Carbon sink function of sedge and Sphagnum patches in a restored cut-away peatland: increased functional diversity leads to higher production.
Cut-away peatlands devoid of vegetation form a persistent source of carbon (C) to the atmosphere. The restoration of the C sink function in such areas can be facilitated by raising the water table. Planting vascular plants and Sphagnum may hasten the restoration process further. However, little is known about the effects of different species on the restoration process. We studied carbon dioxide (CO2) exchange in stands of different plants in a restored cut-away site over two growing seasons to quantify their ability to form a C sink. We sampled five different types of stand: monocultures of Eriophorum vaginatum and Carex rostrata (pure plots), mixtures of Eriophorum or Carex and Sphagnum mosses (mixed plots) and control plots without vegetation. We applied the closed chamber technique to gather CO2 exchange data for modelling of gross photosynthesis (PG) and ecosystem respiration (RE). Finally, we used the models to reconstruct the seasonal net CO2 exchange of the stands formed by different plants. While the control plots without vegetation were sources of 20-71 g CO2-C m-2, all the vegetated plots acted as C sinks during both growing seasons. The monostands of E. vaginatum and C. rostrata created sinks of 23-114 g CO2-C m-2, while the mixtures of sedge and Sphagnum mosses resulted in larger sinks of 75-186 g CO2-C m-2. The larger sinks of the mixed patches were due to the lower respiration/photosynthesis ratio. To eliminate the effect of differences in water table and the abundance of sedges between the patches, we reconstructed the CO2 exchange for constant water table and vascular leaf area for all plots. The simulation further supported our result: the mixtures of sedge and Sphagnum mosses were clearly more efficient in sequestering CO2 than pure sedge stands. Synthesis and applications. The increased functional diversity in a cut-away peatland site resulted in higher net ecosystem exchange. When restoring cut-away peatlands, reintroduction of Sphagna is recommended after the colonization of vascular plants to hasten the formation of a sink for C.