Peatland responses to varying interannual moisture conditions as measured by automatic CO₂ chambers

Abstract

[1] Net ecosystem CO 2 exchange (NEE) was measured from June 2000 through October 2001 by 10 automatic chambers at a peatland in southeastern New Hampshire. The high temporal frequency of this sampling method permitted detailed examination of NEE as it varied daily and seasonally. Summer of 2001 was significantly drier than the 30-year average, while summer of 2000 was wetter than normal. Although NEE varied spatially across the peatland with differences in plant species composition and biomass, maximum CO 2 uptake was 30-40% larger in the drier summer in evergreen and deciduous shrub communities but the same or lower in sedge sites. Ecosystem respiration rates were 13-84% larger in the drier summer depending on plant growth form with water table and temperature as strong predictors. Ecosystem respiration was also correlated with maximum ecosystem productivity and foliar biomass suggesting that plant processes, water table, and temperature are tightly linked in their control of respiratory losses. The ratio between maximum productivity and respiration declined for evergreen shrub and sedge sites between the wet and dry summer, but increased in deciduous shrub sites. A drier climate may reduce the CO 2 sink function of peatlands for some growth forms and increase it for others, suggesting that ecosystem carbon and climate models should account for differences in growth form responses to climate change. It also implies that plant functional types respond on short timescales to changes in moisture, and that the transition from sedges to shrubs could occur rapidly in peatlands under a drier and warmer climate.

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

“…Our findings together with those of others (e.g. Bubier et al, 2003;Aurela et al, 2007;Sullivan et al, 2008;Lohila et al, 2011) demonstrate the critical interaction of temperature with wetness for GPP ff and R ff response as either of the factors alone could not illustrate the overall growth response of bog vegetation under changing microclimatic and environmental conditions.…”

“…As modelled values of maximum GPP were most likely never achieved in reality, these values represented a more realistic estimate of CO 2 exchange when light was not limiting, as reported by Bubier et al (2003). We used these to statistically compare CO 2 exchange at the microforms and to better understand its controls (e.g.…”

Annual carbon balance of a peatland 10 yr following restoration

“…Although water tables were deeper at the restored site than the natural site (Table 1), estimated losses of carbon as CO 2 were greater from the former. This may result from differences in vegetation composition between the sites, a factor that has been observed to influence drought response (Bubier et al, 2003a;Strack et al, 2006). The restored site continues to have higher diversity than the natural site due to a combination of species introduced during restoration and those that have spontaneously colonized the site (Poulin et al, 2012).…”

“…(2) is a theoretical maximum rate of GEP which may never actually be attained, we evaluated differences in maximum rates of GEP and NEE by comparing CO 2 flux when PAR photon flux density was greater than 1000 µmol m −2 s −1 (GEP max , NEE max ) according to Bubier et al (2003a). Data for CO 2 and CH 4 fluxes were nonnormally distributed, thus non-parametric Kruskal-Wallis and Mann-Whitney tests with Bonferroni correction for multiple comparisons were used to evaluate differences between sites resulting in a corrected p value of 0.005.…”

Discovery of a novel methanogen prevalent in thawing permafrost

“…The chambers are connected to the gas analysis system, located in an adjacent temperature controlled cabin, by 3/8 inch Dekoron tubing through which air is circulated at B2.5 l min À 1 . During the 2011 season, the system was updated with a new chamber design similar to that described by Bubier et al 32 The new chambers cover an area of 0.2 m 2 (45 cm  45 cm), with a height ranging from 15 to 75 cm depending on habitat vegetation. At the palsa and bog sites, the chamber base is flush with the ground and the chamber lid (15 cm in height) lifts clear of the base between closures.…”