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Front Plant Sci

Title:		"Impact of Multiple Ecological Stressors on a Sub-Arctic Ecosystem: No Interaction Between Extreme Winter Warming Events, Nitrogen Addition and Grazing"
Author(s):		Bokhorst S; Berg MP; Edvinsen GK; Ellers J; Heitman A; Jaakola L; Maehre HK; Phoenix GK; Tommervik H; Bjerke JW;
Address:		"Norwegian Institute for Nature Research, FRAM - High North Research Centre for Climate and the Environment, Tromso, Norway. Department of Ecological Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands. Community and Conservation Ecology Group, Groningen Institute for Evolutionary Life Sciences, Groningen, Netherlands. Faculty of Biosciences, Fisheries and Economics, Norwegian College of Fishery Science, UiT The Arctic University of Norway, Tromso, Norway. Norwegian Institute of Bioeconomy Research, As, Norway. Climate Laboratory Holt, Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromso, Norway. Department of Animal and Plant Sciences, University of Sheffield, Sheffield, United Kingdom"
Journal Title:		Front Plant Sci
Year:		2018
Volume:		20181130
Issue:
Page Number:		1787 -
DOI:		10.3389/fpls.2018.01787
ISSN/ISBN:		1664-462X (Print) 1664-462X (Electronic) 1664-462X (Linking)
Abstract:		"Climate change is one of many ongoing human-induced environmental changes, but few studies consider interactive effects between multiple anthropogenic disturbances. In coastal sub-arctic heathland, we quantified the impact of a factorial design simulating extreme winter warming (WW) events (7 days at 6-7 degrees C) combined with episodic summer nitrogen (+N) depositions (5 kg N ha(-1)) on plant winter physiology, plant community composition and ecosystem CO(2) fluxes of an Empetrum nigrum dominated heathland during 3 consecutive years in northern Norway. We expected that the +N would exacerbate any stress effects caused by the WW treatment. During WW events, ecosystem respiration doubled, leaf respiration declined (-58%), efficiency of Photosystem II (Fv/Fm) increased (between 26 and 88%), while cell membrane fatty acids showed strong compositional changes as a result of the warming and freezing. In particular, longer fatty acid chains increased as a result of WW events, and eicosadienoic acid (C20:2) was lower when plants were exposed to the combination of WW and +N. A larval outbreak of geometrid moths (Epirrita autumnata and Operophtera brumata) following the first WW led to a near-complete leaf defoliation of the dominant dwarf shrubs E. nigrum (-87%) and Vaccinium myrtillus (-81%) across all experimental plots. Leaf emergence timing, plant biomass or composition, NDVI and growing season ecosystem CO(2) fluxes were unresponsive to the WW and +N treatments. The limited plant community response reflected the relative mild winter freezing temperatures (-6.6 degrees C to -11.8 degrees C) recorded after the WW events, and that the grazing pressure probably overshadowed any potential treatment effects. The grazing pressure and WW both induce damage to the evergreen shrubs and their combination should therefore be even stronger. In addition, +N could have exacerbated the impact of both extreme events, but the ecosystem responses did not support this. Therefore, our results indicate that these sub-arctic Empetrum-dominated ecosystems are highly resilient and that their responses may be limited to the event with the strongest impact"
Keywords:		CO2 fluxes cryptogam fatty acids frost geometrid moth herbivory multiple stress snow;
Notes:		"PubMed-not-MEDLINEBokhorst, Stef Berg, Matty P Edvinsen, Guro K Ellers, Jacintha Heitman, Amber Jaakola, Laura Maehre, Hanne K Phoenix, Gareth K Tommervik, Hans Bjerke, Jarle W eng Switzerland 2018/12/19 Front Plant Sci. 2018 Nov 30; 9:1787. doi: 10.3389/fpls.2018.01787. eCollection 2018"