Search for: All records

Abstract High latitude wetlands are ecologically important ecosystems due to their large carbon (C) storage capacity and because they serve as breeding and nesting habitat for large populations of migratory birds. Goose herbivory in wetland meadows affects leaf chemical and morphological traits and also influences soil properties by increasing soil temperature and depositing faeces. Grazing‐induced changes to above‐ground traits and soil properties impact C cycling, but the influence of grazing on root‐mediated C and nitrogen (N) cycling has not been explored.We investigated how goose herbivory in a low‐Arctic coastal wetland in western Alaska affected root morphological, physiological and chemical traits of a dominant graminoid by assessing plant traits in ungrazed versus heavily grazed sedge meadows. We also performed a 11‐week lab‐based root incubation experiment to determine how grazing affects CO₂‐C efflux, the size and decay rate of the fast‐cycling C pool (i.e. C with a mean residence time of days to weeks, determined via CO₂‐C efflux), and patterns of N mineralization during root decomposition.Goose grazing altered root chemical traits by increasing root N by 7%, cellulose by 12%, and ash content by 17%, indicating that grazing shifted root chemical traits towards a resource‐acquisition strategy. Grazing did not alter root biomass, morphology or bulk C exudation. In our root incubation, soils that included the roots of grazed plants tended to exhibit greater CO₂‐C efflux than those containing ungrazed plant roots due to a larger fast‐cycling C pool. Additionally, grazing‐induced increases in soil temperature led to greater CO₂‐C efflux due to a faster decay rate of the fast‐cycling C pool. Finally, compared with ungrazed roots, we found that the decomposition of grazed roots resulted in more N being transferred to root necromass from the surrounding soil, suggesting that microbial communities decomposing grazed roots immobilized N.Synthesis. Overall, our results indicate that goose grazing increased C‐cycling rates by influencing soil environmental conditions and by altering the ecological strategy of grazed plants. In contrast, grazing decreased net N mineralization by promoting N immobilization. These results suggest that changing patterns and abundances of herbivores can have substantial effects on elemental cycles. 

Abstract With rapid climate warming, some coastal high‐latitude ecosystems are experiencing more frequent tidal floods. Yet little is known about tundra plant‐community responses to flooding, and whether Arctic warming may modulate such responses.In a 2‐year, full‐factorial field experiment in coastal tundra wetlands of the Yukon‐Kuskokwim (Y‐K) Delta (western Alaska), we simulated periodic tidal flood events at two severities under both ambient and warmed summer conditions and measured above‐ground plant‐community responses. Low‐severity flooding represented overbank flooding 1 day per month, which is consistent with projections in the next 5 years. High‐severity flooding represented a more impactful flooding regime (three consecutive days per month) that is projected to occur in the next 10 years. Our warming treatment (+1°C) also represented a change projected in the next 10 years.Regardless of temperature, high‐severity flooding increased graminoid biomass by >45%, in turn increasing live plant‐community biomass by >18%. Low‐severity flooding had similar, though weaker, effects. Flooding had overall negative effects on both forb and shrub biomass, though shrub responses were weaker. Only during the second summer, warming increased graminoid biomass by 20% and tended to increase shrub biomass, regardless of flooding. Concurrently, warming enhanced standing‐dead graminoid biomass by 20%, while high‐severity flooding decreased it by 15%. Therefore, wet tundra that was both flooded and warmed had the greatest proportion of graminoids and total live biomass, but standing‐dead biomass comparable to that of unmanipulated wet tundra.Synthesis. While our manipulations simulated flooding and warming regimes expected in the wetlands of the Y‐K Delta over the same, near‐future (5‐to‐10 years) time frame, flooding had stronger effects than warming. What is striking is the rate at which graminoid increases occurred, becoming apparent after only two monthly flood events in the first experimental year. Flooding‐induced decreases in standing‐dead biomass suggests that the incorporation of dead plant material into the litter layer might be facilitated by tidal floods. These rapid increases in plant biomass and potentially biomass turnover, especially of graminoids, which are characterized by high‐quality litter, may have major implications for carbon and nutrient cycling of more frequently flooded coastal ecosystems in a warmer Arctic.