HR: 1340h
AN: B23D-1594    [Abstracts]
TI: Dissolved Organic Matter as a Mechanism for Carbon Stabilization at Depth in Wet Tropical Forest Volcanic Soils
AU: * Marin-Spiotta, E
EM: ems@geog.ucsb.edu
AF: University of California, Santa Barbara, Geography Dept., Santa Barbara, CA 93106-4060, United States
AU: * Marin-Spiotta, E
EM: ems@geog.ucsb.edu
AF: University of California, Santa Cruz, Earth & Planetary Sciences Dept., Earth & Marine Sciences, Santa Cruz, CA 95064, United States
AU: Kramer, M G
EM: mkramer@es.ucsc.edu
AF: University of California, Santa Cruz, Earth & Planetary Sciences Dept., Earth & Marine Sciences, Santa Cruz, CA 95064, United States
AU: Chadwick, O A
EM: oac@geog.ucsb.edu
AF: University of California, Santa Barbara, Geography Dept., Santa Barbara, CA 93106-4060, United States
AB: Dissolved organic matter (DOM) plays an important role in many biological and chemical processes in soils. Our understanding of the types of plant and microbially-derived organic matter that accumulate in soils and the mechanisms responsible for their transformation and stabilization is still limited. In particular, we know very little about how microbial activity and water movement contribute to the production of DOM and the formation of stable C in soils. In well-drained soils under wet climates, DOM is potentially a primary pathway for the transport of C from the surface litter layers and the zones of highest microbial activity to deeper horizons in the soil profile where the potential for long-term storage increases. The mechanisms for long-term stabilization of organic C in deep mineral horizons include an accumulation of chemically recalcitrant C, strong sorption of soluble and otherwise labile C to mineral and/or metals making them inaccessible to decomposers, and microenvironmental conditions (low pH, low O2) which result in incomplete decomposition and persistence of labile C. Although most work to date has focused on the role of dissolved organic C and N (DOC and DON) in the C and N cycles of temperate forests, DOM fluxes may be even more important in forests in the wet tropics, where high rainfall and high primary productivity could lead to greater DOM production. In order to address the role of DOC in the transport and stabilization of C in mineral horizons, we are studying DOC production, transformation, and loss pathways in volcanic soils dominated by highly reactive, non-crystalline minerals (allophane). We are quantifying flux and solute concentrations (C, N, cations, anions) in rainwater, throughfall, and in soil water. We have installed tension and zero tension lysimeters throughout sequentially deeper organic and mineral horizons in an intermediate aged soil (ca. 350k years) under wet (ca. 3000 mm mean annual rainfall) native tropical forest cover on the island of Hawai'i. Previous research has measured soil organic C with very long mean residence times in the deeper mineral horizons at similar sites. Our study is focused on identifying the source of this highly stabilized C and the role of preferential water flow-paths in the vertical transport of C and nutrients. The soil's strongly blocky structure facilitates the downward movement of DOM to lower horizons where it comes in contact with allophane and is potentially sorbed. Through field sampling and laboratory manipulations, we will identify the zones of greatest DOC production and removal. Using separation by column chromatography (XAD resins), specific UV-absorbance, 13C-NMR, and microbial bioavailability assays, we will describe differences in the chemical composition of the organic material in solution amd solid-phase with depth.
DE: 0428 Carbon cycling (4806)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting