Fig. 6.

Plots for root tip CO₂ (^RP_CO2 in kPa) and soil core radius (rad_s) from which CO₂ enters roots in waterlogged soil as predicted using the model presented in Appendix 3a, for a range of values of D_soil/D₀, and the following conditions: root length = 100 mm, site of entry into the root only the 10-mm root tip, CO₂ production rate = 30 × 10⁻¹² mol cm^–3 soil s^–1, root fractionial porosity = 0·35. This is the combination of soil and plant characteristics shown in column 2 of Table 3. The substantial effects of D_soil/D₀ (i.e. the product of soil porosity and tortuosity) on ^RP_CO2 at the combination of soil and plant characteristics used would also apply to other combinations of characteristics of the soil–plant system (shown in Table 3); the magnitude of the effects on ^RP_CO2 will differ in degree, but not in kind.