Autumnal warming does not change root phenology in two contrasting vegetation types of subarctic tundra

Abstract

Background and aims: Root phenology is important in controlling carbon and nutrient fluxes in terrestrial ecosystems, yet, remains largely unexplored, especially in the Arctic. We compared below- and aboveground phenology and ending of the growing season in two contrasting vegetation types of subarctic tundra: heath and meadow, and their response to experimental warming in autumn. Methods: Root phenology was measured in-situ with minirhizotrons and compared with aboveground phenology assessed with repeat digital photography. Results: The end of the growing season, both below- and aboveground, was similar in meadow and heath and the belowground growing season ended later than aboveground in the two vegetation types. Root growth was higher and less equally distributed over time in meadow compared to heath. The warming treatment increased air and soil temperature by 0.5 °C and slightly increased aboveground greenness, but did not affect root growth or prolong the below- and aboveground growing season in either of the vegetation types. Conclusions: These results imply that vegetation types differ in root dynamics and suggest that other factors than temperature control autumnal root growth in these ecosystems. Further investigations of root phenology will help to identify those drivers, in which including responses of functionally contrasting vegetation types will help to estimate how climate change affects belowground processes and their roles in ecosystem function.