Experimental deepening of the winter snowpack reduces fine root standing crop at treelines in northwest Alaska.

Snow is an important insulator of Arctic soils during winter and may be a source of soil moisture in summer. Changes in snow depth are likely to affect fine root growth and mortality via changes in soil temperature, moisture, and/or nutrient availability, which could alter aboveground growth and reproduction of Arctic vegetation. We explored fine root dynamics at three contrasting treelines in northwest Alaska. We used snowfences to increase snow depth relative to control and minirhizotrons to estimate fine root growth, standing crop, and overwinter loss. Experimental deepening of snowpacks led to warmer winter soils but did not affect growing season soil moisture. Deeper snow reduced fine root standing crop with no significant effects on overwinter fine root loss. Warmer soils in late winter were associated with warmer soils in early and mid-summer. Warmer early summer soils may have promoted early root growth. However, warmer July soils were associated with reduced fine root growth and smaller standing crops. We hypothesize that deeper snow improves plant access to soil nutrients, resulting in reduced investment in fine roots, potentially leaving additional resources to support aboveground growth and reproduction. Our results suggest one mechanism by which deeper snow could promote northern treeline advance.