Bonanza Creek LTER

Reconsidering nitrogen cycling in high-latitude ecosystems

by Knut Kielland, BNZ LTER
Additional investigators: Roger Ruess (PI), Rich Boone (PI), David Jones (Collaborator)
Graduate students: Jack McFarland, Nan Werdin, Trish Loomis, Rich Brenner, and Laura Hughes

The stable isotope signature of soils and plants show that species in high-fertility soils, such as alder, differ greatly from species such as willow and black spruce that grow in low-fertility soils. This divergence underscores the differences in N dynamics among these soils, and suggests variation of N sources across successional gradients.

Both laboratory and in situ field estimates of amino acid turnover suggest that this pool is very dynamic. For example, the flux of nitrogen through the amino acid pool in black spruce soils is over an order-of-magnitude greater than the rate of gross mineralization. Even in the earliest successional stage, the turnover rate of simple amino acids, such as aspartate, glutamate, and glycine, is on the order of less than 1 hour. From these results we suggest that the transformation of protein to amino acids and not amino acids to NH4+ is the major factor limiting N availability in these soils. As DON turnover constitutes a large proportion of the annual N flux in these forests, it warrants inclusion in models of climate change in high-latitude ecosystems.

Relevant literature
Kielland, K. 2001. Short-circuiting the nitrogen cycle: ecophysiological strategies of nitrogen uptake in plants from marginal environments. In: Plant Nutrient Acquisition - New Perspectives. Ae, N., J. Arihara, K. Okada, and A. Srinvasan (eds.), pg. 376-398 Springer-Verlag, Tokyo.

Jones, D.L. and K. Kielland. 2002. Soil amino acid turnover dominates the nitrogen flux in permafrost-dominated taiga forest soils. Soil Biol. Biochem. 34:209-219.