PARENT SESSION
Contributed Oral Session 60: Biogeochemistry: Soil Nutrient Dynamics; Decomposition
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 516 D, Level 5, Palais des congrès de Montréal

Bioavailable organic N dynamics among soils of the United States.

Hofmockel, Kirsten^*,1, Fierer, Noah², Colman, Benjamin ², Jackson, Robert ¹, ¹ Duke University, Durham, NC, US² Bren School of Environmental Science and Management, Santa Barbara, CA, US

ABSTRACT- Recently our understanding of soil N cycling has shifted to stress the importance of simple organic nitrogen compounds as plant available N. This raises questions concerning the physical and biological characteristics that govern the production and pool size of simple organic N compounds. Our purpose is to address the variability of free amino acid availability across ecosystems and the mechanisms controlling depolymerization of organic compounds. We evaluated total free amino acid (TFAA) pools and production rates in 84 soils from North America. The results indicate that across ecosystems the TFAA pools range from 0.003-0.71 mol/g with greatest concentrations in andisols and inceptisols and minimal concentrations in ultisols and aridisols. Concentrations of TFAA were correlated with dissolved organic N and C concentrations (p<0.0001), but were not influenced by depth of the organic horizon. In addition to the dissolved organic pool, abiotic factors including mean annual precipitation (p<0.0001) and pH (p<0.0001) were significantly related to the pool of total free amino acids. Since TFAAs turnover rapidly, we measured production in the absence of consumption. Measurements of proteolytic enzyme activity indicate production rates range from 0.002-2.7 mol N/g/h for ninhydrin reactive N (NRN), from 0-0.40 mol N/g/h for TFAA, and from 0-0.19 mol N/g/h for NH₄. In contrast to pool measurements, ultisols and aridisols were among the soils with the highest production rates of both NRN and TFAA. We conclude that TFAA are strongly correlated with soil physical properties and provide a significant proportion of available N to plants and microbes across ecosystems.

Key words: amino acids, organic N, proteolysis, biogeography