Plant biomass and production and CO2 exchange in an ombrotrophic bog

1 Above-ground biomass was measured at bog hummock, bog hollow and poor-fen sites in Mer Bleue, a large, raised ombrotrophic bog near Ottawa, Ont., Canada. The average above-ground biomass was 587 g m(-2) in the bog, composed mainly of shrubs and Sphagnum capitula. In the poor fen, the average biomass was 317 g m(2), comprising mainly sedges and herbs and Sphagnum capitula. Vascular plant above-ground biomass was greater where the water table was lower, with a similar but weaker relationship for Sphagnum capitula and vascular leaf biomass. 2 Below-ground biomass averaged 2400 g m(2) at the bog hummock site, of which 300 g m(2) was fine roots (<2 mm diameter), compared with 1400 g m 2 in hollows (fine roots 450 g m(2)) and 1200 g m(2) at the poor-fen site. 3 Net Ecosystem Exchange (NEE) Of CO2 was measured in chambers and used to derive ecosystem respiration and photosynthesis. Under high light flux (PAR of 1500 mu mol m(2) s(1)), NEE ranged across sites from 0.08 to 0.22 mg m(2) s(1) (a positive value indicates ecosystem uptake) in the spring and summer, but fell to -0.01 to -0.13 mg m(-2) s(1) (i.e. a release of CO2) during a late-summer dry period. 4 There was a general agreement between a combination of literature estimates of photosynthetic capacity for shrubs and mosses and measured biomass and summertime CO2 uptake determined by the eddy covariance technique within a bog footprint (0.40 and 0.35-0.40 mg m(2) s(1), respectively). 5 Gross photosynthesis was estimated to be about 530 g m(2) year(1), total respiration 460 g m(-2) year(1), and export of DOC, DIC and CH4 10 g m(2) year(1), leaving an annual C sequestration rate of 60 g m(-2) year(1). Root production and decomposition are important parts of the C budget of the bog. Root C production was estimated to be 161-176 g m(2) year(1), resulting in fractional turnover rates of 0.2 and 1 year(1) for total and fine roots, respectively.