Journal Article

Uptake of ant-derived nitrogen in the myrmecophytic orchid <i>Caularthron bilamellatum</i>

Christian Gegenbauer, Veronika E. Mayer, Gerhard Zotz and Andreas Richter

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 110, issue 4, pages 757-766
Published in print September 2012 | ISSN: 0305-7364
Published online July 2012 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcs140
Uptake of ant-derived nitrogen in the myrmecophytic orchid Caularthron bilamellatum

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Background and Aims

Mutualistic ant–plant associations are common in a variety of plant families. Some myrmecophytic plants, such as the epiphytic orchid Caularthron bilamellatum, actively form hollow structures that provide nesting space for ants (myrmecodomatia), despite a substantial loss of water-storage tissue. This study aimed at assessing the ability of the orchid to take up nitrogen from ant-inhabited domatia as possible trade-off for the sacrifice of potential water storage capacity.

Methods

Nitrogen uptake capabilities and uptake kinetics of 15N-labelled compounds (NH4+, urea and l -glutamine) were studied in field-grown Caularthron bilamellatum plants in a tropical moist forest in Panama. Plants were either labelled directly, by injecting substrates into the hollow pseudobulbs or indirectly, by labelling of the associated ants in situ.

Key Results

Caularthron bilamellatum plants were able to take up all tested inorganic and organic nitrogen forms through the inner surface of the pseudobulbs. Uptake of NH4+ and glutamine followed Michaelis–Menten kinetics, but urea uptake was not saturable up to 2 mm. 15N-labelled compounds were rapidly translocated and incorporated into vegetative and reproductive structures. By labelling ants with 15N in situ, we were able to prove that ants transfer N to the plants under field conditions.

Conclusions

Based on 15N labelling experiments we were able to demonstrate, for the first time, that a myrmecophytic orchid is capable of actively acquiring different forms of nitrogen from its domatia and that nutrient flux from ants to plants does indeed occur under natural conditions. This suggests that beyond anti-herbivore protection host plants benefit from ants by taking up nitrogen derived from ant debris.

Keywords: Ant–plant interactions; mutualism; nutrient uptake; Michaelis–Menten kinetics; 15N labelling; myrmecophytes; epiphytes; Caularthron bilamellatum; Orchidaceae; BCNM

Journal Article.  6011 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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