Zur Oekologie des Auwaldes im Hinterland des Donaukraftwerkes Altenwoerth unter dem oekophysiologischen Aspekt der Auswirkung unterschiedlichen Grundwasserstandes auf die Vegetation. : Oekosystemstudie Donaustau Altenwoerth

1989

S. 211-265

36 Abb., 7 Tab., 55 Lit. Ang.

Unselbständiges Werk

200060322

The study presented deals with long-term consequences of different goundwater levels in a floodplain forest ecosystem. Research was carried out during 1986 and 1987 at two sites north to the Danube south east of "Grafenwoerth" on adult individuals of populus alba aff. canescens adapted to the present groundwater situation as well as on the plants of the shrub and the herb layer. Both sites are compaeable in respect to abiotic factors except groundwater. At one of these sites ("Gamsboden") there was a groundwater supply over the whole vegetation period while groundwater was not available at the other one ("Gryanhaeufel"). Poplars kepp their stomata opened until a certain water stress. The water potential within the poplar-leaves at "Gryanhaeufel" was more negative than within those at the "Gamsboden" site but even on warm, sunny days they were not closed because of water stress. This strategy is possible only when the transpiring area correlates with the water available. Therfore poplars at "Gryanhaeufel" have smaller leaves than those at "Gamsboden" without altering the number of leaves per twig or per sam ground. Net photosynthesis per unit leaf-area on both sites shows only slight differencies (steeper notphotosynthesis - light curve; in contrast to the trees at "Gryanhaeufel" photosynthesis is frequently at the maximum rate at "Gamsboden"). The important loss of assimilates at "Gryanhaeufel" compared with "Gamsboden" is due to the lower leaf area index (Gryanhaeufel": 4.0; "Gamsboden": 4,9). These results correspond with data from leaf and twig primary production where poplars at "Gamsboden" were found to be more productive. This true for the shrub layer (Cornus sanguinea) also. Because of the lower light intensity in the herb layer at "Gamsboden" due to the higher production in the abovae layers the production at this site is lower here than at "Gryanhaeufel". The absolute amount of biomass in the herb layer is small when compared to the totally produced biomass. Similar results as in primary production are found when looking at litter production: at "Gryanhaeufel" less litter is found than at "Gamsboden". Decomposition rates are almost equal at both sites, so the lower organic input at "Gryanhaeufel" results in a longterm deficit ot organic matter in soil. This has to be seen in context with the reduced frequency of inunddation due to the power plant. Different litter composition at the two sites can be discerned with respect to the fungal flora too: there are less species of fungi at "Gryanhaeufel", among others less xylophagious fungi can be found there. There are no differencies in the energy content of plants at both sites. Therefore differencies in energy fixation between the two are similar to those in biomass production.