Selection of tree species for forests under climate change: is PSI functioning a more effective predictor for net photosynthesis and growth than PSII?

Selection of tree species for forests under climate change: is PSI functioning a more effective predictor for net photosynthesis and growth than PSII? Pollastrini Martina, Salvatori Elisabetta, Fusaro Lina, Marzuoli Riccardo, Brueggemann Wolgang, Bussotti Filippo Chlorophyll Fluorescence (ChlF) is widely applied to assess stress conditions and vitality of plants, both in experimental conditions, open field and remote sensing. ChlF reflects the events of the first phase of the photosynthetic process (the efficiency of the electron transport chain, ETC). Not necessarily the reductant produced (NADPH) are employed for carbon fixation. The most widely used parameter is the “maximum quantum yield of primary photochemistry”, expressed as FV/FM. There are only limited evidences about the relations of FV/FM (as well other parameters from direct and modulated fluorescence) with real photosynthetic performance (Pn) and growth. Here, we utilize a common garden experiment to assess the suitability of selected JIP-test (direct fluorescence) parameters as predictor for Pn and growth. Methods A common garden was established in April 2017 in Santa Anatolia di Narco (Perugia, Central Italy). Set-up: 1-year old seedlings of Quercus ilex L. (QI), Quercus pubescens Willd. (QP) and Quercus frainetto Ten. (QF) originated from acorns collected in selected forests in Italy and Greece, were assessed. 210 seedlings for each species and provenance (Italy, IT; Greece, GR) were planted (1260 seedlings in total). Parameters assessed: Plant height (H), Specific Leaf Area (SLA), leaf gas exchange (net carbon assimilation, PN, stomatal conductance GS, measured with gas analyzer CIRAS 2, PP System), chlorophyll a fluorescence (Prompt Fluorescence, PF, assessed with HandyPEA fluorimeter, Hansatech), Modulated Reflectance (MR) of Photosystem 1 (assessed with MPEA, Hansatech Inst). Results The physiological state of the plants is assessed with the JIP-test parameters FV/FM and ΔVIP. Significant differences were observed between species but not between provenances. In the first year of the experiment (2017), no differences between species and provenances were detected for FV/FM. ΔVIP was in Q. frainetto with respect to the other species. In the second year (2018) also FV/FM was depressed in Q. frainetto. Considering all the three species together, ΔVIP (but not FV/FM) is positively (significantly) correlated to longitudinal growth and net photosynthesis (Pn). Positive (highly significant) correlation between ΔVIP and the Modulated Reflectance (MR) parameter Vred confirms that the thermal phase in connected to the content of PSI.