The Progressive Nitrogen Limitation Hypothesis Takes Another Hit
Langley, J.A., McKinley, D.C., Wolf, A.A., Hungate, B.A., Drake, B.G. and Megonigal, J.P. 2009. Priming depletes soil carbon and releases nitrogen in a scrub-oak ecosystem exposed to elevated CO2. Soil Biology & Biochemistry 41: 54-60.
The six researchers report that elevated atmospheric CO2 (to 350 ppm above ambient concentrations) tended to increase net N mineralization in the top 10 cm of the soil, but that it also decreased total soil organic carbon content there by 21%. However, that loss of carbon mass was only equivalent to "roughly one-third of the increase in plant biomass that occurred in the same experiment." In addition, they state that the strongest increases in net N mineralization were observed in the 10-30 cm depth increment, and that "release of N from this depth may have allowed the sustained CO2 effect on productivity in this scrub-oak forest," which over the four years leading up to their study "increased litterfall by 19-59%," for which latter figures they cite the work of Hungate et al. (2006).
Once again, we have yet another experimental demonstration of the fact that atmospheric CO2 enrichment generally enables plants to find the extra nitrogen they need to take full advantage of the aerial fertilization effect of elevated atmospheric CO2 concentrations, with the result that total ecosystem carbon content is increased, resulting in a negative feedback to anthropogenic CO2 emissions.
Hungate, B.A., Johnson, D.W., Dijkstra, P., Hymus, G., Stiling, P., Megonigal, J.P., Pagel, A.L., Moan, J.L., Day, F., Li, J., Hinkle, C.R and Drake, B.G. 2006. Nitrogen cycling during seven years of atmospheric CO2 enrichment in a scrub oak woodland. Ecology 87: 26-40.
Reich, P.B., Hungate, B.A. and Luo, Y. 2006. Carbon-nitrogen interactions in terrestrial ecosystems in response to rising atmospheric carbon dioxide. Annual Review of Ecology, Evolution and Systematics 37: 611-636.