Spatial and temporal variations in hectare‐scale net CO₂ flux, respiration and gross primary production of Arctic tundra ecosystems

Abstract

Summary1. Eddy covariance was used to measure the net CO 2 flux of Alaskan moist-tussock and wet-sedge tundra ecosystems between 1 June and 31 August 1995. The sites were located within 2·5 km of each other and, depending on wind speed and thermal stability, the eddy-covariance measurements integrated surface fluxes over 0·8-26·5 ha (mean 3·8 ha) at the moist-tussock site and 0·1-4·2 ha (mean 0·6) at the wet-sedge site. 2. Both sites were net sinks for atmospheric CO 2 during the 92-day measurement period but wet-sedge tundra accumulated 1·5 times more CO 2 than moist-tussock tundra. Wet-sedge tundra was a net CO 2 sink of -6·4 mol m -2 and moist-tussock tundra was a net sink of -4·6 mol m -2 over the June-August measurement period. 3. Estimates of whole-ecosystem respiration ( R ) were made using multiple non-linear regression by quantifying the response of measured nocturnal CO 2 efflux ( F n ) to fluctuations in air temperature and water-table depth ( r 2 = 0·68). Partial regression analysis revealed that water-table depth explained relatively more of the variance in F n (45%) than temperature (11%). R was estimated to be 14·9 mol m -2 for moist-tussock tundra and 5·4 mol m -2 for wet-sedge tundra over the 92-day measurement period. The large difference in R was apparently owing to a substantially higher water table in wet-sedge tundra. 4. Estimated rates of gross primary production (GPP), calculated from measured net CO 2 flux and estimated R , were 40% lower for wet-sedge tundra over the 92-day measurement period. Rates of GPP integrated over diel (24 h) periods were substantially larger for moist-tussock tundra ecosystems throughout June and July but during the month of August, total diel rates of GPP for moist-tussock and wet-sedge tundra were comparable. 5. Our results demonstrate that R and GPP of moist-tussock and wet-sedge tundra ecosystems can be reliably estimated from eddy-covariance measurements using functional relationships developed from plot-scale studies. Given the large spatial differences in hydrology, the larger sink observed for wet-sedge tundra was probably the result of relatively lower rates of R .

The exchange of carbon dioxide between wet arctic tundra and the atmosphere at the Lena River Delta, Northern Siberia

“…The soils at wet sedge tundra sites for which much higher gross photosynthesis was reported in the literature compared to this study (see above) are considered less nutrient-limited than the soils of the investigation site of this study as they were situated at the bottom of mountain valleys (Vourlites et al, 2000;Laurila et al, 2001) or on fine-grained marine sediments at coastal tundra Harazono et al, 2003). On moist tundra sites, e.g.…”

“…It amounted to 60% of average R eco observed at a moist to wet tussock tundra at the Kolyma River lowlands in North-East Siberia (Corradi et al, 2005), to 60% of R eco at moist to wet tundra on the Chukotskiy Peninsula (Zamolodchikov et al, 2003), to 47-54% of R eco at a high arctic fen (Soegaard and Nordstroem, 1999;Nordstroem et al, 2001), to 38-44% of R eco at tussock tundra at an Alaskan mountain valley (Vourlites and Oechel, 1999;Vourlites et al, 2000) and to 50% of the average R eco modelled for the whole Russian tundra area (Zamolodchikov and Karelin, 2001). On the other hand, R eco observed in this study was equal to R eco at wet sedge tundra at an Alaskan mountain valley (Vourlites et al, 2000), about two times higher than R eco reported for flooded wet sedge tundra at the coastal plain of Alaska (Harazono et al, 2003) and about 2.3 times higher than R eco at an high-arctic semi-desert at Svalbard (Lloyd, 2001a).…”

Contrasting carbon dioxide fluxes between a drying shrub wetland in Northern Wisconsin, USA, and nearby forests

“…In an analogous study in an Alaskan tundra ecosystem, Oechel et al (2000) found that the ecosystem initially changed from a CO 2 sink to a source due to warming and drying, but that CO 2 emissions decreased and eventually became negative during summers over a 40-year period. Several studies of CO 2 fluxes at wetlands have also indicated the importance of vegetation, both stand age for forested wetlands (Ball et al, 2007) and dominant plant community among different wetland types (Humphreys et al, 2006;Glenn et al, 2006;Vourlitis et al, 2000;Waddington et al, 1998). Understanding the impact of dominant plant communities on an ecosystem's response to changing climatic and hydrological conditions will be important for complete understanding of this issue.…”

Long‐term sensitivity of a High Arctic wetland to Holocene climate change

“…If the effect of decomposition were to increase nutrient availability, there may be an additional uptake of CO 2 owing to higher rates of photosynthesis (Shaver & Chapin 1986;Shaver et al 1998;Johnson et al 2000), although as sink strength in vascular plants decreases, productivity may be offset by substrate-controlled or nutrient-limited CO 2 loss from soil respiration by microorganisms (Nadelhoffer et al 1991;Hobbie 1996;Jonasson et al 1999). Larger sinks of CO 2 are accordingly associated with lower respiration rates in wetter habitats (Vourtilis et al 2000), while short-term experiments designed to explain the net effect of climate warming on soil moisture and the C-balance of tundra plots (Johnson et al 1996) support observational data demonstrating that a shift from net C-input to C-output accompanies the recent drying of tundra habitats (Oechel et al 1993Weller et al 1995).…”