The effect of photoacclimation on the photosynthetic physiology ofUlva curvataandUlva rotundata(Ulvales, Chlorophyta)

Abstract

The effects of photoacclimation on growth, photosynthesis, pigment content and elemental composition of Ulva curvata and Ulva rotunda& which grow together in eutrophic areas of southern Spain, were investigated. CuItures were grown for 6 days at different photon fluence rates (PFR) ranging from darkness up to 200 #mol m -2 s-1 under nutrient-sufficient conditions (artificial seawater supplemented with ammonium and phosphate). Growth rates were not light-saturated (up to 200 #mol m -2 s-l), reaching a value close to 0"2 d -I. Growth rates based on mass, area or C content were equivalent, except in darkness and very low light levels (2 #molm -2 s 1), where thallus expansion occurred by diluting internal biomass and C. Chlorophyll and absorptance showed a bell-shaped PFR-response curve, with maxima at 30-60#molm -2 s 1 and lower values at light saturation and under light-limiting conditions. Although net NH4 + incorporation was not affected by growth-PFR, there was inefficient assimilation of N at low light levels, which may restrict chlorophyll, protein and membrane synthesis. The light-saturated photosynthesis rate (Pm~x) displayed a bell-shaped PFR-response curve, when expressed on an area basis, whereas it was saturated from 1I #molm 2 s-1 when scaled to internal N. This suggests that ribulose-I,5-bisphosphate carboxylase/oxygenase activity could be the rate-limiting step underlying Pm~x for high-light-acclimated algae, whereas electron transport chain elements may limit Pmax under light-limiting conditions. Pma~ and tissue C were always higher for U. curvata. Dark respiration rates were positively correlated with growth rates, and photon yield of net growth declined with increasing growth-PFR. The results are also discussed in relation to cell size, since U. curvata cells are smaller than those of U. rotundata.

Photosynthesis and daily metabolic carbon balance of the invasive <i>Caulerpa racemosa</i> var. <i>cylindracea</i> (Chlorophyta: Caulerpales) along a depth gradient

“…2 and Table 1), other local factors not controlled by the experimental design can also vary with depth and influence photosynthetic performance. However, the photosynthetic responses observed in this study are in good agreement with general metabolic strategies used by sublittoral macroalgae to optimize light use and productivity under variable light conditions (Markager and Sand-Jensen, 1992;Kirk, 1994;Pérez-Lloréns et al, 1996;Gómez et al, 1997;Lobban and Harrison, 1997;Gómez, 2001). Furthermore, our results are highly consistent with differences in photosynthetic behaviour reported by other studied Mediterranean populations of C. racemosa between shallow and deep habitats (Raniello et al, 2006).…”

Oxidative stress and enzymatic scavenging of superoxide radicals induced by solar UV-B radiation in <i>Ulva</i> canopies from southern Spain

“…These so called Ulva mats are frequently observed within soft bottom habitats along the shallow coastal zones of southern Spain. Previous studies have shown the importance of canopy arrangement for maintaining high production rates of algal assemblages within these highly eutrophic systems (Pérez-Lloréns et al, 1996;Hernández et al, 1997). A recent study on the effects of solar UV radiation on Ulva canopies proposed canopy formation as an ecological strategy for shielding productive material from harmful UV-B radiation (Bischof et al, 2002b): the bleached top layers of mats, which exhibit marked absorption of solar radiation only in the UV-B range of the spectrum, shield the subcanopy layers.…”

Short-term ecophysiological and biochemical responses of Cystoseira tamariscifolia and Ellisolandia elongata to environmental changes

“…Nitrogen limitation affects many processes in macroalgae including photosynthetic capacity (Pérez-Lloréns et al 1996), protein content (Vergara et al 1995, Martínez & Rico 2002 and photoprotection mechanisms (Korbee-Peinado et al 2004, Korbee et al 2005b, Huovinen et al 2006. Under moderate to highly desiccated conditions, some intertidal macroalgae increase their nitrogen and carbon uptake (Lobban & Harrison 1994, Flores-Moya et al 1998, Nygard & Dring 2008.…”