Department of Terrestrial Ecosystem Research, University of Vienna, Austria.
Ann Bot. 2012 Sep;110(4):757-66. doi: 10.1093/aob/mcs140. Epub 2012 Jul 9.
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.
Nitrogen uptake capabilities and uptake kinetics of (15)N-labelled compounds (NH(4)(+), 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.
Caularthron bilamellatum plants were able to take up all tested inorganic and organic nitrogen forms through the inner surface of the pseudobulbs. Uptake of NH(4)(+) and glutamine followed Michaelis-Menten kinetics, but urea uptake was not saturable up to 2 mm. (15)N-labelled compounds were rapidly translocated and incorporated into vegetative and reproductive structures. By labelling ants with (15)N in situ, we were able to prove that ants transfer N to the plants under field conditions.
Based on (15)N 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.
互利共生的蚁-植物共生关系在许多植物科中都很常见。一些蚁栖植物，如附生兰花 Caularthron bilamellatum，尽管大量失去了储水组织，但仍会积极形成提供蚂蚁筑巢空间的中空结构（蚁栖腔）。本研究旨在评估兰花从蚂蚁栖息的蚁栖腔中吸收氮的能力，以作为牺牲潜在储水能力的可能权衡。
在巴拿马的热带湿润森林中，对野外生长的 Caularthron bilamellatum 植物进行了（15）N 标记化合物（NH(4)(+)、尿素和 l -谷氨酰胺）的氮吸收能力和吸收动力学研究。植物通过直接将基质注入中空假鳞茎或间接标记原位共生蚂蚁进行标记。
Caularthron bilamellatum 植物能够通过假鳞茎的内表面吸收所有测试的无机和有机氮形式。NH(4)(+)和谷氨酰胺的吸收遵循米氏动力学，但尿素的吸收在 2mm 内没有达到饱和。（15）N 标记化合物迅速转运并整合到营养和生殖结构中。通过原位标记蚂蚁（15）N，我们能够证明在野外条件下，蚂蚁会将 N 转移到植物上。
基于（15）N 标记实验，我们首次证明了一种蚁栖兰花能够从其蚁栖腔中主动获取不同形式的氮，并且蚂蚁向植物的养分流动确实在自然条件下发生。这表明，除了抗食草动物保护外，宿主植物还通过从蚂蚁残骸中吸收氮来受益于蚂蚁。
