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Effects of CO2 Enrichment on Roots of a Warm Temperate Forest

Paper Reviewed
Taylor, B.N., Strand, A.E., Cooper, E.R., Beidler, K.V., Schonholz, M. and Pritchard, S.G. 2014. Root length, biomass, tissue chemistry and mycorrhizal colonization following 14 years of CO2 enrichment and 6 years of N fertilization in a warm temperate forest. Tree Physiology 34: 955-965.

In a paper published in Tree Physiology, Taylor et al. (2014) state that root systems serve important roles in carbon (C) storage and the acquisition of nitrogen (N) - which is required for the increased photosynthesis typically observed in CO2-enriched atmospheres - noting that "understanding the changes in size, distribution and tissue chemistry of roots is central to predicting the ability of forests to capture anthropogenic CO2."

Therefore, in a study designed to gain that understanding, they extracted fifteen 8000-cm3 soil monoliths from a young loblolly pine (Pinus taeda) stand at the Duke Forest FACE facility that had been exposed to 14 years (August 1996 through October 2010) of free-air CO2 enrichment to approximately 53% above the mean ambient concentration, plus 6 years (2005-2010) of N fertilization, in order to assess any CO2-induced changes in pine root length, biomass, tissue C and N concentrations, and mycorrhizal colonization.

Among the many things the six scientists thus learned were the facts that (1) "CO2 fumigation led to greater root length (98%) in unfertilized plots," that (2) "root biomass increases under elevated CO2 were only found for roots <1 mm in diameter in unfertilized plots (59%)," that (3) "trees did not rely exclusively on increased mycorrhizal associations to acquire greater amounts of required N in CO2-enriched plots," and that (4) "stimulation of root systems by atmospheric CO2 enrichment was seen primarily for fine root length rather than biomass."

An important implication of these findings, as the six scientists write, is that "studies measuring only biomass might overlook shifts in root systems that better reflect treatment effects on the potential for soil resource uptake," noting that their findings suggest that an increase in fine root exploration may be "a primary means for acquiring additional soil resources under elevated CO2" that "has the potential to facilitate increased soil resource uptake allowing for a sustained response to elevated CO2." And this fact could well be one of the chief reasons for the ultimate undoing of the once highly-hyped progressive nitrogen limitation hypothesis.

Posted 10 February 2015