2.7. Gas exchange, chlorophyll a fluorescence, chlorophyll content Gas exchange, chlorophyll a fluorescence and chlorophyll con-tent were determined on recent, fully-expanded leaves selected from July to September, about once per month in 2014 and 2015.Measurements were taken on one single leaf per plant. Leaves were selected on the central part of the canopy. Net photosynthesis(Pn), stomatal conductance (gs), transpiration (E) and intercellular CO2 concentration (Ci) were determined simultaneously on leave susing a LC Pro (ADC Bio Scientific Ltd. United Kingdom) portable infrared gas an alyser (IRGA). The IRGA was equipped with a leaf-clamped cuvette covering 6.25 cm 2 of leaf area, and measurements were taken with constant photosyn the tically active radiation setby a LED light unit at 1100 mol m−2s−1and under field con-ditions for all other parameters (i.e. inlet relative humidity wasaround 25%, and chamber temperature ranged from 20.1 to 29.3◦C).The measurements were carried out between 10:00 a.m. and 3:00p.m. (solar time). Chlorophyll a fluorescence was measured usinga Fim 1500 chlorophyll fluorometer (ADC Bio Scientific Ltd. United Kingdom). The initial fluorescence yield (F0), the variable fluorescence (Fv), and the maximum fluorescence yield (Fm) were assessed in leaves that were dark-adapted for 30 min. The maximum PSII efficiency was calculated according to the methods described by Maxwell