Soil Carbon and Nitrogen in a CO2-Enriched Sweetgum Plantation
Iversen, C.M., Keller, J.K., Garten Jr., C.T. and Norby, R.J. 2012. Soil carbon and nitrogen cycling and storage throughout the soil profile in a sweetgum plantation after 11 years of CO2-enrichment. Global Change Biology 18: 1684-1697.
In an effort to help provide some experimental guidance in this area, Iversen et al. "explored whether greater C [carbon] and N [nitrogen] inputs from increased fine-root production and mortality in a CO2-enriched [to 565 ppm] forest plantation affect C and N cycling throughout the soil profile," which they did within the context of the Oak Ridge National Laboratory (ORNL) Free-Air CO2 Enrichment (FACE) experiment that was conducted in a Liquidambar styraciflua (sweetgum) plantation in eastern Tennessee (USA).
In doing so, Iversen et al. determined that (1) "greater inputs of fine roots resulted in the incorporation of new C into root-derived particulate organic matter pools to 90-cm depth," that (2) "even though production in the sweetgum stand was limited by soil N availability, soil C and N contents were greater throughout the soil profile under elevated CO2 at the conclusion of the experiment," that (3) "greater C inputs from fine-root detritus under elevated CO2 did not result in increased net N immobilization or C mineralization rates," and that (4) there was no indication of "significant priming of the decomposition of pre-experiment soil organic matter."
Given such results, the four U.S. researchers conclude that "taken together with an increased mean residence time of C in deeper soil pools, these findings indicate that C inputs from relatively deep roots under elevated CO2 may increase the potential for long-term soil C storage," and that "expanded representation of biogeochemical cycling throughout the soil profile may improve model projections of future forest responses to rising atmospheric CO2."
Iversen, C.M. 2010. Digging deeper: fine-root responses to rising atmospheric CO2 concentration in forested ecosystems. New Phytologist 186: 346-357.
Rumpel, C. and Kogel-Knabner, I. 2011. Deep soil organic matter - a key but poorly understood component of terrestrial C cycle. Plant and Soil 338: 143-158.