Carbon dynamics and soil microbial functioning in high arctic shrub communities: a comparative study of Dryas octopetala and Salix polaris

Arctic amplification is intensifying climate change impacts across the region, driving increases in air temperature, permafrost thawing, altered carbon cycling, and a higher frequency of rain-on-snow events. We monitored vegetation communities dominated by Dryas octopetala and Salix polaris for four years in order to gain a better understanding of the responses of the High Arctic tundra to climate forcing and its consequences for the carbon balance. These Svalbard Archipelago's predominant vascular plant species are well-known for being extremely sensitive to climate change. The study was carried out in Svalbard, Norway, on the Brøgger Peninsula close to Ny-Ålesund (78°57'00.0"N 11°34'00.0"E). Experimental design followed multidisciplinary approach and involved measurements of CO2 fluxes (ecosystem respiration, gross primary production and net ecosystem exchange), environmental parameters (soil temperature, moisture, photosynthetically active radiation), decomposition rate, spectral indices (NDVI, Greenness index and MCARI) and plants stable isotopes and elemental composition (δ13C, δ15N, %C, %N). Results revealed distinct yet complementary species strategies influencing ecosystem CO₂ exchange, despite similarly slow soil carbon and nitrogen turnover. However, both species, once colonize the soil, stimulate organic matter decomposition (positive priming). Soil microbial community associated with Salix was characterized by higher efficiency in decomposition of labile and recalcitrant substrates. Isotopic and physiological evidence indicates contrasting carbon- and water-use strategies between the two tundra species. Dryas maintains higher stomatal conductance and lower intrinsic water-use efficiency (iWUE), reflecting an acquisitive strategy that favors CO₂ uptake under low-nutrient, well-drained conditions. In contrast, Salix exhibits tighter stomatal control and higher iWUE, consistent with a more conservative, stress-tolerant strategy that allows rapid physiological adjustment to variable light, temperature, and moisture conditions. In conclusion, the future functioning of High Arctic tundra under climate warming will depend on the balance between these contrasting strategies, which jointly shape carbon cycling and vegetation resilience.