Submitted to: Ecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2012
Publication Date: 1/5/2013
Citation: Anderson-Teixeira, K.J., Masters, M.D., Black, C.K., Zeri, M., Hussain, Z., Bernacchi, C.J., DeLucia, E. 2013. Altered belowground carbon cycling following land use change to perennial bioenergy crops. Ecosystems. DOI: 10.1007/s10021-012-9628-x. Interpretive Summary: Globally, soils hold a tremendous amount of carbon, and historic large-scale conversion of natural ecosystems to accommodate annual row crops resulted in a significant release of much of this carbon. While patterns of land-use change are currently relatively stable throughout the Midwestern US, the emerging bioenergy industry is likely to increase feedstock production that will drive large-scale land use changes from annual row crops to perennial grasses. With the transition from annual to perennial species, it is generally thought that there will be an increase in the amount of carbon stored belowground. However, data showing the actual changes coupled with an understanding of the mechanisms are lacking. In this study, we compare the rate in which carbon is sequestered by perennial grasses to the rate it is sequestered by the current dominant agricultural ecosystem, a maize-maize-soybean rotation. The results show that a substantial increase in carbon goes belowground for the perennial grasses relative to the existing agriculture. Interestingly, the increase of carbon belowground is enough to increase carbon sequestration in the soil even when the aboveground biomass is removed completely for bioenergy production. These results are the first to provide direct evidence, with clear understanding of the mechanisms responsible, that converting land from annual crops to perennial grasses can provide, in addition to renewable energy, an important ecosystem service through higher carbon sequestration.
Technical Abstract: Belowground carbon (C) dynamics of terrestrial ecosystems play an important role in the global C cycle and thereby in climate regulation, yet remain poorly understood. Globally, land use change is a major driver of changes in belowground C storage; in general, land clearing and tillage for agriculture strongly reduces belowground C storage, whereas restoration of perennial vegetation on former croplands increases belowground C storage. The emerging bioenergy industry is likely to drive widespread land use changes, including the replacement of annually tilled croplands with perennial bioenergy crops, and thereby to impact the climate system through alteration of belowground C dynamics. Mechanistic understanding of how land use changes impact belowground C storage requires elucidation of changes in belowground C flows; however, altered belowground C dynamics following land use change have yet to be thoroughly quantified through field measurements. Here we show that belowground C cycling pathways were substantially altered upon land conversion from row crop agriculture (corn-soy rotation) to perennial bioenergy crops (miscanthus, switchgrass, and a native prairie mix); specifically, there were substantial increases in belowground C allocation (>400%), belowground biomass (400-750%), and root-associated respiration (up to 2500%) and moderate reductions in litter inputs (20-40%) and respiration in root-free soil (up to 50%). This more active root-associated C cycling of perennial vegetation provides a mechanism for previously observed net C sequestration by these perennial ecosystems, as well as commonly observed increases in soil C under perennial bioenergy crops throughout the world. More broadly, the observed differences in belowground C cycling between perennial vegetation and annual crops clarify the mechanisms through which land use changes alter belowground C storage. The more active root-associated belowground C cycle of perennial vegetation implies a climate benefit of grassland maintenance or restoration, even if biomass is harvested annually for bioenergy production.