Photosystem II efficiency was measured with FluorPen FP100
(Photon Systems Instruments, Brno, Czech Republic), which allows
a non-invasive assessment of plant photosynthetic performance by
measuring chlorophyll a fluorescence. FluorPen quantifies the
quantum yield of photosystem II as the ratio between the actual
fluorescence yield in the light-adapted state (Fv) and the maximum
fluorescence yield in the light-adapted state (Fm), according to
Oxborough and Baker (1997). Measurements of stomatal conductance
and photosynthetic efficiency were taken in the 2nd
youngest leaf of two different plants of each treatment