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).