Photosynthetic traits to select tree species for forest adapted to climate change:photosystem I says more than II

Maximum quantum yield of primary photochemistry (FV/FM) is a common chlorophyll fluorescence parameter to assess photochemistry performance of photosynthetic organisms. It is used as proxy of photosystem II (PSII) efficiency and plant vitality. PSII, however, resulted quite robust to some stress factors. Evidences on the relationships between FV/FM and plant performance (photosynthesis, growth) are limited or contradictories. This contribution reports a study performed in a common garden in central Italy aimed to test the performance of oak species seedlings (Quercus ilex, QI, Q. pubescens, QP, Q. frainetto, QF). Italian and Greek provenances of these species were tested. Seedlings performance was monitored two years, measuring plant height, leaf gas exchange (net photosynthesis Pn, stomatal conductance Gw), prompt chlorophyll fluorescence (PF) and Modulate Reflectance at 820 nm (MR) of the photosystem I (PSI). The results of PF indicate a stable functionality of PSII (expressed with FV/FM) across species and provenances and a decline in photochemistry functionality at the I-P phase (ΔVIP) in Q. frainetto, indicating thus a decline of the content of PSI in this species. This result was confirmed by the findings of MR analysis, being the speed of reduction and subsequent oxidation of PSI (VRED and VOX) strongly correlated to the amplitude of ΔVIP. The photosynthetic rates (Pn) and growth were correlated with the parameters associated with PSI content and function, rather than those related to PSII. The low performance of Q. frainetto in the common garden seem to be related to early foliar senescence with the depletion of nitrogen, due to sub-optimal climatic and edaphic conditions. Chlorophyll fluorescence analysis allows to discriminate populations of oak species and to individuate the less (or/and best) suitable species for future forest ecology and management purposes.