The rhizosphere of two flooding-resistant plant species (Arundinella anomala Steud., Alternanthera philoxeroides Mart.) from Three Gorges Reservoir area (China) has been examined for reactions to waterlogging and submergence. Rhizosphere parameters were monitored in natural sediment substrate by means of a dual-access floodable rhizobox, which allows monitoring of oxygen and pH dynamics noninvasively with planar optodes in high temporal and spatial resolution, as well as simultaneous low-invasive soil-solution sampling. Analysis of samples for low-molecular-weight organic acids (LMWOA) was done by capillary electrophoresis. Roots could be observed easily in situ during growth and exposure to flooding. The floodable rhizobox is therefore considered a valuable tool for root-reaction monitoring also under flooding conditions. During waterlogging, both species exuded oxygen into their rhizosphere and showed diurnal rhythms of rhizospheric acidification. The pH of the rhizosphere of growing root tips decreased up to 0.8 units corresponding to higher LMWOA concentrations. These rhythms weakened during flooding, but gained maximum amplitude again rapidly after resurfacing. We conclude that the root system was still fully functioning during and after flooding, and that flooding poses no threat to the physiology of the root system of the study species

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The construction of the Three Gorges Dam on the Yangtze River in China has a great influence on the ecosystems involved. In order to investigate these environmental effects in the Yangtze catchment area as well as downstream of the dam, Forschungszentrum Jülich has organized a research network for the Chinese and German partners. In the research fields of (1) interaction water/ sediment/contaminants, (2) vegetation/biodiversity, (3) changing land use/erosion/mass movements, and (4) atmosphere, the partners have accumulated a great deal of expertise in handling major issues and also in developing models and recommendations for action. The following provides an overview of the research network and the research tasks. On the German side, five projects in research field (3) have been in operation since 2008. The results are reported in contributions by Ehret et al., Jaehnig and Cai, Schönbrodt et al., and Seeber et al.. Another five projects in research field (1) have started by September 2010. The research tasks undertaken in these five projects are presented below.

The effects of flooding on rhizospheric organic acid concentrations of three abundant flooding tolerant plant species (Alternanthera philoxeroides Mart., Arundinella anomala Steud., Salix variegata Franch.) from the water fluctuation zone of the Three Gorges Reservoir (TGR, Yangtze River) were investigated. Soil solution samples of eight low molecular weight organic acids were obtained from rhizotrons using micro suction cups during 3 weeks of waterlogging, after 6 weeks flooding and after a 1 week recovery. To estimate the contribution of water temperature and microbial community, plants in sterile glass bead substrate and original Yangtze sediment were submerged in laboratory at +10°, +20°and +30°C. Waterlogged plants did seldom express a significantly different pattern of rhizospheric organic acid (OA) composition compared to control plants. Flooding caused no burst of organic acid concentration in soil solution: All species express a silencing strategy. Average OA levels were higher in A. anomala rhizosphere than in the other two species, but increased again after resurfacing in all species. Temperature had a stronger influence in sediment than in sterile setup. In contrast to field measurements, succinate, malate and citrate were detected in the sterile setup. Microbial contribution appeared to have great influence on increasing OA occurrence.

Abstract. The major topic of the present experiment was the investigation of the antioxidative enzymes and the root exudate excretion after plant exposure to copper. The copper was added for each treatment as copper sulphate and copper nitrate in the concentrations of 10 µM, 5 0 µM and 100 µM , respectively. The plant species chosen for the study was Typha latifolia. The experiment gives insight into the plant responses to different copper supplies during the same conditions of exposure. Remarkable results were obtained during the time course about the excretion of organic acids from Typha latifolia roots during one week of copper exposure. Oxalic acid, malic acid, acetic acid and lactic acid were detected. Interestingly, not all organic acids are excreted from the roots in the first hours after copper addition.