WSC2018 Talks: ISBW044 - Twenty-two years of photosynthetic measurements using PAM fluorometry

Presented by Prof Sven Beer Tel Aviv University, Israel Recorded on 13 June 2018 Abstract Our research groups bought some of the first water-proof PAMs (Walz Diving-PAMs, and later the Aquation in situ Fluorometers), and have used them extensively. Looking back, we would now like to summarise some of our principal findings regarding their usefulness in seagrass research:  Electron-transport rates (ETR) correlate well with oxygen evolution (i.e. ~1 mol O2 evolved from PSII / 4 mol e- transported) in thin-bladed species, using an easily obtained absorption factor (AF), whereas other forms often show O2/ETR less than 0.25.  Rapid light curves (RLC), whether based on true ETRs or relative rates, is a good indicator of photosynthetic responses to different light fields, e.g. along depth gradients or diurnally.  If RLCs are initiated immediately after darkening a leaf, the first Y-reading of the RLC (Y0) equals the maximal effective quantum yield, α. Thus, α does not have to be calculated from the initial slope of an RLC.  If the effective quantum yields (Y, =change in F/Fm’) are less than 0.1 (often the case at high irradiances), they are unreliable.  Maximal quantum yields (Y, =Fv/Fm) can be good indicators of plant “health”, and effective quantum yields (Y, =change in F/Fm’) in light can nicely predict e.g. desiccation damage to seagrasses.  Our best use of the Diving-PAM relates to photosynthetic responses to various irradiance regimes.  Using in situ approaches, we have found good correlations between diurnal ETRs and O2 exchange of seagrass communities. Detailed guidelines on the use of PAM fluorometry for seagrasses are given in “Photosynthesis in the Marine Environment” (2014, Wiley-Blackwell).