Photoinhibition and the diurnal variation of phytoplankton photosynthesis--I. Development of a photosynthesis--irradiance model from studies of in situ responses |
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Authors: | Neale Patrick J; Richerson Peter J |
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Institution: | Institute of Ecology, University of California Davis, CA 95616, USA |
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Abstract: | Diurnal series of fluorescence and photosynthesis assays wereconducted in high altitude (3803 m), tropical (16°), LakeTiticaca (Peru/Bolivia). Near-surface diurnal thermoclines formedon typical days of high photon flux density (PFD, {small tilde}2000 µE m2 s1). In the depth range of diurnalstratification profiles of in vivo fluorescence, both without(Fa and with (Fb DCMU, exhibited a mean decrease of 64% frommorning to mid-day, but little change (mean increase of 1.5%)through the afternoon. Three times during the day surface, mid-depth(35 m) and deep (1520 m) phytoplankton sampleswere incubated with H14CO3 under short (<2 h) exposuresto a range of in situ PFDs. Comparison of phytoplankton in differentsamples (ANOVA) showed identical photosynthetic response insunrise (isothermal) samples but a significant drop in surfaceand mid-depth photosynthesis at all PFDs during times of diurnalstratification. Similarly, both low-light () and light-saturated(P2 max photosynthetic parameters were lower in mid-day surfacesamples compared to deep samples. In addition, previously photoinhibitedsamples had a higher threshold intensity for photoinhibition,IT. These results, together with diurnal time series of fluorescencefrom in situ incubations, demonstrate that recovery from extendedepisodes of photoinhibition during diurnal stratification isslower than suggested by previous observations in vitro. Photosynthesisby near-surface phytoplankton is different in light increasingup to IT than light decreasing from IT. This effect can be modeledby reducing and Pmax as a function of the maximum photoinhibitingPFD in the diurnal light history.
1Present address: Division of Molecular Plant Biology, Universityof California, Berkeley, Berkeley, CA 94720, USA |
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