What was done
The authors write that among terrestrial ecosystems, "forests are considered as the most important terrestrial reservoirs of biological diversity, containing as much as two thirds of all plant and animal species," noting that they cover four billion hectares or 30% of the earth's land surface, and that 20-40% of forest biomass is made up of roots. Hence, in a Special Feature Invited Review, they briefly discuss the status of our knowledge of trees and their roots in our globally-changing environment.

What was learned
Starting with the bad, Brunner and Godbold report that soils of forest ecosystems "have been affected by high atmospheric inputs of acidifying pollutants (S and N compounds) originating from the combustion of fossil fuels in power generation, industry, and transportation," and that "these inputs have led to an acceleration of soil acidification, loss of basic cations, and release of Al ions into soil solution," noting that "besides its effect on soil acidification, excessive inputs of atmospheric N result in nitrate leaching and relative shortage of other nutritional elements for plants." Nevertheless, as they continue, "a trend of increasing aboveground growth of trees in European forests over a long term can be observed (Spiecker, 1999)," and they say that "these positive trends are attributed mainly to the increased contents of CO2 in the atmosphere and to enhanced N depositions," noting that "both elevated CO2 concentrations and N depositions lead to increased plant biomass, including that of roots." More specifically, they report that "recent analysis in experiments with elevated CO2 concentrations have shown increases of the forest net primary productivity by about 23% (Norby et al., 2005), and, in the case of poplars, an increase of the standing root biomass between 47%-76% (Lukac et al., 2003) and 113% (King et al., 2002)." In addition, they state that "the turnover of fine roots is also positively influenced by elevated CO2 concentrations and can be increased in poplars by 25%-45% (Lukac et al., 2003)."

What it means
In spite of all of the negative aspects attributed to increasing fossil fuel combustion over the past several decades, earth's trees and their roots are generally doing better than ever, thanks, it would appear, to the dual factors of increasing atmospheric CO2 concentrations and N depositions that come from the very same source.

References
King, J.S., Albaugh, T.J., Allen, H.L., Buford, M., Strain, B.R. and Dougherty, P. 2002. Seasonal dynamics of fine roots relative to foliage and stem growth in loblolly pine (Pinus taeda L.) as affected by water and nutrient availability. New Phytologist 154: 389-398.

Lukac, M., Calfapietra, C. and Godbold, D.L. 2003. Production, turnover and mycorrhizal colonization of root systems of three Populus species grown under elevated CO2 (POPFACE). Global Change Biology 9: 838-848.

Norby, R.J., DeLucia, E.H., Gielen, B., Calfapietra, C., Giardina, C.P., King, S.J., Ledford, J., McCarthy, H.R., Moore, D.J.P., Ceulemans, R., De Angelis, P., Finzi, A.C., Karnosky, D.F., Kubiske, M.E., Lukac, M., Pregitzer, K.S., Scarasci-Mugnozza, G.E., Schlesinger, W.H. and Oren, R. 2005. Forest response to elevated CO2 is conserved across a broad range of productivity. Proceedings of the National Academy of Sciences USA 102: 18,052-18,056.

Spiecker, H. 1999. Overview of recent growth trends in European forests. Water, Air and Soil Pollution 116: 33-46.