Tanja Žuna Pfeiffer

Assessment of flood-induced changes of phytoplankton along a river–floodplain system using the morpho-functional approach

In this research, we aimed to find out how the differences in hydrological connectivity between the main river channel and adjacent floodplain influence the changes in phytoplankton community structure along a river–floodplain system. The research was performed in the River Danube floodplain (Croatian river section) in the period 2008–2009 characterised by different flooding pattern on an annual time scale. By utilising the morpho-functional approach and multivariate analyses, the flood-derived structural changes of phytoplankton were analysed. The lake stability during the isolation phase triggered the specific pattern of morpho-functional groups (MFG) which were characterised by cyanobacterial species achieving very high biomass. Adversely, the high water turbulence in the lake during the frequent and extreme flooding led to evident similarity between lake and river assemblages. Besides different diatom species (groups of small and large centrics and pennates), which are the most abundant representatives in the river phytoplankton, many other groups such as cryptophytes and colonial phytomonads appeared to indicate altered conditions in the floodplain driven by flooding. Having different functional properties, small centric diatom taxa sorted to only one MFG cannot clearly reflect environmental changes that are shown by the species-level pattern. Disadvantages in using the MFG approach highlight that it is still necessary to combine it with taxonomical approach in monitoring of phytoplankton in the river–floodplain ecosystems.

Heavy Metal-Induced Oxidative Stress in Plants: Response of the Antioxidative System

Heavy metals (HMs) are among the most important environmental pollutants, particularly in areas with strong anthropogenic pressure. For plants, high levels of HMs are extremely toxic since they may act in several different modes: by the direct inhibition of plant growth and biosynthetic pathways or through the production of reactive oxygen species (ROS). Certain metals generate ROS due to their involvement in redox reactions like Fenton and/or Haber–Weiss reactions, while metals without redox capacity enhance ROS production by reducing the antioxidant glutathione pool, activating calcium-dependent systems and influencing iron-mediated processes. ROS production affects lipids, proteins, and DNA and consequently leads to cell death. In response, plants are equipped with complex enzymatic and nonenzymatic mechanisms involved in antioxidative defense to neutralize HM toxicity, and the main components of these mechanisms will be reviewed in this chapter.

S-metolachlor promotes oxidative stress in green microalga Parachlorella kessleri - A potential environmental and health risk for higher organisms

The estimation of the toxic influences of herbicide products on non-target aquatic organisms is essential for evaluation of environmental contamination. We assessed the effects of the herbicide S-metolachlor (S-MET) on unicellular green microalga Parachlorella kessleri during 4-72 in vitro exposure to concentrations in the range 2-200μg/L. The results have shown that S-MET had a significant effect on algae, even in doses 10 and 20 times lower than the EC50 values obtained for P. kessleri (EC50-72h=1090μg/L). It generates reactive oxygen species in algae, decreases their growth and photosynthetic pigment concentration, changes their ultrastructure and alters the cellular antioxidant defence capacities. The levels of protein adducts with the reactive aldehyde 4-hydroxy-2-nonenal (HNE), the end-product of lipid peroxidation, were significantly elevated in S-MET treated cells revealing the insufficient effectiveness of P. kessleri antioxidant mechanisms and persistent lipid peroxidation. Since algae are fundamental aquatic food component, the damaged algal cells, still capable of dividing while having persistently increased content of HNE upon S-MET contamination could represent an important environmental toxic factor that might further affect higher organisms in the food chain.

Abiotic Stress Response in Plants: The Relevance of Tocopherols

In the natural environment, plants are continuously exposed to a variety of abiotic stresses yielding higher concentrations of reactive oxygen species (ROS), which may cause strong oxidation of cellular structures. To cope with oxidative stress plants have evolved very efficient antioxidant machinery, among which, lipophilic tocopherols represent an important nonenzymatic component. Tocopherol exists in four isomeric forms (α-, β-, γ-, δ-) and its composition depends on plant genotypic features and tissue type. It plays a crucial role together with other antioxidants (e.g., ascorbic acid, carotenoids, glutathione) in detoxifying ROS that emerge during stress conditions. As a component of thylakoid membranes, tocopherol acts as an important scavenger of singlet oxygen and other ROS thereby preventing lipid peroxidation and maintaining stable redox status in plant cells. In addition, tocopherols may protect the embryo from ROS during germination, under both aging and stress conditions. In this chapter, the role of tocopherols in the regulation of abiotic stress responses in plants will be emphasized.

The importance of microphytic composition on coarse woody debris for nematode colonization: a case study in a fluvial floodplain environment

Abstract Coarse woody debris (CWD) are an important structural feature of many aquatic ecosystems. This study focused on the relationships between nematode colonization and microphytic community structure on CWD. In situ investigations were performed using white willow branches introduced into the floodplain lake, a part of the large natural floodplain in the middle section of the Danube River (Europe) impacted by strong sandy and silt accumulations. Our results showed that CWD support rapid colonization and high species richness of microphytes, regardless of seasonality and flood-induced environmental changes. Successional stages during the accrual of microphytic communities were expressed. Nematode functional feeding group compositions closely followed microphytic composition. The epistrate feeder Chromadorina bioculata over-dominated in diatom-dominated communities with adnate/prostrate and stalk-forming species in spring and autumn. The complex structure of cyanobacterial mats associated with green algae and diatom assemblages in summer attracted suction feeders, represented by the Dorylaimidae family. The obtained results indicated that nematodes are involved in strong trophic coupling with a microbial habitat on CWD. The retention of CWD in aquatic environments or addition of CWD to systems with little or no wood may have important implications for the primary and secondary production in these ecosystems.

Oxidative stress in leaves of two olive cultivars under freezing conditions.

Olive is one of the most important cultivated Mediterranean plants. In order to determine the differences in frost resistance of two, two-year-old olive cultivars (Olea europaea cv. Leccino and cv. Oblica) growing on different types of nutrient substrates (soil and coconut fibres), the trees were exposed to low temperature (-5 °C) in the dark. It was shown that low temperature caused an increase in H2O2 concentration, level of lipid peroxidation and carbonyl protein content in both cultivars and on both nutrient substrates, respectively. The CAT and APX activities significantly varied depending on the cultivar, the nutrient substrate type and the time of exposure to low temperature. Cv. Oblica and cv. Leccino growing on coconut fibres showed a better antioxidative response to low temperature probably due to the higher nitrogen and phosphorus concentration established in this type of nutrient substrate. That positive antioxidative response determined on coconut fibres was more pronounced in leaves of cv. Leccino.