Fig. 5.

Diurnal gas-exchange responses of Bulnesia retama stems over a 15-day period, during which severe and then moderate drought treatments were imposed on initially well-watered plants. Diurnal net CO₂ assimilation rate (A), stomatal conductance (g_s) and the ratio of intercellular to ambient CO₂ partial pressure (C_i/C_a) over a 15-day period of controlled water stress with 13 h light–11 h dark photoperiod from one representative glasshouse-grown B. retama plant in drought trial 2. The experiment began at 12:00 h on day 0. The plant was given water each day at 10:00 h; 1.5 L of water on the first 2 days, decreasing to 250 mL over 5 days in 250 mL increments on each day until day 7, and 500–750 mL thereafter. White arrows indicate days when the plants received an additional 250 mL above the regular 500 mL of water owing to low photosynthetic rates indicative of drought stress. Black arrows represent plant ${\mathrm{\Psi }}_{\mathrm{w}}$ values measured at 07:00 h, which are indicated in megapascals. The grey dashed line in the C_i/C_a panel indicates 1.0. See Supplementary Data Table S3 for summaries of gas-exchange values at 0:00, 10:00, 12:00, 14:00 and 18:00 h. Grey shading indicates the mocturnal periods.