In this work we propose some fluorescense tests, based on a fast data acquisition (10 us per data point with 12 bit resolution) over five orders of magnitude in time (10 us to 1s) with an optoelectronic shutterless instrument (Plant Efficiency Analyser - PEA), to evaluate the response of micropropagated cork oak plantlets with or without mycorrhiza, in vitro and ex vitro conditions. Indexes have been defined which indicate the activity, efficiency, stress resistance, adaptability and developmental complexity of a plant. The shape of the observed fluorescence transient (on a logarithmic time scale) showed the typical Fo-J-I-P levels. The results obtained showed that mycorrhization increases the quantum yield of photochemistry as well as the electron transport and the photosynthetic metabolism. The density of photosynthetic units per leaf area is highly increased in mycorrhized plantlets. Therefore the productivity per leaf area is increased in these plantlets as well. During acclimatization mycorrhized plantlets show a much higher general fitness than non-mycorrhized plantlets in relation to the defined indexes.