Recent studies suggest that changes in leaf traits due to interactions between plants affect resource utilisation by herbivores, as well as herbivore distribution. However, this has not yet been confirmed experimentally. Here, we investigated the effects of phenotypic plasticity in leaf traits of Rumex obtusifolius (host plant) in response to intraspecific and interspecific interactions on the distribution of two leaf beetles, Gastrophysa atrocyanea (specialist herbivore) and Galerucella grisescens (generalist herbivore). We investigated the local population density of R. obtusifolius plants and the presence of leaf beetles on the plants at five study sites. Leaf chemicals (condensed tannins and total phenolics) were compared between aggregated and solitary R. obtusifolius plants. To clarify the effects of the interaction environment of R. obtusifolius plants on their leaf traits and on resource utilisation by the leaf beetles, we compared leaf chemicals and preferences of adult leaf beetles among treatments where R. obtusifolius experienced intraspecific interaction, interspecific interaction or no interaction in cultivation experiments. Finally, we evaluated the independent and combined effects of patch size and intraspecific interaction on leaf beetle distribution in mesocosm experiments. In the field, the presence of the specialist leaf beetle G. atrocyanea was positively correlated with the local population density (rosette overlap ratio) of R. obtusifolius plants; however, there was no correlation in the case of the generalist leaf beetle G. grisescens. In the cultivation experiments, plants in the intraspecific interaction treatment increased their leaf concentrations of condensed tannins and total phenolics, and G. atrocyanea consumed more of these leaves than leaves in other treatments. Similar results were observed in the field. In the mesocosm experiments, larger numbers of G. atrocyanea were distributed on R. obtusifolius plants exposed to below‐ground intraspecific interaction than on plants not exposed to intraspecific interaction. Our results provide experimental evidence that leaf‐trait changes in response to intraspecific interaction between host plants influence specialist herbivore distribution. This highlights the need to integrate plant–plant interactions into our understanding of plant–animal interactions. A free Plain Language Summary can be found within the Supporting Information of this article.
Seeds express various germination behaviors in response to competitor plants. However, germination behaviors in response to facilitator plants are not yet well understood. Rumex obtusifolius seedlings usually appear on the ground near adult conspecific plants, and their survival rate under the canopy of adult conspecifics is higher than that outside the canopy, indicating that adult R. obtusifolius plants facilitate their seedling establishments. We hypothesized that emergence of R. obtusifolius seedlings is promoted by cues from adult conspecifics, but emergence of heterospecific seedlings is not. To test this, we investigated emergence responses of seedlings of R. obtusifolius and three other species that grow with R. obtusifolius in the presence of R. obtusifolius leaf phytochemicals. Emergence of R. obtusifolius seedlings was promoted by the presence of R. obtusifolius leaves. In contrast, emergence of other species seedlings was not promoted by R. obtusifolius leaves. We conclude that germination of R. obtusifolius seeds is facilitated in the presence of conspecifics, via water-soluble chemical exposure, and that recognizing these chemicals has adaptive value.
Plants typically grow in soil in which resources (e.g., water and nutrients) are distributed heterogeneously (Farley and Fitter, 1999; Wei et al., 2017), and individual plants encounter both high-and low-quality resource patches (Wei et al., 2017). Not surprisingly, plants use multiple behavioral strategies to forage for patchy resources (Cahill and McNickle, 2011). The best-studied strategy is the ability to grow more roots (biomass, length, etc.) in highnutrient patches than in low-nutrient patches (Cahill and McNickle, 2011). Such preferential allocation of root biomass is widespread among plant species (Hodge, 2004) and is generally referred to as foraging precision (Cahill and McNickle, 2011). The mechanisms underlying root foraging precision include signaling within and among organs. For example, increased root development in response to soil nitrogen involves signals sent from the shoot that coordinate overall growth and development (Ko and Helariutta, 2017). Various substances, including proteins, peptides, and phytohormones, have been detected as signaling substances and induce diverse root responses via long-distance transport through the phloem (Ko and Helariutta, 2017). In patchy soil environments, there is some evidence of a tripartite root-shoot-root signaling system (Keeble et al., 1930; Ruffel et al., 2011; Tabata et al., 2014; Ko and Helariutta, 2017), including the observation that when some roots encounter lownutrient patches, other parts of the root system can increase nitrate uptake, mediated by long-distance signaling through leaf veins (Tabata et al., 2014; Ohkubo et al., 2017). For example,
Previous study reported a novel type of self-discrimination in the tendrils of the vine Cayratia japonica (Vitaceae). However, whether self-discrimination in tendrils is common in vine plant species has not been elucidated. Here, we investigated whether tendrils of Momordica charantia var. pavel (Cucurbitaceae), Cucumis sativus (Cucurbitaceae) and Passiflora caerulea (Passifloraceae) can discriminate self and non-self plants. We also investigated whether the tendrils of M. charantia and C. sativus can discriminate differences in cultivars to determine the discrimination ability for genetic similarity. We found that tendrils of the M. charantia and P. caerulea were more likely to coil around non-self plant than self plants, but not in C. sativus. Our findings support the common occurrence of self-discrimination in tendrils in different plant taxa, although some species lacked it. Furthermore, tendrils of M. charantia more rapidly coil around different cultivars than around same cultivars. The tendrils of M. charantia may can discriminate differences in cultivars.
Recent studies suggest that changes in leaf traits due to interactions between plants affect the resource utilisation and distribution of herbivores. However, this has not yet been confirmed experimentally. Here, we investigated the effects of phenotypic plasticity in leaf traits of Rumex obtusifolius (host plant) in response to the intra and interspecific interaction on distribution of two leaf beetles, Gastrophysa atrocyanea (specialist herbivore) and Galerucella grisescens (generalist herbivore). We investigated the local population density of R. obtusifolius plants and the presence of leaf beetles on the plants at five study sites. Leaf chemicals (condensed tannins and total phenolics) were compared between aggregated and solitary R. obtusifolius plants. To clarify the effects of the interaction environment of R. obtusifolius plants on their leaf traits and resource utilisation by leaf beetles, we conducted cultivation and preference experiments. Leaf chemicals (chlorophylls, organic acids, primary metabolites, condensed tannins and total phenolics) and preferences of adult leaf beetles were compared between intraspecific, interspecific plant interaction, or no-interaction treatments. Finally, we evaluated the effects of interaction between R. obtusifolius on leaf beetle distribution in mesocosm experiments. In the field, the presence of the specialist leaf beetle, G. atrocyanea, was positively correlated with the local population density (rosette overlap ratio) of R. obtusifolius plants; however, no correlation was observed in the case of the generalist leaf beetle, G. grisescens. In the cultivation experiment, plants in the intraspecific interaction treatment increased their leaf contents of condensed tannins and total phenolics, and G. atrocyanea consumed more of these leaves than leaves in other treatments. Similar results were observed in the field. In the mesocosm experiment, larger numbers of G. atrocyanea were distributed on R. obtusifolius plants exposed to below-ground intraspecific interaction than on plants not exposed to intraspecific interaction. Our results provide experimental evidence that leaf trait changes in response to intraspecific interaction between host plants influence specialist herbivore distribution. This highlights the need to integrate plant plant interactions into our understanding of plant animal interactions.
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