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

Abstract:

Future increase in atmospheric CO2 concentrations will potentially enhance grassland biomass production and shift the functional group composition with consequences for ecosystem functioning. In the “GiFACE” experiment (Giessen Free Air Carbon dioxide Enrichment), fertilized grassland plots were fumigated with elevated CO2 (eCO2) year-round during daylight hours since 1998, at a level of +20% relative to ambient concentrations (in 1998, aCO2 was 364 ppm and eCO2 399 ppm; in 2014, aCO2 was 397 ppm and eCO2 518 ppm). Harvests were conducted twice annually through 23 years including 17 years with eCO2 (1998 to 2014). Biomass consisted of C3 grasses and forbs, with a small proportion of legumes. The total aboveground biomass (TAB) was significantly increased under eCO2 (p = .045 and .025, at first and second harvest). The dominant plant functional group grasses responded positively at the start, but for forbs, the effect of eCO2 started out as a negative response. The increase in TAB in response to eCO2 was approximately 15% during the period from 2006 to 2014, suggesting that there was no attenuation of eCO2 effects over time, tentatively a consequence of the fertilization management. Biomass and soil moisture responses were closely linked. The soil moisture surplus (c. 3%) in eCO2 manifested in the latter years was associated with a positive biomass response of both functional groups. The direction of the biomass response of the functional group forbs changed over the experimental duration, intensified by extreme weather conditions, pointing to the need of long-term field studies for obtaining reliable responses of perennial ecosystems to eCO2 and as a basis for model development.

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:

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.

Abstract:

Future increase in atmospheric CO2 concentrations will potentially enhance grassland biomass production and shift the functional group composition with consequences for ecosystem functioning. In the “GiFACE” experiment (Giessen Free Air Carbon dioxide Enrichment), fertilized grassland plots were fumigated with elevated CO2(eCO2) year-round during daylight hours since 1998, at a level of +20% relative to ambient concentrations (in 1998, aCO2 was 364 ppm and eCO2 399 ppm; in 2014, aCO2 was 397 ppm and eCO2 518 ppm). Harvests were conducted twice annually through 23 years including 17 years with eCO2 (1998 to 2014). Biomass consisted of C3 grasses and forbs, with a small proportion of legumes. The total aboveground biomass (TAB) was significantly increased under eCO2 (p = .045 and .025, at first and second harvest). The dominant plant functional group grasses responded positively at the start, but for forbs, the effect of eCO2 started out as a negative response. The increase in TAB in response to eCO2 was approximately 15% during the period from 2006 to 2014, suggesting that there was no attenuation of eCO2 effects over time, tentatively a consequence of the fertilization management. Biomass and soil moisture responses were closely linked. The soil moisture surplus (c. 3%) in eCO2 manifested in the latter years was associated with a positive biomass response of both functional groups. The direction of the biomass response of the functional group forbs changed over the experimental duration, intensified by extreme weather conditions, pointing to the need of long-term field studies for obtaining reliable responses of perennial ecosystems to eCO2 and as a basis for model development.

Abstract:

Elevated CO2 (eCO2) reduces transpiration at the leaf level by inducing stomatal closure. However, this water saving effect might be offset at the canopy level by increased leaf area as a consequence of eCO2 fertilization. To investigate this bi-directional effect, we coupled a plant growth and a soil hydrological model. The model performance and the uncertainty in model parameters were checked using a 13 year data set of a Free Air Carbon dioxide Enrichment (FACE) experiment on grassland in Germany. We found a good agreement of simulated and observed data for soil moisture and total above-ground dry biomass (TAB) under ambient CO2 (?395 ppm) and eCO2 (?480 ppm). Optima for soil and plant growth model parameters were identified, which can be used in future studies. Our study presents a robust modelling approach for the investigation of effects of eCO2 on grassland biomass and water dynamics. We show an offset of the stomatal water saving effect at the canopy level because of a significant increase in TAB (6.5%, p < 0.001) leading to an increase in transpiration by +3.0 ± 6.0 mm, though insignificant (p = 0.1). However, the increased water loss through transpiration was counteracted by a significant decrease in soil evaporation (?2.1 ± 1.7 mm, p < 0.01) as a consequence of higher TAB. Hence, evapotranspiration was not affected by the increased eCO2 (+0.9 ± 4.9 mm, p = 0.5). This in turn led to a significantly better performance of the water use efficiency by 5.2% (p < 0.001). Our results indicate that mown, temperate grasslands can benefit from an increasing biomass production while maintaining water consumption at the +20% increase of eCO2 studied.

Abstract:

Progress Report of AP B3 for the FACE2FACE plenary meeting