Kirst, Gunther
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Kirst, Gunther
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Kirst, Gunther
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Item-typ:Veröffentlichung, Der Effekt der Ektomykorrhiza auf die Aufnahme und Verteilung von Calcium in Sämlingen von Pinus sylvestris L.(2006-05-09); ; ; The objective of this thesis was to investigate the influence of ectomycorrhiza on the uptake and distribution of calcium in pine seedlings (Pinus sylvestris). A focal point of interest was the apoplastic permeability of the fungal sheath of the fungi Suillus bovinus and Rhizopogon roseolus. Using different methods (micro- and macroautoradiography, liquid scintillation spectrometry, atom absoption spectrometry, EDXS), the distribution of calcium within the mycorrhizae and the uptake into the shoots were examined in order to obtain detailed knowledge of the transport processes in the mycorrhizal roots.Using the radiotracer 45Ca, an apoplastic transport through the fungal sheath of the fungi Suillus bovinus and Rhizopogon roseolus could be proven. This was shown by microautoradiographs, which established radioactive marking in the cell walls of the fungal sheath, the harting net and the stele. However, a part of the calcium was precipitated by the fungi by means of exudation of oxalic acid in form of calciumoxalat, and therefore existed in a physiologically inactive form. Another part of the disposable calcium was bound to free cation-binding sites of the cell walls, and therefore temporarily unavailable for transport into the shoot. The absence of the fungal sheath and its ?buffer-effect? explains the faster transport of 45Ca into the shoot of non-mycorrhizal pine. The transport capability of calcium into the shoot was also a distinguishing factor between the two fungal partners. Rhizopogon roseolus displayed a higher calcium intake, which can be explained by its thinner fugal sheath. Additionally, using X-ray microanalysis, higher S-contents could be shown to exist in the cell walls of Suillus bovinus. This could be an indication for a higher hydrophobin accumulation and therefore also a higher hydrophobicity compared to Rhizopogon roseolus. Exposure in an aqueous milieu resulted for Suillus bovinus in lower S-contents, which can be explained by a diffusion of the hydrophobines into the surrounding medium.Experiments with different external calcium concentrations (1mM and 50 mM) showed that an increased calcium supply primarily influenced the calcium concentration in the shoots of the non-mycorrhizal pines. While the calcium was transported relatively freely into the shoot by the non-mycorrhizal roots, the ectomycorrhizae held back part of the excess calcium. Investigating the vacuolar polyphosphate granules of the fungal partners it could be shown that the composition of Suillus bovinus strongly depended on external factors. It could be proven that in the presence of a surplus of calcium, even when using cryotechiques, calcium is nevertheless present to a large degree in the polyphosphate granules.In this thesis it could be shown that the apoplastic transport of calcium through the fungal sheaths of Suillus bovinus and Rhizopogon roseolus is possible. However, a part of the calcium is held back by the mycorrhizae, and is therefore temporarily unavailable for further transport into the shoot. Most important for the transport processes in the fungal sheaths are, beside the species of the symbiotic partners, the form of the fungal sheaths and the experimental conditions.Dissertation237 128 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Microbial activity and transport processes in near-shore, permeable sediments(2005-10-14); ; ; High organic carbon turnover in permeable sands is considered to be fueled by the efficient supply of solutes (e.g., oxygen) and organic matter from the overlying water by pore water advection. In situ quantifications of microbial activity in the presence of pore water advection are still rare. In this thesis, microbial activity and transport processes were investigated in near-shore, permeable sediments. A novel method for the measurement of volumetric oxygen consumption rate (OCR) profiles with high depth resolution in permeable sediments was evaluated in chapter 2. Three technical approaches were presented using either oxygen micro-sensors or planar optodes. For the calculation of areal OCR, the volumetric OCR can be integrated over the oxygen penetration depths measured in situ over extended time periods. These areal OCR reflect the influence of hydrodynamics on oxygen distribution. The method was consistent with established methods (interfacial gradients combined with Fick's first law of diffusion, benthic-chambers). The importance of pore water advection for sediment oxygenation and benthic mineralization was shown at the intertidal sand flat Hausstrand (Sylt/Germany) (chapter 3). Three stations were chosen on a transect from the low - to the high water line. Due to pore water advection, oxygen penetrated deeper and more dynamically during inundation than during exposure of the flat. The oxygen penetration depths were closely coupled to bottom water current velocities, proving the impact of pore water advection on sediment oxygenation. Driven by the advective oxygen supply, benthic OCR were high: 71 - 90% of oxygen consumption took place during inundation and aerobic mineralization was the dominant mineralization process at all stations. Mineralization rates were linked to the inundation time of the stations: Oxygen consumption rates were elevated at the lower flat, sulfate reduction rates decreased sharply from the low- to the high-waterline. At two stations (upper- and lower flat) at the intertidal sand flat Janssand near the island of Spiekeroog (German Wadden Sea), also a deeper oxygen penetration was found during inundation (chapter 4). Similar to the Hausstrand, OCR were high and highest during inundation, and sulfate reduction contributed only between 3 - 25% to total mineralization. However, at the two stations, similar surface mineralization rates were measured. In contrast to this, the concentrations of mineralization end products in the pore water at the low water flat were up to 15 times higher than at the upper flat, and the solute concentrations varied independent of season at this station. It was concluded that two filtration processes influence the distribution of metabolic products: (1) a rapid 'skin filtration' in the upper sediment layer during inundation driven by pore water advection and (2) a slow 'body filtration' through deeper sediment layers during exposure driven by drainage. In the coral reef sediments of Heron Reef (Australia), four sites exhibiting different hydrodynamic regimes were investigated (chapter 5). Oxygen penetration and dynamics as well as oxygen consumption, aerobic mineralization and sulfate reduction rates were highly variable between these sites. The supply of oxygen by pore water advection stimulated aerobic mineralization. A simple estimate of the organic matter supplied to the sediments by pore water advection only explained a fraction of the mineralization rates, indicating the importance of other organic carbon sources like benthic primary production. The microphytobenthos at Heron Reef was dominated by diatoms, dinoflagellates and cyanobacteria (chapter 6). Episammic colonies were highly diverse with respect to cyanobacterial 16S rDNA sequences. Photosynthesis was high per unit chlorophyll-a, indicating an active microphytobenthic community. Estimates on the microphytobenthic photosynthetic production in the entire reef were in the order of magnitude as the estimated production by corals. Photosynthesis stimulated calcification at the four investigated sites. The sediments of at least three stations were net calcifying. Sedimentary N2-fixation (acetylene reduction) was highest in the light, indicating the importance of heterocystous cyanobacteria. In coral fingers no N2-fixation was measurable, which stresses the importance of the sediment compartment for reef nitrogen cycling.Dissertation218 106