Table I. Parameters from Laisk curves used to model rates of cyclic electron flow.

CO₂ assimilation rates measured at subsaturating light intensities (Laisk curves) were used to determine Γ*, rates of R_d, and CO₂ assimilation at 36 Pa of CO₂ and 1,000 μmol m⁻² s⁻¹ PPFD. V_cmax was determined from the linear portions of photosynthetic CO₂ response curves measured under 1,000, 377, 210, 120, 66, and 24 μmol m⁻² s⁻¹ PPFD. Measurements were made in hydroponically grown plants starved of all nitrogen for 24 h and then fed either NO₃⁻ or NH₄⁺ as the sole nitrogen form. Values shown are averages of five separate plants ± se. There were no significant differences in any values as determined using Student’s t test with P < 0.05.

Parameter	NO3− Feeding	NH4 Feeding
Γ* (Pa of CO2)	4.11 ± 0.25	3.91 ± 0.25
Rd (μmol CO2 m−2 s−1)	0.41 ± 0.03	0.57 ± 0.10
CO2 assimilation at 36 Pa of CO2 (μmol CO2 m−2 s−1)	9.6 ± 0.8	9.9 ± 0.9
Vcmax (μmol CO2 m−2 s−1)
1,000 μmol m−2 s−1 PPFD	31.6 ± 3.1	32.4 ± 3.3
377 μmol m−2 s−1 PPFD	27.3 ± 2.1	28.7 ± 3.2
210 μmol m−2 s−1 PPFD	23.3 ± 1.9	25.5 ± 1.6
120 μmol m−2 s−1 PPFD	14.4 ± 1.5	15.2 ± 1.1
66 μmol m−2 s−1 PPFD	7.6 ± 0.6	9.4 ± 1.2
24 μmol m−2 s−1 PPFD	1.8 ± 0.5	2.2 ± 0.5