Department of Biology, University of Chicago, 60637, Chicago, IL, USA.
Oecologia. 1989 Mar;80(1):27-31. doi: 10.1007/BF00789927. Epub 2013 Mar 13.
Symbiotic nitrogen fixation in angiosperms normally occurs in buried root nodules and is severely inhibited in flooded soils. A few plant species, however, respond to flooding by forming nodules on stems, or, in one case, submerged roots with aerenchyma. We report here the novel occurrence of aerial rhizobial nodules attached to adventitious roots of the legume,Pentaclethra macroloba, in a lowland tropical rainforest swamp in Costa Rica. Swamp sapdings (1-10 cm diameter) support an average 12 g nodules dry weight per plant on roots 2-300 cm above water, and nodules remain in aerial positions at least 6 months. Collections from four swamp plants maintained linear activity rates (3-14 μmoles C2H4/g nodule dry weight/hr) throughout incubations for 6 and 13 hrs; excised nodule activity in most legumes declines after 1-2 hrs. Preliminary study of the anatomy and physiology suggest aerial nodules possess unusual features associated with tolerance to swamp conditions. High host tree abundance and nodulation in the swamp compared to upland sites indicate the aerial root symbiosis may contribute more fixed nitrogen to the local ecosystem than the more typical buried root symbiosis.
被子植物共生固氮通常发生在埋在地下的根瘤中，但在水淹的土壤中会受到严重抑制。然而，有少数几种植物在水淹时会在茎上形成根瘤，或者在一种情况下，在具有气腔的浸没根上形成根瘤。我们在这里报告了一个新的例子，即在哥斯达黎加低地热带雨林沼泽中，豆科植物Pentaclethra macroloba 的不定根上附着有气生根瘤。沼泽 sapdings（直径 1-10 厘米）在距水面 2-300 厘米的根系上平均每株支持 12 克干重的根瘤，根瘤在气生位置至少保持 6 个月。从四种沼泽植物中采集的样本在 6 和 13 小时的孵育过程中保持线性活性率（3-14 μmoles C2H4/g 根瘤干重/小时）；大多数豆科植物的离体根瘤活性在 1-2 小时后下降。对解剖学和生理学的初步研究表明，气生根瘤具有与耐受沼泽条件相关的不寻常特征。与高地相比，沼泽中宿主树的丰富度和根瘤化程度表明，与更典型的埋根共生关系相比，气生根共生可能为当地生态系统提供更多的固定氮。
