Carbon-phosphorus cycle models overestimate CO₂ enrichment response in a mature <i>Eucalyptus</i> forest.

Abstract

The importance of phosphorus (P) in regulating ecosystem responses to climate change has fostered P-cycle implementation in land surface models, but their CO₂ effects predictions have not been evaluated against measurements. Here, we perform a data-driven model evaluation where simulations of eight widely used P-enabled models were confronted with observations from a long-term free-air CO₂ enrichment experiment in a mature, P-limited <i>Eucalyptus</i> forest. We show that most models predicted the correct sign and magnitude of the CO₂ effect on ecosystem carbon (C) sequestration, but they generally overestimated the effects on plant C uptake and growth. We identify leaf-to-canopy scaling of photosynthesis, plant tissue stoichiometry, plant belowground C allocation, and the subsequent consequences for plant-microbial interaction as key areas in which models of ecosystem C-P interaction can be improved. Together, this data-model intercomparison reveals data-driven insights into the performance and functionality of P-enabled models and adds to the existing evidence that the global CO₂-driven carbon sink is overestimated by models.