Fig. 1.

Experimental design and time course of the experiment. After a 1-year acclimation period, the vegetation was cut at 5 cm height (14 March) and the monoliths were submitted to four climatic scenarios: ambient (aCO₂: 390 ppm, blue) or elevated (eCO₂: 520 ppm, red) atmospheric CO₂ concentration, combined with an extreme climatic event (390 ECE and 520 ECE) or without ECE (390 Con and 520 Con). The ECE included a reduction in precipitation by 50% during 4 weeks in midsummer (25 June to 21 July: D1) followed by 2 weeks (22 July to 4 August: D2) with no irrigation and a concomitant heat wave (+3.4 °C compared with the projected 2050s average). Thereafter, the precipitation was gradually increased. The vegetation was cut at 5 cm height again on 26 April, 9 June, and 3 November. Leaf meristematic tissues were sampled at D1 (21 July) and D2 (4 August).