Gesche Blume-Werry, Roland Jansson, Ann Milbau

When snow melts earlier, plants often respond by advancing the time of leaf-out and flowering. This change can affect the interaction between plants and their pollinators and thus plant reproduction, but it also affects larger-scale ecosystem processes such as water, carbon and nutrient cycles. For example, when plants have leaves and are actively growing, they take carbon dioxide out of the air and store carbon in their tissues. Plant roots are key players in these ecosystem processes because plants use them to take up water and nutrients, and because they are a substantial part of both plant biomass and production they are also important for carbon storage. However, as they are hidden in the soil they are more difficult to measure and the role of an earlier snowmelt on timing of plant processes belowground has never been assessed.

We experimentally advanced snowmelt (with black cloth on the snow surface) in two very different plant communities and measured timing of leaf-out and flowering as well as timing of root growth. To measure the timing of root growth we used minirhizotrons, which are non-destructive in-situ measurements of fine root growth that utilize transparent tubes permanently buried in the soil and a camera system to take recurrent pictures of roots.

Our results show that earlier snowmelt increased soil temperatures and advanced leaf-out and flowering of plants, as we expected from previous studies. However, timing and amounts of root growth were unaffected in both plant communities, even though we effectively manipulated those factors that have previously been suggested as important drivers of root growth. Importantly, our findings show that aboveground plant responses cannot be directly translated belowground, and suggest that root growth starts early in spring regardless of temperature or snowmelt conditions.

Image caption: Close-up of a fine root, picture taken with a minirhizotron camera. Picture by Gesche Blume-Werry.
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