Ecosystem theory for a new generation of vegetation and land surface models

IAIN COLIN PRENTICE CAhill

Leverhulme Wildfires Centre, Imperial College London, United Kingdom

c.prentice@imperial.ac.uk

Link to seminar: https://umontpellier-fr.zoom.us/webinar/register/WN_Scp6gs-OQIaZ9lwx_awJow

The role of land ecosystems in climate regulation is well established. Climate models represent the land-atmosphere exchanges of energy, water and carbon. Current land surface models (LSMs) are based explicitly on the leaf-level coupling between CO₂ uptake and water loss. Most use the Farquhar, von Caemmerer and Berry (1980) photosynthesis scheme. Yet despite these conmmonalities, LSMs give divergent predictions. Attempts to reduce this uncertainty have mainly yielded increased complexity. Moroever, complex models are usually treated as black boxes, which does not help.

    The reasons for this impasse are rooted in the sociology of ecosystem science. LSM development is increasingly concentrated in climate modelling centres (and generally relegated to a minor role). This enterprise is only tangentially engaged in the underlying science. On the other hand, despite surging interest in plant functional ecology, its practitioners have not focused on creating new theory for global models.

    The problem is acute for processes working on ecological (rather than physiological) time scales. Photosynthetic and respiratory acclimation are examples. Acclimated responses to environmental variables, notably temperature, can differ greatly from those seen in laboratory experiments. But thermal acclimation is still largely neglected by LSMs. On the other hand, the plant literature almost universally attributes the acclimation of photosynthetic capacity under enhanced CO2 to an incorrect mechanism, perpetuating a misconception among LSM developers about how nitrogen availability influences the land carbon sink.

    Eco-evolutionary optimality hypotheses are a broad class of ideas derived from the concept that plant traits must be focused, and/or closely coordinated with other traits, in resource-efficient ways – or suffer rapid elimination by natural selection. In today’s data-rich world, it is possible to devise tests of such hypotheses for each process, one by one, drawing on data from many or all climate zones. I will give examples of how this approach is transforming our understanding of the controls on stomatal behaviour, primary production, leaf and stem respiration, leaf economics, carbon allocation, phenology, and more.

Watch previous seminars on our YouTube channel: https://www.youtube.com/channel/UCrX4IsZ8WIFcDa0ZmC7rcQg