Throughout its broad range in eastern North America, Carex stricta forms organic tussocks (average ~15-20 cm tall) that structure wetland vegetation and are capable of storing significant amounts of carbon. To investigate internal tussock dynamics and the mechanisms that stabilize their organic matter, I initiated two incubation experiments (22.5°C) that evaluated carbon dioxide and methane production rates at two moisture levels (field moist and inundated). The first compared carbon (C) mineralization among four components of tussock sedge meadow substrates (top and base of tall tussocks (18-22cm), center of short tussocks (8-12cm), and peat (0-20 cm below tussocks)). The second experiment compared C mineralization rates from tussock and peat samples from four sites (a 12-year old restoration, a storm-water influenced site, and two relatively undisturbed remnant sites). Incubation results are compared with preliminary field flux data.
Results/Conclusions
Cumulative C mineralized (mg C g C-1) during the first 385 days decreased with depth from tall tussock tops (moist: 151 ± 215; inundated: 136± 19), to tall tussock bases (moist: 41 ± 12; inundated: 64± 18), to peat (moist: 33 ± 4; inundated: 23 ± 4). As predicted, short tussocks and tall tussocks tops had similarly high C mineralization rates, likely due to the undecomposed nature of these surface substrates. Comparison among sites indicated that carbon stored in tussocks at the 12-year old restoration was more labile than that from the storm-water and remnant sites. Laboratory results suggested that tussock substrates have the capacity to produce significant amounts of methane when inundated, accounting for 24 to 51% of total carbon mineralized. In the field however, tussocks emitted less methane (12 ± 2 mg C m-2hr-1) than inter-tussock areas (35 ± 12 mg C m-2hr-1) when standing water was present. The results suggest that the carbon stored in the older, more decomposed C. stricta tussock sedge meadow substrates (both within and between sites) is relatively stable, indicating that remnant sedge meadows with tall tussocks could be important carbon reservoirs.
