Response of Sphagnum fuscum to water levels and CO2 concentration

Abstract

Sphagnum fuscum samples collected from an ombrotrophic bog were grown in a greenhouse at six water levels (0, 5, 10, 15, 25 and 30 cm) below the capitulum level and in four concentrations of CO₂ (350, 700, 1000 and 2000 ppm). The cores of S. fuscum were treated for 87 days and length increment was measured by the plastic strip method and by innate time markers. Water content of the shoot, dry mass of the capitulum, dry mass per unit length of stem and production of dry mass were measured at the end of the experiment.

The water content, capitulum dry mass, dry mass per unit length of stem, length increment and dry mass production differed markedly for S. fuscum grown in different water levels. With lower water levels, the water content of the shoot decreased and the dry mass of both the capitulum and unit length of stem increased. The total length increment was highest when the water level was at or near the capitulum level (0–10 cm). No clear trend in dry mass production on an areal basis could be found due to uncoupled responses in length increment and stem dry mass at the experimental water levels.

Neither capitulum dry mass nor dry mass per unit length of stem showed distinct trends in S. fuscum grown at different ambient CO₂ concentrations. Some increase in length increment and in dry mass production was detected at CO₂ concentrations above 350 ppm, but this effect appeared only at high water levels. It is suggested that the low response in length increment and production to CO₂ concentration resulted in part from insufficient moisture for photosynthesis at the lower water levels. Also, the possibility of increased nonstructural production is discussed.