title: Does photosynthesis affect grassland soil-respired CO2 and its carbon isotope composition on a diurnal timescale?
abstract: Soil respiration is the largest flux of carbon (C) from terrestrial ecosystems to the atmosphere. Here, we tested the hypothesis that photosynthesis affects the diurnal pattern of grassland soil-respired CO(2) and its C isotope composition (delta(13)C(SR)). A combined shading and pulse-labelling experiment was carried out in a mountain grassland. delta(13)C(SR) was monitored at a high time resolution with a tunable diode laser absorption spectrometer. In unlabelled plots a diurnal pattern of delta(13)C(SR) was observed, which was not explained by soil temperature, moisture or flux rates and contained a component that was also independent of assimilate supply. In labelled plots delta(13)C(SR) reflected a rapid transfer and respiratory use of freshly plant-assimilated C and a diurnal shift in the predominant respiratory C source from recent (i.e. at least 1 d old) to fresh (i.e. photoassimilates produced on the same day). We conclude that in grasslands the plant-derived substrates used for soil respiratory processes vary during the day, and that photosynthesis provides an important and immediate C source. These findings indicate a tight coupling in the plant-soil system and the importance of plant metabolism for soil CO(2) fluxes.
authors.affiliation: Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Bahn
authors.affiliation: Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Schmitt
authors.affiliation: Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.
authors.forename: Rolf
authors.initials: R
authors.lastname: Siegwolf
authors.affiliation: Department of Chemical Ecology & Ecosystem Research, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Richter
authors.affiliation: Institute of Meteorology & Climate Research, Atmospheric Environmental Research Division (IMK-IFU), Forschungszentrum Karlsruhe, Kreuzeckbahnstrasse 19, 82467 Garmisch-Partenkirchen, Germany.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Brüggemann
mesh_terms: D001686:Biological Phenomena; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes / Q000378:metabolism; D002940:Circadian Rhythm; D017753:Ecosystem; D010788:Photosynthesis / Q000502:physiology*; D006109:Poaceae; D012987:Soil
chemical_list: D002247:Carbon Isotopes; D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon