Chemical Defense, Mycorrhizal Colonization and Growth Responses in Plantago lanceolata L

Allelochemicals defend plants against herbivore and pathogen attack aboveground and belowground. Whether such plant defenses incur ecological costs by reducing benefits from plant mutualistic symbionts is largely unknown. We explored a potential trade-off between inherent plant chemical defense and...

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Published in:	Oecologia 2009-06, Vol.160 (3), p.433-442
Main Authors:	De Deyn, Gerlinde Barbra, Biere, A., van der Putten, W. H., Wagenaar, R., Klironomos, J. N.
Format:	Article
Language:	eng
Subjects:	Analysis of Variance Animal and plant ecology Animal, plant and microbial ecology Biological and medical sciences Biomass Biomedical and Life Sciences biosynthesis carbon metabolism Defoliation deterrent iridoid glycosides Ecology Fundamental and applied biological sciences. Psychology fungi General aspects Glomus intraradices herbivore Herbivores Hydrology/Water Resources induction Iridoid glycosides Iridoids - analysis Leaves Life Sciences Mycorrhizae - physiology nutrient pathogens Physiological Ecology - Original Paper Physiological Ecology - Original Papers Plant genetics Plant growth Plant Leaves - chemistry Plant roots Plant Roots - chemistry Plant Sciences Plantago - genetics Plantago - growth & development Plantago - microbiology Plantago lanceolata Plants Regrowth resistance root Soil - analysis Symbiosis
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Summary:	Allelochemicals defend plants against herbivore and pathogen attack aboveground and belowground. Whether such plant defenses incur ecological costs by reducing benefits from plant mutualistic symbionts is largely unknown. We explored a potential trade-off between inherent plant chemical defense and belowground mutualism with arbuscular mycorrhizal fungi (AMF) in Plantago lanceolata L., using plant genotypes from lines selected for low and high constitutive levels of the iridoid glycosides (IG) aucubin and catalpol. As selection was based on IG concentrations in leaves, we first examined whether IG concentrations covaried in roots. Root and leaf IG concentrations were strongly positively correlated among genotypes, indicating genetic interdependence of leaf and root defense. We then found that root AMF arbuscule colonization was negatively correlated with root aucubin concentration. This negative correlation was observed both in plants grown with monocultures of Glomus intraradices and in plants colonized from whole-field soil inoculum. Overall, AMF did not affect total biomass of plants; an enhancement of initial shoot biomass was offset by a lower root biomass and reduced regrowth after defoliation. Although the precise effects of AMF on plant biomass varied among genotypes, plants with high IG levels and low AMF arbuscule colonization in roots did not produce less biomass than plants with low IG and high AMF arbuscule colonization. Therefore, although an apparent trade-off was observed between high root chemical defense and AMF arbuscule colonization, this did not negatively affect the growth responses of the plants to AMF. Interestingly, AMF induced an increase in root aucubin concentration in the high root IG genotype of P. lanceolata. We conclude that AMF does not necessarily stimulate plant growth, that direct plant defense by secondary metabolites does not necessarily reduce potential benefits from AMF, and that AMF can enhance concentrations of root chemical defenses, but that these responses are plant genotype-dependent.
ISSN:	0029-8549 1432-1939