Climate change is altering the timing of spring green-up and the timing of migratory herbivores, especially in northern latitudes. Shifts in timing of plant-herbivore interactions have the potential to alter nitrogen (N) cycling and availability, a critical resource in Arctic ecosystems. While earlier springs and earlier goose herbivory are expected to increase N resources, the relative impact of timing on soil resources is not well understood.
Ryan Choi and colleagues conducted a 3-year experiment in coastal western Alaska that simulated different timings of arrival by Pacific black brant (Brant bernicla nigricans) (3 weeks early, typical arrival, 3 weeks late, or no-arrival) and timings of the growing season for Carex subspathacea (3 week advancement and ambient conditions). They measured changes in soil-adsorbed and mobile inorganic (NH4+-N, NO3–-N) and mobile organic N (amino acids).
Soil N increased with early goose grazing and decreased with late grazing. While both early goose arrival and season advancement lead to greater soil N, the timing of goose grazing had a greater influence on N availability than the advanced growing season. Because N is a limiting resource in northern ecosystems, even short-term impacts on soil N pools can have lasting effects on forage quality, plant community composition and productivity, and increase the likelihood of N leaching and loss in Arctic coastal wetlands.
The article is available at Ecosystems.
Reference: Choi, R.T., Beard, K.H., Kelsey, K.C., Leffler, A.J., Schmutz, J.A., Welker, J.M. (2020) Early Goose Arrival Increases Soil Nitrogen Availability More Than an Advancing Spring in Coastal Western Alaska. Ecosystems doi:10.1007/s10021-019-00472-9
Text by Ryan Choi, PhD student at Utah State University
Picture: Flock of Pacific black brant (Brant bernicla nigricans) (photo: Ryan Choi, Utah State University, 2019)