Document: SER-3-59-100

Fungal translocation as a mechanism of external nitrogen inputs to decomposing surface residues in a no-tillage agroecosystem.

FREY, S.D.* ¹, J.SIX ², E.T.ELLIOTT ² and K.PAUSTIAN ²

Ohio State University, Columbus, OH 43210 USA ¹
Colorado State University ²

Abstract:
Additions of (¹⁵NH₄)₂SO₄ to the soil inorganic nitrogen (N) pool were used to measure rates of N flux from the mineral soil to surface-applied wheat straw decomposing in intact soil cores collected from a NT field. Half of the soil cores were treated with a fungicide to reduce fungal populations. Fungicide application significantly reduced fungal biomass, decomposition rates, and net N immobilization of surface residues. Net N immobilization over the study period was estimated to be 1.5 and 0.9 g m^-2 for untreated and fungicide-treated residues, respectively. The rate of ¹⁵N transfer averaged 13.4 g g^-1 residue d^-1 for untreated wheat straw. Fungal inhibition reduced ¹⁵N flux by 59-78%, reductions of similar magnitude to those observed for fungal biomass. Nitrogen transfer in sterilized soil cores accounted for 7.8 % of the total upward N transport in control cores, indicating that abiotic processes did not contribute substantially to N flux. We estimate a total annual fungal-mediated N flux of 2.4 g m^-2, which is nearly equivalent to the N immobilization potential predicted, based on initial N and lignin content, for the wheat straw used in this study. We conclude that fungal N translocation is a significant exogenous N input and can account for the net N immobilized by surface residues decomposing in the field. Both residue quality and N availability appear to be important controls on fungal biomass associated with surface residues and rates of soil-to-residue N translocation.

Keywords: fungi, nitrogen, residue decomposition

This abstract is being presented at: 2:30 PM in session:
Oral Session #31: Agroecology.