Goose Feces Effects on Subarctic Soil Nitrogen Availability and Greenhouse Gas Fluxes.

Vertebrate herbivore excrement is thought to influence nutrient cycling, plant nutrition, and growth; however, its importance is rarely isolated from other aspects of herbivory, such as trampling and leaf removal, leaving questions about the extent to which herbivore effects are due to feces. We hypothesized that as a source of additional nutrients, feces would directly increase soil N concentrations and N₂O emission, alleviate plant, and microbial nutrient limitations, resulting in increased plant growth and foliar quality, and increase CH₄ emissions. We tested these hypotheses using a field experiment in coastal western Alaska, USA, where we manipulated goose feces such that naturally grazed areas received three treatments: feces removal, ambient amounts of feces, or double ambient amounts of feces. Doubling feces marginally increased NH₄⁺-N in soil water, whereas both doubled feces and feces removal significantly increased NO₃⁻-N; N₂O flux was also higher in removal plots. Feces removal marginally reduced root biomass and significantly reduced productivity (that is, GPP) in the second year, measured as greater CO₂ emissions. Doubling feces marginally increased foliar chemical quality by increasing %N and decreasing C:N. Treatments did not influence CH₄ flux. In short, feces removal created sites poorer in nutrients, with reduced root growth, graminoid nutrient uptake, and productivity. While goose feces alone did not create dramatic changes in nutrient cycling in western Alaska, they do appear to be an important source of nutrients for grazed areas and to contribute to greenhouse gas exchange as their removal increased emissions of CO₂ and N₂O to the atmosphere. [ABSTRACT FROM AUTHOR]