Volume 9, Number 35: 30 August 2006
In an Opinion piece recently published in Global Change Biology, Phoenix et al. (2006) report that "the stability of vegetation in many natural and semi-natural ecosystems is dependent upon low [our italics] soil fertility," citing the work of Bobbink et al. (1998) and Aerts and Chapin (2000). Stating further that nitrogen (N) deposition "is known to be an important driver of biodiversity loss," they say that "some expert opinion considers that N deposition will be the third greatest driver of biodiversity loss at the global scale (after land use and climate change) over the coming century (Sala et al., 2000)."
What brought about this unfortunate state of affairs? The twelve authors of the opinion piece report that "human activities have lead to major increases in global emissions of nitrogen to the atmosphere (Holland et al., 1999) with global emissions of fixed N now estimated to be nearly four fold greater [our italics] than before the agricultural and industrial revolutions," referencing Fowler et al. (2004a) as the source of this comparison. In fact, in some areas of both Northern Europe and North America, they say that rates of N deposition "are currently an order of magnitude greater [our italics] than in preindustrial times," based on the work of Holland et al. (1999), Bobbink and Lamers (2002) and Fowler et al. (2004b). As for the future, the researchers suggest that global emissions of anthropogenic N will continue to increase, and that the total deposition of reactive N likely will be "nearly twofold greater [our italics] by 2050 compared with deposition in the early 1990s (Galloway et al., 2004)."
What can be done about this unfortunate state of affairs? Phoenix et al. sidestep the question and make no recommendations for either preventive or ameliorative measures, pushing only for further study of the subject via "a greater global approach to assessing the impacts of N deposition" that includes "better regional and local mapping of N deposition rates." Humanity as a whole, however, is doing something about the problem -- albeit at a subconscious and unplanned level -- via the burning of the coal, gas and oil that have fueled both the agricultural and industrial revolutions.
The rationale for this statement derives from the fact that the CO2 released to the air as a consequence of the combustion process is also "fueling," i.e., enhancing, the growth of nearly all of earth's plants (see, for example, the items filed under Greening of the Earth in our Subject Index, as well the many items archived in our Plant Growth Databases); and this enhanced growth provides a huge sink for the extra N that is delivered to the environment as a consequence of anthropogenic N deposition. In fact, as noted in the many reviews we have written about the progressive nitrogen limitation hypothesis (find them using the Search feature of our website), many researchers believe there is currently (and will continue to be) insufficient environmental N to sustain the full potential of the aerial fertilization effect produced by mankind's CO2 emissions. Hence, it can be appreciated that the two phenomena (anthropogenic CO2 emission and N deposition) tend to impact each other in ways that positively impact the biosphere, with anthropogenic N deposition bringing out the best in the aerial fertilization effect resulting from anthropogenic CO2 emissions, and with anthropogenic CO2 emissions suppressing the worst of the biodiversity-destroying effect of anthropogenic N deposition.
Yes, "checks and balances" are operative in more than the constitutions of countries; they play major roles in the constitution of nature as well.
Sherwood, Keith and Craig Idso
References
Aerts, R. and Chapin, F.S. 2000. The mineral nutrition of wild plants revisited: a re-evaluation of processes and patterns. Advances in Ecological Research 30: 1-67.
Bobbink, R., Hornung, M. and Roelofs, J.M. 1998. The effects of airborne pollutants on species diversity in natural and semi-natural European vegetation. Journal of Ecology 86: 717-738.
Bobbink, R. and Lamers, L.P.M. 2002. Effects of increased nitrogen deposition. In: Bell, J.N.D. and Treshow, M., Eds. Air Pollution and Plant Life. John Wiley and Sons Ltd., Chichester, United Kingdom.
Fowler, D., Muller, J.B.A. and Sheppard, L.J. 2004a. The GaNE programme in a global perspective. Water, Air and Soil Pollution: Focus 4: 3-8.
Fowler, D., O'Donoghue, M., Muller, J.B.A., Smith, R.I., Dragosits, U., Skiba, U., Sutton, M.A. and Brimblecombe, P. 2004b. A chronology of nitrogen deposition in the UK between 1900 and 2000. Water, Air and Soil Pollution: Focus 4: 9-23.
Galloway, J.N., Dentener, F.J., Capone, D.G., Boyer, E.W., Howarth, R.W., Seitzinger, S.P., Asner, G.P., Cleveland, C.C., Green, P.A., Holland, E.A., Karl, D.M., Michaels, A.F., Porter, J.H., Townsend, A.R. and Vöosmarty, C.J. 2004. Nitrogen cycles: past, present, and future. Biogeochemistry 70: 153-226.
Holland, E.A., Dentener, F.J., Braswell, B.H. and Sulzman, J.M. 1999. Contemporary and pre-industrial global reactive nitrogen budgets. Biogeochemistry 46: 7-43.
Phoenix, G.K., Hicks, W.K., Cinderby, S., Kuylenstierna, J.C.I., Stock, W.D., Dentener, F.J., Giller, K.E., Austin, A.T., Lefroy, R.D.B., Gimeno, B.S., Ashmore, M.R. and Ineson, P. 2006. Atmospheric nitrogen deposition in world biodiversity hotspots: the need for a greater global perspective in assessing N deposition impacts. Global Change Biology 12: 1-7.
Sala, O.E., Chapin III, F.S., Armesto, J.J., Berlow, E., Bloomfield, J., Dirzo, R., Huber-Sanwald, E., Huenneke, L.F., Jackson, R.B., Kinzig, A., Leemans, R., Lodge, D.M., Mooney, H.A., Oesterheld, M., Poff, N.L., Sykes, M.T., Walker, B.H., Walker, M. and Wall, D.H. 2000. Global biodiversity scenarios for the year 2100. Science 287: 1770-1774.