Implementing a framework of carbon and nitrogen feedback responses into a plant resource allocation model

Theallocation of resources to roots andshootscangreatlyalter total plant mass. Allocation is thought to be the consequenceof uptake rates, transport rates, and growth rates and the communication between them via signalling mechanisms. Feedbacks that alter resource uptake and use are induced in nature by changes in the internal pools of carbon and nitrogen, but how these function together to define allocation remains unclear. We introduce a framework model of internal feedback responses to changes in plant carbon and nitrogen concentrations. We evaluate how well the model responds to changes in carbon and nitrogen availability by simulating external environmental perturbations that influence the uptake of carbon andnitrogen. Themodelreflects experimental results when looking at the effect of atmospheric CO2 and soil nitrogen concentrations on total plant mass and replicates observed responses to leaf defoliation events. Overall, this shows that a combination of knownsignallingmechanismsaresufficienttoreproduceexperimentallyobservedresponsestoexternalresourceavailability.Modelsimulations highlight key areas of uncertainty where more empirical data are needed. In particular, quantitative data are needed to establish the strengths and rates at which feedback responses to carbon and nitrogen substrate concentrations alter growth and uptake rates.