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Thinking outside the box?

How well plants – and plant-like organisms – will function with forecast elevated levels of atmospheric CO2 – and the attendant increases in temperature associated with climate change/global warming – is a legitimate topic of concern and subject for research investment. And, given the importance of marine phytoplankton organisms to global productivity, understanding how those phytoplankters might be impacted by increased CO2 concentrations is of paramount importance.

Cyanobacteria responding well to warming in Roman Bath.
Cyanobacteria responding well to warming in Roman Bath.

Work by David Hutchings et al. reveals that growing the N(nitrogen)-fixing marine cyanobacterium (OK, bluegreen alga if that makes this item more acceptable to the hard-core botanists amongst you) Trichodesmium erythraeum strain IMS101 in elevated levels of CO2 (780 ppm – designed to mimic those anticipated in 2100 AD/CE) caused increases in both N-fixation and growth rate that were not reversed when the organism was subsequently transferred to present-day (380 ppm) CO2 levels.[*]

Because of the major role that Trichodesmium plays in the marine environment, the team speculate that such permanent alterations to the microbe’s physiology are likely to have dramatic effects on biogeochemical nutrient cycling and foodweb ecology in the world’s oceans in a future where CO2 concentrations are higher. Which is fine and helps to put the research into context, but I think there’s an overlooked terrestrial dimension here: what if this insight could be translated to other N-fixing microbes, but ones that live in mutual symbiosis with crop plants, such as legumes?

If suitably elevated-CO2-enhanced metabolising microbes could be inoculated into legume seeds and sown as one complete symbiotic unit we might solve several issues in one go. For example, we could enhance those crops’ growth rates – via enhanced microbial-provided N-supply – thereby increasing global food supply. Not only would this be of great benefit in areas where soil N levels are limiting (and thereby avoid the expense and associated environmental damage of adding ‘artificial’ N fertiliser), but would also increase draw-down of CO2 via enhanced photosynthetic C-fixation now, which, apart from ultimately fuelling the increase in growth, would also thereby remove some of the excess CO2 levels in the atmosphere. And we’d have crops that were to some extent ‘future-proofed’ if anticipated increases in CO2 come to pass.

Although the higher-CO2-exposed Trichodesmium also had higher growth rate in P(phosphorus)-limited conditions, whether our imagined legume crops would fare better in P-poor soil is questionable since I’m not aware that there is any transfer of P from microbe to host, but the other potential benefits make this an attractive idea. So go on, make it happen, my people![**]

* Such work also shows the benefits of research over time scales that permit evolution to operate. Here the cell lines were grown for 4·5 years under either present-day or elevated CO2 levels, followed by a further 2 years at 380 ppm CO2 for the latter group, rather than the much more usual time scales of a few weeks. Clearly patience brings its own rewards. But I bet the workers heaved a great collective sigh of relief that they’d found something suitably publication-worthy after such a long time!

** And just think what the future would hold if we could get cereals to nodulate with such enhanced-N-fixing bacteria!!!

[As interesting as Mr P. Cuttings’ notion is, I see at least two flies in the ointment. Do we know that the host legumes will still function in a future world of elevated atmospheric CO2 and increased temperatures? And traditional N-fixing legume symbionts – such as rhizobia species – are not CO2-photosynthesisers as for cyanobacteria. So is this terrestrial dimension really ‘blue skies’ research or merely ‘pie in the sky’? – Ed.]

Nigel Chaffeyhttps://www.bathspa.ac.uk/our-people/nigel-chaffey/
Nigel is a botanist and was a full-time academic at Bath Spa University (Bath, near Bristol, UK) until 31st July, 2019. As News Editor for the Annals of Botany he contributed the monthly Plant Cuttings column to that august international botanical organ (until March 2019). He remains a botanist and is now a freelance plant science communicator who continues to share his Cuttingsesque items with a plant-curious audience. In that guise his main goal is to inform (hopefully, in an educational, and entertaining way...) about plants and plant-people interactions.

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