Elevated carbon dioxide (CO2) can increase plant growth, but the magnitude of this CO2 fertilisation effect is modified by soil nutrient availability.

Predicting how nutrient availability affects plant responses to elevated CO2 is a key consideration for ecosystem models, and many modelling groups have moved to, or are moving towards, incorporating nutrient limitation in their models.

The choice of assumptions to represent nutrient cycling processes has a major impact on model predictions, but it can be difficult to attribute outcomes to specific assumptions in complex ecosystem simulation models.

Here we revisit the quasi-equilibrium analytical framework introduced by Comins and McMurtrie (1993) and explore the consequences of specific model assumptions for ecosystem net primary productivity (NPP).

This framework unlocked insights into the representation of plant nitrogen uptake, the response to priming and the down-regulation of NPP when nutrients are limiting.

Overall, our results highlight the fact that the quasi-equilibrium analytical framework is effective for evaluating both the consequences and mechanisms through which different model assumptions affect predictions.

  • Paper: Jiang, M., Zaehle, S., De Kauwe, M. G., Walker, A. P., Caldararu, S., Ellsworth, D. S., and Medlyn, B. E.: The quasi-equilibrium framework revisited: analyzing long-term CO2 enrichment responses in plant–soil models, Geosci. Model Dev., 12, 2069-2089, https://doi.org/10.5194/gmd-12-2069-2019, 2019.