Abiotic Nitrogen Uptake in Semiarid Grassland Soils of the U.S. Great Plains

Abstract

Soils represent the largest terrestrial sink for N, yet current understanding of nutrient cycling cannot account for some of the mechanisms and sinks that stabilize anthropogenic N. We assessed the influence of soil properties, particularly soil organic C, pH, and clay content on potential biotic and abiotic N assimilation in soils collected across a temperature gradient in the U.S. Great Plains. We pulse labeled HgCl2-sterilized and unsterilized soils with 15N to examine the relative importance of abiotic and biotic N assimilation in short-term laboratory incubations. Estimates of total N assimilation in unsterilized soils ranged from 1.21 to 2.40 mg N kg−1 soil. Soil C content accounted for 50 and 60% of the variance in estimates of biotic immobilization and total N assimilation, respectively. Estimates of abiotic N assimilation ranged from 0.089 to 0.80 mg N kg−1 soil. Abiotic N uptake represented a large proportion of total N assimilation (mean equals 20%) in short-term laboratory incubations. In contrast to previous reports, abiotic N uptake was negatively correlated to soil clay content and pH, perhaps because of differences in mineralogy and soil organic matter composition across the gradient. These results emphasize the importance of nonbiological N uptake in semiarid soils and suggest that abiotic pools could be an important sink for N.