Can browsing by deer in winter induce defence responses in bilberry ( Vaccinium myrtillus )?

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Defenses induced by herbivore feeding or phytohormones such as methyl jasmonate (MeJA) can affect growth, reproduction, and herbivory, not only on the affected individual but also in its neighboring plants. Here, we report multiannual defense, growth, and reproductive responses of MeJA‐treated bilberry (Vaccinium myrtillus) and neighboring ramets. In a boreal forest in western Norway, we treated bilberry ramets with MeJA and water (control) and measured responses over three consecutive years. We observed the treatment effects on variables associated with herbivory, growth, and reproduction in the MeJA‐treated and untreated ramet and neighboring ramets distanced from 10 to 500 cm. MeJA‐treated ramets had fewer grazed leaves and browsed shoots compared to control, with higher effects in 2014 and 2015, respectively. In 2013, growth of control ramets was greater than MeJA‐treated ramets. However, MeJA‐treated ramets had more flowers and berries than control ramets 2 years after the treatment. The level of insect and mammalian herbivory was also lower in untreated neighboring ramets distanced 10–150 cm and, consistent with responses of MeJA‐treated ramets, the stronger effect was also one and 2 years delayed, respectively. The same neighboring ramets had fewer flowers and berries than untreated ramets, indicating a trade‐off between defense and reproduction. Although plant–plant effects were observed across all years, the strength varied by the distance between the MeJA‐treated ramets and its untreated neighbors. We document that induced defense in bilberry reduces both insect and mammalian herbivory, as well as growth, over multiple seasons. The defense responses occurred in a delayed manner with strongest effects one and 2 years after the induction. Additionally, our results indicate defense signaling between MeJA‐treated ramets and untreated neighbors. In summary, this study shows that induced defenses are important ecological strategies not only for the induced individual plant but also for neighboring plants across multiple years in boreal forests.

Section: Discussionsupporting

confidence: 92%

Section: Inducible Defense Responsessupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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Multiannual effects of induced plant defenses: Are defended plants good or bad neighbors?

Benevenuto

Hegland

Töpper

et al. 2018

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“…The plant is considered as a key food source for herbivores, pollinators, and fruit eating birds and mammals in northern European boreal forest ecosystems (Hegland et al, ; Hjältén, Danell, & Ericson, ; Jacquemart, ; Selas, ), and has been found to be sensitive to environmental changes. In previous studies, we showed that defenses induced by herbivore feeding or treatment with MeJA reduce herbivory and increase reproduction of the damaged or treated plants (Benevenuto et al, ; Hegland, Seldal, Lilleeng, & Rydgren, ; Seldal, Hegland, Rydgren, Rodriguez‐Saona, & Töpper, ). These studies provide evidence of potential trade‐offs between growth and defense in bilberry plants when coping with herbivore attack.…”

Section: Introductionmentioning

confidence: 82%

“…Within each block, two ramets (between 10–25 cm height) at least 10 m apart were randomly selected ( N = 120 plants), and each was exposed to one of two different treatments following the same methodology as previous studies (Benevenuto et al, ; Seldal et al, ): (a) 10 mM MeJA application (treated plants), and (b) water/ethanol application (control plants). Several studies have shown that inducible defense responses in plants can be activated by exogenous application of MeJA (Baldwin, ; Benevenuto et al, ; Hegland et al, ; Van Dam & Baldwin, ; Yang, Huihui, Xie, & Rantala, ). To achieve the desired concentration of MeJA, 4.1 M MeJA stock (Bedoukian Research, Danbury, CT) was diluted 1:10 with 95% (v/v) ethanol and rediluted with water to get a final concentration of 10 mM MeJA (Seldal et al, ).…”

Section: Methodsmentioning

confidence: 99%

Molecular and ecological plant defense responses along an elevational gradient in a boreal ecosystem

Benevenuto

Seldal

Polashock

et al. 2020

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Plants have the capacity to alter their phenotype in response to environmental factors, such as herbivory, a phenomenon called phenotypic plasticity. However, little is known on how plant responses to herbivory are modulated by environmental variation along ecological gradients. To investigate this question, we used bilberry (Vaccinium myrtillus L.) plants and an experimental treatment to induce plant defenses (i.e., application of methyl jasmonate; MeJA), to observe ecological responses and gene expression changes along an elevational gradient in a boreal system in western Norway. The gradient included optimal growing conditions for bilberry in this region (ca. 500 m a.s.l.), and the plant's range limits at high (ca. 900 m a.s.l.) and low (100 m a.s.l.) elevations. Across all altitudinal sites, MeJA‐treated plants allocated more resources to herbivory resistance while reducing growth and reproduction than control plants, but this response was more pronounced at the lowest elevation. High‐elevation plants growing under less herbivory pressure but more resource‐limiting conditions exhibited consistently high expression levels of defense genes in both MeJA‐treated and untreated plants at all times, suggesting a constant state of “alert.” These results suggest that plant defense responses at both the molecular and ecological levels are modulated by the combination of climate and herbivory pressure, such that plants under different environmental conditions differentially direct the resources available to specific antiherbivore strategies. Our findings are important for understanding the complex impact of future climate changes on plant–herbivore interactions, as this is a major driver of ecosystem functioning and biodiversity.

How to induce defense responses in wild plant populations? Using bilberry (Vaccinium myrtillus) as example

Seldal

Hegland

Rydgren

et al. 2017

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Inducible plant defense is a beneficial strategy for plants, which imply that plants should allocate resources from growth and reproduction to defense when herbivores attack. Plant ecologist has often studied defense responses in wild populations by biomass clipping experiments, whereas laboratory and greenhouse experiments in addition apply chemical elicitors to induce defense responses. To investigate whether field ecologists could benefit from methods used in laboratory and greenhouse studies, we established a randomized block‐design in a pine‐bilberry forest in Western Norway. We tested whether we could activate defense responses in bilberry (Vaccinium myrtillus) by nine different treatments using clipping (leaf tissue or branch removal) with or without chemical treatment by methyljasmonate (MeJA). We subsequently measured consequences of induced defenses through vegetative growth and insect herbivory during one growing season. Our results showed that only MeJA‐treated plants showed consistent defense responses through suppressed vegetative growth and reduced herbivory by leaf‐chewing insects, suggesting an allocation of resources from growth to defense. Leaf tissue removal reduced insect herbivory equal to the effect of the MeJa treatments, but had no negative impact on growth. Branch removal did not reduce insect herbivory or vegetative growth. MeJa treatment and clipping combined did not give an additional defense response. In this study, we investigated how to induce defense responses in wild plant populations under natural field conditions. Our results show that using the chemical elicitor MeJA, with or without biomass clipping, may be a better method to induce defense response in field experiments than clipping of leaves or branches that often has been used in ecological field studies.