3.6. Chlorophyll content, gas exchange, chlorophyll a fluorescence The concentration of leaf chlorophyll (expressed as SPAD units)increased during the 2014 season. A higher chlorophyll concentration was measured during the whole 2014 season for plants on silt loam soil compared to plants on the peat treatment on the SY location while differences were less intense on the FR location. Overtime, differences in chlorophyll concentration attenuated in 2015(Fig. 3).