Background
The authors write that "global warming has the potential to elicit a positive feedback between increased temperature, decomposition, and carbon dioxide emissions, further increasing global temperatures." Given this possibility, global warming has been claimed by some to increase rates of plant litter decomposition, which would return more CO2 to the air at increasingly faster rates and thereby augment global warming in a disconcerting positive feedback cycle.

What was done
Working with data obtained from the Long-Term Intersite Decomposition Experiment Team (LIDET), Bontti et al. evaluated "the influence of climatic variables (temperature, precipitation, actual evapotranspiration, and climate decomposition index), and litter quality (lignin content, carbon:nitrogen, and lignin:nitrogen ratios) on leaf and root decomposition in the US Great Plains."

What was learned
"Contrary to expectations," as the ten researchers report, "temperature did not explain variation in root and leaf decomposition," while precipitation only partially explained variation in root decomposition. Percent lignin, on the other hand, was found to be "the best predictor of leaf and root decomposition" and "also explained most variation in root decomposition in models which combined litter quality and climatic variables." These latter consequences were said by them to be due to the fact that "litter that is high in percent lignin contains a large amount of decay-resistant carbon material and a relatively small proportion of easily decomposable compounds," so that it decomposes at relatively slower rates. And as reported in the Lignin section of our Subject Index, atmospheric CO2 enrichment, such as the earth has been experiencing since the dawn of the Industrial Revolution, has been found to increase lignin concentrations in the tissues of many plants and, of course, to produce a much larger quantity of total plant biomass.

What it means
Based on the results of their specific study, Bontti et al. conclude that "carbon flux from root decomposition in grasslands would increase, as a result of increasing temperature, only if precipitation is not limiting [our italics]," and that "where precipitation is limiting, increased temperature would decrease root decomposition, thus likely increasing carbon storage in grasslands."

These observations suggest that global warming likely does not possess "the potential to elicit a positive feedback between increased temperature, decomposition, and carbon dioxide emissions, further increasing global temperatures." Indeed, the research team explicitly states that the results of their study "do not support the hypothesis of increased decomposition as a result of increased global temperature."