Plant biomass and production and CO₂ exchange in an ombrotrophic bog

Abstract

Summary1 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 -2was 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 CO 2 was measured in chambers and used to derive ecosystem respiration and photosynthesis. Under high light flux (PAR of 1500 µ 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 CO 2 ) 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 CO 2 uptake determined by the eddy covariance technique within a bog footprint (0.40 and 0.35-0.40 mg m -2 s -1 , respectively). . 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.

Scots pine litter decomposition along drainage succession and soil nutrient gradients in peatland forests, and the effects of inter-annual weather variation

“…The soil C sink of a peatland (mire) is labile, and its persistence is sensitive to weather variations, especially moisture conditions. Large soil C losses from pristine mires have resulted following extended summer droughts (Alm et al, 1997(Alm et al, , 1999Moore et al, 2002). These results have raised a postulate that long-term water-level drawdown will diminish or end the C sink function of a peatland.…”

Carbon dioxide flux and net primary production of a boreal treed bog: Responses to warming and water-table-lowering simulations of climate change

“…Interactions between soil and plant communities have been predicted to play a major role in determining the response of the net exchange of CO 2 in peatlands to a climate change scenario (Weltzin et al, 2001;Kardol et al, 2010;Moore et al, 2002) of water level lowering and global warming (Ciais et al, 2013). Ground-layer biomass was significantly affected by 13 years of drainage (water level ∼ 120 cm; .…”

Species-specific temporal variation in photosynthesis as a moderator of peatland carbon sequestration

“…The cumulative growing season P G of 230 g C m −2 is very similar to the 205 g C m −2 obtained by Alm et al (1999) at an ombrotrophic bog site under similar climatic conditions and comparable water levels but where the exceptionally dry conditions during the measured season reduced the photosynthetic capacity of many Sphagnum species. Our growing season P G was considerably lower than the 500 g C m −2 obtained by Moore et al (2002) and Roulet et al (2007) at a temperate ombrotrophic bog with much lower water table levels. While our value only covers the period from May until September, it falls just below the large range of annual GPP values (250 to 900 g C m −2 ) measured with the EC method from seven northern peatland sites (Lund et al, 2010).…”

“…Several studies (e.g., Weltzin et al, 2000;Moore et al, 2002;Leppälä et al, 2008) have reported that patterned bogs produce more biomass and have less variation in gross photosynthesis over the growing season than fens, which receive additional nutrients from the surrounding mineral soil and generally have more homogenous, sedgedominated vegetation (Weltzin et al, 2000). Experimental studies have shown that bog plant growth forms have differential responses to warming and water table level manipulation, which can help to maintain the level of total ecosystem productivity under changing environmental conditions (Weltzin et al, 2000;Breeuwer et al, 2009).…”

“…Boreal bogs are peatland ecosystems where photosynthetic productivity is limited by midsummer dry periods, light induced stress and, in particular, low nutrient availability (Frolking et al, 1998;Moore et al, 2002). Due to the low rate of photosynthesis, the annual C sink of boreal bogs is weak and sensitive to changes; even a small change in the environmental conditions that regulate the C cycle can turn the ecosystem into a C source (Waddington and Roulet, 2000;Lund et al, 2012).…”