HR: 1340h
AN: B43B-1168    [Abstracts]
TI: Climate and soil-age constraints on nutrient uplift by plants.
AU: * Porder, S
EM: stephen_porder@brown.edu
AF: Brown University, Dept. of Ecology and Evolutionary Biology 80 Waterman St Box G-W, Providence, RI 02912, United States
AU: Chadwick, O A
EM: oac@geog.ucsb.edu
AF: University of California, Santa Barbara, Dept. of Geography, Santa Barbara, CA 93106, United States
AB: We analyzed changes in nutrient availability and elemental losses from the entire weathering zone at 28 sites arrayed across climatic and soil-age gradients on the island of Hawai'i. The sites are located on three basaltic lava flows (10, 170, and 350 ky) each of which crosses a precipitation gradient from <500 to 2,500 mm yr^{- 1}. The results identify a sweet spot of plant nutrient uplift where nutrient cations and phosphorus are retained in upper horizons as a result of plant activity. The gradients also elucidate several abiotic constraints on plant- driven retention of nutrients. At the dry sites (<750 mm yr^-1on all three flows, plant slow the loss of nutrient (e.g. potassium) vs. non-nutrient (e.g. sodium) cations, but the effect is small because of low plant cover and productivity. At intermediate rainfall (750 - 1300 mm yr^-1) plants substantially enrich both nutrient cations and P in the upper soils, an effect that increases with flow age. In contrast, at high rainfall (>1500 mm yr-1), the effect of plants on nutrient distributions diminishes with soil age and is largely absent after 350 ky of soil development. Unlike the major plant macronutrients, the distribution of the transition metals iron (Fe) and aluminum (Al) is driven more by chemical reactions than by plant uptake. Dry sites exhibit very little movement of either element, even after 350 ky of soil development. However at high rainfall the older flows show substantial Al and Fe translocations, and wet sites on all three flows have increased Al on soil exchange sites. These transition metals are key constituents of the secondary minerals that strongly influence the availability of cations and P to plants. The loss of Fe and Al is highly correlated with the loss of P in the older and wetter sites, and increased Al on exchange sites limits the availability of nutrient cations to plants. Thus redox driven redistribution of Fe and acid solublization of Al place a further abiotic constraint on nutrient retention by plants.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting