Roy Melanie, Pozzi Adrien C, Gareil Raphaëlle, Nagati Melissande, Manzi Sophie, Nouioui Imen, Sharikadze Nino, Jargeat Patricia, Gryta Hervé, Moreau Pierre-Arthur, Fernandez Maria P, Gardes Monique
Laboratoire Evolution Diversité Biologique (EDB UMR 5174), Université Toulouse 3 Paul Sabatier, CNRS, ENFA, Toulouse, France.
Laboratoire Ecologie Microbienne (UMR5557), Université Claude Bernard (Lyon I), CNRS, Villeurbanne, France.
PeerJ. 2017 Jul 18;5:e3479. doi: 10.7717/peerj.3479. eCollection 2017.
Recent climatic history has strongly impacted plant populations, but little is known about its effect on microbes. Alders, which host few and specific symbionts, have high genetic diversity in glacial refugia. Here, we tested the prediction that communities of root symbionts survived in refugia with their host populations. We expected to detect endemic symbionts and a higher species richness in refugia as compared to recolonized areas.
We sampled ectomycorrhizal (EM) root tips and the nitrogen-fixing actinomycete communities in eight sites colonized by subsp close to the Caucasus in Georgia. Three sites were located in the Colchis, one major Eurasian climatic refugia for Arcto-Tertiary flora and alders, and five sites were located in the recolonized zone. Endemic symbionts and plant ITS variants were detected by comparing sequences to published data from Europe and another Tertiary refugium, the Hyrcanian forest. Species richness and community structure were compared between sites from refugia and recolonized areas for each symbionts.
For both symbionts, most MOTUs present in Georgia had been found previously elsewhere in Europe. Three endemic strains were detected in the Colchis two in the recolonized zone, and the five endemic EM fungi were detected only in the recolonized zone. species richness was higher in the Colchis while the contrary was observed for EM fungi. Moreover, the genetic diversity of one alder specialist was particularly high in the recolonized zone. The EM communities occurring in the Colchis and the Hyrcanian forests shared closely related endemic species.
The Colchis did not have the highest alpha diversity and more endemic species, suggesting that our hypothesis based on alder biogeography may not apply to alder's symbionts. Our study in the Caucasus brings new clues to understand symbioses biogeography and their survival in Tertiary and ice-age refugia, and reveals that isolated host populations could be of interest for symbiont diversity conservation.
近期的气候历史对植物种群产生了强烈影响，但对其对微生物的影响却知之甚少。桤木宿主的共生体种类少且具特异性，在冰川避难所中具有较高的遗传多样性。在此，我们检验了这样一个预测，即根共生体群落与其宿主种群一起在避难所中存活了下来。我们预期与重新定殖区域相比，在避难所中能检测到地方性共生体和更高的物种丰富度。
我们在格鲁吉亚靠近高加索地区的八个被 亚种定殖的地点采集了外生菌根（EM）根尖和固氮放线菌群落样本。三个地点位于科尔基斯，这是北极第三纪植物群和桤木的一个主要欧亚气候避难所，另外五个地点位于重新定殖区域。通过将序列与来自欧洲和另一个第三纪避难所——里海森林的已发表数据进行比较，检测地方性共生体和植物ITS变体。比较了避难所和重新定殖区域各共生体的物种丰富度和群落结构。
对于这两种共生体，格鲁吉亚存在的大多数分子操作分类单元（MOTUs）此前在欧洲其他地方也有发现。在科尔基斯检测到三个地方性菌株，在重新定殖区域检测到两个，五个地方性EM真菌仅在重新定殖区域被检测到。科尔基斯的物种丰富度更高，而EM真菌的情况则相反。此外，一种桤木专性菌在重新定殖区域的遗传多样性特别高。科尔基斯森林和里海森林中的EM群落共有密切相关的地方性物种。
科尔基斯并没有最高的α多样性和更多的地方性物种，这表明我们基于桤木生物地理学的假设可能不适用于桤木的共生体。我们在高加索地区的研究为理解共生生物地理学及其在第三纪和冰河时代避难所中的生存带来了新线索，并揭示了孤立的宿主种群对于共生体多样性保护可能具有重要意义。
