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

Abstract

Forest defoliation by insects can lead to severe disruptions of the nitrogen (N) cycle resulting in elevated NO levels in stream water. To trace the movement of insect-mobilized N in a forest soil, N-labeled gypsy moth frass orN-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 N by oak seedlings 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. Significant differences were found among the treatments in the distribution of theN tracer. Forty percent of the N added as frass became incorporated in the soils, with less than 1% found in oak seedlings. Almost 80% ofN added as leaves remained in the undecomposed leaf material after 2 years. Less than 0.001% of the added N was leached in both treatments. Our data indicate that N in frass is mobilized more quickly than N in leaf litter. However, this frass N may be largely unavailable to plants and microorganisms as little of it was found in the extractable, microbial, or readily mineralizable pools.

The biogeochemical consequences of litter transformation by insect herbivory in the Subarctic: a microcosm simulation experiment

“…1b), particularly when observed relative to added substrate N (frass = 17%, litter = -8% (less than control), Table 2). Interestingly, the time-series of ammonium-N concentrations ( Figure S2) suggested quite strong and rapid immobilisation capacities in all treatments (except the control), which is in line with most findings from temperate forests that suggest a temporal and spatial redistribution of N due to insect herbivory rather than a net loss from the system (Lovett and Ruesink 1995;Christenson et al 2002;Lovett et al 2002;Hunter 2007, 2008). This may be explained by lower N mineralisation rates in the frass ?…”

Absence of effects on nutrient budgets after insect defoliation

“…In our site, apparently, no increase in nitrate production or aluminium and iron mobilization seemed to have occurred, and the low sulfate concentrations in streamwater reflect the high sulfate adsorption capacity of these desaturated soils with high organic matter content (Dambrine et al, 2000). Absence of response in nutrient concentration after insect defoliations was also reported by Bormann and Likens (1979) and Christenson et al (2002) in watersheds covered by other tree species different from E. globulus. The insect defoliation may cause an increase of nitrogen and labile carbon to the forest floor (Rinker et al, 2001;Lovett et al, 2002;Frost and Hunter, 2008).…”

Effets d’une attaque de tordeuse des bourgeons de l’épinette sur l’exportation d’éléments au-dessous de la zone racinaire : une étude de cas dans une forêt de sapins baumiers

“…Increases in NO 3 export have also been observed following gypsy moth (Lymantria dispar) defoliation (Eshleman et al, 1998;Webb et al, 1995). Christenson et al (2002) have shown that the nitrogen comprised within gypsy moth frass can be rapidly immobilized within the soil in northern hardwood stands. Lovett et al (2002) suggested that most of the nitrogen released from foliage through defoliation by the gypsy moth is redistributed within other forest compartments, and that leaching losses are relatively small.…”