Table 1.

Leaf trait and gas exchange parameters of C. squarrosa measured under the same environmental conditions as during growth (leaf temperature 25 °C, PPFD 800 μmol m⁻²s⁻¹, [CO₂] 390 μmol mol⁻¹, VPD 0.8 kPa for V1 and 1.6 kPa for V2)

Plants were grown at low or high N fertilizer supply (N1 or N2) combined with low or high VPD (V1 or V2). Leaf trait parameters include N content per unit dry mass (N_mass, % DM) and per leaf area (N_area, g m⁻²), and specific leaf area (SLA, cm² mg⁻¹). Gas exchange parameters: net CO₂ assimilation rate (A, μmol m⁻² s⁻¹), transpiration rate (E, mmol m⁻² s⁻¹), stomatal conductance to water vapor (g_s, mol m⁻² s⁻¹), respiration rate in light (R_L, μmol m⁻² s⁻¹), the ratio of internal to atmospheric CO₂ concentration (C_i/C_a), instantaneous water use efficiency (WUE_ins=A/E, mmol mol⁻¹), and intrinsic water use efficiency (WUE_i=A/g_s, μmol mol⁻¹). Data are shown as mean±SE (n=6 for R_L, n=9–10 for the other parameters). Significant treatment effects (P<0.05) are shown in bold.

	N1		N2		P-value
	V1	V2	V1	V2	N	VPD	N×VPD
Nmass	2.4 ± 0.1	2.4 ± 0.1	3.0 ± 0.1	3.0 ± 0.2	0.01	0.81	0.79
Narea	1.2 ± 0.2	1.3 ± 0.2	1.6 ± 0.2	1.6 ± 0.2	0.06	0.82	0.92
SLA	0.21 ± 0.02	0.20 ± 0.02	0.21 ± 0.02	0.21 ± 0.02	0.91	0.82	0.85
A	14.8 ± 0.9	13.1 ± 0.9	14.9 ± 0.9	12.3 ± 1.0	0.81	0.03	0.58
E	0.93 ± 0.08	1.14 ± 0.09	0.93 ± 0.08	1.23 ± 0.09	0.69	0.01	0.60
g s	0.10 ± 0.01	0.08 ± 0.01	0.11 ± 0.01	0.07 ± 0.01	0.69	0.01	0.45
R L	0.81 ± 0.26	0.62 ± 0.30	0.53 ± 0.10	0.51 ± 0.10	0.36	0.62	0.71
C i/Ca	0.35 ± 0.03	0.26 ± 0.04	0.35 ± 0.03	0.25 ± 0.04	0.93	0.01	0.91
WUEins	15.9 ± 0.6	11.7 ± 0.6	16.8 ± 0.6	10.0 ± 0.6	0.82	0.01	0.04
WUEi	153 ± 9	173 ± 9	154 ± 9	178 ± 10	0.79	0.02	0.82