NATEX project

Participants: Jeff Welker, Jace Fahnestock, Carol Bilbrough, Paddy Sullivan, Kevin OĈDea, Seth Arens, Ashley Burt, Tom Antonini, Mark McNeal

Title: Species responses to changes in climate across arctic gradients using the North American ITEX network (NATEX): influences on community and ecosystem processes

Overall goals: 1) Quantify growing season CO2 exchange in high and low Arctic tundra communities. 2) Minirhizotron studies of roots at Toolik Lake.

Summary: We measured net ecosystem CO2 exchange, respiration and photosynthesis throughout the 2000 growing season at Toolik Lake and Alexandra Fiord, Canada. Measurements were made approximately every two weeks in moist and dry tundra ecosystems at Toolik Lake and in wet, mesic and dry ecosystems at Alexandra Fiord. In addition, measurements were taken at all sites in plots that were warmed by open-topped chambers. At Toolik Lake we also took measurements in the long-term experimental manipulation of increased wintertime snow accumulation.

In 2001, we increased our sampling at Alexandra Fiord and made measurements in wet, mesic and dry ecosystems on a weekly basis. Again, measurements included long-term (8-years) warming and ambient plots. The long-term warming experiment was initiated by Greg Henry. In conjunction with these gas exchange measurements, we measured snow depth (as necessary), depth of thaw, soil moisture, and air and soil temperatures.

Whole plant measurements of net CO2 exchange, respiration, and photosynthesis were made in mid- to late-July (peak season) at Alexandra Fiord on the dominant plant species at each of the major ecosystems (i.e., wet, mesic, and dry). These measurements, along with soil respiration measurements, will enable us to identify species-specific responses to warming and to ecosystem carbon exchange patterns.

Weekly plant samples were collected at Toolik Lake and Alexandra Fiord throughout the 2000 (and 2001 at Alex Fiord) growing season. These samples are currently being processed for C and N analyses which will be related back to our gas exchange measurements.

In 2001, we initiated a new component of our NATEX research at Toolik Lake to examine belowground root dynamics. We installed minirhizotron tubes in three treatments (ITEX open-topped chambers), fertilization (2 applications: June 5 and July 9, each at a rate of 15g N m-2) and increased winter snow deposition. We have initially installed 8 control tubes, 6 warmed tubes, 14 fertilized tubes and 8 tubes with increased winter snow deposition. Root images were collected every week from June 9 to August 15 at a vertical interval of 0.87cm. We will also make a trip to Toolik Lake in mid-October to look for evidence of fall/early winter root growth and activity.

The minirhizotron root images will be used to quantify root growth rate, decomposition rate, annual production (nutritive and massive), annual turnover (nutritive and massive), age class ratios, age class specific mineral nutrition, age class specific vertical distribution and relative abundance and standing belowground biomass.

To better correlate our minirhizotron images to above and belowground vegetation dynamics, we also collected soil cores and clipped aboveground vegetation every two weeks from June 11 to August 8. Soil cores were sorted into white, gray, brown, crown, fine and non-E. vaginatum roots. This data will be used to determine age-class specific root length density, age-class specific mineral nutrition, age-class specific and temporal variations in vertical distribution and relative abundance, age class ratios, standing below-ground biomass, annual production and above: below ground biomass ratio. Aboveground vegetation has been sorted into species, and live vs. dead material, to quantify species composition, species specific live: dead material ratio, species specific aboveground biomass, species specific mineral nutrition and above: below ground biomass. Aboveground growth measurements were taken about every week from June 5 to August 13 under all treatment regimes. Eriophorum vaginatum old shoots, new shoots and Betula nana stems were tagged and measured. These measurements yielded species-specific and age class specific growth rates and 2000 and 2001 net growth. Vegetation was sampled every week from June 6 to August 13 for species-specific mineral nutrition and temporal variation in mineral nutrition.

Publications resulting from these projects

Bilbrough CB, Welker JM and Bowman W. 2000. Early spring N uptake by snow-covered plants: A comparison of arctic and alpine plant function under snowpack. Arctic, Antarctic and Alpine Research 32:404-411.

Bilbrough CB, Schimel J and Welker JM. The effects of changing snow cover on year-round soil N dynamics in Arctic tundra. Unpublished manuscript.

Fahnestock JT, Jones MH, Brooks PD, Walker DA and Welker JM. 1998. Winter and early spring CO2 efflux from tundra communities of northern Alaska. Journal of Geophysical Research - Atmospheres 103: 29023-29027.

Fahnestock JT, Jones MH and Welker JM. 1999. Wintertime CO2 efflux from arctic soils: Implications for annual carbon budgets. Global Biogeochemical Cycles 13: 775-779.

Fahnestock JT, Povirk KL and Welker JM. 2000. Ecological significance of litter redistribution by wind and snow in arctic landscapes. Ecography 23: 623-631.

Fahnestock JT, Welker JM, OĈDea KW and Henry GHR. 2001. Annual carbon exchange in high and low arctic tundra: comparative responses to ambient and warmed conditions. Unpublished manuscript.

Jones MH, Fahnestock JT, Walker DA, Walker MD and Welker JM. 1998. Carbon dioxide fluxes in moist and dry arctic tundra during the snow-free season: responses to increases in summer temperature and winter snow accumulation. Arctic and Alpine Research 30: 373-380.

Jones MH, Fahnestock JT and Welker JM. 1999. Early and later winter CO2 efflux from arctic tundra in the Kuparuk River watershed, Alaska, U.S.A. Arctic, Antarctic, and Alpine Research 31: 187-190.

Jones MH, Fahnestock JT, Stahl PD and Welker JM. 2000. A note on summer CO2 flux, soil organic matter, and microbial biomass from different high arctic ecosystem types in northwestern Greenland. Arctic, Antarctic, and Alpine Research 32: 104-106.

Schimel JP, Fahnestock JT, Michaelson G, Mikan C, Ping C-L, Romanovsky VE and Welker JM. 2001. A microbial activity based model of winter CO2 fluxes in Arctic tundra communities. Unpublished manuscript.

Walker MD, Walker DA, Welker JM, Arft AM, Bardsley T, Brooks PD, Fahnestock JT, Jones MH, Parsons AN, Seastedt TR and Turner PL. 1999. Long-term experimental manipulation of winter snow regime and summer temperature in arctic and alpine tundra. Hydrological Processes 13: 2315-230.

Welker JM, Brown KB and Fahnestock JT. 1999. CO2 flux in arctic and alpine dry tundra: comparative field responses under ambient and experimentally warmed conditions. Arctic, Antarctic, and Alpine Research 31: 272-277.

Welker JM, Fahnestock JT and Jones MH. 2000. Annual CO2 flux in dry and moist arctic tundra: field responses to increases in summer temperatures and winter snow depth. Climatic Change 44: 139-150.

Welker JM, Fahnestock JT , OĈDea KW and Henry GHR. 2001. Previously entombed ecosystems at the margins of shrinking arctic ice sheets and glaciers supply CO2 to the atmosphere. Unpublished manuscript.