Does elevated CO2 alter silica uptake in trees?

Area of Science:

• Environmental Science
• Plant Ecology
• Biogeochemistry

Background:

• Human activities have significantly altered global carbon (C) and Nitrogen (N) cycles, with atmospheric CO2 increasing by 40% and N cycling doubling.
• Long-term free-air CO2 enrichment experiments globally investigate plant responses to rising CO2 levels.

Purpose of the Study:

• To investigate the effects of elevated atmospheric CO2 and N fertilization on silicon (Si) uptake in diverse tree species.
• To quantify foliar biogenic silica concentrations and forest Si uptake rates under different experimental conditions.

Main Methods:

• Measurements of foliar biogenic silica concentrations in six tree species (Pinus taeda and five hardwoods) across three treatments: CO2 enrichment, N enrichment, and combined CO2 and N enrichment.
• Calculation of forest Si uptake rates based on net primary production and aboveground Si concentrations under ambient and elevated CO2.

Main Results:

• No consistent trends in foliar Si concentration were observed under elevated CO2, N fertilization, or combined treatments.
• Two-thirds of the studied tree species exhibited higher foliar Si concentrations than known Si accumulators like grasses.
• Elevated CO2 increased forest Si uptake by 20-26%, primarily driven by increased net primary production.

Conclusions:

• Forests, particularly under elevated CO2, play a significant role in the terrestrial silica cycle.
• Enhanced forest Si uptake intensifies the terrestrial silica pump, with implications for carbon sequestration and downstream ecosystems.