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Herbivore impacts on marsh production depend upon a compensatory continuum mediated by salinity stress.

ABSTRACT: Plant communities are disturbed by several stressors and they are expected to be further impacted by increasing anthropogenic stress. The consequences of these stressors will depend, in part, upon the ability of plants to compensate for herbivory. Previous studies found that herbivore impacts on plants can vary from negative to positive because of environmental control of plant compensatory responses, a.k.a. the Compensatory Continuum Hypothesis. While these influential studies enhanced our appreciation of the dynamic nature of plant-herbivore interactions, they largely focused on the impact of resource limitation. This bias limits our ability to predict how other environmental factors will shape the impact of herbivory. We examined the role of salinity stress on herbivory of salt marsh cordgrass, Spartina foliosa, by an herbivore previously hypothesized to influence the success of restoration projects (the scale insect, Haliaspis spartinae). Using a combination of field and mesocosm manipulations of scales and salinity, we measured how these factors affected Spartina growth and timing of senescence. In mesocosm studies, Spartina overcompensated for herbivory by growing taller shoots at low salinities but the impact of scales on plants switched from positive to neutral with increasing salinity stress. In field studies of intermediate salinities, scales reduced Spartina growth and increased the rate of senescence. Experimental salinity additions at this field site returned the impact of scales to neutral. Because salinity decreased scale densities, the switch in impact of scales on Spartina with increasing salinity was not simply a linear function of scale abundance. Thus, the impact of scales on primary production depended strongly upon environmental context because intermediate salinity stress prevented plant compensatory responses to herbivory. Understanding this context-dependency will be required if we are going to successfully predict the success of restoration efforts and the ecological consequences of anthropogenic disturbances.

SUBMITTER: Long JD

PROVIDER: S-EPMC4195738 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Herbivore impacts on marsh production depend upon a compensatory continuum mediated by salinity stress.

Long Jeremy D JD Porturas Laura D LD

PloS one 20141013 10

Plant communities are disturbed by several stressors and they are expected to be further impacted by increasing anthropogenic stress. The consequences of these stressors will depend, in part, upon the ability of plants to compensate for herbivory. Previous studies found that herbivore impacts on plants can vary from negative to positive because of environmental control of plant compensatory responses, a.k.a. the Compensatory Continuum Hypothesis. While these influential studies enhanced our appr ...[more]

PMID: 25310475

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Project description:Flowering plants use volatiles to attract pollinators while deterring herbivores. Vegetative and floral traits may interact to affect insect behavior. Pollinator behavior is most likely influenced by leaf traits when larval stages interact with plants in different ways than adult stages, such as when larvae are leaf herbivores but adult moths visit flowers as pollinators. Here, we determine how leaf induction and corresponding volatile differences in induced plants influence behavior in adult moths and whether these preferences align with larval performance. We manipulated vegetative induction in four Nicotiana species. Using paired induced and control plants of the same species with standardized artificial flowers, we measured foraging and oviposition choices by their ecologically and economically important herbivore/pollinator, Manduca sexta. In parallel, we measured growth rates of M. sexta larvae fed leaves from control or induced plants to determine if this was consistent with female oviposition preference. Lastly, we used plant headspace collections and gas chromatography to quantify volatile compounds from both induced and control leaves to link changes in plant chemistry with moth behavior. In the absence of floral chemical cues, vegetative defensive status influenced adult moth foraging preference from artificial flowers in one species (N. excelsior), where females nectared from induced plants more often than control plants. Plant vegetative resistance consistently influenced oviposition choice such that moths deposited more eggs on control plants than on induced plants of all four species. This oviposition preference for control plants aligned with higher larval growth rates on control leaves compared with induced leaves. Control and induced plants of each species had similar leaf volatile profiles, but induced plants had higher emission levels. Leaves of N. excelsior produced the most volatile compounds, including some inducible compounds typically associated with floral scent. We demonstrate that vegetative plant defensive volatiles play a role in host plant selection and that insects assess information from leaves differently when choosing between nectaring and oviposition locations. These results underscore the complex interactions between plants, their pollinators, and herbivores.

Project description:Background and aimsOver the last decade, the importance of plant biomechanical properties in shaping wave dissipation efficiency of marsh vegetation has gained growing attention. Here we provide the first analyses of how biomechanical stem properties vary with seasons and along environmental gradients in coastal and estuarine marshes, which is essential to enable accurate assessments of flood defence value of marsh vegetation.MethodsWe quantified both spatial and seasonal variation in stem flexibility and breakability for a variety of common marsh vegetation (Spartina anglica, Scirpus maritimus, Phragmites australis, Elymus athericus, Suaeda maritima, Aster tripolium, Saliconia procumbens) distributed along both salinity and inundation gradients.Key resultsIncreasing salinity tends to induce a shift from species with tall shoots, high flexural stiffness (stem resistance to bending; N mm2) towards species with shorter and more flexible stems. The same trend was found with increasing inundation stress (i.e. decreasing elevation) from the higher part of the low marsh towards the pioneer zone. Stem breakability (the force required to break or fold a stem, N) followed the same pattern of stem stiffness due to the positive relationship between flexural strength (material resistance to flexure, N mm-2) and Young's bending modulus (material resistance to bending; N mm-2). Shifts in stem stiffness and breakability at the community level were found to relate positively to the variation in canopy height between species, highlighting the concurrence of changes in morphological and biomechanical traits under environmental changes. Compared to the differences between species, within-species variability between sampling locations and between seasons is generally minor.ConclusionsOur findings imply that environmental changes may significantly modify wave attenuation capacity of coastal vegetation by inducing species shifts. This emphasizes the need to understand the response of community composition to climate change and human disturbances, when using nature-based flood protection by coastal vegetation as an adaptive response to global change.

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Herbivore impacts on marsh production depend upon a compensatory continuum mediated by salinity stress.

Publications

Herbivore impacts on marsh production depend upon a compensatory continuum mediated by salinity stress.

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