Climate change is stronger at high than at temperate and tropical latitudes. The natural geothermal conditions in southern Iceland provide an opportunity to study the impact of warming on plants, because of the geothermal bedrock channels that induce stable gradients of soil temperature. We studied two valleys, one where such gradients have been present for centuries (long-term treatment), and another where new gradients were created in 2008 after a shallow crustal earthquake (short-term treatment). We studied the impact of soil warming (0 to +15 °C) on the foliar metabolomes of two common plant species of high northern latitudes: Agrostis capillaris, a monocotyledon grass; and Ranunculus acris, a dicotyledonous herb, and evaluated the dependence of shifts in their metabolomes on the length of the warming treatment. The two species responded differently to warming, depending on the length of exposure. The grass metabolome clearly shifted at the site of long-term warming, but the herb metabolome did not. The main up-regulated compounds at the highest temperatures at the long-term site were saccharides and amino acids, both involved in heat-shock metabolic pathways. Moreover, some secondary metabolites, such as phenolic acids and terpenes, associated with a wide array of stresses, were also up-regulated. Most current climatic models predict an increase in annual average temperature between 2-8 °C over land masses in the Arctic towards the end of this century. The metabolomes of A. capillaris and R. acris shifted abruptly and nonlinearly to soil warming >5 °C above the control temperature for the coming decades. These results thus suggest that a slight warming increase may not imply substantial changes in plant function, but if the temperature rises more than 5 °C, warming may end up triggering metabolic pathways associated with heat stress in some plant species currently dominant in this region.

Agricultural University of Iceland IS 311 Borgarnes Iceland

BETA Technological Centre Aquatic Ecology Group University of Vic Central University of Catalonia Vic 08500 Barcelona Spain

Consejo Superior de Investigaciones Científicas Global Ecology Unit CREAF CSIC UAB 08193 Bellaterra Spain

Department of Biology University of Antwerp BE 2610 Antwerp Belgium

Ecological and Forestry Applications Research Centre 08193 Cerdanyola del Vallès Spain

Global Change Research Institute The Czech Academy of Sciences Belidla 986 4a CZ 60300 Brno Czech Republic

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Soil Moisture and Its Interaction With Temperature Determine Root Metabolomes of a Himalayan Alpine Shrub

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A systemic overreaction to years versus decades of warming in a subarctic grassland ecosystem

Root exudate metabolomes change under drought and show limited capacity for recovery