Effects of climate factors and vegetation on the CO2 fluxes and δ13C from re-established grassland

The relationship between stable carbon isotope composition (delta C-13-CO2) of soil CO2 flux, vegetation cover and weather conditions was investigated in a short-term campaign at a temperate re-established grassland in Germany. During August-September 2016, we measured surface CO2 flux with a closed-chamber method at high and low soil moisture content ('wet', 'dry'), with and without above ground vegetation ('planted', 'clear-cut') and estimated the effects of treatments on respective delta C-13-CO2 values. The concentration and stable carbon isotope composition of CO2 were determined using the gas chromatography and mass spectrometry analyses. The delta C-13-CO2 of the soil fluxes decreased over sampling time for the 'dry-warm' conditions and canopy manipulation. The ecosystem-derived delta C-13-CO2 values (corrected for the atmospheric delta C-13-CO2) which included predominately soil-and rhizosphere respiration were -26.2 +/- 0.8 parts per thousand for the 'dry-warm' conditions and decreased down to -28.1 +/- 1.4 parts per thousand over a period of 28 days from late August to the end of September. The decrease coincided with the lowering of CO2 flux and could be attributed to changes in plant physiological processes at the end of the vegetation season. Though the removal of shoots did not significantly affect the delta C-13-CO2 values as compared with the control, the pattern of further delta C-13-CO2 decrease (down to -28.8 +/- 0.8 parts per thousand) supported the role of living vegetation in a contribution of C-13-enriched CO2 to the ecosystem respiration.