Reference
Nadelhoffer, K.J., Emmett, B.A., Gundersen, P., Kjonaas, O.J., Koopmans, C.J., Schleppi, P., Tietema, A. and Wright, R.F. 1999. Nitrogen deposition makes a minor contribution to carbon sequestration in temperate forests. Nature 398: 145-148.
What was done
The authors conducted a number of 15N-tracer studies in six European and three North American forests over periods of one to three years to evaluate the potential of aerial nitrogen deposition to enhance the carbon sink strengths of temperate forests.
What was learned
The data from the several studies revealed that elevated nitrogen deposition due to human activities is "unlikely to be a major contributor" to the large CO2 sink that is implicated to exist in northern temperate forests by several other types of analysis. The authors thus conclude that "other factors" must be responsible for the great terrestrial carbon sink that has been documented to be drawing huge amounts of carbon out of the air as a result of the ongoing acceleration in the growth rates of the world's forests (see our Journal Reviews: CO2 Sequestration in North America and CO2 Sequestration by Tropical Trees).
What it means
As more and more potential candidates are eliminated from the global CO2 sequestration sweepstakes, the aerial fertilization effect of CO2 on plants stands taller and taller with each passing day. With Nadelhoffer et al.'s elimination of anthropogenic nitrogen deposition and Idso et al.'s (1999) elimination of global warming as prime contenders, all of the credible evidence points to the ongoing rise in the air's CO2 content as the major cause of this biospheric growth-enhancing phenomenon.
References
Idso, C.D., Idso, S.B., Balling, R.C., Jr. 1999. The relationship between near-surface air temperature over land and the annual amplitude of the atmosphere's seasonal CO2 cycle. Environmental and Experimental Botany 41: 31-37.
Reviewed 15 April 1999