Date of Award


Document Type

Masters Thesis

Degree Name


Organizational Unit

College of Natual Science and Mathematics

First Advisor

Robert Sanford Jr., Ph.D.

Second Advisor

Anna Sher

Third Advisor

Keith Miller


Amino acid, Colorado, Plant available nitrogen, Soil, Tree line


The classic view of the nitrogen cycle in soils is for plants to take up inorganic N in solution for N nutrition. More recent studies reveal plants can take up low molecular weight dissolved organic N such as amino acids directly from the soil. In ecosystems where the rate of microbial mineralization is limited, plants may take up 10 to 200 percent more amino acid N than mineral N. It is not known if plants take up amino acids in all ecosystems, however recent research shows that plants generally take up amino acids when they are present in high quantities relative to mineral N. Therefore, high proportions of soil amino acids correspond with a significant role in the N cycle. Amino acids, NH4+ and NO3- were measured to record plant available N in alpine, montane and lower tree line soils in the Colorado Front Range. Soils were sampled in forest and non-forest at three sites with varying temperatures and productivity. Some species in the dominant genera at each site, Kobresia, Artemisia, Festuca, Pinus and Picea are known to take up amino acids. Soils cores were collected in a) forest and tundra in the alpine tree line ecotone; b) montane forest and open forest; and c) the forest and shortgrass steppe at the lower tree line and shortgrass steppe ecotone. For this study, soil amino acids were extracted with water, and quantities of free amino acids were analyzed with OPAME fluorescence. Mineral N was extracted with KCl and measured on the Lachat QuikChem 8000. Amino acids were present in all ecosystems ranging from 1.05 to 1.78 mg N/kg soil. Quantities measured were sufficient to contribute N for plant uptake which is known to occur with concentrations of soil amino acids as low as 0.01 mg N/kg soil and may be very rapid when amino acids are > 0.8 mg N/kg soil. The largest proportion of amino acids relative to mineral N was measured at upper tree line and smallest proportion at lower tree line, indicating the amino acids make up a greater proportion of plant available N where mineralization is limited by environmental variables. Amino acids likely contribute most to the N cycle in the upper tree line ecosystem where mineral N cannot fulfill plants annual N requirement.

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Rights Holder

Kelly C. Owens


Received from ProQuest

File Format




File Size

94 p.


Ecology, Biochemistry