Question: Can mixing ratio and species affect the use of substrate-derived CO₂ by Sphagnum?

Location: Poor fen in south Sweden and greenhouse in Wageningen, The Netherlands.

Methods: Two mixing ratios of Sphagnum cuspidatum and S. magellanicum were exposed to two levels of CO₂ by pumping CO₂ enriched and non-enriched water through aquaria containing the species mixtures in the greenhouse.

Results: Enhanced CO₂ stimulated the production of S. cuspidatum, but only in aquaria co-dominated by S. magellanicum, coinciding with higher CO₂ concentrations in the water layer. The denser growing S. magellanicum seemed to reduce gas escape from the water, resulting in accumulation of dissolved CO₂. Adding CO₂ did not affect species replacement.

Conclusions: The use of substrate-derived CO₂ for Sphagnum production depended on species identity and mixing ratio. The effect of mixing ratio on CO₂ concentrations in the water layer suggests that species composition may affect both the efficiency with which substrate-derived CO₂ is trapped and subsequently used. This could result in hitherto unexplored feedbacks between vegetation composition and gas exchange.

Nomenclature: Daniels & Eddy (1990).