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Biotic, abiotic, and management controls on the net ecosystem CO2 exchange of European mountain grassland ecosystems

By Georg Wohlfahrt, Margaret Anderson-Dunn, Michael Bahn, Manuela Balzarolo, Frank Berninger, Claire Campbell, Arnaud Carrara, Alessandro Cescatti, Torben Christensen, Sabina Dore, Werner Eugster, Thomas Friborg, Markus Furger, Damiano Gianelle, Cristina Gimeno, Ken Hargreaves, Pertti Hari, Alois Haslwanter, Torbjorn Johansson, Barbara Marcolla, Celia Milford, Zoltan Nagy, Eiko Nemitz, Nele Rogniers, Maria J. Sanz, Rolf T. W. Siegwolf, Sanna Susiluto, Mark Sutton, Zoltan Tuba, Francesca Ugolini, Riccardo Valentini, Roberto Zorer and Alexander Cernusca

Abstract

The net ecosystem carbon dioxide (CO2) exchange (NEE) of nine European mountain grassland ecosystems was measured during 2002–2004 using the eddy covariance method. Overall, the availability of photosynthetically active radiation (PPFD) was the single most important abiotic influence factor for NEE. Its role changed markedly during the course of the season, PPFD being a better predictor for NEE during periods favorable for CO2 uptake, which was spring and autumn for the sites characterized by summer droughts (southern sites) and (peak) summer for the Alpine and northern study sites. This general pattern was interrupted by grassland management practices, that is, mowing and grazing, when the variability in NEE explained by PPFD decreased in concert with the amount of aboveground biomass (BMag). Temperature was the abiotic influence factor that explained most of the variability in ecosystem respiration at the Alpine and northern study sites, but not at the southern sites characterized by a pronounced summer drought, where soil water availability and the amount of aboveground biomass were more or equally important. The amount of assimilating plant area was the single most important biotic variable determining the maximum ecosystem carbon uptake potential, that is, the NEE at saturating PPFD. Good correspondence, in terms of the magnitude of NEE, was observed with many (semi-) natural grasslands around the world, but not with grasslands sown on fertile soils in lowland locations, which exhibited higher maximum carbon gains at lower respiratory costs. It is concluded that, through triggering rapid changes in the amount and area of the aboveground plant matter, the timing and frequency of land management practices is crucial for the short-term sensitivity of the NEE of the investigated mountain grassland ecosystems to climatic drivers. \u

Topics: Atmospheric Sciences
Year: 2008
DOI identifier: 10.1007/s10021-008-9196-2
OAI identifier: oai:nora.nerc.ac.uk:5342
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