Table 2.

Mean photosynthetic water use efficiency (mmol CO₂ mol⁻¹ H₂O) for young fully expanded leaves of Aechmea ‘Maya’ under ambient (380 μmol mol⁻¹) and elevated (700 μmol mol⁻¹) CO₂ concentrations

CO2 (μmol mol−1)	Phase I 2200–0600	Phase II 0600–0900	Phase IV 1800–2200*	Total 24 h 1200–1200
380	13·1 ± 1·3	5·7 ± 0·8	6·6 ± 1·2	7·4 ± 1·2
700	24·7 ± 3·0	16·6 ± 1·0	24·6 ± 4·2	15·3 ± 2·8
P-value	<0·05	<0·05	<0·05	<0·05

Because no net CO₂ uptake occurred during phase III, WUE was not calculated for this period. The data are means ± s.e. for five leaves, each from a separate plant and were compared for each phase between the two treatments by two-sample t-test (α = 0·05).

*Due to elevated CO₂ phase IV extended by starting 3 h earlier at 1500 h compared with controls.