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United States Department of Agriculture

Agricultural Research Service

Research Project: SOIL CONSERVATION SYSTEMS FOR SUSTAINABILITY OF PACIFIC NORTHWEST AGRICULTURE

Location: Land Management and Water Conservation Research

Title: Spatial heterogeneity of forest soil carbon and nitrogen controls nitrogen transformations and trace gas production

Authors
item Smith, Ed - NORTHERN ARIZONA UNIV
item Hart, Steve - NORTHERN ARIZONA UNIV
item Smith, Jeffrey

Submitted to: Soil Ecology Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: February 10, 2007
Publication Date: N/A

Technical Abstract: Small-scale spatial heterogeneity of soil nitrogen (N) and carbon (C) pools and net transformation processes in forested ecosystems are not well understood. Two forests in central Oregon (Black Butte and Santiam Pass) were used to test the hypothesis that spatial distribution of soil nutrients controls nutrient transformations by microorganisms. We measured soil water, ammonium, nitrate, total C, total N, net N mineralization, net nitrification, and fluxes of the trace gases nitrous oxide, carbon dioxide, and methane. Regression techniques indicated that soil nutrient pools were stronger predictors of net N mineralization and net nitrification at Santiam Pass as compared to Black Butte (mineralization: r2 = 0.765 vs. 0.455, respectively; nitrification: r2 = 0.776 vs. 0.650, respectively). Geostatistical analyses using semivariograms indicated a high degree of spatial dependence for some pools and processes at both sites sampled within 2.5-55 cm of each other, but distinct differences occurred between sites. The nugget-to-sill ratios at Santiam Pass were lower than at Black Butte, suggesting that a larger proportion of the sample variability at Santiam Pass was more spatially dependent than at Black Butte. Cross correlograms of all variables demonstrated greater spatial correlation of soil nutrient pools with all microbial transformation processes (except CH4 flux) at Santiam Pass over Black Butte. These differences in spatial patterning of soil pools and process correlations may explain the differences between sites in microbially mediated C and N transformations, and may influence aboveground vegetation structure.

Last Modified: 4/17/2014
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