As a consequence of more intense but less frequent rainfall events in northern temperate to arctic regions, local carbon (C) dynamics are expected to change ( Blodau and Moore, 2003 Gerten et al., 2008 Knapp et al., 2008 Frank et al., 2015 Dai et al., 2018). In the past three decades, extreme precipitation events have become more common ( Lehmann et al., 2015), particularly in North America and Europe ( Ummenhofer and Meehl, 2017). Moreover, current observations of increased heavy precipitation confirm earlier predictions ( Fischer and Knutti, 2016). Even though the increased CO 2 assimilation under extreme precipitation patterns signals peatland resistance under changing climatic conditions, it may instead mark the onset of vascular plant encroachment and the associated C loss.Ĭlimatic change includes shifting precipitation patterns along with increases in temperature and drought ( Dai, 2013). Not only do our results illustrate that shifting rainfall patterns translate in altered WTD dynamics and, consequentially, influence C fluxes, they also demonstrate that exposure to altered rainfall early in the growing season can have lasting effects on CO 2 exchange. Furthermore, we found that CH 4 emissions decreased with deeper mean WTD, but this showed a high resilience once WTD dynamics stabilised. After a three-week recovery period, CO 2 fluxes still displayed responses to the earlier WTD dynamics, suggesting lagged effects of precipitation regime shifts. We observed similar patterns for CO 2 uptake, which were likely mediated by improved vascular plant performance. Decomposition and respiration rates increased with a deeper mean water table depth (WTD) and larger WTD fluctuations. We find that more intense but less frequent rainfall destabilized water table dynamics, with cascading effects on peatland C fluxes. How will these immense stocks of C be able to withstand and recover from extreme rainfall? We tested the resistance and resilience effects of extreme precipitation regimes on peatland carbon dioxide (CO 2) and methane (CH 4) fluxes, pore water dissolved organic carbon (DOC) and litter decomposition rates by exposing intact peat cores to extreme, spring-time rainfall patterns in a controlled mesocosm experiment. Shifts in rainfall regimes could disrupt peatland C dynamics and speed-up the rates of C loss. At northern latitudes, peatlands store one third of the terrestrial carbon and their functioning is highly dependent on water. While droughts have been repeatedly studied in many ecosystems over the last decades, the consequences of increasingly intense, but less frequent rainfall events, on carbon (C) cycling are not well understood. Current climate models predict that this trend will continue in the future. Precipitation patterns are becoming increasingly extreme, particularly at northern latitudes.
Laboratoire Ecologie Fonctionelle et Environnement, Université de Toulouse, CNRS, Toulouse, France.Barel*, Vincent Moulia †, Samuel Hamard, Anna Sytiuk and Vincent E.
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