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GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 17, NO. 2, 1041, doi:10.1029/2002GB001925, 2003

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

Erika L. Williams

Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, USA

Lynn M. Walter

Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, USA

Timothy C. W. Ku

Department of Earth and Environmental Sciences, Wesleyan University, Middletown, Connecticut, USA

George W. Kling

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA

Donald R. Zak

School of Natural Resources and Environment, University of Michigan, Ann Arbor, Michigan, USA

Abstract

We sought to determine the effect of elevated atmospheric CO₂ on mineral weathering reactions in midlatitude carbonate-bearing forest soils of differing nutrient availability. Increased plant growth and soil respiration under elevated atmospheric CO₂ 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 CO₂ and soil N. Soil solution chemistry and soil gas PCO₂ profiles beneath aspen were collected from planting (1997) to harvest (1999). Carbonate mineral weathering products (Ca²⁺, Mg²⁺, HCO₃⁻) dominated solutions, which were saturated with respect to calcite. Soil PCO₂ values at 25 cm depth were 41% higher in high N soils, but CO₂ treatment was not significant. An ANOVA model tested treatment effects on spring 1998 solution chemistry. CO₂ treatment had a significant effect on DIC, which was 12% higher in elevated than ambient CO₂ chambers. Little effect of CO₂ treatment was observed in low N soils. In high N soils, solutions had higher concentrations of carbonate weathering products (DIC, 15%; HCO₃⁻, 27%; Ca²⁺, 3%, not significant; Mg²⁺, 5%, not significant). Soil N availability had a significant, positive, effect on mean concentrations of Ca²⁺, Mg²⁺, K⁺, Na⁺, NO₃⁻, SO₄²⁻, and DOC. The soil N treatment difference in solutes may result from differences in PCO₂ and, additionally, NO₃⁻ from organic matter decomposition. Our results suggest that increased carbonate weathering may occur under increased atmospheric CO₂ and in fertile soils.

Published 2 May 2003.

Index Terms: 1030 Geochemistry: Geochemical cycles (0330); 1045 Geochemistry: Low-temperature geochemistry; 1886 Hydrology: Weathering (1625); 1615 Global Change: Biogeochemical processes (4805); 1806 Hydrology: Chemistry of fresh water.

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Citation: Williams, E. L., L. M. Walter, T. C. W. Ku, G. W. Kling, and D. R. Zak (2003), Effects of CO₂ and nutrient availability on mineral weathering in controlled tree growth experiments, Global Biogeochem. Cycles, 17(2), 1041, doi:10.1029/2002GB001925.

Copyright 2003 by the American Geophysical Union.