Photosynthetic performance of freshwater Rhodophyta in response to temperature, irradiance, pH and diurnal rhythm

Abstract

SUMMARY Responses of net photosynthetic rates to temperature, irradiance, pH/inorganic carbon and diurnal rhythm were analyzed in 15 populations of eight freshwater red algal species in culture and natural conditions. Photosynthetic rates were determined by oxygen concentration using the light and dark bottles technique. Parameters derived from the photosynthesis–irradiance curves indicated adaptation to low irradiance for all freshwater red algae tested, confirming that they tend to occur under low light regimes. Some degree of photo‐inhibition (β= ‐0.33–0.01 mg O2 g−1 DW h−1 (μmol photons m−2 s−1)−1) was found for all species/populations analyzed, whereas light compensation points (Ic) were very low (≤ 2 μmol photons m‐ photons s−1) for most algae tested. Saturation points were low for all algae tested (Ik = 6–54 μmol photons m−2 s−1; Is = 20–170 umol photons m−2 s−1). Rates of net photosynthesis and dark respiration responded to the variation in temperature. Optimum temperature values for net photosynthesis were variable among species and populations so that best performances were observed under distinct temperature conditions (10, 15, 20 or 25°C). Rates of dark respiration exhibited an increasing trend with temperature, with highest values under 20–25°C. Results from pH experiments showed best photosynthetic performances under pH 8.5 or 6.5 for all but one species, indicating higher affinity for inorganic carbon as bicarbonate or indistinct use of bicarbonate and free carbon dioxide. Diurnal changes in photosynthetic rates revealed a general pattern for all algae tested, which was characterized by two relatively clear peaks, with some variations around it: a first (higher) during the morning (07.00–11.00 hours.) and a second (lower) in the afternoon (14.00–18.00 hours). Comparative data between the ‘Chantransia’ stage and the respective gametophyte for one Batrachospermum population revealed higher values (ca 2‐times) in the latter, much lower than previously reported. The physiological role of the ‘Chantransia’ stage needs to be better analyzed.

Daily dynamics of photosynthesis of the freshwater red alga Sirodotia delicatula (Batrachospermales, Rhodophyta)

“…The typical pattern of daily variation for marine macroalgae (Ramus 1981) is characterized by two peaks: first, in the middle of the morning, followed by a decline around midday and a second (smaller) in the middle of the afternoon. Necchi and Zucchi (2001) described essentially similar results for freshwater red algae, including a population of Sirodotia delicatula (treated as Batrachospermum ). Necchi and Alves (2005) described a general pattern of daily variation for all populations tested of S. delicatula characterized by two relatively evident peaks: a higher one by the morning and another (smaller) by the afternoon.…”

“…Incubations were carried out during periods of 50 min along the light period (06.00–18.00 hours) at constant temperature and irradiance (20°C and 75 ± 3 µmol photons m −2 s −1 ), following sub‐optimal values from previous studies (Necchi & Zucchi 2001; Necchi 2005; Necchi & Alves 2005). Two daily profiles were obtained at the day following field measurements.…”

“…Experiments using oxygen evolution followed the general procedures described in previous studies (Necchi & Zucchi 2001; Necchi 2005). Net photosynthetic rates were determined by changes in oxygen concentration using the light and dark bottles technique (Littler & Arnold 1985; Thomas 1988).…”

UV-radiation effects on photosynthesis, photosynthetic pigments and UV-absorbing substances in three species of tropical lotic macroalgae

“…Sirodotia delicatula showed lower values of ETR max and E k and higher values of photoinhibition (b ETR ), typical of shaded-adapted algae. Adaptations to low irradiance were consistently observed for Rhodophyta (Necchi and Zucchi 2001;Necchi 2004). In contrast, most species of Chlorophyta has been reported as sun-adapted algae (Graham et al 1995;Ensminger et al 2001;Necchi 2004).…”

“…Freshwater red algae have been indicated as shadeadapted in previous studies (Necchi and Zucchi 2001;Necchi 2004Necchi , 2005, although some species can tolerate high irradiances. Photosynthetic characteristics of Sirodotia delicatula Skuja (treated as Batrachospermum delicatulum) exhibited a wide range of responses to irradiance (Necchi and Alves 2005), suggesting they have mechanisms that enable them to avoid photodamage of the photosynthetic apparatus (Necchi 2005).…”