HR: 0800h
AN: B31A-0061    [Abstracts]
TI: Non-Linear Nitrogen Cycling and Ecosystem Calcium Depletion Along a Temperate Forest Soil Nitrogen Gradient
AU: * Sinkhorn, E R
EM: emily.sinkhorn@oregonstate.com
AF: Department of Forest Science Oregon State University, 321 Richardson Hall, Corvallis, OR 97331, United States
AU: Perakis, S S
EM: steven.perakis@oregonstate.edu
AF: Department of Forest Science Oregon State University, 321 Richardson Hall, Corvallis, OR 97331, United States
AU: Perakis, S S
EM: steven.perakis@oregonstate.edu
AF: US Geological Survey Forest and Rangeland Ecosystem Science Center, 3200 SW Jefferson Way, Corvallis, OR 97331, United States
AU: Compton, J E
EM: compton.jana@epamail.epa.gov
AF: Department of Forest Science Oregon State University, 321 Richardson Hall, Corvallis, OR 97331, United States
AU: Compton, J E
EM: compton.jana@epamail.epa.gov
AF: US Environmental Protection Agency National Health and Environmental Effects Research Laboratory Western Ecology Division, 200 SW 35th Street, Corvallis, OR 97333, United States
AU: Cromack, K
EM: kermit.cromack@oregonstate.edu
AF: Department of Forest Science Oregon State University, 321 Richardson Hall, Corvallis, OR 97331, United States
AU: Bullen, T D
EM: tdbullen@usgs.gov
AF: US Geological Survey Water Resources Division Branch of Regional Research, Western Region, MS 420 345 Middlefield Rd., Menlo Park, CA 94025, United States
AB: Understanding how N availability influences base cation stores is critical for assessing long-term ecosystem sustainability. Indices of nitrogen (N) availability and the distribution of nutrients in plant biomass, soil, and soil water were examined across ten Douglas-fir (Pseudotsuga menziesii) stands spanning a three-fold soil N gradient (0-10 cm: 0.21 – 0.69% N, 0-100 cm: 9.2 – 28.8 Mg N ha^-1) in the Oregon Coast Range. This gradient is largely the consequence of historical inputs from N₂-fixing red alder stands that can add 100-200 kg N ha^-1 yr^-1 to the ecosystem for decades. Annual net N mineralization and litterfall N return displayed non-linear relationships with soil N, increasing initially, and then decreasing as N-richness increased. In contrast, nitrate leaching from deep soils increased linearly across the soil N gradient and ranged from 0.074 to 30 kg N ha^-1 yr^-1. Soil exchangeable Ca, Mg, and K pools to 1 m depth were negatively related to nitrate losses across sites. Ca was the only base cation exhibiting concentration decreases in both plant and soil pools across the soil N gradient, and a greater proportion of total available ecosystem Ca was sequestered in aboveground plant biomass at high N, low Ca sites. Our work supports a hierarchical model of coupled N-Ca cycles across gradients of soil N enrichment, with microbial production of mobile nitrate anions leading to depletion of readily available Ca at the ecosystem scale, and plant sequestration promoting Ca conservation as Ca supply diminishes. The preferential storage of Ca in aboveground biomass at high N and low Ca sites, while critical for sustaining plant productivity, may also predispose forests to Ca depletion in areas managed for intensive biomass removal. Long-term N enrichment of temperate forest soils appears capable of sustaining an open N cycle and key symptoms of N-saturation for multiple decades after the cessation of elevated N inputs.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0469 Nitrogen cycling
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting