Circadian rhythms have significant effects on leaf-to-canopy scale gas exchange under field conditions

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Table 1 Quantification of the circadian-driven range in variation of diurnal gas exchange

Process	Species	Scale	Variation during entrainment			Variation during constant conditions			% clock-driven variation
Process	Species	Scale	Max (SE)	Min	Max-Min	Max (SE)	Min (SE)	Max-Min	% clock-driven variation
Carbon assimilation	P. vulgaris	Leaf (μmol m⁻² s⁻¹)	19.30 (0.97)	0	19.30	15.67 (0.66)	7.79 (0.63)	7.88	40.83
	P. vulgaris	Ecosystem (μmol m⁻² s⁻¹)	14.21 (0.37)	0	14.21	13.92 (0.32)	11.12 (0.30)	2.79	19.67
	G. hirsutum	Leaf (μmol m⁻² s⁻¹)	16.32 (1.42)	0	16.32	14.00 (0.80)	5.13 (0.84)	8.87	54.35
	G. hirsutum	Ecosystem (μmol m⁻² s⁻¹)	13.38 (1.11)	0	13.38	12.51 (0.91)	7.48 (0.90)	5.03	37.63
Water fluxes	P. vulgaris	Leaf (conductance, mol m⁻² s⁻¹)	0.48 (0.04)	0	0.48	0.43 (0.03)	0.05 (0.03)	0.38	79.17
	P. vulgaris	Ecosystem (l h⁻¹)	0.40 (0.07)	0	0.40	0.37 (0.03)	0.25 (0.03)	0.12	28.39
	G. hirsutum	Leaf (conductance, mol m⁻² s⁻¹)	0.22 (0.02)	0	0.22	0.21 (0.01)	0.05 (0.01)	0.16	72.73
	G. hirsutum	Ecosystem (l h⁻¹)	0.39 (0.04)	0	0.39	0.39 (0.03)	0.14 (0.03)	0.25	64.55

The variation in fluxes attributable to the clock in Fig. 1 was derived from the ratio between the range (maximum value predicted by generalized additive mixed model (GAMM) analysis minus minimum GAMM predicted value) in each flux while keeping environmental conditions constant (the last 48 h shown in Fig. 1), divided by the range during the entrainment phase (first 24 h in Fig. 1). Although nocturnal stomatal conductance and transpiration were always above 0 during entrainment, even during dark periods, we forced their minimum to be zero for this calculation. This increased the magnitude of the variation during entrainment, thus leading to under-estimations of the % variation attributable to the clock. Nocturnal carbon assimilation was also fixed at 0, because no C assimilation occurs in the dark

ISSN: 2047-217X