Limited variation in proportional contributions of auto- and heterotrophic soil respiration, despite large differences in vegetation structure and function in the Low Arctic

Abstract

Arctic ecosystems contain vast stores of soil carbon (C), yet our understanding of the factors controlling CO2 efflux from tundra soils remains poor. Partitioning soil respiration (RS) into heterotrophic (RH) and autotrophic (RA) sources can help elucidate the relative contributions from microbial breakdown of soil organic matter (SOM) and root and rhizospheric activities—two processes that can have contrasting effects on long-term soil C stocks. Using two techniques, we quantified the magnitudes, relative proportions and environmental drivers of RH and RA in four common arctic vegetation types in West Greenland. We employed a trenching method in large patches of Betula nana, Salix glauca, mixed-shrub (equal mix of Betula and Salix) and graminoids dominated by Poa spp. At a nearby location, we introduced 13CO2 to Betula- and graminoid-dominated plots. The difference in the autotrophic proportion (RA/RS) between methods was minimal, providing confidence that our more extensive trenching approach provided accurate estimates of RA and RH. Despite contrasting microclimate conditions, large differences in vegetation structure and wide variation in RS, there were minimal differences in mean RA/RS (0.40–0.48 across all vegetation types). Our results suggest that RA/RS may be more conservative than previously thought for low-productivity ecosystems. We suggest that partitioning RS into RA and RH may be a useful tool to identify ecosystems that have fallen out of equilibrium and may be poised to either gain or lose soil C.