Abstract

The Arctic is warming at double the average global rate, affecting the carbon cycle of tundra ecosystems. Most research on carbon fluxes from Arctic tundra ecosystems has focused on abiotic environmental controls (e.g. temperature, rainfall, or radiation). However, Arctic tundra vegetation, and therefore the carbon balance of these ecosystems, can be substantially impacted by herbivory. In this study we tested how vegetation consumption by brown lemmings (Lemmus trimucronatus) can impact carbon exchange of a wet-sedge tundra ecosystem near UtqiaÄ¡vik, Alaska during the summer, and the recovery of vegetation during a following summer. We placed brown lemmings in individual enclosure plots and tested the impact of lemmings’ herbivory on carbon dioxide (CO2) and methane (CH4) fluxes and the normalized difference vegetation index (NDVI) immediately after lemming removal and during the following growing season. During the first summer of the experiment, lemmings’ herbivory reduced plant biomass (as shown by the decrease in the NDVI) and decreased CO2 uptake, while not significantly impacting CH4 emissions. Methane emissions were likely not significantly affected due to CH4 being produced deeper in the soil and escaping from the stem bases of the vascular plants. The summer following the lemming treatments, NDVI and CO2 fluxes returned to magnitudes similar to those observed before the start of the experiment, suggesting recovery of the vegetation, and a transitory nature of the impact of lemming herbivory. Overall, lemming herbivory has short-term but substantial effects on carbon sequestration by vegetation and might contribute to the considerable interannual variability in CO2 fluxes from tundra ecosystems.

Highlights

  • The Arctic is warming at twice the rate of the global average (IPCC, 2014), impacting tundra vegetation and the carbon cycle.Vegetation influences the carbon stored in the tundra ecosystem through the exchange of carbon dioxide (CO2) and methane (CH4)from the soil into the atmosphere via respiration or by CO2 uptake through photosynthesis

  • The study area was located near the Barrow Atmospheric Baseline Observatory and an atmospheric monitoring site managed by the National Oceanic and Atmospheric Administration (NOAA) (Fig. 1b), approximately 2 km south of the Arctic Ocean and m elevation above sea level (71°19′21.10′′ N: 156°36′33.04′′ W)

  • Environmental controls on CO2 and CH4 fluxes such as air temperature, soil temperature, thaw depth, and soil moisture were similar between the control and experimental plots in 2018 (Fig. 2a-h) and 2019 (Fig. 2i-p)

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Summary

Introduction

The Arctic is warming at twice the rate of the global average (IPCC, 2014), impacting tundra vegetation and the carbon cycle.Vegetation influences the carbon stored in the tundra ecosystem through the exchange of carbon dioxide (CO2) and methane (CH4)from the soil into the atmosphere via respiration or by CO2 uptake through photosynthesis. The Arctic is warming at twice the rate of the global average (IPCC, 2014), impacting tundra vegetation and the carbon cycle. Vegetation influences the carbon stored in the tundra ecosystem through the exchange of carbon dioxide (CO2) and methane (CH4). Microbes can convert stored carbon into greenhouse gases that enter the atmosphere, contributing to global warming (McGuire et al, 2009; Schuur et al, 2008). This positive feedback could have dramatic effects on warming rates, and these effects are why most carbon cycle research in tundra systems focuses on abiotic controls on carbon fluxes (Kwon et al, 2019; Oechel et al, 2014; Sturtevant et al, 2012; Zona et al, 2010). Since herbivores remove photosynthetic tissues of vegetation, the ability of vegetation to photosynthesize and sequester

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