Redundancy and independence of chlorophyll fluorescence (JIP-test) parameters in plant ecological studies

The analysis of prompt fluorescence (PF) of chlorophyll is a powerful tool that joins the richness of information with the operational quickness. This technique is especially suitable in large ecological surveys, where it is required to screen many samples in brief time to cope with the variability of environmental conditions. The so-called JIP-test (Strasser et al., 2004) proposes many parameters that describe the different phases of the photochemical processes in terms of energy absorption, trapping and electron transport. To effectively describe the photosynthetic responses in samples in a field survey, one of the problems in the application of the JIP-test is the selection of the most suitable parameters to capture their intrinsic variability. In this presentation we re-analyse 11 large datasets obtained in past researches. Six of these researches were carried out in field conditions(forests and pasture meadows), and 5 in experimental setups. The aim was to explore the relationships (redundancy and independence) among the JIP-test parameter by applying the Principal Component Analysis (PCA). A total of about 35,000 measurements was considered for analysis. The overall PCA results evidenced, in almost all cases, that the variability is explicated mainly by two factors, connected respectively to the processes of photon capture and first photochemical events (Factor 1), and the I-P phase (Factor 2). This result suggests that, in ecological studies, the photosynthetic behaviour of the member of a population can be effectively described with Fv/Fm and ΔVIP. The correlations between Fv/Fm and ΔVIP in the various datasets displayed different signs, being positive or negative in relation to the environmental factors considered in each singular survey. This result confirms the independence of the two parameters examined and suggests the presence of a down-regulation mechanism between trapping capacity and overall efficiency to feed the end-acceptors beyond the photosystem I.