Elevated rates of heterotrophic respiration in shrub-conditioned arctic tundra soils

•Heterotrophic respiration is higher in soils under deciduous shrubs vs. non-shrub vegetation in a tundra ecosystem.•The addition of litter stimulates heterotrophic respiration in both soil types.•Shrubs may enhance heterotrophic respiration via higher litter inputs, but differences in soil organic matter quality or microbial community composition may also contribute to this pattern.