Joanna C. Carey, Thomas C. Parker, Ned Fetcher and Jianwu Tang
Arctic ecosystems are experiencing the effects of climate change to a much larger degree than most other places on Earth. Rapid Arctic warming is changing the types of plants that proliferate in tundra ecosystems, with shrubs often outcompeting grass and sedge species, and permafrost thaw increasing the area of wetlands.
Such changes in plant species composition have direct impacts for plant silica (SiO2) cycling in the Arctic. Land plants consume vast quantities of silica, typically incorporated passively in their tissue as the plant consumes water (i.e. transpires). However, the amount of silica accumulated by plants varies dramatically by species type, with large ranges of plant silica concentrations observed across species.
We made the first measurements of how much silica is stored in above- and belowground portions of the three main types of tundra found in the Alaskan Arctic (moist acidic tundra, moist non-acidic tundra, and wet sedge tundra). We then estimated how shift in tundra species composition alters net plant silica storage. We find that increasing shrub abundance will increase aboveground net silica storage in land plants, whereas increasing wetland area will have the opposite effect, by decreasing net silica storage in aboveground vegetation. These results are driven mostly by shifts in total biomass production, rather than plant silica concentrations, as shrub tundra ecosystems are more productive than tussock tundra ecosystems, while wetlands are less productive than the other tundra types.
Changes in the amount of silica stored in land plants will likely alter the amount of silica exported from terrestrial systems into downstream waters. Rates of silica export from land to the sea have important consequences for carbon cycling in aquatic systems, since silica concentrations in coastal Arctic waters can often dictate phytoplankton growth rates, or rates of primary production. Our results highlight that Arctic warming will alter the amount of silica stored in land plants, with potential unrealized consequences for downstream ecosystems.
Image Caption: A tussock (dominated by Eriophorum vaginatum) at Toolik Field Station (Alaska, USA). Photo credit: Joanna C. Carey