Plant biomass and production and CO2 exchange in an ombrotrophic bog

Abstract

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 μmol 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 summer-time 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.