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Cost of defense in the context of plant competition: brassica rapa may grow and defend

Publication ,  Journal Article
Siemens, DH; Garner, SH; Mitchell-Olds, T; Callaway, RM
Published in: Ecology
February 2002

Theory on costs of plant defense against herbivory in stressful environments predicts that costs should increase when competition is intense. This amplifies a fundamental dilemma that plants are thought to face: allocate limited resources to grow fast enough to compete, or invest these resources in secondary metabolites to maintain defense. We studied costs associated with genetic and environmental variation in secondary metabolite production of Brassica rapa in the presence and absence of the generalist competitor Lolium perenne. We used experimental quantitative genetics (artificial selection) to manipulate genetic variation, and herbivore‐induction treatments to produce environmental variation in myrosinase and glucosinolate concentrations and resistance. Glucosinolates, and their byproducts after breakdown by myrosinase, are known to affect herbivory on plants in the Brassicaceae family. Defense costs were significant in the absence of competitors, but in contrast to theoretical predictions, costs of constitutive defense (measured as growth rates) were not detectable and the cost of induced defense remained the same in the competitive environment. To understand what factors made constitutive defense costs not detectable under competition we conducted several experiments to assess the effects of limited resources and allelopathy on costs and benefits of the defense chemicals. None of the experiments involving nutrient supply and weak competition supported the hypothesis that the lack of defense costs in competitive environments was due to limited resources. Instead, the breakdown products of the glucosinolate–myrosinase reaction appeared to function as allelopathic agents, which may benefit B. rapa plants in competition, thereby reducing net costs of chemical defense. We found that: (1) the effects of exogenous glucosinolates on Lolium root length depended on the presence of myrosinase. (2) In the absence of nutrients, Lolium root lengths were shorter when seeds germinated with B. rapa. (3) Genetic increases in glucosinolate concentration negatively affected Lolium seedling growth only when there were simultaneous genetic increases in myrosinase concentration. Activated carbon treatments designed to neutralize allelopathic effects and restore costs in the competitive environments were, however, not statistically significant. When plant defenses also function to benefit plants in competitive interactions, plants may evolve to compete and defend.

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Published In

Ecology

DOI

EISSN

1939-9170

ISSN

1939-9170

Publication Date

February 2002

Volume

83

Issue

2

Start / End Page

505 / 517

Related Subject Headings

  • Ecology
  • 4102 Ecological applications
  • 3109 Zoology
  • 3103 Ecology
  • 0603 Evolutionary Biology
  • 0602 Ecology
  • 0501 Ecological Applications
 

Citation

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Siemens, D. H., Garner, S. H., Mitchell-Olds, T., & Callaway, R. M. (2002). Cost of defense in the context of plant competition: brassica rapa may grow and defend. Ecology, 83(2), 505–517. https://doi.org/10.1890/0012-9658(2002)083[0505:coditc]2.0.co;2
Siemens, David H., Shannon H. Garner, Thomas Mitchell-Olds, and Ragan M. Callaway. “Cost of defense in the context of plant competition: brassica rapa may grow and defend.” Ecology 83, no. 2 (February 2002): 505–17. https://doi.org/10.1890/0012-9658(2002)083[0505:coditc]2.0.co;2.
Siemens DH, Garner SH, Mitchell-Olds T, Callaway RM. Cost of defense in the context of plant competition: brassica rapa may grow and defend. Ecology. 2002 Feb;83(2):505–17.
Siemens, David H., et al. “Cost of defense in the context of plant competition: brassica rapa may grow and defend.” Ecology, vol. 83, no. 2, Feb. 2002, pp. 505–17. Epmc, doi:10.1890/0012-9658(2002)083[0505:coditc]2.0.co;2.
Siemens DH, Garner SH, Mitchell-Olds T, Callaway RM. Cost of defense in the context of plant competition: brassica rapa may grow and defend. Ecology. 2002 Feb;83(2):505–517.
Journal cover image

Published In

Ecology

DOI

EISSN

1939-9170

ISSN

1939-9170

Publication Date

February 2002

Volume

83

Issue

2

Start / End Page

505 / 517

Related Subject Headings

  • Ecology
  • 4102 Ecological applications
  • 3109 Zoology
  • 3103 Ecology
  • 0603 Evolutionary Biology
  • 0602 Ecology
  • 0501 Ecological Applications