Elevated CO₂ has been shown to increase plant biomass, which also stimulates the growth of fine roots and root secretions in soils (Pendall et al. 2004). The increase in root growth allows for more carbon below ground, which can help accelerate decomposition and nutrient cycling. However, any changes in the chemical composition of organic materials, such as litter, from elevated CO₂ can also result in changes to decomposition, which would also alter soil nutrients. Increased lignin and decreased nitrogen content from elevated CO₂ are known to lower decomposition rates and can make some nutrients less available over time. Site-specific effects will be very dependent on local soil and vegetation conditions.

Pendell E., S. Bridgham, P.J. Hanson, B. Hungate, D.W. Kicklighter, D.W. Johnson, B.E. Law, Y. Luo, J.P. Megonigal, M. Olsrud, M.G. Ryan, and S. Wang. 2004. Belowground process responses to elevated CO₂ and temperature: a discussion of observations, measurement methods, and models. New Phytologist. 162: 311-322.

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