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

Abstract

The allocation of resources to roots and shoots can greatly alter total plant mass. Allocation is thought to be the consequence of growth processes (i.e uptake rates, transport rates, growth rates) and the communication between them via signalling mechanisms. Feedbacks that alter growth processes 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 resources. The model reflects 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 known signalling mechanisms are sufficient to reproduce experimentally observed responses to external resource availability. Model simulations highlight key areas of uncertainty where more empirical data is needed. In particular, quantitative data is needed to establish the strengths and rates at which feedback responses to carbon and nitrogen substrate concentrations alter growth and uptake rates.