Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/22/2013
Publication Date: 3/7/2013
Citation: Skinner, R.H. 2013. Respiration partitioning during pasture regrowth. Crop Science. doi: 10.2135/cropsci2012.10.0572. Interpretive Summary: The ability of managed grazing lands to help mitigate the adverse effects of global climate change depends on their ability to sequester C in the soil. To understand and model grazing land C sequestration we need a better understanding of plant and soil respiration which are the major processes that remove C from the system and regulate the balance between C accumulation and loss. Separating root respiration from respiration by free-living soil fauna has been difficult because their location within the soil makes them relatively inaccessible. This information is particularly lacking for the regrowth period following defoliation of perennial forages. This study took advantage of differences in stable C isotopes between respired carbon dioxide from roots and soil fauna to quantify the relative contribution of each to total soil respiration. Respiration by soil fauna was always lowest soon after defoliation but this was not always the case for root respiration. Differences among years in respiration responses during regrowth suggest that both source and sink constraints might have been limiting respiration following defoliation. This information will be useful in constructing models to describe and predict management effects on respiration and soil C sequestration.
Technical Abstract: Understanding the regulation of net ecosystem exchange and soil C sequestration within pasture systems requires knowledge of its component fluxes, including photosynthetic uptake and respiratory loss. However, little information is available on the partitioning of soil respiration between its heterotrophic and rhizosphere components for perennial cool-season pasture species. The purpose of this study was to use stable C isotopes to examine the effects of regrowth after defoliation on the components of ecosystem respiration for orchardgrass-white clover mixtures, two cool-season grassland species commonly found in Northeastern USA pastures. Respiration components were quantified during the first three weeks following defoliation at the beginning of July in 2010 and 2011. In 2010, total soil, heterotrophic, and rhizosphere respiration were all lowest 1 d after cutting (DAC). Both soil respiration and heterotrophic respiration significantly increased by 8 DAC then remained unchanged for the next two weeks. In contrast, rhizosphere respiration continued to increase throughout the regrowth period. In 2011, soil respiration was greater at 1 DAC than in 2010, but did not change thereafter. During that period heterotrophic respiration increased slightly, whereas rhizosphere respiration experienced a slight decrease. The rhizosphere contribution to soil respiration averaged 0.49, and ranged from 0.35 to 0.62. Differences among years in respiration responses during regrowth suggest that both source and sink constraints might have been limiting respiration following defoliation.