Did elevated atmospheric CO 2 alter soil mineral weathering?: an analysis of 5‐year soil water chemistry data at Duke FACE study

• Published in: Global Change Biology
• Main Authors: OH, NEUNG‐HWAN, HOFMOCKEL, MICHAEL, LAVINE, MICHAEL L., RICHTER, DANIEL D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2007
• Subjects: Carbonic acid
• Online Access: http://dx.doi.org/10.1111/j.1365-2486.2007.01452.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2486.2007.01452.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2486.2007.01452.x

Abstract A principal driver of biogeochemical weathering of the Earth's crust is soil CO 2 , produced mainly by plant roots and soil heterotrophs, a water‐soluble gas that forms carbonic acid which reacts with soil minerals via cation exchange and mineral dissolution. We examined effects of elevated atmospheric CO 2 (ambient + 200 ppmv) in a young pine forest on belowground carbonic acid chemistry of soil water. Soil water was collected every 2–3 weeks over a 5‐year period from O horizons and at 15, 70, and 200 cm in mineral soils at the Duke free air CO 2 enrichment facility located in a warm temperate climate in North Carolina, USA. Concentrations of major ions were volume‐weighted and statistically analyzed using linear mixed‐effects models. Experimental interest was placed on interactive effects of CO 2 treatment and time: to test effects of gradually increasing CO 2 in deep soil horizons where CO 2 is highest in concentration, and to protect against inherent plot‐to‐plot differences in soil water chemistry being interpreted as responses to CO 2 treatments. Although significant time‐dependent interactive effects were reported for soil CO 2 , interactive effects were not significant for soil water constituents. These data, combined with limited pretreatment sampling of soil water chemistry and recently determined large heterogeneity in soil solid chemistry at this site, indicate that CO 2 ‐weathering response is smaller than the more‐than‐doubling of weathering reported previously and that increases in weathering are masked by in situ soil heterogeneity. Although the hypothesis that elevated CO 2 increases cation leaching and weathering dissolution is supported in laboratory experiments and field studies, quantifying the stimulation of chemical weathering by elevated atmospheric CO 2 remains to be tested rigorously in the field.