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Maternal effects and environmental filtering shape seed fungal communities in oak trees

Tania Fort, Charlie Pauvert, Amy E. Zanne, Otso Ovaskainen, Thomas Caignard, Matthieu Barret, Stéphane Compant, Arndt Hampe, Sylvain Delzon, Corinne Vacher

Preprint posted on July 03, 2019 https://www.biorxiv.org/content/10.1101/691121v1

What could shape the fungal communities in seeds? Fort et al. investigate the seed mycobiome of sessile oaks across different locations and reveal maternal and environmental effects.

Selected by Kiran Gurung

Categories: ecology, microbiology

Acorns of sessile oak (Source: Penny Mayes; under CC BY-SA 2.0)

 

 

Background and idea of the preprint:

Seeds serve as  residence for a number of microorganisms. Fungi are one of the microbial members that colonize a seed early on during its life cycle. Generally, fungi provide a multitude of benefits to their host such as nutrient provision, protection against pathogens etc. The fungal microbes that associate with the seeds shape their ecology, their life history and further act as a deciding factor for their overall survival. Given the fact that a substantial sphere of global biodiversity is composed of microbes, they have a great impact on the forest ecosystem.

In this preprint, the authors collected seeds (acorns) of sessile oak from canopies and from the ground across different elevations. They sampled fungal communities using a sequencing approach and used a model called Hierarchical Models of Species Communities to examine the effect that various factors may play in shaping the microbial communities in these seeds. Using microscopy, the authors also checked for the presence of fungi on the inner and external surface of the acorns.

Fungal communities were present on both the external and internal fruit surface implying that fungi are a key component in shaping the ecology of the fruits. Fungal communities differed significantly in the acorns of canopy and in the ground. Importantly, the acorns in the ground were influenced significantly by the soil associated fungi. Due to the difference in the seed fungal microbiome of canopy and the ground, the fall of the fruit plays a pivotal role in shaping fungal composition.
Fungal communities also differed across different populations of trees, not just between trees at different elevations but also between those at the same elevation, thus suggesting a strong maternal effect. Due to this maternal effect, the acorns not only transmit resident microbiomes but also the pathogens.

Key findings:

  • Seeds are the foundation for fungal acquisition from the parent tree.
  •  Parent trees have an impact on shaping the microbial colonization of their seeds and subsequently the fruits by transmitting both pathogens and pathogen antagonists.
  • With the elevation, there is variation in the fungal community composition of the seeds.

 

Why do I think this work is important?

It is well known that forests are  essential parts of the ecosystem and the species they host make up a huge part of biodiversity. But trees start harbouring a number of species as early as their germination stage, a time when they encounter microorganisms. However, several questions remain unclear, such as: what kind of influence do these microorganisms pose on the seeds? Do they help in shaping both the early and later phase of life history traits in these trees?

This study is a starting point to begin thinking about how a seed lays the foundation for development of the microbial communities and vice versa. While earlier studies have reported such phenomenon in crop plants where the seeds acquire both pathogens and their enemies , this is one of the first and very few studies to report a similar phenomenon in wild plants of the forest ecosystem.

Questions for the authors:

  • Was there any kind of difference in abundance of ascomycetes and basidiomycetes across the individual tree as well?
  • Why did you keep the ASVs belonging to ascomycetes and basidiomycetes? Were these the only 2 phyla present in your samples?
  • How do the non-pathogenic fungi influence the life history of these acorns in plants?
  • Were the authors able to examine and/or speculate if the internal surface of the fruit had any overlap with the fungal communities of the soil?

Tags: ecology, fungi, microbes

Posted on: 9th August 2019 , updated on: 13th August 2019

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