Ericaceous dwarf shrubs contribute a significant but drought-sensitive fraction of soil respiration in a boreal pine forest

Boreal forests often have a dense understory of ericaceous dwarf shrubs with ecological adaptations that contrast those of the canopy-forming trees. It is therefore important to quantify contributions by understory shrubs to ecosystem processes and disentangle shrub- and tree-driven responses, and their interactions, to climatic factors. We quantified soil respiration driven by the pine canopy and the ericaceous shrub understory over three years, using a factorial pine root-exclusion and shrub-removal experiment in a mature Pinus sylvestris forest. Soil temperature and moisture-related responses of respiration attributed to autotrophic (shrubs, pine roots) and heterotrophs were compared. Additionally, we assessed effects of interactions between these functional groups on soil nitrogen availability and respiration. Understory shrubs accounted for 22 ± 10% of total autotrophic respiration, reflecting the ericaceous proportion of fine root production in the ecosystem. Heterotrophic respira...