Department of Botany and Biodiversity Research, University of Vienna, Vienna, Austria.
Department of Microbiology and Ecosystem Science, Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria.
BMC Biol. 2022 Jun 9;20(1):135. doi: 10.1186/s12915-022-01289-0.
Symbiotic ant-plant associations, in which ants live on plants, feed on plant-provided food, and protect host trees against threats, are ubiquitous across the tropics, with the Azteca-Cecropia associations being amongst the most widespread interactions in the Neotropics. Upon colonization of Cecropia's hollow internodes, Azteca queens form small patches with plant parenchyma, which are then used as waste piles when the colony grows. Patches-found in many ant-plant mutualisms-are present throughout the colony life cycle and may supplement larval food. Despite their initial nitrogen (N)-poor substrate, patches in Cecropia accommodate fungi, nematodes, and bacteria. In this study, we investigated the atmospheric N fixation as an N source in patches of early and established ant colonies.
Via N tracer assays, N fixation was frequently detected in all investigated patch types formed by three Azteca ant species. Quantified fixation rates were similar in early and established ant colonies and higher than in various tropical habitats. Based on amplicon sequencing, the identified microbial functional guild-the diazotrophs-harboring and transcribing the dinitrogenase reductase (nifH) gene was highly diverse and heterogeneous across Azteca colonies. The community composition differed between early and established ant colonies and partly between the ant species.
Our data show that N fixation can result in reasonable amounts of N in ant colonies, which might not only enable bacterial, fungal, and nematode growth in the patch ecosystems but according to our calculations can even support the growth of ant populations. The diverse and heterogeneous diazotrophic community implies a functional redundancy, which could provide the ant-plant-patch system with a higher resilience towards changing environmental conditions. Hence, we propose that N fixation represents a previously unknown potential to overcome N limitations in arboreal ant colonies.
共生蚁-植物关系中，蚂蚁以植物为食，生活在植物上，并保护宿主树免受威胁，这种关系在整个热带地区都很普遍，其中 Azteca-Cecropia 关系是新热带地区最广泛的相互作用之一。当 Azteca 蚁后殖民 Cecropia 的中空节间时，它们会在植物薄壁组织上形成小块，然后当蚁群生长时，这些小块就会被用作废物堆。在许多蚁-植物共生关系中都会发现这些斑块，它们存在于蚁群的整个生命周期中，并可能补充幼虫的食物。尽管最初的氮（N）贫乏的基质，但 Cecropia 中的斑块容纳了真菌、线虫和细菌。在这项研究中，我们调查了大气氮固定作为早期和建立中的蚁群斑块中的氮源。
通过 N 示踪剂测定，在三种 Azteca 蚁形成的所有研究斑块类型中，经常检测到氮固定。在早期和建立中的蚁群中，固定的氮量相似，并且高于各种热带栖息地。基于扩增子测序，鉴定的微生物功能群-固氮生物，携带并转录二氮还原酶（nifH）基因，在 Azteca 蚁群中高度多样和异质。群落组成在早期和建立中的蚁群之间以及部分蚁种之间存在差异。
我们的数据表明，氮固定可以导致蚁群中产生相当数量的氮，这不仅可以使斑块生态系统中的细菌、真菌和线虫生长，而且根据我们的计算，甚至可以支持蚁群的生长。多样和异质的固氮生物群落意味着功能冗余，这可以使蚁-植物-斑块系统对环境变化具有更高的弹性。因此，我们提出氮固定代表了一个以前未知的潜力，可以克服树栖蚁群中的氮限制。
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