Document: LYN-3-59-21

The fate of nitrogen in gypsy moth frass deposited to an oak forest floor.

CHRISTENSON, L.M.* ¹, G.M.LOVETT ¹, M.J.MITCHELL ² and P.M.GROFFMAN ¹

Institute of Ecosystem Studies, Millbrook, NY 12545 USA ¹
SUNY, Syracuse, NY 13210 USA ²

Abstract:
Research investigating the impacts of insect defoliation on nitrogen (N) loss from forest ecosystems has shown elevated NO₃^- levels in stream water output. These studies have measured the loss of N from the system, but have not shown the pathway of N movement within the system. To trace the movement of N, ¹⁵N-labeled gypsy moth frass or ¹⁵N-labeled oak leaf litter was added to trenched plots in an oak forest over 29 months. Nitrogen movement from the frass or litter was measured in the available, mineralizable, microbial and total soil pools. Uptake of ¹⁵N by plants and inorganic N leaching losses were also measured. No significant differences were found between the frass or leaf treatments for total N in any of the pools measured. Significant differences were found among the treatments in the distribution of the ¹⁵N tracer. Forty percent of the ¹⁵N added as frass became incorporated in the soils, with less than 1% found in oak seedlings. Almost 80% of ¹⁵N added as leaves remained in the undecomposed leaf material after 2 years. Less than 0.001% of the added ¹⁵N was leached in both treatments. Our data suggest that N in frass is mobilized more quickly than N in leaf litter. However, the frass N is largely unavailable to plants and organisms, because little of it ends up in the extractable, microbial, or readily mineralizable pools. This may alter the cycling of N within forest ecosystems that are repeatedly defoliated by gypsy moths.

Keywords: N cycling, insect defoliation, frass, gypsy moth, ¹⁵N

This abstract is being presented at: 3:30 PM in session:
Poster Session #15: Nutrient Cycling.