Belowground Carbon Storage in a Grassland Community

Adair et al. (2009) employed mass balance calculations to quantify the effects of biodiversity, atmospheric CO₂ concentration and soil nitrogen (N) content on the total amount of C allocated belowground by plants (total belowground C allocation or TBCA), as well as ecosystem C storage, in an eight-year experiment that was part of the BioCON study of a periodically-burned Minnesota grassland.

Results indicated that annual TBCA increased in response to all three treatment variables - "elevated CO₂, enriched N, and increasing diversity" - and that it was also "positively related to standing root biomass." Upon removing the influence of root biomass, however, they found that the effects of N and diversity became neutral or even negative (depending on the year), but that "the effect of elevated CO₂ remained positive." In the case of years with fire, on the other hand, they found that "greater litter production in high diversity, elevated CO₂, and enhanced N treatments increased annual ecosystem C loss."

Given these findings, under normal non-fire conditions, elevated CO₂, N and biodiversity generally tend to increase ecosystem carbon gain; but if grasslands are frequently burned, they could actually remain neutral in this regard.