Soil and Water Sciences
Winter Seminar
Dr. Craig Rasmussen
Department of Soil, Water and Environmental Science
The University of Arizona
- Location: 1002 CHASS Interdisciplinary Building - North
- Time: Wednesday, February 11, 2009, 12:10-1:00 pm
- Campus Map CHASS (INTN)
"Soil Carbon Sequestration in Conifer Forests - A Dynamic Interaction of Geology and Biology"
Abstract: Global and regional carbon budgets indicate temperate forest soil organic carbon (SOC) accounts for a substantial portion of terrestrial carbon stocks. The role of forest SOC as a source or sink for atmospheric CO2 remains unclear and depends on complex interactions between climate, geology, and plant litter. It is therefore critical to understand the controls of SOC sequestration in these ecosystems and their potential role in moderating atmospheric CO2 levels. We undertook a series of coupled field and laboratory studies focused on identifying mineralogic controls of SOC sequestration across a range of geologic materials and forest-types in the Western U.S. Results from these studies demonstrate that the soil mineral assemblage moderates SOC sequestration via control of: (i) partitioning of SOC into physically defined pools with varying mean residence time; (ii) cumulative SOC mineralization and mineralization rates; and (iii) SOC response to increased temperature and litter additions. In particular, soils enriched in short-range-order Fe- and Al-oxyhydroxides and Al-humus complexes exhibited greater partitioning of SOC into stable pools and significantly reduced SOC mineralization relative to soils dominated by crystalline minerals. Ongoing research in Pinus ponderosa ecosystems of Arizona indicates variation in both the microbial community and SOC dynamics with increasing soil acidity and Al availability, further indicating the importance of geologic and mineralogic controls of SOC cycling. These studies all indicate a significant role for Al, including short-range-order Al-oxydrydroxides, Al-humus complexes, and exchangeable Al, in control of sequestration of SOC in temperate conifer ecosystems of the Western U.S. Geology and soil mineralogy are therefore fundamental controls of SOC sequestration and must be considered in landscape and regional scale models of soil carbon sequestration.