Wintertime carbon uptake of managed temperate grassland ecosystems may influence grassland dynamics

Abstract

<p><strong>Abstract.</strong> Rising temperatures and changes in snow cover, as can be expected under a global warmer climate, may have large impacts on mountain grassland productivity limited by cold and long winters. Here, we elaborated a multi-layer atmosphere-soil-vegetation model to account for snow, freeze-thaw events, grass growth, and soil microbiology. The model was applied to simulate the responses of managed grasslands to anomalously warm winter conditions. The grass growth module represented key ecological processes under a cold environment, such as leaf formation, elongation and death, tillering, carbon allocation, and cold acclimation, in terms of photosynthetic activity. Input parameters were derived for the pre-alpine grassland sites in Germany, for which the model was run using three years of data that included a winter with an exceptionally limited amount of snow cover. The model reproduced the temporal variability of observed daily mean heat fluxes, soil temperatures and snow depth throughout the simulation period. High physiological activity levels during the extremely warm winter led to a simulated CO<sub>2</sub> uptake of 100 gC m<sup>−2</sup>, which was mainly allocated into the below-ground biomass and only to a minor extend used for additional plant growth during early spring. If this temporary dynamics is representative of the long-term changes, this process, which is so far largely unaccounted for in scenario analysis using global terrestrial biosphere models, may lead to carbon accumulation in the soil and/or carbon loss from the soil as a response to global warming.</p>