Variation in Peak Growing Season Net Ecosystem Production Across the Canadian Arctic

摘要

Tundra ecosystems store vast amounts of soil organic carbon, which may be sensitive to climatic change. Net ecosystem production, NEP, is the net exchange of carbon dioxide (CO_2) between landscapes and the atmosphere, and represents the balance between CO_2 uptake by photosynthesis and release by decomposition and autotrophic respiration. Here we examine CO_2 exchange across seven sites in the Canadian low and high Arctic during the peak growing season (July) in summer 2008. All sites were net sinks for atmospheric CO_2 (NEP ranged from 5 to 67 g C m~(-2)), with low Arctic sites being substantially larger CO_2 sinks. The spatial difference in NEP between low and high Arctic sites was determined more by CO_2 uptake via gross ecosystem production than by CO_2 release via ecosystem respiration. Maximum gross ecosystem production at the low Arctic sites (average 8.6 μmol m~(-2) s~(-1)) was about 4 times larger than for high Arctic sites (average 2.4 μmol m~(-2) s~(-1)). NEP decreased with increasing temperature at all low Arctic sites, driven largely by the ecosystem respiration response. No consistent temperature response was found for the high Arctic sites. The results of this study clearly indicate there are large differences in tundra CO_2 exchange between high and low Arctic environments and this difference should be a central consideration in studies of Arctic carbon balance and climate change.