Serpentine soils do not limit mycorrhizal fungal diversity

Our plain-English summary of Serpentine soils do not limit mycorrhizal fungal diversity, by S. Branco, R.H. Ree (PloS One, 2010).

The study

• Authors: S. Branco, R.H. Ree
• Journal: PloS One
• Published: 2010;5(7):e11757
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Physiologically stressful environments tend to host depauperate and specialized biological communities. Serpentine soils exemplify this phenomenon by imposing well-known constraints on plants; however, their effect on other organisms is still poorly understood.

Methodology/principal Findings: We used a combination of field and molecular approaches to test the hypothesis that serpentine fungal communities are species-poor and specialized. We conducted surveys of ectomycorrhizal fungal diversity from adjacent serpentine and non-serpentine sites, described fungal communities using nrDNA Internal Transcribed Spacer (ITS) fragment and sequence analyses, and compared their phylogenetic community structure. Although we detected low fungal overlap across the two habitats, we found serpentine soils to support rich fungal communities that include representatives from all major fungal lineages. We failed to detect the phylogenetic signature of endemic clades that would result from specialization and adaptive radiation within this habitat.

Conclusions/significance: Our results indicate that serpentine soils do not constitute an extreme environment for ectomycorrhizal fungi, and raise important questions about the role of symbioses in edaphic tolerance and the maintenance of biodiversity.

In plain English

This study did not look at asbestos or human health. It was a field survey of fungi that live on tree roots in serpentine soils. Serpentine soils come from serpentine-type (ultramafic) rocks and have little calcium compared with magnesium, and toxic levels of chromium, nickel and other elements. The authors sampled root tips of the oak Quercus ilex subsp. ballota in two serpentine and two non-serpentine forests in Trás-os-Montes, northeastern Portugal, between 2005 and 2008. They identified the root fungi (ectomycorrhizal fungi) by DNA sequencing. Soil tests confirmed that the serpentine sites had a low calcium to magnesium ratio, high magnesium, and high nickel and chromium. The authors found 45 fungal species from 16 genera on serpentine soil and 43 species from 14 genera on non-serpentine soil. Only 15% of all species were found in both habitats. Statistically, the two fungal communities could not be told apart in richness or structure, and the analysis did not support the idea that the serpentine fungi formed closely related groups. Most fungi turned up in only one sample. The authors concluded that serpentine soils impose no detectable constraints on the richness or phylogenetic diversity of these fungi.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Field survey of fungal communities on tree roots, with DNA-based identification and phylogenetic (family-tree) analysis, comparing serpentine and non-serpentine forests
• Who was studied: Ectomycorrhizal fungi on oak (Quercus ilex subsp. ballota) root tips from two serpentine forests (Serra da Nogueira, Espinhosela) and two non-serpentine forests (Rabal, Petisqueira) in Trás-os-Montes, northeastern Portugal. Twenty focal trees were sampled per forest, in spring between 2005 and 2008, and fungal samples were obtained from 62 soil cubes.
• Exposure: Growth on serpentine soil compared with non-serpentine soil. The serpentine soil had a low calcium to magnesium ratio, high magnesium, and high nickel and chromium. No asbestos fibers were studied.
• Main results:
  • Serpentine forests: 45 fungal species from 16 genera. Non-serpentine forests: 43 species from 14 genera.
  • Only 15% of all fungal species were shared between the serpentine and non-serpentine habitats. In both habitats most fungi were found in only a single sample.
  • The species accumulation curves for serpentine and non-serpentine soil could not be told apart and had overlapping confidence intervals. The ordination analysis did not group samples by soil type or forest.
  • There was no support for phylogenetic clustering in either community. Serpentine: NRI = 1.28 (p = 0.12) and NTI = 1.62 (p = 0.06). Non-serpentine: NRI = 0.20 (p = 0.6); the NTI p value was 0.68 (the NTI value itself is garbled in the text).
  • Fungi in the Boletales group (Boletus, Leccinum, Melanogaster) were detected only in serpentine forests.
• The authors' conclusion: The authors concluded that serpentine soils impose no detectable constraints on the richness or phylogenetic diversity of ectomycorrhizal fungi, and that their results do not support serpentine soil as an environmental constraint for these fungi.
• Limitations the authors state:
  • The authors were not able to fully describe the fungal communities, and many fungi were found in single samples.
  • Because most species were detected only once, it was hard to tell whether they are specific to one soil type.
  • Local adaptation by soil-specialized fungal populations was not addressed in this study.
  • Phylogenetic structure alone is not enough to draw conclusions about ecological processes or the traits underlying serpentine tolerance.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Serpentine Group, Endemic.

Related studies

• Serpentine soils promote ectomycorrhizal fungal diversity — S. Branco (2010)
• Fungal diversity is not determined by mineral and chemical differences in serpentine substrates — S. Daghino, C. Murat, et al. (2012)
• Serpentine and non-serpentine ecotypes of Collinsia sparsiflora associate with distinct arbuscular mycorrhizal fungal assemblages — S.P. Schechter, T.D. Bruns (2008)
• Microbial diversity and mineral composition of weathered serpentine rock of the Khalilovsky massif — I.V. Khilyas, A.V. Sorokina, et al. (2019)
• Serpentine soils affect heavy metal tolerance but not genetic diversity in a common Mediterranean ant — F. Frizzi, A. Masoni, et al. (2017)
• Microbial diversity in The Cedars, an ultrabasic, ultrareducing, and low salinity serpentinizing ecosystem — S. Suzuki, S. Ishii, et al. (2013)

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