Delayed responses of an Arctic ecosystem to an extreme summer: impacts on net ecosystem exchange and vegetation functioning

[摘要] The importance and consequences of extreme events on the global carbon budgetare inadequately understood. This includes the differential impact of extremeevents on various ecosystem components, lag effects, recovery times, andcompensatory processes. In the summer of 2007 in Barrow, Arctic Alaska,there were unusually high air temperatures (the fifth warmest summer over a65-year period) and record low precipitation (the lowest over a 65-yearperiod). These abnormal conditions were associated with substantialdesiccation of the Sphagnum layer and a reduced netSphagnum CO₂ sink but did not affect net ecosystem exchange(NEE) from this wet-sedge arctic tundra ecosystem. Microbial biomass,NH₄⁺ availability, gross primary production (GPP), and ecosystemrespiration (R_eco) were generally greater during this extremesummer. The cumulative ecosystem CO₂ sink in 2007 was similar to theprevious summers, suggesting that vascular plants were able to compensate for Sphagnum CO₂ uptake, despite the impact on other functions and structure such asdesiccation of the Sphagnum layer. Surprisingly, the lowestecosystem CO₂ sink over a five summer record (2005–2009) was observedduring the 2008 summer (~70% lower), directly following theunusually warm and dry summer, rather than during the extreme summer. Thissink reduction cannot solely be attributed to the potential damage to mosses,which typically contribute ~40% of the entire ecosystem CO₂sink. Importantly, the return to a substantial cumulative CO₂ sinkoccurred two summers after the extreme event, which suggests a substantialresilience of this tundra ecosystem to at least an isolated extreme event.Overall, these results show a complex response of the CO₂ sink and itssub-components to atypically warm and dry conditions. The impact of multipleextreme events requires further investigation.

[学科分类] 地球化学与岩石