Substrate-derived CO2 is important in the development of Sphagnum spp.

. The effects of different CO2 concentrations in the acrotelm pore water on the development of Sphagnum magellanicum monoliths grown in wet conditions in the laboratory are reported here. . Decomposition processes result in much higher CO2 concentrations in bog acrotelms than atmospheric concentrations. We therefore hypothesized that this substrate-derived carbon provides an important carbon source for Sphagnum. . S. magellanicum hummocks developed only when CO2 concentrations in the acrotelm water were high. Plants in the low CO2 treatment appeared to be carbon-limited; they had increased nutrient concentrations and decreased ratios of carbon to other nutrients. Chlorophyll concentrations were much higher in these plants, probably allowing them to harvest more CO2 but the allocation of carbon to structural tissues was lower, resulting in weak stems that were unable to remain upright. As a result of carbon-limitation, net biomass and height increases of the monoliths were much lower in the low CO2 treatment. . Results indicate that, at least in wet conditions, atmospheric CO2 alone is not sufficient to enable S. magellanicum to develop its normal vertical growth pattern. We conclude that the role of substrate-derived CO2 as a carbon source for Sphagna is underestimated and requires reconsideration.