The Application of Variable Chlorophyll Fluorescence to Microphytobenthic Biofilms

Abstract

The successful application of variable chlorophyll fluorescence methodology to higher plants and other phototrophs inspired workers in the 1990s to apply the methods to microalgal communities inhabiting benthic soft sediments, the microphytobenthos (MPB) of estuarine and other coastal habitats. It was quickly identified that particular aspects of the physiology (cellular vertical migration within the sediment matrix), photophysiology (high capacity for down regulation, e.g. NPQ, and chlororespiration in the dark) and the effects of the physical structure of the sediment/biofilm matrix (light attenuation by the matrix itself) confounded the interpretation of fluorescence information obtained. In this chapter, the authors attempt to explain these and other issues pertinent to MPB biofilms and to summarise how methods have been developed to alleviate the problems encountered. Although much work is still needed to fully understand fluorescence data for the MPB, studies to date have been highly illuminating with regard to rhythms of productivity, photoacclimatory mechanisms and the behavioural ecology and physiology of MPB at an integrated biofilm level and at a cellular level. This chapter therefore introduces benthic biofilms and relevant specific fluorescence methodological issues, expands on subsurface fluorescence signal and migration, discusses down regulatory nonphotochemical quenching (NPQ) resulting from xanthophylls cycle induction, compares measurement of electron transport rate proxies, examines light curve methodology, and concludes by comparing fluorescence productivity measurements with those of other methodologies such as oxygen evolution and carbon uptake. Contents 1. Introduction to benthic biofilms 2. The effects of subsurface signal 2.1 Microphytobenthic biofilms on soft sediments 2.2 Stromatolites -the effect of "layered" biofilms 2.3 Deconvolution of depth integrated signals 3. Down regulation through Non Photochemical Quenching 3.1 NPQ and the Xanthophyll cycle in diatoms 3.2 NPQ in the dark 4. The quantification of the microalgal biomass using fluorescence 5. Calculation of electron transport rate: ETR v rETR 5.1 Multiple and single turnover methods 5.2 The MT-method. 5.3 The ST-method 5.4 Assumptions and uncertainties.

Photophysiology and albedo-changing potential of the ice algal community on the surface of the Greenland ice sheet

“…A saturating pulse of duration 700 ms at 10 000 mmol m À 2 s À 1 PAR was used. The rETR was then calculated (Perkins et al, 2010a):…”

“…Curves for chlorophyll fluorescence measurements with plotted using an iterative curve fitting using Sigmaplot software (V. 15). Derived coefficients (a, b and c) were tested by analysis of variance (Po0.001) and light curve parameters were then calculated from these coefficients (Perkins et al, 2010a). A Kruskal-Wallis test was used to identify inter-station variability in light curve parameters determined from PAM fluorometry.…”

Microphytobenthos Primary Production Estimated by Hyperspectral Reflectance

“…This was achieved by coupling PAM-fluorometry measurements for estimating primary production [14][15][16], and spectroradiometry of five MPB species representative of the main growth forms. Growth-forms are known to strongly affect eco-physiological response to light exposure: Non Photochemical Quenching (NPQ) and xanthophyll cycle (XC) patterns [17,18].…”

“…The choice of PAMfluorometry to estimate ETR to calibrate a radiometric index was based on the fact that data time acquisition is in the same time range for both techniques. Using NSLCs and other light curves [16], photosynthetic parameters and reflectance data are obtained in less than 1 second [34] reflecting similar involved processes. Alternative techniques [16] require much longer measuring times, e.g.…”

“…Using NSLCs and other light curves [16], photosynthetic parameters and reflectance data are obtained in less than 1 second [34] reflecting similar involved processes. Alternative techniques [16] require much longer measuring times, e.g. fluxes using micro-electrodes can take more than 20 min [35]; 14 C based techniques take even longer [36], due to processes more longer than pigment de-epoxydation or electron transfer.…”