Fig. 4.

Simulation of McCree's equation [eqn (2); McCree, 1970]. A 12-h daylength is applied followed by 12-h darkness. In (A), (B) and (C), light during the day was varied from a low value to 1000 J (PAR) m⁻² s⁻¹ (4600 µmol PAR m⁻² s⁻¹). Two values of utilization rate constant k_S were applied, giving high and low substrate plants. Plants are in 24 h exponential growth, attained after 10 d from low initial values (Table 1a). (A) McCree's formulation [eqns (1), (2); McCree, 1970] is followed. (B) Slopes of the lines in (A) are calculated numerically. (C) The fraction of 24 h respiration occurring during the night is calculated assuming eqn (13) for respiration R is valid during the day and night [eqns (47)]. (D) Time courses of the substrate fraction are illustrated for a daytime light flux density of I₀ = 100 J (PAR) m⁻² d⁻¹ (460 µmol PAR m⁻² d⁻¹). Specific 24-h respiration ρ_24h and specific daily gross photosynthesis π_g,day are calculated in eqns (48). The vertical dashed lines labelled μ = 0 in (A), (B) and (C) indicate where daily specific growth rate μ = 0.