Redwood Reader

Our friends at CO2 Science magazine had this article in the April 13 issue of their newsletter. It confirms trees biologically condition soil to a greater extent under elevated CO2. We wonder about the “no effect on mycorhizzia” though. If you are looking for living material to increase over four years that may be right. However, knowing glomalin is not part of any living structure and that its production rises 5 fold in a doubling of CO2, we can guess the Forest Service didn’t know to look for it there, only noticing the same amount of producers existed, rather than counting product. We see their terms for infiltrating the soil are extensity, or distance, and intensity, or density. The reference study is from this year. We see science rapidly stacking the facts to the same conclusions we have reached. Publication brings wider recognition than I have been able to achieve.

CO2 Effects on Fine Roots of Ponderosa Pine Trees
Reference Tingey, D.T., Johnson, M.G. and Phillips, D.L. 2005. Independent and contrasting effects of elevated CO2 and N-fertilization on root architecture in Pinus ponderosa. Trees 19: 43-50.
What was done: The effects of atmospheric CO2 enrichment (to approximately 350 ppm above ambient) on the fine-root architecture of seedlings of Ponderosa pine (Pinus ponderosa Dougl. ex P. Laws & C. Laws) growing in open-top chambers were studied via minirhizotron tubes at the U.S. Forest Service Institute of Forest Genetics near Placerville, California, USA, over a period of four years.
What was learned: The authors report that "elevated CO2 increased both fine root extensity (degree of soil exploration) and intensity (extent that roots use explored areas) but had no effect on mycorrhizae," the latter of which observations was presumed to be due to the fact that soil nitrogen was not limiting to growth in this study. More specifically, they report that "extensity increased 1.5- to 2-fold in elevated CO2 while intensity increased only 20% or less," noting that similar extensity results had been obtained over shorter periods of 4 months to 2 years by Arnon (1997), Berntson and Bazzaz (1998), DeLucia et al. (1997) and Runion et al. (1997), while similar intensity results had been obtained by Berntson (1994).
What it means: The results of this study add to the growing body of evidence that suggests that the ongoing rise in the air's CO2 content will enable trees to continually increase the volume of soil from which they can access water and nutrients, as well as enable them to more thoroughly explore that enlarged volume of soil, both of which responses should allow earth's trees to acquire more of these essential resources and thereby realize the enhanced potential for growth that is provided by the aerial fertilization effect of atmospheric CO2 enrichment.
References
Arnone, J.A. 1997. Temporal responses of community fine root populations to long-term elevated atmospheric CO2 and soil nutrient patches in model tropical ecosystems. Acta Oecologia 18: 367-376.
Berntson, G.M. 1994. Modeling root architecture: are there tradeoffs between efficiency and potential of resource acquisition? New Phytologist 127: 483-493.
Berntson, G.M. and Bazzaz, F.A. 1998. Regenerating temperate forest mesocosms in elevated CO2: belowground growth and nitrogen cycling. Oecologia 113: 115-125.DeLucia, E.H., Callaway, R.M., Thomas, E.M. and Schlesinger, W.H. 1997. Mechanisms of phosphorus acquisition for ponderosa pine seedlings under high CO2 and temperature. Annals of Botany 79: 111-120.
Runion, G.B., Mitchell, R.J., Rogers, H.H., Prior, S.A. and Counts, T.K. 1997. Effects of nitrogen and water limitation and elevated atmospheric CO2 on ectomycorrhiza of longleaf pine. New Phytologist 137: 681-689.Reviewed 13 April 2005