The impact of co-occurring tree and grassland species on carbon sequestration and potential biofuel production

We evaluated how three co-occurring tree and four grassland species influence potentially harvestable biofuel stocks and above- and belowground carbon pools. After 5 years, the tree Pinus strobus had 6.5 times the amount of aboveground harvestable biomass as another tree Quercus ellipsoidalis and 10 times that of the grassland species. P. strobus accrued the largest total plant carbon pool (1375 g C m-2 or 394 g C m-2 yr), while Schizachyrium scoparium accrued the largest total plant carbon pool among the grassland species (421 g C m-2 or 137 g C m-2 yr). Quercus ellipsoidalis accrued 850 g C m-2, Q. macrocarpa 370 g C m-2, Poa pratensis 390 g C m-2, Solidago canadensis 132 g C m-2, and Lespedeza capitata 283 g C m-2. Only P. strobus and Q. ellipsoidalis significantly sequestered carbon during the experiment. Species differed in total ecosystem carbon accumulation from -21.3 to +169.8 g C m-2 yr compared with the original soil carbon pool. Plant carbon gains with P. strobus were paralleled by a decrease of 16% in soil carbon and a nonsignificant decline of 9% for Q. ellipsoidalis. However, carbon allocation differed among species, with P. strobus allocating most aboveground in a disturbance prone aboveground pool, whereas Q. ellipsoidalis, allocated most carbon in less disturbance sensitive belowground biomass. These differences have strong implications for terrestrial carbon sequestration and potential biofuel production. For P. strobus, aboveground plant carbon harvest for biofuel would result in no net carbon sequestration as declines in soil carbon offset plant carbon gains. Conversely the harvest of Q. ellipsoidalis aboveground biomass would result in net sequestration of carbon belowground due to its high allocation belowground, but would yield lower amounts of aboveground biomass. Our results demonstrate that plant species can differentially impact ecosystem carbon pools and the distribution of carbon above and belowground.