90 research outputs found
Growth form rather than phylogenetic relationship predicts broad volatile emission patterns in the Brassicaceae
No full textVolatile organic compounds (VOCs) released from plants are known to mediate indirect defense against herbivores and trigger intra- and interplant signaling. While systemic defense response can be mediated both via volatile and vascular signals, it is not clear whether common ancestry and/or plant growth forms influence the choice of either mode in planta. We hypothesize that larger woody plants with a complex anatomy should rely more on volatile-mediated signaling, apparently to circumvent vascular restrictions that slow down the communication over a large distance. On the other hand, in smaller herbaceous plants faster systemic response can be achieved via vascular signaling. To investigate whether plant VOCs emission is related to plant phylogeny or growth form, we studied the composition of herbivory-induced plant volatiles in 13 Brassicaceae species representing all four evolutionary lineages, because this family is characterized by both a well-resolved phylogeny and highly diverse growth forms. Our results revealed that woody species consistently emitted a more complex blend of volatiles than herbaceous species. However, phylogenetic relatedness of the species did not explain the observed volatile emission patterns. This emphasizes the influence of growth form, rather than phylogenetic relationships on the variation in plant volatile emissions. Our findings suggest that woody, perennial plant species emit diverse VOCs, likely because these compounds comprise a more efficient mode of defense response in these large, anatomically complex plants
Isotope labeling reveals contribution of newly fixed carbon to carbon storage and monoterpenes production under water deficit and carbon limitation
No full textSecondary metabolites play important roles in plant responses to environmental stress but may also represent a large carbon (C) cost, resulting in trade-offs with other C sinks like growth and storage. However, it remains uncertain how such trade-offs may vary with changes in resource availability including water and CO2 availability. We conducted a glasshouse experiment with peppermint (Mentha x piperita L.) exposed to four treatments: control (sufficient irrigation and near-ambient CO2), water deficit (50% irrigation and near-ambient CO2), CO2 limitation (sufficient irrigation and below-ambient CO2) and the combination of water and CO2 deficits. Continuous 13CO2 labelling was used to trace allocation of newly-assimilated C. Concentrations of soluble sugars significantly increased under water deficit but decreased along with aboveground biomass under low CO2, while monoterpene concentrations remained relatively constant, independent of treatments. Under water deficit, there were no differences in allocation of new vs old C to monoterpenes production, structural growth and storage; plants grown under low CO2 even invested proportionally more newly-assimilated C for monoterpenes production, suggesting a preferential allocation to defense at the expense of growth. We concluded that C allocation to monoterpenes is actively regulated in coordination with growth and storage under water and C stresses, consistent with an optimal defense strategy to protect young tissues
Herbivore preference drives plant community composition
Get PDFHerbivores are important drivers of plant species coexistence and community assembly. However, detailed mechanistic information on how herbivores affect dominance hierarchies between plant species is scarce. Here, we used data of a multi-site herbivore exclusion experiment in grasslands to assess changes in the cover of 28 plant species in response to aboveground pesticide application. Moreover, we assessed species-specific values of plant defense of these 28 species measured as the performance of a generalist caterpillar, and the preference of the caterpillar and a slug species in no-choice and choice feeding experiments, respectively. We show that more preferred species in the feeding experiments were those that increased in cover after herbivore exclusion in the field, whereas less preferred ones decreased. Herbivore performance and several measured leaf traits were not related to the change in plant cover in the field in response to herbivore removal. Additionally, the generalist slug and the generalist caterpillar preferred and disliked the same plant species, indicating that they perceive the balance between defense and nutritional value similarly. We conclude that the growth-defense trade-off in grassland species acts via the preference of herbivores and that among-species variation in plant growth and preference to herbivores drives plant community composition
Being a generalist herbivore in a diverse world: how do diets from different grasslands influence food plant selection and fitness of the grasshopper Chorthippus parallelus?
No full textFranzke A, Unsicker SB, Specht J, Koehler G, Weisser WW. Being a generalist herbivore in a diverse world: how do diets from different grasslands influence food plant selection and fitness of the grasshopper Chorthippus parallelus? ECOLOGICAL ENTOMOLOGY. 2010;35(2):126-138.2. Grasshopper diet consisted of grasses (92.5%), legumes (6.7%) and, in small quantities, other forbs (0.8%). Diet selection differed between the four food plant mixtures, and depended on grasshopper sex and developmental stage. There was no correlation between the relative abundance of plant species in the field and the fraction of these species in the grasshopper diet. 3. Grasshoppers survived on average for 40.4 +/- 1.0 days before maturity, grew 106.8 mg until maturity moult, and females laid 4.1 +/- 0.4 egg pods, each of which contained 8.5 +/- 0.4 eggs. However, despite the differences in feeding behaviour, grasshopper fitness was the same in all of the four food plant mixtures. While the digestibility of ingested food was similar in the four different treatments, indices indicated differences in the conversion efficiency to body mass. 4. Our results show that C. parallelus is a plastic feeder with no fixed preferences in diet composition. The results emphasise that generalist herbivores can counteract putative quality deficiencies of single food plants by selective dietary mixing
Phytochemical variation in treetops: causes and consequences for tree-insect herbivore interactions
Get PDFThe interaction of plants and their herbivorous opponents has shaped the evolution of an intricate network of defences and counter-defences for millions of years. The result is an astounding diversity of phytochemicals and plant strategies to fight and survive. Trees are specifically challenged to resist the plethora of abiotic and biotic stresses due to their dimension and longevity. Here, we review the recent literature on the consequences of phytochemical variation in trees on insect–tree–herbivore interactions. We discuss the importance of genotypic and phenotypic variation in tree defence against insects and suggest some molecular mechanisms that might bring about phytochemical diversity in crowns of individual trees
Invasive earthworms reduce chemical defense and increase herbivory and pathogen infection in native trees
Get PDFRecent research shows that earthworms can alter defense traits of plants against herbivores and pathogens by affecting soil biochemistry. Yet, the effects of invasive earthworms on defense traits of native plants from previously earthworm-free ecosystems as well as the consequences for multitrophic interactions are virtually unknown. Here we use a combination of an observational study and a complementary experimental study to investigate the effects of invasive earthworms on leaf defense traits, herbivore damage and pathogen infection in two poplar tree species (Populus balsamifera and Populus tremuloides) native to North American boreal forests. Our observational study showed that earthworm invasion was associated with enhanced leaf herbivory (by leaf-chewing insects) in saplings of both tree species. However, we only detected significant shifts in the concentration of chemical defense compounds in response to earthworm invasion for P. balsamifera. Specifically, leaf phenolic concentrations, including salicinoids and catechin, were lower in P. balsamifera from earthworm-invaded sites. Our experimental study confirmed an earthworm-induced reduction in leaf defense levels in P. balsamifera for one of the defense compounds, tremulacin. The experimental study additionally showed that invasive earthworms reduced leaf dry matter content, potentially increasing leaf palatability, and enhanced susceptibility of trees to infection by a fungal pathogen, but not to aphid infestation, in the same tree species. Synthesis. Our results show that invasive earthworms can decrease the concentrations of some chemical defense compounds in P. balsamifera, which could make them susceptible to leaf-chewing insects. Such potential impacts of invasive earthworms are likely to have implications for tree survival and competition, native tree biodiversity and ecosystem functioning
Impact of invertebrate herbivory in grasslands depends on plant species diversity
Get PDFInvertebrate herbivores are ubiquitous in most terrestrial ecosystems and theory predicts that
their impact on plant community biomass should depend on diversity and productivity of the
associated plant communities. To elucidate general patterns in the relationship between
invertebrate herbivory, plant diversity, and productivity we carried out a long-term herbivore
exclusion experiment at multiple grassland sites in a mountainous landscape of central Germany.
Over a period of five years, we used above-and belowground insecticides as well as a
molluscicide to manipulate invertebrate herbivory at 14 grassland sites, covering a wide range of
plant species diversity (13 – 38 species m-2) and aboveground plant productivity (272 - 1125 g m-
2 year-1), where plant species richness and productivity of the sites were not significantly
correlated.
Herbivore exclusion had significant effects on the plant communities: it decreased plant
species richness and evenness, and it altered plant community composition. In particular,
exclusion of belowground herbivores promoted grasses at the expense of herbs. In contrast to our
expectation, herbivore effects on plant community biomass were not influenced by productivity.
However, effect size of invertebrate herbivores was negatively correlated with plant diversity of
the grasslands: the effect of herbivory on biomass tended to be negative at sites of high diversity
and positive at sites of low diversity. In general, the effects of aboveground herbivores were
relatively small as compared to belowground herbivores which were important drivers of plant
community composition. Our study is the first to show that variation in the effects of invertebrate
herbivory on plant communities across a landscape is significantly influenced by plant species
richness
Plant species richness in montane grasslands affects the fitness of a generalist grasshopper species
No full textUnsicker SB, Franzke A, Specht J, et al. Plant species richness in montane grasslands affects the fitness of a generalist grasshopper species. ECOLOGY. 2010;91(4):1083-1091.Theory predicts negative effects of increasing plant diversity on the abundance of specialist insect herbivores, but little is known about how plant diversity affects the performance and abundance of generalist insect herbivores. We studied oviposition rates and offspring numbers in females of the generalist grasshopper Chorthippus parallelus that were collected in 15 montane grasslands in 2005 and 2007 along a gradient of plant species richness in central Germany. In addition to plant species richness, we determined evenness and plant community composition in the grasslands and measured aboveground plant biomass and other habitat variables such as leaf area index, vegetation height, and solar radiation. There was substantial variation among sites in grasshopper fecundity and the number of nymphs that hatched from the egg pods. Both fitness measures were positively influenced by plant species richness at the sites, while female fitness did not correlate with any of the other habitat parameters. Abundance of C. parallelus in the grasslands was positively correlated with plant species richness, plant community composition, and incident solar radiation of the sites. There were no phenological differences between grasshoppers from the different study sites. Our results suggest that decreasing biodiversity threatens the persistence not only of specialist, but also of generalist insect herbivores via a variety of mechanisms including a decrease in diversity of the generalists' food plants
Within-crown variability in herbivore performance and leaf traits
No full textFunctional trait variation within individual plants is predicted to have important ecological consequences. However, our understanding of the sources contributing to subindividual trait heterogeneity, and the ramifications thereof, is poor.
In a common garden, we sampled multiple genotypes of mature trembling aspen (Populus tremuloides) at different vertical crown levels and quantified the contributions of genetic, spatial and biotic (herbivory) factors to subindividual morphological and chemical leaf trait variance. Bioassays using gypsy moth (Lymantria dispar L.) caterpillars were conducted to study impacts of spatial and genotypic factors on insect performance.
Crown position was the primary source of subindividual variation in leaf morphology and explained more of the variance in morphological traits than tree genotype. Effects of spatial, genetic and biotic factors on within-crown chemistry were highly compound-specific. For many compounds, changes in within-crown concentrations differed among genotypes, revealing that genotypic variation not only contributes to phytochemical diversity among individuals of the same population, but also affects subindividual chemical trait heterogeneity. For many defense related compounds, total within-crown variance itself differed among genotypes and was in many cases a heritable trait. Bioassays revealed that effects of crown position on caterpillar performance varied among tree genotypes and caterpillar sexes.
We demonstrate that even relatively small trees can express subtle but distinct levels of within-crown leaf-trait variation. In aspen, this variation is shaped not only by spatial factors, but also by genetics and to a lesser degree by herbivory. Within-crown variation in defense chemistry might itself provide a defensive phenotype against herbivores and contribute to the biological diversity of canopy insect communities
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