The rosettes of 7 week old plants were placed in individual paper bags after microscopic imaging was
completed and dried at 70 °C for 3 weeks. Plant material was then ground to fine powder using
a 25mm steel bead and a mixer mill (Retsch, MM 301). Isotope composition was determined
using an ISOTOPE cube elemental analyzer coupled to an Isoprime 100 isotope ratio mass
spectrometer (both from Elementar, Hanau, Germany) according to (Gowik, Bräutigam, Weber,
Weber, & Westhoff, 2011). The carbon isotope ratio is expressed as ‰ against the Vienna Pee
Dee Belemnite (VPDB) standard.
Plants were grown for 7 weeks in growth chambers (one per block) under the following conditions: 16 hr light; 95μmol s−¹mm−² light intensity; and 20°Cday‐and 18°C night temperature. Plants were watered twice a weekand trays shuffled and rotated every two to three days to accoun tfor variable conditions within the chambers