Future challenges in coupled C-N-P cycle models for terrestrial ecosystems under global change: a review

Climate change has consequences for terrestrial functioning, but predictions of plant responses remain uncertain because of the gaps in the representation of nutrient cycles and C-N-P interactions in ecosystem models. Here, we review the processes that are included in ecosystem models, but focus on coupled C-N-P cycle models. We highlight important plant adjustments to climate change, elevated atmospheric CO2, and/or nutrient limitations that are currently not-or only partially-incorporated in ecosystem models by reviewing experimental studies and compiling data. Plant adjustments concern C:N:P stoichiometry, photosynthetic capacity, nutrient resorption rates, allocation patterns, symbiotic N-2 fixation and root exudation (phosphatases, carboxylates) and the effect of root exudation on nutrient mobilization in the soil rhizosphere (P solubilization, biochemical mineralization of organic P and priming effect). We showed that several plant adjustments could be formulated and calibrated using existing experimental data in the literature. Finally, we proposed a roadmap for future research because improving ecosystem models necessitate specific data and collaborations between modelers and empiricists.