Understanding the chemical ‘language’ of plants and seaweeds under climate change

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By Milthon Lujan

UK – A new paper highlights a ‘missing’ link and novel aspect of studying plant and seaweed responses to climate change by considering the chemical communication of plants and seaweeds with their associated complex communities of microbes.

The concept of a ‘holobiont’ describes an entire cluster of species including both an individual host like plant or seaweed and all of the microorganisms that are associated with it. This allows researchers to take into account many additional factors that could influence and affect the entire entity.

One very important and less studied factor is how certain chemical compounds released by the microbes and hosts can facilitate communication between the species. These infochemicals can be intentionally released to supply specific information, or unintentionally released, but still offer information to surrounding organisms.

In plants, the researchers, from Institut Armand Frappier, Montreal, and PML, highlighted the crucial importance of the rhizosphere, the area of soil surrounding the roots. Here, millions of chemical compounds are exchanged between the plant and its microbiota, spreading out into the soil. Some help to maintain soil health, promote plant growth and drive resistance to harmful pathogens.

On the surface of seaweeds, a ‘second skin’ of microbes together with the seaweed surface creates a hotspot for chemically-mediated ecological interactions. The authors proposed a new term for this layer, and its equivalent on organisms like sponges and corals: the ‘eco-chemosphere’. The infochemicals here can guide the interactions of bacteria and infochemicals from the surface of seaweeds could also act as a chemical defence against microbial colonizers, as could other microbes living on the surface.

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Climate change stressors, such as warming and increased carbon dioxide, can alter both the production and composition of infochemical, with profound effects on entire ecosystems.

In the plant holobiont, stress can alter the shape of the roots and the chemicals released by them, affecting the surrounding microbiota. The microbial chemical compounds are themselves changed by stressors, influencing the health of their plant host.

As ocean acidification increases, marine infochemicals can lose functionality, while increasing temperatures make diseases a greater threat to heat-stressed corals. The impact of climate change on the seaweed holobiont, however, remains underexplored.

Taking this wider view of host organisms with all of the microorganisms that live on or around them offers insights to the many ways that a changing climate is affecting ecosystems around the world, but there are many unknowns when it comes to the complex chemical communication happening between them all.

Dr Mahasweta Saha, study author and PML Marine Chemical Ecologist, said: “We can see infochemicals as the ‘missing link’ in understanding how plant and seaweed holobionts are responding to climate change. This research sets the basis for improving our knowledge of holobiont responses to climate change stress right across both terrestrial and aquatic ecosystems.”

Reference (free access):
Ruth Schmidt and Mahasweta Saha. 2020. Infochemicals in terrestrial plants and seaweed holobionts: current and future trends. New Phytologist. https://doi.org/10.1111/nph.16957 

Source: Plymouth Marine Laboratory (PML) 

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