Abstract
Six populations of the freshwater red alga Batrachospermum delicatulum (Skuja) Necchi & Entwisle, including gametophyte and 'Chantransia' stage, were analysed in culture and natural conditions applying chlorophyll fluorescence and oxygen evolution. Parameters derived from the photosynthesis-irradiance curves indicated adaptation to low irradiance for all populations, which was characterized by photoinhibition, low values of Ik and Ic and high values of a. Data from both techniques revealed significant differences among populations and phases for most photosynthetic parameters. Similarly, photosynthesis responded differently to variations in temperature in each population with similar rates under a wide range of temperature. No consistent pattern was found when the same population or phase was tested, suggesting high capacity to adjust the photosynthetic apparatus to distinct conditions of irradiance and temperature. pH experiments showed a decreasing trend towards higher pH or higher rates at pH 6.5, suggesting, respectively, higher affinity to inorganic carbon as CO2 or indistinct use of bicarbonate and CO2. The diurnal pattern of photosynthesis essentially agree with that for seaweeds and freshwater red algae, consisting of two peaks: a first (generally higher) during the morning and a second (typically lower) in the afternoon. Photosynthetic characteristics of B. delicatulum (Skuja) Necchi & Entwisleexhibited a wide range of responses to irradiance, temperature and pH/inorganic carbon, reflecting its wide tolerance to these variables, which probably contributes to its wide spatial and temporal distribution.
Highlights
The temperature and light regime have been recognized as major environmental factors affecting distribution and seasonality (Sheath 1984; Sheath & Hambrook 1990; Necchi et al 1999), as well as growth, pigment content and photosynthetic characteristics of freshwater Rhodophyta (Zucchi & Necchi 2001; Necchi & Zucchi 2001)
PI curves - PI curves based on oxygen evolution (Tab. 2, Fig. 1) were characterized by photoinhibition (β-0.09), low values of Ik (
Photoinhibition was observed in all populations of both phases, under either field or culture conditions (Tab. 2, Fig. 1)
Summary
The temperature and light regime have been recognized as major environmental factors affecting distribution and seasonality (Sheath 1984; Sheath & Hambrook 1990; Necchi et al 1999), as well as growth, pigment content and photosynthetic characteristics of freshwater Rhodophyta (Zucchi & Necchi 2001; Necchi & Zucchi 2001). Leukart & Hanelt (1995) reported the photosynthesisirradiance (PI) curves and their respective parameters for some stream macroalgae, including three red algal species. Both studies indicate characteristics of shade plants, e.g. low compensation and saturation irradiances and high photosynthetic efficiencies. Necchi & Zucchi (2001) investigated the responses of photosynthesis to temperature and irradiance in 15 populations of eight species of freshwater red algae in culture and natural conditions. Parameters derived from PI curves indicated adaptation to low irradiance for all freshwater red algae tested, including low saturation and compensation points, and photoinhibition
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