Scientists predict that rising winter temperatures will reduce snow cover in mountainous and temperate forests. Without the insulating effects of snow, the underlying soil will freeze more readily. New research by Maguire et al. suggests that increased soil freezing will hinder uptake of silicon by sugar maple roots. This lack of silicon could have significant ecological effects.
Sugar maples and other plants obtain silicon-containing substances from groundwater. The trees convert this silicon into biogenic silica, which can perform a variety of functions, such as structural support and protection against harmful fungi. Increased availability of silicon for plants has been linked to thicker leaves, increased chlorophyll content, enhanced seedling growth, and increased seed production. Silicon uptake by plants also affects silicon levels in downstream ecosystems.
The team hypothesized that silicon uptake could be hindered by reduced snow cover (previous research had shown similar results for nitrogen uptake). To test this idea, they obtained sugar maple roots that had been collected during a prior study in the Hubbard Brook Experimental Forest. Some roots were from trees grown in plots that were left alone for the first 6 weeks of two consecutive winters. The rest were from plots that had been cleared of snow in the first 48 hours after the winter’s first 6 weeks of snowfall.
The researchers measured and compared the amount of biogenic silica in sugar maple roots from each type of plot. Specifically, they examined the fine roots: the thin, filamentous roots responsible for absorbing water and nutrients from surrounding soil.
They found that soil freezing caused by snow cover removal reduced biogenic silica in sugar maple fine roots by 28%. This decrease represents a reduced uptake of about 8 kilomoles of silica per square kilometer of forest; a similar amount of silica is regularly transported out of temperate forests by streams and rivers. These results suggest that warmer winters could raise downstream silicon levels significantly, potentially affecting downstream ecosystems.
The researchers also made the first reported estimates of silicon content in sugar maple fine roots. The team calculated that the fine roots of a single sugar maple contain 29% of the total amount of biogenic silica in the tree, although accounting for just 4% of its total biomass.
Why might sugar maple fine roots contain such a high proportion of biogenic silica? The researchers hypothesize that biogenic silica could protect growing, water-seeking roots from abrasive soils. As temperatures rise and soils freeze more often, reduced silicon uptake could hinder the ability of trees to find and obtain water and nutrients.
Overall, the findings highlight the importance of sugar maples in controlling silicon levels in their ecosystem. Future studies could reveal further details of this role and clarify the potential impacts of climate change. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1002/2016JG003755, 2017)
—Sarah Stanley, Freelance Writer