### 2.18.6.1. Response of C expenditure to Nitrogen uptake cost[¶](#response-of-c-expenditure-to-nitrogen-uptake-cost "Permalink to this headline")

The environmental cost of Nitrogen (\\(N\_{cost,tot}\\)) is used to determine \\(\\gamma\_{FUN}\\).

> \\\[\\gamma\_{FUN} = max(0.0,1.0 - (N\_{cost,tot}-a\_{cnflex})/b\_{cnflex})\\\]

where \\(a\_{cnflex}\\) and \\(b\_{cnflex}\\) are parameters fitted to give flexible C:N ranges over the operating range of N costs of the model. Calibration of these parameters should be subject to future testing in idealized experimental settings; they are here intended as a placeholder to allow some flexible stoichiometry, in the absence of adequate understanding of this process. Here \\(a\_{cnflex}\\) operates as the \\(N\_{cost,tot}\\) above which there is a modification in the C expenditure (to allow higher C:N ratios), and \\(b\_{cnflex}\\) is the scalar which determines how much the C expenditure is modified for a given discrepancy between \\(a\_{cnflex}\\) and the actual cost of uptake.

