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Title: Nitrogen-mediated effects of elevated CO2 on intra-aggregate soil pore structure

Author
item CAPLAN, JOSHUA - Rutgers University
item GIMENEZ, DANIEL - Rutgers University
item SUBROY, VANDANA - Rutgers University
item HECK, RICHARD - University Of Guelph
item Prior, Stephen - Steve
item Runion, George
item Torbert, Henry - Allen

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2016
Publication Date: 4/1/2017
Publication URL: https://handle.nal.usda.gov/10113/5763055
Citation: Caplan, J.S., Gimenez, D., Subroy, V., Heck, R.J., Prior, S.A., Runion, G.B., Torbert III, H.A. 2017. Nitrogen-mediated effects of elevated CO2 on intra-aggregate soil pore structure. Global Change Biology. 23:1585-1597. doi:10.1111/gcb.13496.

Interpretive Summary: Past global change research has shown that N enrichment and elevated atmospheric CO2 can affect belowground activities in the soil. The long-term effects of elevated CO2 and N fertilization in a bahiagrass pasture grown on a sandy loam soil were studied. Results showed that soil pore structure and water retention could be altered by elevated CO2 and the direction of change depends strongly on N availability. Root dynamics could explain pore structural responses to N availability, but CO2 related changes may be explained by microbial processes that affected the availability of organic matter needed for soil aggregation. Findings suggest that soil aggregation, and thus pore structure, could undergo N-dependent changes as atmospheric CO2 concentrations rise, having global-scale implications for water balance, carbon storage, and related rhizosphere functions.

Technical Abstract: While previous elevated atmospheric CO2 research has addressed changes in belowground processes, its effects on soil structure remain virtually undescribed. This study examined the long-term effects of elevated CO2 and N fertilization on soil structural changes in a bahiagrass pasture grown on a sandy loam soil. This work utilized image analysis and fractal dimension techniques to investigated soil structural changes. Results suggest that biotic changes may induce soil structural changes that can alter soil water storage with these response dependent on N availability. Root dynamics could explain pore structural responses to N availability, but CO2 related changes may be explained by microbial processes that affected the availability of organic matter needed for soil aggregation. Results suggest that elevated CO2-induced soil structural loss is possible when large aggregates are degraded and therefore lose the ability to hold water in large pores. However, our results also suggest that, in soils with potential for further aggregation, additions of organic matter can reverse this effect, inducing structural development and raising soil water retention. Soil structural change is a poorly understood consequence of global change. This can partly be attributed to methodological challenges that new tools are helping to overcome. The combination of a long-term, multi-factor global change experiment and sensitive measurement tools yielded useful insights in this case. Similar approaches could be applied to soils from other global change field studies, especially those focused on multiple, interacting factors including warming and altered precipitation regimes.