Does photosynthesis affect grassland soil-respired CO2 and its carbon isotope composition on a diurnal timescale?
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.
Bahn
Michael
M
Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria.
Schmitt
Michael
M
Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria.
Siegwolf
Rolf
R
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.
Richter
Andreas
A
Department of Chemical Ecology & Ecosystem Research, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.
Brüggemann
Nicolas
N
Institute of Meteorology & Climate Research, Atmospheric Environmental Research Division (IMK-IFU), Forschungszentrum Karlsruhe, Kreuzeckbahnstrasse 19, 82467 Garmisch-Partenkirchen, Germany.
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
D002247:Carbon Isotopes; D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon