- Effects from climate change, adaptations and
greenhouse gas reduction at 2050

Abstract:

The sampling design in the all six Gi-FACE rings is standardised. Subplots 1-3 are used for weekly measurements of greenhouse gas fluxes and biannual biomass harvest. Subplots 4-25 are used for biannual biomass harvests and cover more or less the two species inventory subplots for biannual vegetations surveys. Subplots 24 and 25 have been used in 2013 for a 15N-13C Tracing study and in Subplot 25 the topsoil (7.5 cm) was used in 2014 for an incubation study and the soil was replaced by soil from outside the rings. Small circles within the ring area indicate Licor soil colomne for soil respiration measurements. The yellow rectangles mark the area where soil profiles have been opened in 2015 to install new soil moisture and temperature sensors. "Needles" and asterix mark positions where soil samples have been taken.

Abstract:

Facing rising atmospheric CO2 concentrations, subsoils may play an important role in the global carbon (C) cycle due to the presence of unsaturated mineral surfaces. Further, macroaggregation is considered a crucial process influencing C sequestration. However, analyses on subsoil aggregation and C retention processes under long-term elevated CO2 (eCO2) are lacking. In this study we investigated the long-term effect of +20% above ambient CO2 concentration (corresponds to conditions reached 2035–2045) in a temperate grassland ecosystem at the Giessen Free Air CO2 Enrichment (Gi-FACE), Germany. A depth-dependent response of macroaggregation to eCO2 was observed: While in subsoil (15–45?cm depth) macroaggregation increased under eCO2, no CO2 induced change in macroaggregation was detected in topsoil (0–15?cm). Increased macroaggregation in subsoil coincided with higher SOC content of large macroaggregates (LM). Mean residence time (MRT) of SOC in aggregate-size classes were not different among each other under eCO2. However, macroaggregates and bulk soil differed in their MRT between soil depths. Despite increased macroaggregation and an estimated high SOC sequestration potential in subsoil we could not observe an increase in SOC content of bulk soil.

Abstract:

Overview of the B3 working package of the FACE2FACE Programme. Includes methods and model setup, N balance of the field site, simulation results of biomass and CO2 emissions with and without groundwater, as well as an outlook for the phase-out period.

Abstract:

Overview of the model setup for the Giessen FACE grassland ecosystem, including preliminary simulation results for CO2 emissions and outlook.

Abstract:

Rising atmospheric CO2 concentrations are expected to increase nitrous oxide (N2O) emissions from soils via changes in microbial nitrogen (N) transformations triggering a positive feedback reaction that could accelerate climate change. Several studies have shown N2O emission increases under elevated atmospheric CO2 (eCO2), but the underlying processes are not yet fully understood. Here we present results showing changes in soil N transformation dynamics from the Giessen Free Air CO2 Enrichment (GiFACE): a permanent grassland that has been exposed to eCO2, +20% relative to ambient concentrations (aCO2), for 15 years. We applied in the field an ammonium-nitrate fertilizer solution, in which either ammonium (NH4+) or nitrate (NO3-) was labelled with 15N. The simultaneous gross N transformation rates were analysed with a 15N tracing model and a solver method. The results confirmed that after 15 years of eCO2 the N2O emissions under eCO2 were still more than 2-fold higher than under aCO2. The tracing model results indicated that plant uptake of NH4+ did not differ between treatments, but uptake of NO3- was significantly reduced under eCO2. However, the ratio of gross production and consumption of NH4+ remained unchanged under eCO2, but decreased slightly for NO3-, which increased NO3- availability under eCO2. The N2O isotopic signature indicated that under eCO2 the sources of the additional emissions, 8407 µg N2O-N m-2 during the first 58 days after labelling, were associated with NO3- reduction (+2.0%), NH4+ oxidation (+11.1%) and organic N oxidation (+86.9%). We presume that increased root exudation under eCO2 provided an additional source of bioavailable supply of energy that triggered the stimulation of microbial soil organic matter (SOM) mineralization, as a priming effect, and an increased activity of bacterial nitrite reductase, which caused the shift in N2O:N2 emission ratio, via incomplete denitrification, explaining the positive feedback reaction of doubled N2O emissions.

Abstract:

Satellite map of the Umweltbeobachtungs und Klimafolgenforschungsstation Linden

Abstract:

Compares simulations of plant biomass and CO2 emissions of the Giessen FACE grassland with and without groundwater-borne nitrate.

Abstract:

Shows how simulated biomass, soil moisture and greenhouse gas emissions are affected by the measured N deficit of the Giessen FACE grassland.

Abstract:

Displays how field site data from the Giessen FACE are processed into simulations of soil moisture, biomass and greenhouse gas emissions (CO2 and N2O). Simulations are displayed in GLUE-like uncertainty analysis. Gives an outlook how the N-deficit of the field site may be connected to groundwater N supply.