect effects of climate change on aphid population growth despite changes in plant defense, nutritional quality and biomass induced by our environmental change scenarios. We thus demonstrate interactions between abiotic and biotic processes on plant metabolite profiles, but more importantly, that climate change effect on a selection of the metabolic pathways are altered by herbivory and competition. Our experiment under semi-natural conditions thus demonstrates the non-additive and often neutralizing effects of biotic interactions on plant metabolism and species performance under climate-associated environmental change.

Climate models project an important increase in the frequency and intensity of heat waves. In gauging the impact on plant responses, much of the focus has been on air temperatures, while a critical analysis of leaf temperatures during heat extremes has not been conducted. Nevertheless, direct physiological consequences from heat depend primarily on leaf rather than on air temperatures. We discuss how the interplay between various environmental variables and the plants’ stomatal response affects leaf temperatures and the potential for heat stress by making use of both an energy balance model and field data. The results demonstrate that this interplay between plants and environment can cause leaf temperature to vary substantially at the same air temperature. In general, leaves tended to heat up when radiation was high and when stomates were closed, as expected. But perhaps counterintuitively, high air humidity also raised leaf temperatures, while humid conditions are typically regarded as benign with respect to plant survival since they limit water loss. High wind speeds brought the leaf temperature closer to the air temperature, which can imply either cooling or warming (i.e. abating or reinforcing heat stress) depending on other prevailing conditions. The results thus indicate that heat waves characterized by similar extreme air temperatures may pose little danger under some atmospheric conditions but could be lethal in other cases. The trends illustrated here should give ecologists and agronomists a more informed indication about which circumstances are most conducive to the occurrence of heat stress.

Global warming impacts natural communities through effects on performance of individual species and through changes in the strength of interactions between them. While there is a body of evidence of the former, we lack experimental evidence on potential changes in interaction strengths. Knowledge about multispecies interactions is fundamental to understand the regulation of biodiversity and the impact of climate change on communities. This study investigated the effect of warming on a simplified community consisting of three species: rosy apple aphid Dysaphis plantaginea feeding on plantain, Plantago lanceolata, and a heterospecific neighbouring plant species, perennial ryegrass, Lolium perenne. The aphid does not feed on L. perenne. The experimental design consisted of monocultures and mixtures of L. perenne and P. lanceolata at three temperature levels. We did not find indication for indirect temperature effects on D. plantaginea through changes in leaf nitrogen or relative water content. However, experimental warming affected the life history traits of the aphid directly, in a non-linear manner. Aphids performed best at moderate warming, where they grew faster and had a shorter generation time. In spite of the increased population growth of the aphids under warming, the herbivory rates were not changed and consequently the plant-herbivore interaction was not altered under warming. This suggests reduced consumption rates at higher temperature. Also plant competition affected the aphids but through an interaction with temperature. We provide proof-of-concept that net interactions between plants and herbivores should not change under warming despite direct effects of warming on herbivores when plant-plant interaction are considered. Our study stresses the importance of indirect non-trophic interactions as an additional layer of complexity to improve our understanding of how trophic interactions will alter under climate change.

Climate change models project an important increase in the frequency and intensity of heat waves. In gauging the impact on plant responses, much of the focus has been on air temperatures while a critical analysis of leaf temperatures during heat extremes has not been made. Nevertheless, direct physiological consequences from heat depend primarily on leaf rather than on air temperatures. We discuss how the interplay between various environmental variables and the plants' stomatal response affects leaf temperatures and the potential for heat stress by making use of both an energy balance model and field data. The results demonstrate that this interplay between plants and environment can cause leaf temperatures fluctuations in excess of 10 °C (for narrow leaves) to even 20 °C (for big broad leaves) at the same air temperature. In general, leaves tended to heat up when radiation was high and when stomates were closed, as expected. But perhaps counterintuitively, also high air humidity raised leaf temperatures, while humid conditions are typically regarded as benign with respect to plant survival since they limit water loss. High wind speeds brought the leaf temperature closer to the air temperature, which can imply either cooling or warming (i.e. abating or reinforcing heat stress) depending on other prevailing conditions. The results thus indicate that heat waves characterized by similar extreme air temperatures may pose little danger under some atmospheric conditions, but could be lethal in other cases. The trends illustrated here should give ecologists and agronomists a more informed indication about which circumstances are most conductive for heat stress to occur.

Future climate scenarios predict increases in elevated atmospheric CO2, air temperature and drought, but the impacts of multiple climate change factors on ecosystem functioning remain unclear. In this study, we compared drought responses of plants under future versus current climate conditions. In addition to focusing on stress during the drought itself, we also examined post-drought lagged effects, and whether warming and elevated CO2 alter these. We grew monocultures and mixtures of two grassland species (Lolium perenne L. and Plantago lanceolata L.) in four simulated climate scenarios: (1) current climate, (2) current climate with drought, (3) warmer temperature with drought and (4) combined warming, elevated CO2 and drought. L. perenne and P. lanceolata were influenced by the climate scenario but not differently enough to modify the competitive balance. Warming aggravated drought impacts on L. perenne and elevated CO2 only partly compensated for these effects. In a warmer climate, with or without elevated CO2, drought continued to enhance senescence and mortality in L. perenne long after the water shortage, while such lag effects were not observed in current climate. In P. lanceolata, a similar stimulation of senescence and mortality was induced, but only under combined warming and elevated CO2. These lag effects induced by the future climate may reduce resilience.

We hypothesized that the contrasting soil conditions resulting from different historical land use in heathlands mediate the interactions of Calluna vulgaris with pollinators. We compared using a common garden experiment, the flowering phenology, the interaction with pollinators, and the colonization by ericoid mycorrhiza of mature C. vulgaris on three types of soils namely: (1) natural rhizospheric soil collected in a natural heath, (2) soil from an arable land recently restored into a heathland, and (3) soil of C. vulgaris from an area in which a high degree of heterospecific competition with perennial grasses occurred. The results of the experiment showed a strong effect of soil on flower phenology and synchrony. There was also an interaction with pollinators because not only did visitation rates depend on soil provenance but also the choice of plant by the pollinator, at least for honeybees, was affected by soil provenance. An a posteriori correlation analysis suggests that ericoid mycorrhizal fungi and not abiotic conditions across the different soil provenances may be involved in the interaction between plants and pollinators. The results obtained from this study highlight the importance of soil processes to understand plant–pollinator interactions and point at plant–soil feedbacks as an important mechanism for understanding heathland ecology.