Intercalibration of fluorimeters and comparability of results

This work describe the results of an intercalibration exercise carried out in June 2007 at Passo Pura (Udine, Italy). Five Handypea and one MiniPAM provided from different working groups participated in order to verify the comparability of the results. Before starting the exercise each instrument was fitted with the same measurement conditions (intensity of illumination, gain). Each participant took the measurements on the same leaf clip. Ten plants. with four leaf clips, were used. The results evidenced a quite high different sensitivity in recording the values of F0 and FM also among Handypea fluorimeters (CV,coefficient of variation = 23% for F0 and 20% for FM), but the ratio F0/FM was less variable (CV = 8%). FV/FM was quite stable also in the comparison between Handypea and MiniPAM (CV= 4.6 %), as well as the parameters calculated on the normalized transient curves. The highest CV was detected for the Performance Index (PIabs, CV = 30%; CV=12% if considering the Driving Foreces (Log PIabs). From an operational point of view, if different instruments are used in a same campaign of measurement, one should be checked and compared before starting the measurements; FV/FM allows the better comparison even with different measurement conditions (e.g. different instruments, different settings). Normalized transients are less variable (and comparable) than the raw ones; Driving Forces allow a better comparison tha PIabs.