Ecological controls on net ecosystem productivity of a mesic arctic tundra under current and future climates

• Published in: Journal of Geophysical Research
• Main Authors: Grant, R.F., Humphreys, E. (Elyn), Lafleur, P.M., Dimitrov, D.D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2011
• Subjects: Arctic; Canada; Daring Lake; Climate change; Tundra
• Online Access: https://ir.library.carleton.ca/pub/5432; https://doi.org/10.1029/2010JG001555

Changes in arctic C stocks with climate are thought to be caused by rising net primary productivity (NPP) during longer and warmer growing seasons, offset by rising heterotrophic respiration (R h ) in warmer and deeper soil active layers. In this study, we used the process model ecosys to test hypotheses for these changes with CO 2 and energy fluxes measured by eddy covariance over a mesic shrub tundra at Daring Lake, Canada, under varying growing seasons. These tests corroborated substantial rises in NPP, smaller rises in R h , and, hence, rises in net ecosystem productivity (NEP) from 17 to 45 g C m -2 yr -1 (net C sink), modeled with higher T a and longer growing seasons. However, NEP was found to decline briefly during midsummer warming events (T a > 20°C). A model run under climate change predicted for Daring Lake indicated that rises in NPP would exceed those in R h during the first 100 years, causing NEP to rise. Rises in NPP were driven by more rapid net N mineralization from more rapid R h in warming soils. However, greater declines in NEP were modeled during more frequent and intense midsummer warming events as climate change progressed. Consequently, average annual NEP (± interannual variability) rose from 30 (±13) g C m -2 yr -1 under current climate to 57 (±40) g C m -2 yr -1 after 90 years but declined to 44 (±51) g C m -2 yr -1 after 150 years, indicating that gains in tundra NEP under climate change may not be indefinite. Copyright 2011 by the American