Auswirkung von Weidedegradation auf die Zusammensetzung und Funktion mikrobieller Gemeinschaften in Böden des Tibetischen Plateaus

Das Tibetische Plateau, mit seinen Kobresia pygmea Weiden, stellt eine globale Senke für organischen Kohlenstoff (OC) dar. Überweidung führt zur Zerstörung der Kobresia Wurzelmatten und damit zur Graslanddegradation. Dies hat massive OC Verluste und die Destabilisierung des Ökosystems zur Folge. Diese Arbeit analysiert den Effekt der degradationsbedingten veränderten Zusammensetzung der organischen Bodensubstanz (SOM) auf die Zusammensetzung der mikrobiellen Gemeinschaft und deren Funktion entlang einer Sequenz von sechs Degradationsstufen. Dazu wurden die Aktivitäten von sechs extrazellulären Enzyme gemessen sowie die Zusammensetzung der bakteriellen und pilzlichen Gemeinschaft (mittels t-RFLP Analyse gefolgt von Illumina MiSeq Sequenzierung) analysiert. So konnte die Zusammensetzung der mikrobiellen Gemeinschaft mit den vertikalen Gradienten der δ13C und δ15N-Werte, sowie den Neutralzucker-, Cutin-, Suberin- und Ligningehalten in Beziehung gesetzt werden. Mit zunehmender Degradation deuten negativere δ13C-Werte auf eine relative Anreicherung an 13C-armen Makromolekülen wie bspw. Lignin hin. Zusammen mit ebenfalls verringerten δ15N-Werten und veränderten C/N-Verhältnissen belegt dies einen verstärkten SOM-Abbau. Gleichzeitig nimmt die Aktivität von hydrolytischen Enzymen, mit fortschreitender Degradation zu. Lediglich in der letzten Degradationsstufe ist ein drastischer Rückgang der Aktivität dieser Enzymgruppe zu beobachten. Im Gegensatz dazu zeigen Phenoloxidasen (Mineralisation komplexer SOM) zunehmende Aktivitäten mit steigender Degradation die mit einer Anreicherung dieser Substrate (z.B. Ligin) einhergeht. Die beobachteten Änderungen der Enzymaktivitäten sind mit einer veränderten Zusammensetzung der mikrobiellen Gemeinschaft, besonders des Unterbodens, begleitet. So nehmen Actinobacteria mit der Degradation ab während Nitrosomonas zunehmenden, was einen steigenden Verlust von mineralisiertem N aus dem Boden erklärt. Bis jetzt ist unklar ob die degradationsbedingten funktionellen und strukturellen Veränderungen der mikrobiellen Gemeinschaft der Kobresia Grasländer reversibel sind, oder ob mit steigendem Verlust an Nährstoffen und Boden ein Punkt erreicht wird, der eine Erholung der Kobresia-Matten nicht mehr erlaubt

Coping with Temperature at the Warm Edge – Patterns of Thermal Adaptation in the Microbial Eukaryote Paramecium caudatum

Ectothermic organisms are thought to be severely affected by global warming since their physiological performance is directly dependent on temperature. Latitudinal and temporal variations in mean temperatures force ectotherms to adapt to these complex environmental conditions. Studies investigating current patterns of thermal adaptation among populations of different latitudes allow a prediction of the potential impact of prospective increases in environmental temperatures on their fitness.In this study, temperature reaction norms were ascertained among 18 genetically defined, natural clones of the microbial eukaryote Paramecium caudatum. These different clones have been isolated from 12 freshwater habitats along a latitudinal transect in Europe and from 3 tropical habitats (Indonesia). The sensitivity to increasing temperatures was estimated through the analysis of clone specific thermal tolerances and by relating those to current and predicted temperature data of their natural habitats. All investigated European clones seem to be thermal generalists with a broad thermal tolerance and similar optimum temperatures. The weak or missing co-variation of thermal tolerance with latitude does not imply local adaptation to thermal gradients; it rather suggests adaptive phenotypic plasticity among the whole European subpopulation. The tested Indonesian clones appear to be locally adapted to the less variable, tropical temperature regime and show higher tolerance limits, but lower tolerance breadths.Due to the lack of local temperature adaptation within the European subpopulation, P. caudatum genotypes at the most southern edge of their geographic range seem to suffer from the predicted increase in magnitude and frequency of summer heat waves caused by climate change

The response of temperate aquatic ecosystems to global warming: novel insights from a multidisciplinary project

This article serves as an introduction to this special issue of Marine Biology, but also as a review of the key findings of the AQUASHIFT research program which is the source of the articles published in this issue. AQUASHIFT is an interdisciplinary research program targeted to analyze the response of temperate zone aquatic ecosystems (both marine and freshwater) to global warming. The main conclusions of AQUASHIFT relate to (a) shifts in geographic distribution, (b) shifts in seasonality, (c) temporal mismatch in food chains, (d) biomass responses to warming, (e) responses of body size, (f) harmful bloom intensity, (f), changes of biodiversity, and (g) the dependence of shifts to temperature changes during critical seasonal windows

Spatial, temporal, and inter-compartmental environmental monitoring of lipophilic pollutants by virtual organisms.

Sampling points belonging to the Harz National Park river system, Germany, were selected between the period of 2014 and 2017 for monitoring polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in water, air, and sediment. Triolein-containing Virtual Organisms (VO) were employed to assess the levels of chemicals in water, air and triolein as surrogate for natural fat. To avoid overestimation of the concentrations 20 performance reference compounds (PRCs)-16 PRCs-PAHs and 4 PRCs-PCBs were covering the range of properties of native compounds. Results manifested the highest concentration of individual PAH as follows: 31 ng fluoranthene/L water, 3600 ng pyrene/g fat, 62 ng phenanthrene/m3 air and 2800 ng fluoranthene/g dw sediment. All PCBs and OCPs values were below above mentioned PAH concentrations and far below EU-limit levels. Environmental partition of chemicals was investigated by calculating fugacity, suggesting a mass transport from water to air. Only quite volatile compounds such as hexachlorobutadiene showed higher fugacity in air. Ratios of sediment/water concentrations and log Kow within individual sampling periods at Holtemme River exhibited strong linear relationships. Interestingly, during summer months of the years water and fat contents well correlate to the flow rates of Holtemme River. Our results show that VO can be successfully used as a tool for ongoing exposure assessment studies and predictions of worst case levels in food and nutrition

A new approach for evaluating transformations of dissolved organic matter (DOM) via high-resolution mass spectrometry and relating it to bacterial activity.

Streams are important sites of transformation of dissolved organic matter (DOM). The molecular characterization of DOM-quality changes requires sophisticated analytical evaluation techniques. The goal of our study was to link molecular DOM transformation with bacterial activity. We measured the degradation of leaf leachate over a gradient of bacterial production obtained by different rates of percolation of sediments in seven experimental flumes on five sampling dates. We developed a new strategy for evaluating molecular formula data sets obtained by ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS), in which the time-dependent change of component abundance was fitted by a linear regression model after normalization of mass peak intensities. All components were categorized by calculating the slope (change of percent intensity per day) in each of the seven flumes. These slopes were then related to cumulative bacterial production. The concentration of DOM decreased quickly in all flumes. Bacterial activity was higher in flumes with percolated sediment than in those without percolation, whereas plankton bacterial activity was higher in flumes without percolation or without sediment. There were no differences in molecular-DOM characteristics between flumes, but there were distinct changes over time. Positive slopes, i.e. increasing intensities over time, were found for small molecules (MW < 450 Da) and high O/C ratios, whereas decreasing intensities were observed less often and only for large molecules and low O/C ratios. The positive slopes of produced components showed a positive relationship to bacterial production for small and for oxygen-rich components. The negative slopes of degraded components were negatively related to bacterial production for large and for oxygen-deficient molecules. Overall, the approach provided new insights into the transformation of specific molecular DOM components

Biofilm-specific uptake does not explain differences in whole-stream DOC tracer uptake between a forest and an agricultural stream

Benthic biofilms are often assumed to control terrestrially-derived dissolved organic carbon (tDOC) uptake in streams. We tested this by comparing ¹³C-enriched ryegrass leachate uptake in an agricultural and a forest stream, hypothesizing that a greater abundance of autotrophic biofilms in the agricultural stream would cause its whole-stream tDOC uptake to be comparatively low. We measured whole-stream and biofilm tDOC tracer uptake, metabolism, bacterial and algal diversity, and nutrient status of benthic epilithic biofilms, and assessed whole-stream hydromorphology. Whole-stream uptake of tDOC was six times lower in the agricultural (3.0 mg m¯² day¯¹) than in the forest (19.0 mg m¯² day¯¹) stream, and tDOC uptake velocity indicated lower tDOC demand in the agricultural (1.2 mm min¯¹) than in the forest (1.9 mm min¯¹) stream. The agricultural stream differed from the forest stream by slightly lower transient storage capacity and higher benthic biofilm bacterial abundance and production, lower biofilm biomass and lower biofilm molar C:N, C:P, and N:P ratios. Changes in epilithic biofilms contributed little to the differences in whole-stream tDOC tracer uptake between streams, as biofilm tDOC uptake only amounted to 4% and 13% of whole-stream uptake in the forest and agricultural stream, respectively. This comparison of a forest and an agricultural stream suggests that agricultural stressors have the potential to diminish both whole-stream tDOC uptake and uptake efficiency. Furthermore, the weak link between biofilm and whole-stream tDOC uptake implies that benthic biofilms characteristics are poor predictors for human impacts on tDOC uptake in agricultural streams and that hot spots of tDOC uptake are likely situated in the hyporheic zone or in the stream water column