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Godschalx, Adrienne

Preferred name
Godschalx, Adrienne
Main Affiliation
Job title
Ancien.ne collaborateur.trice
Identifiers
https://libra.unine.ch/handle/123456789/30731

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  • Publication
    Open Access
    Host plant cyanotype determines degree of rhizobial symbiosis
    (2017-9-8)
    Godschalx, Adrienne 
    ;
    Vy, Tran
    ;
    Ballhorn, Daniel
    Plants with nitrogen-fixing bacteria, such as legumes with rhizobia, can tap the atmospheric nitrogen pool to obtain resources for defense compounds. Cyanogenesis, a nitrogen-based plant defense against herbivores, increases in response to rhizobial colonization, but depends on plant genotype. Here, we tested whether genotypic differences in host plant cyanogenesis influence symbiotic reliance on nitrogen-fixing rhizobia. Using thin, clear soil containers, we counted nodules on live root systems of distinct high (HC) and low (LC) lima bean (Phaseolus lunatus) cyanotypes across the duration of an eight-week study. We measured changes in cyanogenic potential (HCNp) and protein content to reveal quantitative interactions between nodule number and both leaf traits. High cyanogenic plants maintained consistently twice as many nodules as LC plants. Including both cyanotypes, nodule number correlated positively with HCNp, but negatively with foliar protein content. However, within-cyanotype interactions between nodule number and plant traits were not significant except for foliar protein in HC plants, which decreased with increasing nodule number. Our results imply that while genotypes with higher levels of nitrogen-based defense invest more in the rhizobial partner, the costs involved in maintaining the symbiosis may cause resource allocation constraints in the plants' primary nitrogen metabolism.
  • Publication
    Open Access
    Is protection against florivory consistent with the optimal defense hypothesis?
    (2016-1-28)
    Godschalx, Adrienne 
    ;
    Stady, Lauren
    ;
    Watzig, Benjamin
    ;
    Ballhorn, Daniel
    Plant defense traits require resources and energy that plants may otherwise use for growth and reproduction. In order to most efficiently protect plant tissues from herbivory, one widely accepted assumption of the optimal defense hypothesis states that plants protect tissues most relevant to fitness. Reproductive organs directly determining plant fitness, including flowers and immature fruit, as well as young, productive leaf tissue thus should be particularly well-defended. To test this hypothesis, we quantified the cyanogenic potential (HCNp)—a direct, chemical defense—systemically expressed in vegetative and reproductive organs in lima bean (Phaseolus lunatus), and we tested susceptibility of these organs in bioassays with a generalist insect herbivore, the Large Yellow Underwing (Noctuidae: Noctua pronuba). To determine the actual impact of either florivory (herbivory on flowers) or folivory on seed production as a measure of maternal fitness, we removed varying percentages of total flowers or young leaf tissue and quantified developing fruit, seeds, and seed viability. Results We found extremely low HCNp in flowers (8.66 ± 2.19 μmol CN− g−1 FW in young, white flowers, 6.23 ± 1.25 μmol CN− g−1 FW in mature, yellow flowers) and in pods (ranging from 32.05 ± 7.08 to 0.09 ± 0.08 μmol CN− g−1 FW in young to mature pods, respectively) whereas young leaves showed high levels of defense (67.35 ± 3.15 μmol CN− g−1 FW). Correspondingly, herbivores consumed more flowers than any other tissue, which, when taken alone, appears to contradict the optimal defense hypothesis. However, experimentally removing flowers did not significantly impact fitness, while leaf tissue removal significantly reduced production of viable seeds. Conclusions Even though flowers were the least defended and most consumed, our results support the optimal defense hypothesis due to i) the lack of flower removal effects on fitness and ii) the high defense investment in young leaves, which have high consequences for fitness. These data highlight the importance of considering plant defense interactions from multiple angles; interpreting where empirical data fit within any plant defense hypothesis requires understanding the fitness consequences associated with the observed defense pattern.
  • Publication
    Open Access
    Ants are less attracted to the extrafloral nectar of plants with symbiotic, nitrogen-fixing rhizobia
    (2015-2-1)
    Godschalx, Adrienne 
    ;
    Schädler, Martin
    ;
    Trisel, Julie
    ;
    Balkan, Mehmet
    ;
    Ballhorn, Daniel
    Plants simultaneously maintain mutualistic relationships with different partners that are connected through the same host, but do not interact directly. One or more participating mutualists may alter their host's phenotype, resulting in a shift in the host's ecological interactions with all other mutualists involved. Understanding the functional interplay of mutualists associated with the same host remains an important challenge in biology. Here, we show belowground nitrogen-fixing rhizobia on lima bean (Phaseolus lunatus) alter their host plant's defensive mutualism with aboveground ants. We induced extrafloral nectar (EFN), an indirect defense acting through ant attraction. We also measured various nutritive and defensive plant traits, biomass, and counted ants on rhizobial and rhizobia-free plants. Rhizobia increased plant protein as well as cyanogenesis, a direct chemical defense against herbivores, but decreased EFN. Ants were significantly more attracted to rhizobia-free plants, and our structural equation model shows a strong link between rhizobia and reduced EFN as well as between EFN and ants: the sole path to ant recruitment. The rhizobia-mediated effects on simultaneously expressed defensive plant traits indicate rhizobia can have significant bottom-up effects on higher trophic levels. Our results show belowground symbionts play a critical and underestimated role in determining aboveground mutualistic interactions.
  • Publication
    Open Access
    Chemical defense lowers plant competitiveness
    (2014-8-31)
    Ballhorn, Daniel
    ;
    Godschalx, Adrienne 
    ;
    Smart, Savannah
    ;
    Kautz, Stefanie
    ;
    Schädler, Martin
    Both plant competition and plant defense affect biodiversity and food web dynamics and are central themes in ecology research. The evolutionary pressures determining plant allocation toward defense or competition are not well understood. According to the growth–differentiation balance hypothesis (GDB), the relative importance of herbivory and competition have led to the evolution of plant allocation patterns, with herbivore pressure leading to increased differentiated tissues (defensive traits), and competition pressure leading to resource investment towards cellular division and elongation (growth-related traits). Here, we tested the GDB hypothesis by assessing the competitive response of lima bean (Phaseolus lunatus) plants with quantitatively different levels of cyanogenesis—a constitutive direct, nitrogen-based defense against herbivores. We used high (HC) and low cyanogenic (LC) genotypes in different competition treatments (intra-genotypic, inter-genotypic, interspecific), and in the presence or absence of insect herbivores (Mexican bean beetle, Epilachna varivestis) to quantify vegetative and generative plant parameters (above and belowground biomass as well as seed production). Highly defended HC-plants had significantly lower aboveground biomass and seed production than LC-plants when grown in the absence of herbivores implying significant intrinsic costs of plant cyanogenesis. However, the reduced performance of HC- compared to LC-plants was mitigated in the presence of herbivores. The two plant genotypes exhibited fundamentally different responses to various stresses (competition, herbivory). Our study supports the GDB hypothesis by demonstrating that competition and herbivory affect different plant genotypes differentially and contributes to understanding the causes of variation in defense within a single plant species.
  • Publication
    Open Access
    Co-variation of chemical and mechanical defenses in lima bean (Phaseolus lunatus L.)
    (2013-10-13)
    Ballhorn, Daniel
    ;
    Godschalx, Adrienne 
    ;
    Kautz, Stefanie
    Plants usually express multiple chemical and mechanical defenses simultaneously. The interplay of these defenses is still poorly understood, as predictions range from negative associations such as allocation tradeoffs to positive correlations forming synergistic defense syndromes. Surprisingly, little empirical evidence exists on the co-variation of multiple plant defenses. In the present study, we analyzed different genotypes of lima bean (Phaseolus lunatus L.) for the expression of two direct chemical defenses [cyanogenic potential (constitutive), polyphenol oxidase activity (inducible)], two indirect chemical defenses [volatiles (VOCs) and extrafloral nectar (EFN; both inducible)] and a constitutive mechanical defense (hook-shaped trichomes). While the occurrence of trichomes was positively correlated with cyanogenesis, these traits showed a tradeoff with polyphenol oxidase activity, release of VOCs, and secretion of EFN. Hook-shaped trichomes were abundantly present in four of 14 genotypes investigated, and were found only in one monophyletic group of an AFLP-based tree, thus indicating a single evolutionary origin within the species. Our findings show that different lima bean genotypes express either one of two defense systems: 1) high constitutive defense via cyanogenesis and trichomes or 2) high inducible defense via VOCs, EFN, and PPO activity.