title: Tradeoffs between global warming and day length on the start of the carbon uptake period in seasonally cold ecosystems.
abstract: It is well established that warming leads to longer growing seasons in seasonally cold ecosystems. Whether this goes along with an increase in the net ecosystem carbon dioxide (CO2) uptake is much more controversial. We studied the effects of warming on the start of the carbon uptake period (CUP) of three mountain grasslands situated along an elevational gradient in the Alps. To this end we used a simple empirical model of the net ecosystem CO2exchange, calibrated and forced with multi-year empirical data from each site. We show that reductions in the quantity and duration of daylight associated with earlier snowmelts were responsible for diminishing returns, in terms of carbon gain, from longer growing seasons caused by reductions in daytime photosynthetic uptake and increases in nighttime losses of CO2. This effect was less pronounced at high, compared to low, elevations, where the start of the CUP occurred closer to the summer solstice when changes in day length and incident radiation are minimal.
authors.affiliation: Institute of Ecology, University of Innsbruck, Innsbruck, AUSTRIA.
authors.forename: Georg
authors.initials: G
authors.lastname: Wohlfahrt
authors.affiliation: Environmental Protection Agency of Aosta Valley, ARPA VdA, Climate Change Unit, Aosta, ITALY.
authors.forename: Edoardo
authors.initials: E
authors.lastname: Cremonese
authors.affiliation: Institute of Ecology, University of Innsbruck, Innsbruck, AUSTRIA.
authors.forename: Albin
authors.initials: A
authors.lastname: Hammerle
authors.affiliation: Institute of Ecology, University of Innsbruck, Innsbruck, AUSTRIA.
authors.forename: Lukas
authors.initials: L
authors.lastname: Hörtnagl
authors.affiliation: Environmental Protection Agency of Aosta Valley, ARPA VdA, Climate Change Unit, Aosta, ITALY.
authors.forename: Marta
authors.initials: M
authors.lastname: Galvagno
authors.affiliation: Sustainable Agro-ecosystems and Bioresources Department, Research and Innovation Centre, Fondazione Edmund Mach, San Michele all'Adige, ITALY ; Foxlab, Research and Innovation Centre, Fondazione Edmund Mach, San Michele all'Adige, ITALY.
authors.forename: Damiano
authors.initials: D
authors.lastname: Gianelle
authors.affiliation: Sustainable Agro-ecosystems and Bioresources Department, Research and Innovation Centre, Fondazione Edmund Mach, San Michele all'Adige, ITALY.
authors.forename: Barbara
authors.initials: B
authors.lastname: Marcolla
authors.affiliation: Environmental Protection Agency of Aosta Valley, ARPA VdA, Climate Change Unit, Aosta, ITALY.
authors.forename: Umberto Morra
authors.initials: UM
authors.lastname: di Cella