Langzeitwirkungen der atmosphärischen CO2-Anreicherung auf den Kohlenstoff- und Wasserhaushalt von Rotklee-Wiesenschwingelgemeinschaften
Manfred Forstreuter
Manfred.Forstreuter@fu-berlin.de
citation: FORSTREUTER, M (1993) Langzeitwirkungen der atmosphärischen CO2-Anreicherung auf den Kohlenstoff- und Wasserhaushalt von Rotklee-Wiesenschwingelgemeinschaften. Dissertation, Universität Osnabrück, Landschaftsentwicklung und Umweltforschung (Berlin) 91: 208 S.
Zusammenfassung
Die vorliegende Arbeit behandelt die Wirkungen der atmosphärischen CO2-Anreicherung auf das Wachstum, den Kohlenstoff- und Wasserhaushalt von Modell-Ökosystemen. In drei Teilversuchen wurden Mischkulturen (1:1) von Trifolium pratense Huds. und Festuca pratensis L. bei CO2-Konzentrationen von 350, 450, 600 und 800 ppm in Langzeitversuchen bis zu 1007 Tage begast.
Für diese Untersuchungen wurde eine Freiland-Versuchsanlage entwickelt, mit der vier Modell-Ökosysteme, bestehend aus den obengenannten Pflanzen und einem eingeschlossenen Bodenmonolithen von 80×80×60 cm³, über mehrere Vegetationsperioden unter freilandnahen Bedingungen untersucht werden konnte.
ZurückSummary
This work studies the effect of increased atmospheric carbon dioxide concentration on carbon and water budgets of model ecosystems. In three long-term investigations, mixed plant stands of Trifolium pratense Huds. and Festuca pratensis L. were exposed to CO2-concentrations of 350, 450, 600, and 800 ppm over a period of up to 1007 days.
For these experiments, a measuring system was specially constructed and was located outside. This made it possible to expose four model ecosystems - consisting of the aforesaid species in a soil block of 80 × 80 × 60 cm³ - to natural environmental conditions for several vegetation periods.
The continuous measurements of the atmospheric concentration from 1984 to 1991 showed a significant yearly increase of 2.8 ppm.
The dry-matter accumulation (aboveground plus roots) of the herbaceous plant stands was highly enhanced by the elevated CO2-concentrations.
A fertilization factor was determined by using all phytomass data and developing a saturation model, showing that the average dry matter accumulation was increased by 18% (450 ppm), by 50% (600 ppm), and by 52% (800 ppm). Particularly at the beginning of the vegetation period and after mowing, the dry-matter accumulation was highly enhanced.
Aboveground phytomass accumulation showed an optimum at nearly 600 ppm, whereas the roots were able to act as a "storage organ" and incorporated additional amounts of carbon at CO2-concentrations over 600 ppm.
The reproductive organs were shown to get heavier with increasing CO2-concentrations. This was significantly the case for the weight of the seeds and caryopses of the investigated species.
Leaf area index (LAI) of the whole plant stand was also higher at increased CO2-concentrations. This change could be shown by an exponential model. At 450 ppm the leaf area index was practically unchanged, whereas at CO2-concentrations of 600 and 800 ppm the leaf area index increased in average by 14% and 35%.
At all CO2 treatments, a saturation level of NCER was determined at high LAI. With increased CO2 levels, higher NCER occurred at higher LAI.
At all phenological stages of the investigated model ecosystems, a linear correlation between the daily sums of photon flux densities was observed. On days with high sums of photon flux densities, the model ecosystems at high CO2-concentration showed higher net CO2 exchange rates, on cloudy days the CO2 amounts were reduced or showed greater CO2 losses in comparison to the plant stands at 350 ppm CO2-concentration.
The water budget of the model ecosystems was influenced by elevated CO2-concentrations. At 450 ppm the evapotranspiration was reduced; at 600 ppm they were hardly affected. However, the evapotranspiration observed at 800 ppm was higher than that of the 350 ppm system.
This led to reduced soil water storage in the system at 800 ppm, whereas the soil water storage at 450 ppm was increased.
At higher CO2-concentrations, water use efficiency was significantly increased and resulted in a more efficient productivity.