Measurements of photosynthesis and respiration
Measurements of photosynthetic capacity were made using a LiCor LI-6400 infra-red gas analyser, at a temperature of 20°C in an atmosphere of 2000 µl l-1 CO2 flow rate 200 cm-3.min-1, and an irradiance of 2000 µmol m−2 s−1 provided by a warm white LED (colour temperature 2800–3200 K). Leaves were illuminated for 30 mins to fully induce photosynthesis before a measurement was recorded. The light was then switched off to allow an estimate of the dark rate of gas exchange. Measurements of photosynthesis and respiration under growth conditions were carried out using the same gas analyser, in the growth cabinet where plants were grown, using ambient air conditions. The gas analyser was placed in the cabinet and allowed to equilibrate for at least 1 hour prior to any measurements. The analyser chamber was placed to give a light intensity in the chamber equivalent to that of plants during growth. Respiration was measured by interrupting illumination, covering the plant and analyser chamber with aluminium foil. All measurements were performed between the 5th and 6th hour of the photoperiod. Data were analysed using an analysis of variance, followed by a Tukey post-hoc tests in SPSS (IBM).