Inorganic carbon supply to algae submerged in acid wetland pools: Analysis using the natural abundance of carbon isotopes

Abstract

Summary The inorganic C supply to macroalgae in two acid pools in a highland wetheath was analysed using 13C/12C natural abundance measurements. The inorganic C in the pools (pH 3.9 – 4.5) is all present as CO2, and is more than three times the air-equilibrium concentration. The 13C/12C value of the pool CO2 was predicted from the 13C/12C of rainwater CO2 and that of CO 2derived from terrestrial plant (peat) respiration in a quantity adequate to account for the over- saturation of CO2. This 13C/12C value, at least in one pool, is lower than the measured value; this could relate to preferential removal of 12CO2 in submerged photosynthesis and methanogenesis in producing the measured CO2 concentration and 13C/12C in the pool. The algae Batrachospermum keratophytum and Mougeotia capucina appear to be dependent on CO2 diffusion followed by C3 biochemistry; the algal 13C/12C ratio relative to pool CO2 13C/ 12C predicts a fractional limitation of photosynthesis by CO2 diffusion of 0.85 – 0.96. This is much high...