Respiration from soil and ground cover vegetation under tundra shrubs

Atmospheric warming is expected to cause shifts in arctic tundra vegetation composition, especially in the abundance and distribution of shrub species. Greater shrub abundance will impact the carbon exchanges between tundra ecosystems and the atmosphere, including ecosystem respiration. Here, total respiration under the shrub canopy (R-T) and its components soil respiration (R-S) and respiration from the ground cover vegetation (R-G) were investigated at three tundra sites in the Canadian Low Arctic with varying shrub coverage. Seasonal R-T and R-S mean values were significantly greater (P < 0.05) at the site with greatest shrub abundance; mean values were 3.70 and 3.22 mu mol m(-2) s(-1), respectively. Mean R-G did not differ among sites; mean values ranged from 0.45 to 0.52 mu mol m(-2) s(-1). Soil temperature exerted a stronger control on R-T and R-S compared to soil moisture. Differences in R-T and R-S among sites were attributed to differences in soil properties, such as soil total N content and bulk density. These findings suggest that belowground sources of respired carbon dioxide in Low Arctic tundra may vary with long-term shrub expansion as soil microclimate conditions and physiochemical properties adjust to changes in shrub coverage.