Effects of CO₂ and nutrient availability on mineral weathering in controlled tree growth experiments

Abstract

[1] We sought to determine the effect of elevated atmospheric CO 2 on mineral weathering reactions in midlatitude carbonate-bearing forest soils of differing nutrient availability. Increased plant growth and soil respiration under elevated atmospheric CO 2 suggest increased rates of carbon cycling, which may affect mineral weathering. A randomized complete block experiment was conducted, where aspen and maple saplings were grown in open top chambers under two levels of atmospheric CO 2 and soil N. Soil solution chemistry and soil gas PCO 2 profiles beneath aspen were collected from planting (1997) to harvest (1999). Carbonate mineral weathering products (Ca 2+ , Mg 2+ , HCO 3 À ) dominated solutions, which were saturated with respect to calcite. Soil PCO 2 values at 25 cm depth were 41% higher in high N soils, but CO 2 treatment was not significant. An ANOVA model tested treatment effects on spring 1998 solution chemistry. CO 2 treatment had a significant effect on DIC, which was 12% higher in elevated than ambient CO 2 chambers. Little effect of CO 2 treatment was observed in low N soils. In high N soils, solutions had higher concentrations of carbonate weathering products (DIC, 15%; HCO 3 À , 27%; Ca 2+ , 3%, not significant; Mg 2+ , 5%, not significant). Soil N availability had a significant, positive, effect on mean concentrations of Ca , and DOC. The soil N treatment difference in solutes may result from differences in PCO 2 and, additionally, NO 3 À from organic matter decomposition. Our results suggest that increased carbonate weathering may occur under increased atmospheric CO 2 and in fertile soils.

CO<sub>2</sub> enrichment increases nutrient leaching from model forest ecosystems in subtropical China

“…This result is in accordance with previous studies (Andrews and Schlesinger, 2001;Williams et al, 2003). Andrews and Schlesinger (2001) and Williams et al (2003) demonstrated that under elevated atmospheric CO 2 , increased plant growth and soil respiration affected mineral weathering.…”

“…This result is in accordance with previous studies (Andrews and Schlesinger, 2001;Williams et al, 2003). Andrews and Schlesinger (2001) and Williams et al (2003) demonstrated that under elevated atmospheric CO 2 , increased plant growth and soil respiration affected mineral weathering. Carbonic acid, which is a byproduct of soil and root respiration, can accelerate the weathering of silicates and carbonates, thus releasing greater amounts of Si and base cations in the soil solution (Berner et al, 1983).…”

“…This was due to both reduced leaching water volume and decreased ion concentrations in leachates. Williams et al (2003) obtained the opposite results, with greater element concentrations in the soil solution when they applied high CO 2 to Nenriched soils. This might be attributed to the differences in the soils used.…”

“…This might be attributed to the differences in the soils used. Williams et al (2003) worked on a carbonate dominated soil which was saturated in base cations while we worked on an acid lateritic soil which is already largely depleted in base cations. As a consequence, it is possible that the maximum weathering rates were already attained by the sole application of the high CO 2 treatment in our experiment.…”

Process‐based modeling of silicate mineral weathering responses to increasing atmospheric CO2 and climate change

“…The underlying rationale for assuming this is, broadly, that vegetation productivity increases (1) the secretion of organic acids and chelators into soils by roots and their associated network of mycorrhizal fungi to obtain nutrient elements (principally P, K, Ca and Mg) from silicate minerals [Berner et al, 2003], (2) soil carbon dioxide partial pressure (PCO 2 , thus depressing pH) as a result of root and mycorrhizal respiration and microbial decomposition of organic matter, and (3) creation and retention of reactive mineral surfaces through mechanical cleavage by root growth and mycorrhizal biomass, and by anchoring colloidal soil particles against erosion to permit greater retention of soil water. The increased production of organic acids, elevated soil PCO 2 and decreased pH can all accelerate the weathering of silicate minerals through abiotic mineral dissolution mechanisms that occur in terrestrial ecosystems [Andrews and Schlesinger, 2001;Williams et al, 2003].…”