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Title:   Author  item
                                            SMART, DAVID - UCD VIT & ENOLOGY DEPT.item
                                            PIERCE, DANIELLE - UCD VIT & ENOLOGY DEPT.item
                                            Steenwerth, Kerriitem
                                            CARLISLE, ELI - UCD VIT & ENOLOGY DEPT.item
                                            Hunt, Joshuaitem
                                            STRAND, BRIAN - UCD VIT & ENOLOGY DEPT.
  Submitted to: Ecological Society of America Proceedings
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 6/1/2005
                                    Publication  Date: 8/1/2005
                                    Citation: Smart, D.R., Pierce, D.L., Steenwerth, K.L., Carlisle, E.A., Hunt, J.M., Strand, B.K. 2005. Partioning of soil respiration into aboveground and rhizosphere components using 13co2 labeling in conventional and conservation tillage systems. Ecological Society of America Proceedings.Interpretive Summary: Soil carbon (C) sequestration is a topic of intense national and international interest in ecosystem science with respect to mitigating greenhouse gas emissions to the atmosphere. Partitioning of ecosystem respiration among aboveground and soil labile and recalcitrant C pools is critical to understand soil C sequestration. We partitioned soil respired CO2 between recently assimilated C and recalcitrant C in tilled and no-till vineyard cover crops. Soil C derived from the cover crop was retained in soils throughout summer 2004, and was strongly oxidized with the onset of autumn rain. In April 2005, unusually high seasonal precipitation greatly increased both soil moisture and C loss from labile and recalcitrant C pools. The quantity of C oxidized and emitted as soil respiration following tillage in 2005, when moisture contents were high, was prolonged and challenges previous assumptions concerning the timing and intensity of decomposition following tillage disturbance. Our results suggest decomposition will be driven by seasonal variation in soil moisture content in Mediterranean systems. Thus, influence of climatic change on precipitation patterns may have a stronger effect on soil organic C dynamics than temperature shifts alone.
                                Technical Abstract: Soil carbon (C) sequestration is a topic of intense national and international interest in ecosystem science with respect to mitigating greenhouse gas (GHG) emissions to the atmosphere. Partitioning of ecosystem respiration among aboveground and soil labile and recalcitrant C pools is critical to understand soil C sequestration. Previous efforts have used radioactive 14CO2 labels or natural abundance levels of 13C and 14C on soil respired CO2 to determine age, or partition among C sources oxidized. We used 13CO2 in situ labeling to partition soil respired CO2 between recently assimilated C and recalcitrant C in tilled and no-till vineyard cover crops. We employed Keeling analysis in conjunction with an isotope-mixing model ( 13CT = fn13Cn + fo 13Co). CT is  13C of total soil respired CO2. fn and fo are fractions derived from the more labile (13C labeled) and recalcitrant pools respectively. Rhizosphere respiration was one half of aboveground respiration. Labile C sources were retained in soils throughout the summer of 2004, and were strongly oxidized with the onset of autumn rainfall. In 2005, unusually high seasonal precipitation in April greatly increased both soil moisture and 13C loss from both labile and recalcitrant pools. The quantity of C oxidized and emitted by soil respiration following tillage in 2005, when moisture contents were high, was prolonged. 13C pools retained in 2004 in the tilled system were predominantly respired following soil wet-up in both 2004 and 2005. In addition to partitioning aboveground versus rhizosphere respiration using 13CO2, our results suggest decomposition will be driven by seasonal variation in soil moisture content in Mediterranean systems. Thus, influence of climatic change on precipitation patterns may have a stronger influence on soil organic C dynamics than shifts in temperature alone.


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