title: Biotic, abiotic and management controls on methanol exchange above a temperate mountain grassland.
abstract: Methanol (CH3OH) fluxes were quantified above a managed temperate mountain grassland in the Stubai Valley (Tyrol, Austria) during the growing seasons 2008 and 2009. Half-hourly methanol fluxes were calculated by means of the virtual disjunct eddy covariance (vDEC) method using 3-dimensional wind data from a sonic anemometer and methanol volume mixing ratios measured with a proton-transfer-reaction mass spectrometer (PTR-MS). During (undisturbed) mature and growing phases methanol fluxes exhibited a clear diurnal cycle with close-to-zero fluxes during nighttime and emissions, up to 10 nmol m-2s-1, which followed the diurnal course of radiation and air temperature. Management events were found to represent the largest perturbations of methanol exchange at the studied grassland ecosystem: Peak emissions of 144.5 nmol m-2s-1were found during/after cutting of the meadow reflecting the wounding of the plant material and subsequent depletion of the leaf internal aqueous methanol pools. After the application of organic fertilizer, elevated methanol emissions of up to 26.7 nmol m-2s-1were observed, likely reflecting enhanced microbial activity associated with the applied manure. Simple and multiple linear regression analyses revealed air temperature and radiation as the dominant abiotic controls, jointly explaining 47 % and 70 % of the variability in half-hourly and daily methanol fluxes. In contrast to published leaf-level laboratory studies, the surface conductance and the daily change in the amount of green plant area, used as ecosystem-scale proxies for stomatal conductance and growth, respectively, were found to exert only minor biotic controls on methanol exchange.
authors.affiliation: Institute of Ecology, University of Innsbruck, Austria.
authors.forename: Lukas
authors.initials: L
authors.lastname: Hörtnagl
authors.affiliation: Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria.
authors.forename: Ines
authors.initials: I
authors.lastname: Bamberger
authors.affiliation: Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria ; Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309.
authors.forename: Martin
authors.initials: M
authors.lastname: Graus
authors.affiliation: Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria.
authors.forename: Taina M
authors.initials: TM
authors.lastname: Ruuskanen
authors.affiliation: Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria.
authors.forename: Ralf
authors.initials: R
authors.lastname: Schnitzhofer
authors.affiliation: Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria.
authors.forename: Markus
authors.initials: M
authors.lastname: Müller
authors.affiliation: Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria.
authors.forename: Armin
authors.initials: A
authors.lastname: Hansel
authors.affiliation: Institute of Ecology, University of Innsbruck, Austria.
authors.forename: Georg
authors.initials: G
authors.lastname: Wohlfahrt
keywords: PTR-MS; disjunct eddy covariance; flux; grassland; management; methanol; volatile organic compounds