CO 2 exchange in three Canadian High Arctic ecosystems: response to long‐term experimental warming

• Published in: Global Change Biology
• Main Authors: Welker, Jeffrey M., Fahnestock, Jace T., Henry, Greg H. R., O'Dea, Kevin W., Chimner, Rodney A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2004
• Subjects: Arctic; Nunavut; Ellesmere Island; Alexandra Fiord; Tundra
• Online Access: http://dx.doi.org/10.1111/j.1365-2486.2004.00857.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2486.2004.00857.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2486.2004.00857.x

Abstract Carbon dioxide exchange, soil C and N, leaf mineral nutrition and leaf carbon isotope discrimination (LCID‐Δ) were measured in three High Arctic tundra ecosystems over 2 years under ambient and long‐term (9 years) warmed (∼2°C) conditions. These ecosystems are located at Alexandra Fiord (79°N) on Ellesmere Island, Nunavut, and span a soil water gradient; dry, mesic, and wet tundra. Growing season CO 2 fluxes (i.e., net ecosystem exchange (NEE), gross ecosystem photosynthesis (GEP), and ecosystem respiration ( R e )) were measured using an infrared gas analyzer and winter C losses were estimated by chemical absorption. All three tundra ecosystems lost CO 2 to the atmosphere during the winter, ranging from 7 to 12 g CO 2 ‐C m −2 season −1 being highest in the wet tundra. The period during the growing season when mesic tundra switch from being a CO 2 source to a CO 2 sink was increased by 2 weeks because of warming and increases in GEP. Warming during the summer stimulated dry tundra GEP more than R e and thus, NEE was consistently greater under warmed as opposed to ambient temperatures. In mesic tundra, warming stimulated GEP with no effect on R e increasing NEE by ∼10%, especially in the first half of the summer. During the ∼70 days growing season (mid‐June–mid‐August), the dry and wet tundra ecosystems were net CO 2 ‐C sinks (30 and 67 g C m −2 season −1 , respectively) and the mesic ecosystem was a net C source (58 g C m −2 season −1 ) to the atmosphere under ambient temperature conditions, due in part to unusual glacier melt water flooding that occurred in the mesic tundra. Experimental warming during the growing season increased net C uptake by ∼12% in dry tundra, but reduced net C uptake by ∼20% in wet tundra primarily because of greater rates of R e as opposed to lower rates of GEP. Mesic tundra responded to long‐term warming with ∼30% increase in GEP with almost no change in R e reducing this tundra type to a slight C source (17 g C m −2 season −1 ). Warming caused LCID of Dryas integrafolia ...