Suchergebnisse

This article is part of the FORHOT project ; Increasing temperatures can accelerate soil organic matter decomposition and release large amounts of CO2 to the atmosphere, potentially inducing positive warming feedbacks. Alterations to the temperature sensitivity and physiological functioning of soil microorganisms may play a key role in these carbon (C) losses. Geothermally active areas in Iceland provide stable and continuous soil temperature gradients to test this hypothesis, encompassing the full range of warming scenarios projected by the Intergovernmental Panel on Climate Change for the northern region. We took soils from these geothermal sites 7 years after the onset of warming and incubated them at varying temperatures and substrate availability conditions to detect persistent alterations of microbial physiology to long-term warming. Seven years of continuous warming ranging from 1.8 to 15.9 °C triggered a 8.6–58.0% decrease on the C concentrations in the topsoil (0–10 cm) of these sub-arctic silt-loam Andosols. The sensitivity of microbial respiration to temperature (Q10) was not altered. However, soil microbes showed a persistent increase in their microbial metabolic quotients (microbial respiration per unit of microbial biomass) and a subsequent diminished C retention in biomass. After an initial depletion of labile soil C upon soil warming, increasing energy costs of metabolic maintenance and resource acquisition led to a weaker capacity of C stabilization in the microbial biomass of warmer soils. This mechanism contributes to our understanding of the acclimated response of soil respiration to in situ soil warming at the ecosystem level, despite a lack of acclimation at the physiological level. Persistent increases in the respiratory costs of soil microbes in response to warming constitute a fundamental process that should be incorporated into climate change-C cycling models. ; This research was supported by the European Union's Seventh Framework Program, the Ministry of Economy, Innovation, Science and Employment of the Junta de Andalucía (postdoctoral fellowship of the Andalucía Talent Hub Program, Marie Skłodowska-Curie actions, COFUND—Grant Agreement No 291780, to SMJ), the European Research Council Synergy grant 610028 (IMBALANCE-P), the research project "GEISpain" (CGL2014-52838-C2-1-R) of the Spanish Ministry of Economy and Competitiveness and the Research Council of the University of Antwerp (FORHOT TOP-BOF project). This work contributes to the FSC-Sink, CAR-ES and ClimMani COST Action (ES1308). The Agricultural University of Iceland and Mogilsá—the Icelandic Forest Research, provided logistical support for the present study. We thank Matthias Meys, Sara Diels, Johan De Gruyter, Giovanni Dalmasso, Fabiana Quirós and Nadine Calluy for their invaluable help in the laboratory and Sara Vicca and James Weedon for their constructive suggestions. We further thank Anne Cools and Tom Van Der Spiet for their assistance with the lab chemical analyses. ; Peer Reviewed

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. ; This research was supported by the European Research Council Synergy grant ERC-2013-SyG-610028 IMBALANCE-P, the Spanish Government grant CGL2016-79835, the Catalan Government grant SGR 2014-274, the Scholarly Studies programme of the Smithsonian Institution, projects LM2015061 and LO1415 of the Ministry of Education, Youth and Sports of the Czech Republic, and the Research Foundation—Flanders (FWO aspirant grant to N.L.). ; Peer Reviewed