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Harvard Forest REU Symposium Abstract 2008
- Title: Amino acid production and soil nitrogen assessment in an Eastern hemlock forest
- Author: Sarah Betzler (Gustavus Adolphus College)
- Abstract:
This project involved measuring the effects of temperature and protein substrate availability on the production of amino acids (proteolysis) in Eastern hemlock dominated soils. In addition, three assays for measuring inorganic and amino acid nitrogen (N) availability in these soils were compared. Soil and soil solution samples were taken from organic and mineral soil in five different hemlock-dominated plots in the Harvard Forest.
To create a proteolysis activity profile, soils were incubated at five different temperatures with and without added protein; amino acid production was then assayed. Amino acid production was consistently higher in organic soil than in the mineral soil, and increased with temperature in both soil types. The samples with added protein were also uniformly higher in amino acid production than the samples with only ambient protein levels. Although both temperature and substrate availability limited amino acid production, substrate availability had a more pronounced effect.
The concentrations of amino acid N, ammonium and nitrate were assayed using three methods: water extracts, 2M potassium chloride (KCl) extracts, and soil solution collected with tension lysimeters. In all three assays, the organic soils had the highest concentrations of all forms of N. The 2M KCl extracts had an order of magnitude higher concentration of all forms of N than the water extracts and lysimeter samples. Inorganic N concentrations in the lysimeter samples were at or below the detection limit. This suggests that KCl extracts may overestimate the availability of N in forest soils; however, it is also possible that water extracts and lysimeter sampling underestimate N availability. - Research Category: Soil Carbon and Nitrogen Dynamics
