Climate change-related effects on carbon emissions and net ammonification across lowland to upland soils from a high-latitude coastal ecosystem

Abstract Warming, sea-level rise, and changing herbivory patterns are affecting ecosystem processes in northern coastal soils, including carbon and nitrogen cycling, although their combined effects are poorly understood. We studied the impact of these changes in a full-factorial microcosm experiment using four distinct soil types from the Yukon-Kuskokwim Delta of western Alaska. Soil was collected from three coastal wetlands, which differ in flooding frequency and use by migratory geese, and one rarely-flooded upland tundra used by geese in late summer. Microcosms containing these soils were incubated for 16 weeks at 10 °C or 18 °C, with or without three short-term floods, and with or without goose feces. We measured soil carbon dioxide (CO 2 ) and methane (CH 4 ) emissions weekly and net ammonification during the experiment. While higher temperature generally increased CO 2 and CH 4 emissions and net ammonification, and feces addition increased CO 2 emissions, the impact of flooding on both gas fluxes and net ammonification differed among soil types. Flooding suppressed soil CO 2 emissions in the historically least-frequently flooded wetland and upland tundra but had no effect on the other two wetland soils. Conversely, under warmer temperatures, flooding increased CH 4 emissions in the most-frequently flooded wetland but decreased CH 4 emissions in the tundra soil. Flooding also decreased net ammonification in the most-frequently flooded wetland, but increased net ammonification in the tundra soil. Our results suggest that climate change-related effects, particularly flooding, interact with soil-specific conditions that may amplify or dampen carbon loss and net ammonification in coastal Arctic soils depending on landscape position.