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Disturbance Ecology

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Schürings, J*; Jentsch, A; Kreyling, J: Winter warming pulses affect decomposition and nitrogen cycling in temperate heath and grassland communities
Talk, 42nd Annual Meeting of the Ecological Society of Germany, Austria and Switzerland (GfÖ), Lüneburg: 2012-09-10 - 2012-09-14

Ongoing global warming is predicted to increase variability of winter air temperatures and to decrease snow cover over large areas of the temperate zone. This leads to more variable winter soil temperatures which potentially influence many biogeochemical processes. In a controlled field experiment we investigated the effects of winter warming pulses on plant available nitrogen (N), plant N uptake, decomposition and N mineralization at two different sites (lowland site: Ecological-Botanical Garden Bayreuth and upland site with a more severe winter climate: Waldstein, Fichtelgebirge). Lysimeters with six different plant communities (4 monocultures of: Holcus lanatus, Plantago lanceolata, Calluna vulgaris, Deschampsia flexuosa; and two-species mixtures: H. lanatus and P. lanceolata, C. vulgaris and D. flexuosa) and one bare ground control were installed. Winter warming pulses were applied by IR-heaters and aboveground heating wires. This treatment was compared to ambient conditions in five replicates per site. We tested for differences in (1) plant available N (resin sticks), (2) N uptake by plants (15N), (3) mineralization rates (net mineralization bags) and (4) decomposition (litter bags and bait-lamina sticks). Winter warming pulses increased plant available N by 34.5%. N uptake was per unit biomass was increased ( 15N) while ANPP decreased. This led to no change in total N uptake. Decreased plant biomass despite increased N availability in response to winter warming pulses (higher mineralization rates and decomposition) indicates that plant uptake was limited by other factors, presumably frost damage. Consequently increased N leaching has to be expected against which plant activity cannot buffer. The results indicate the high ecological importance of winter climate change in the temperate zone.
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