Líffræðifélag Íslands
Líffræðiráðstefnan 2015
Erindi/veggspjald / Talk/poster V10
Niki I. W. Leblans (1,2), Bjarni D. Sigurdsson (2) and Ivan A. Janssens (1)
1. University of Antwerp, 2. Agricultural University of Iceland
Kynnir / Presenter: Steven Dauwe
Tengiliður / Corresponding author: Niki Leblans (niki.leblans@uantwerpen.be)
In the FORHOT research project (www.forhot.is), natural geothermal soil temperature gradients are used to study the soil temperature (Ts) dependence of ecosystem processes of Icelandic grasslands. The main advantage of these natural Ts gradients are 1) that short-term (transient) warming effects can be distinguished from long-term (permanent) effects by comparing recently established Ts gradients (that arose after a major earthquacke in 2008 caused geothermal system to shift under previously unwarmed soils) and centuries-old Ts gradients (where the natural soil warming has been continuous for at least 300 year), 2) that non-linear responses can be identified as we cover a broad temperature gradient (+0,+1,+3,+5, +10 and +20°C), 3) that the temperature gradients encompass the IPCC RCP scenario’s for the sub-arctic. The increase in Ts proved to be constant over all seasons. Here we report some key findings of the ForHot project: (1) Both in the short-term and long-term warmed grassland ecosystem, a loss of soil organic carbon of 40% was observed at 5-10 °C soil warming, which is a realistic temperature increase for northern latitudes within this century. This provides empirical support that northern grassland could shift into a substantial source of CO2 in the near future (losing 5-22% of their soil organic carbon before 2100), potentially influencing global change. (2) Soil warming (> +5°C) had a pronounced effect on the timing of the onset of the growing season of both the short-term and the long-term warmed grassland. The vegetation greening was advanced with a month in years with warm or moderate spring air temperatures. Cold spring air temperatures, however, reduced this effect. As the length of the growing season plays an important role in the carbon, water and energy exchange between biosphere and atmosphere at higher latitudes, changes induced by increasing Ts can therefore induce important climate-controlling feedback mechanisms. (3) Increasing Ts caused a decline of vascular plant species richness, where the loss of species was more severe in the long-term warmed grassland (loss of 0.47 species per °C) than in the short-term warmed grassland (loss of 0.25 species per °C). The observation that several species disappeared at higher Ts after long-term warming but after short-term warming indicates that changes in species composition need time (species deficit).