Variability in Spectral and Nonspectral Measurements of Photosynthetic Light Utilization Efficiencies

摘要: The aim of this study was to quantify the variability in and differences between spectral nonspectral measurements: light utilization efficiencies for natural phytoplankton communities, order evaluate possible consequences blo-opt~cal models sj t~l p]-1ma1-y production (P). Field samples were collected at 4 coastal stations durlng a 1 d transect (July 23, 1988) across Southern California Counter ('urrent (SCCC) time when communities dominated largely by picoplankton (0 5 pm). Concurrent determlnations made down~ve l l~ng ~rradiance [QCl(A,z)], photosynthetically available radiation (Qpclr), attenuation coefficients [&(A,z)], detrital-corrected absorption [a,,,,(A,z)], white photosynthesis-irradiance parameters (P,,,,. a, I*) carbon action spectra a(AA,,z). From these parameters, estimates situ absorbed [AQ,,h(AA,.z)l, maximum quantum yield [d,,,.(AA,.z)], operational [&(AA,,z)l, efficiency [c(AA,,z)] productivity P(AA,,z) derived. Significant spatial all bio-optical noted surface waters chlorophyll maximum. For waters, there significant 525 600 nm region signatures dl[dA,,z) which attributable phycobilins not resolved In spectra. importance photosynthetic pigments other than (chl), thcir assoc~ated Impact upon absorption-based increased w ~ t h depth. One consequence close correspondence AQ,, depth c evident A second that while spectrally weighted whlte g occasionally s im~lar 4to 6-fold higher measurements. Results confirm previous observations measures can significantly underestimate subsurface (Prezelin e al. 1989) provide conceptual base on improve existing future yield. INTRODUCTION be placed processes. are based mechanistic linkages Phytoplankton occupies central posiwater-column optical properties, penetration phototion several large-scale processes, including food synthetically (Q,,,), phytoweb dynamics, biogeochemical cycles, particle flux, plankton production. Photosynthesis-irradiance (P-I) bioluminescence. Bio-optical increase curves physiological information our ability resolve temporal/spatial environmental effects algal photophysiophytoplankton will allow constraints logy used empirical describ0 Inter-Reseal-ch/Printed Germany 017 -8630/91/0078/0253/$03.00 254 Mar. Ecol. Prog. Ser 78: 253-271, 1991 ing primary (Platt & Jassby 1976, hlacCaull& Platt 1977, Cote 1984, Prezelin et 1986, 1987, 1989, 1991, Glover 1991). P-I also key components sophisticated attempt predict changes rates growth photosynthesis (Shuter 1979, Laws Bannister 1980, Kiefer Mitchell 1983, Falkowski 1985, Lewis Geider Bidigare Sathyendranath 1988, Sakshaug Smith 1989b, Baker 1990). These generally require term fixation ( ) is with (AQph) converted photosynthate. Based limited field many have been developed assuming cb independent wavelength, near theoretical (0.125 m01 C Ein-') and/or has predictable light-dependent relationship ($,,). Recent studies indicate such generalities cannot universally applied without affecting predictive accuracy (Smith 198913, Schofield Spectral (Lewis 1990) recognize wavelength dependence properties adaptable underwater fields (cf. Boczar 1986). observation (Kirk 1983) (P) any given (2) depends field, its phytoplankton, utilized fix carbon. (C) . Thus Taking into account AQph(z) signiflcantly 1989b). By taking 4(z) may offer more general applications then models. Our interests rnodeling mechanisms diverse utilize radiant energy, regulate photosynthesis, influence ch.aracten.stics water column prompted multidisciplinary cruise (Watercolors '88). purpose Watercolors '88 assess ocean optics wavelength-dependent photosynthesis. presented here part exercise designed measurements outlines demonstrates shifts community composition irradiance large effect signature confirms 'white light' provides MATERIALS AND METHODS Physical/chemical sample collection. program conducted July-August 1988 aboard RV 'Melville'. Using procedures previously described 1987), total 129 vertical proflles completed during repeated transects highly variable Bight (SCB) (Fig. 1). Hydrographic analyses 1990, pers. comm.) led sorting profiles 12 groupings had similar hydrographic signatures. cluster casts represent Station (Stn) L most representative Current (CC) flowing from north, Stn K intermediate those CC post-upwelling subducting offshore J Although groups I appeared hydrographically related (SCCC), some along east-west line. pronounced centered over Continental Shelf Break. At present study, 12.01 showed SCCC postupwelling off Pt. Conception within (chl max). On July biological 150 km SCCC. cast numbers (Stns 9.02, 10.02, 11.01, 12.01) their distinguishable types (A L) shown Fig 1. Vertical profiling Stns 9.02 carried out dawn dusk single day times listed Table distin.guishes instantaneous different day, noon-time parameters. latter correct known diurnal variations time-independent compariSchofield al.. yield, radiat~on ut~lization efflclency 255