Substrate availability affects abundance and function of soil microorganisms in the detritusphere

Plant litter is the major source of soil organic carbon (SOC). Its decomposition plays a pivotal role in nutrient recycling and influences ecosystem functioning and structure. Soil microorganisms are the main protagonists of litter decomposition. Among other factors, their activity is controlled by the physicochemical conditions of the soil. This interaction is strongly influenced by the soil structure, resulting in a heterogeneous distribution of microorganisms, substrates and physicochemical conditions at the small-scale. Due to this heterogeneity, microhabitats differ in their decomposition rate of organic C. Considering microhabitat diversity is therefore important for understanding C turnover. In the detritusphere, plant litter closely interacts with the soil by releasing soluble C into the adjacent soil and providing new sites for microorganisms. The abundant readily available substrates characterise the detritusphere as a hot spot of microbial activity and C turnover. Despite the important role of this microhabitat, the interaction of physicochemical conditions with soil microorganisms remains unclear. This thesis was designed to clarify the effect of litter C transport on the spatial and temporal availability of substrates and therefore on microbial abundance and activity in the detritusphere. This goal was addressed in three studies. The first study focused on the influence of solute transport conditions on microbial activity and substrate utilisation by the microbial community. In two 2-week microcosm experiments, diffusion and convection were considered as transport mechanisms; both mechanisms were studied at two different water contents. The second study aimed to identify temporal patterns of diffusive solute transport and microbial activity at two water contents during an 84-day incubation. Both studies emphasised the important role of fungi in the detritusphere. The third study therefore identified fungi that benefit from freshly added litter. The three studies combined classical soil biological methods and modern techniques. Analysis of microbial biomass, ergosterol content, CO2 production, and enzyme activities provided general information on the mineralisation of litter C as well as on microbial activity and abundance. A convective-diffusive solute transport model with a first-order decay was used to interpret enzyme activity profiles. This allowed the underlying factors determining the spatial dimension of the detritusphere to be identified. By adding plant residues with a different 13C signature than the SOC, it was possible to quantify the transport of litter C into different C pools. The incorporation litter C into different microbial groups, for example, was traced by coupling of phospholipid fatty acid (PLFA) extraction with 13C analysis. Fungal species were identified by constructing clone libraries based on 18S rDNA and subsequent sequencing. The results of the first study indicated that the transport rate of soluble substrates determines the spatial dimension of the detritusphere, with an enlarged detritusphere after convective versus diffusive transport. The isotopic ratios of bacterial and fungal PLFAs differed under both transport mechanisms, indicating different substrate utilisation strategies: bacteria relied on the small-scale transport of substrates, whereas fungi assimilated new C directly in the litter layer. Water content affected only diffusive C transport and modified the temporal pattern of microbial activity by enhancing transport at higher soil water content. The expected chronological order of C transport, microbial growth and enzyme release was verified in the second and third study. During the first two weeks, mainly easily available and soluble litter compounds were mineralised and transported into the adjacent soil. After this initial phase, depolymerisation of complex litter compounds started. During the initial phase, enhanced C transport induced greater microbial biomass and activity, and increased fungal diversity. During the later phase, however, substrate availability and microbial activity were reduced. Measurements of microbial biomass C and ergosterol indicated that the initial phase was dominated by bacterial r strategists, whereas fungal K strategists dominated the later phase. Sequencing of fungal 18S rDNA detected a shift in the fungal community during the initial phase, pointing to growth of pioneer colonisers, especially Mortierellaceae. These fungi do not produce ergosterol and therefore were not detected by the ergosterol measurements. Accordingly, the r strategists consist of both bacteria and fungi. During the later phase, the fungal community was dominated by the cellulose-degrading fungus Trichocladium asperum. Based on these results, the original concept was modified and a two-phase conceptual model of litter C turnover and microbial response in the detritusphere was developed. In conclusion, this thesis yields new insight into litter decomposition at the small-scale. Combining classical methods with modern techniques enabled the development of a conceptual model of litter C turnover and microbial response in the detritusphere. This provides a useful basis for future studies addressing, for example, the impact of global change on the interaction of decomposition and soil microorganisms.Pflanzliche Biomasse ist die Hauptquelle organischer Bodensubstanz (OBS). Ihr Abbau ist von großer Bedeutung für die pflanzliche Nährstoffversorgung und beeinflusst somit die Funktion und Struktur von Ökosystemen. Hauptakteure in diesem Prozesses sind Boden-mikroorganismen, deren Aktivität u.a. durch die physikalisch-chemischen Eigenschaften des Bodens bestimmt wird. Ein weiterer Einflussfaktor ist die Bodenstruktur. Sie bedingt eine kleinräumige heterogene Verteilung von Bodenmikroorganismen, organischer Substanz und wechselnden physikalisch-chemischen Bodeneigenschaften. Diese Heterogenität des Bodens erzeugt eine Vielzahl an unterschiedlichen Mikrohabitaten, die sich u.a. in der Abbaurate organischer Substanz unterscheiden und somit von großer Bedeutung für den C-Umsatz im Boden sind. Die Detritussphäre umfasst die Streuschicht und den durch Transport von streubürtigem C beeinflussten Boden. Sie gehört wegen des großen Angebots an leichtverfügbaren Substraten zu den ?hot spots? mikrobieller Aktivität und des C-Umsatzes. Trotz dieser wichtigen Eigenschaften bestehen große Wissenslücken in Bezug auf das Wirkungsgefüge zwischen physikalisch-chemischen Bodeneigenschaften und Bodenmikroorganismen. Ziel der vorliegenden Arbeit war es daher, den Einfluss des C Transportes in der Detritussphäre auf die räumliche und zeitliche Variabilität der Substratverfügbarkeit und damit auf die mikrobiologische Abundanz und Aktivität zu untersuchen. In der ersten Studie wurden zwei 2-wöchige Experimente etabliert, um den Einfluss unterschiedlicher Transportmechanismen auf die mikrobielle Substratnutzung und Aktivität zu untersuchen. Im ersten Experiment war der Transport auf Diffusion beschränkt, während im zweiten Konvektion dominierte. In beiden Experimenten wurden zusätzlich zwei Wassergehalte eingestellt. Aufbauend auf den Ergebnissen der ersten Studie wurde ein weiteres Experiment angesetzt, um den zeitlichen Verlauf des C Transportes und der mikrobiellen Aktivität zu verfolgen. Das Experiment beschränkte sich auf Diffusion als Transportprozess und wurde mit denselben Wassergehalten über einen Zeitraum von 84 Tagen durchgeführt. Da die vorigen Experimente auf die große Bedeutung der Pilze hinwiesen, sollte in einer dritten Untersuchen festgestellt werden, welche Pilze von dem großen Nährstoffangebot in der Detritussphäre profitieren. Für die Bearbeitung der Fragestellung wurde eine Kombination klassischer boden-biologischer und moderner Methoden eingesetzt. Messungen der mikrobiellen Biomasse, des Ergosterolgehaltes, der CO2 Produktion sowie von Enzymaktivitäten lieferten allgemeine Informationen über die Mineralisierung des Streukohlenstoffs und die mikrobielle Aktivität und Abundanz. Die Interpretation von Enzymaktivitäten mittels eines Konvektions Diffusions-Models erlaubte es, Einflussfaktoren auf die räumliche Ausdehnung der Detritussphäre zu identifizieren. Die Verwendung von Streu und Boden mit unterschiedlicher 13C Abundanz ermöglichte es, den Transport streubürtigen C in verschiedene Pools zu quantifizieren. Mit Hilfe des 13C-Gehaltes von Phospholipidfettsäuren (PLFA) wurde zum Beispiel der Einbau streubürtigen C in verschiedene Mikroorganismengruppen verfolgt. Einzelne Pilzarten wurden durch die Klonierung und Sequenzierung von 18S rDNA bestimmt. Konvektion erhöhte im Vergleich zur Diffusion die Transportrate streubürtigen C. Dies führte in der ersten Studie zu einer Ausdehnung der Detritussphäre. Außerdem deuteten die 13C-Gehalte bakterieller und pilzlicher PLFAs unter diffusiven und konvektiven Transport-bedingungen auf unterschiedliche Ernährungsstrategien hin: Bakterien sind auf klein-räumigen C-Transport angewiesen, während Pilze C direkt in der Streuschicht assimilieren können. Der Wassergehalt spielte nur bei Diffusion eine Rolle und veränderte durch eine erhöhte Transportrate das zeitliche Auftreten mikrobieller Aktivität. Die daraus abgeleitete Abfolge von diffusivem C-Transport, mikrobiellem Wachstum and der Produktion von extrazellularen Enzymen wurde in einem weiteren Experiment überprüft. Während der ersten 14 Tage wurden leicht verfügbare, lösliche Streukomponenten mineralisiert und in den Boden verlagert. Nach dieser Anfangsphase setzte der Abbau pflanzlicher Polymere ein. In der Anfangsphase wurden mikrobielle Biomasse und Aktivität sowie pilzliche Diversität durch einen erhöhten Wassergehalt gefördert. Dies reduzierte jedoch die Substratverfügbarkeit und verringerte dadurch die mikrobielle Aktivität am Ende des Experimentes. Mikrobielle Biomasse und Ergosterolgehalte deuteten auf eine anfängliche Dominanz bakterieller r Strategen hin, während pilzliche K Strategen erst in der späteren Phase auftraten. Die anfängliche bakterielle Dominanz wurde allerdings durch die DNA Analysen widerlegt. Diese zeigten bereits während der Anfangsphase Wachstum von pilzlichen Pionierarten, insbesondere Mortierellaceae, an. Diese Pilze produzieren kein Ergosterol, so dass ihr Wachstum nicht durch die Messung des Ergosterolgehaltes detektiert wurde. Die anfangs dominierende Gruppe der r Strategen besteht daher vermutlich sowohl aus Bakterien als auch aus Pilzen. Am Ende des Experimentes wurde die pilzliche Gemeinschaft durch den Cellulose abbauenden Pilz Trichocladium asperum dominiert. Aufgrund der Ergebnisse wurde das ursprüngliche Konzept über den Prozessablauf in der Detritussphäre zu einem Zwei-Phasen-Model weiter entwickelt. Zusammenfassend lässt sich festhalten, dass die vorliegende Arbeit das Verständnis über kleinräumige Prozesse des Streuabbaus vertieft hat. Die Kombination von klassischen sowie aktuellen bodenbiologischen Methoden hat hierbei wesentlich zu der Entwicklung eines konzeptionellen Models beigetragen. Solche Modelle sind grundlegend für zukünftige Studien, die zum Beispiel die Auswirkungen des Global Change auf den Streuabbau abschätzen wollen

Are we going for greener Products?

Der Fokus von Forschungen zur Integrierten Produktpolitik lag bisher vor allem auf den Möglichkeiten der Einflussnahme: Welche Instrumente führen zu einer Verbesserung entlang des gesamten Lebensweges? Ob der Ansatz der Integrierten Produktpolitik wirklich erfolgreich ist, wurde dagegen bisher kaum untersucht

SmartPIV: flow velocity estimates by smartphones for education and field studies

In this paper, a smartphone application is presented that was developed to lower the barrier to introduce particle image velocimetry (PIV) in lab courses. The first benefit is that a PIV system using smartphones and a continuous wave (cw-) laser is much cheaper than a conventional system and thus much more affordable for universities. The second benefit is that the design of the menus follows that of modern camera apps, which are intuitively used. Thus, the system is much less complex and costly than typical systems, and our experience showed that students have much less reservations to work with the system and to try different parameters. Last but not least the app can be applied in the field. The relative uncertainty was shown to be less than 8%, which is reasonable for quick velocity estimates. An analysis of the computational time necessary for the data evaluation showed that with the current implementation the app is capable of providing smooth live display vector fields of the flow. This might further increase the use of modern measurement techniques in industry and education

Effects of soil warming and altered precipitation patterns on photosynthesis, biomass production and yield of barley

Crop productivity and plant physiology are affected by rising temperatures and altered precipitation patterns due to climate change. We studied the impacts of an increase in soil temperature of 2.5 °C, a decrease in summer precipitation amount of 25%, a reduction in summer precipitation frequency of 50%, and their interactions on photosynthesis, biomass production, and yield of spring barley (Hordeum vulgare L. cv. RGT Planet) in a temperate agricultural ecosystem near Stuttgart (Germany). Leaf gas exchange of barley appeared to be affected mainly by drought in the form of reduced precipitation frequency or by a combination of changes in soil temperature and precipitation patterns. In contrast, biomass production and yield parameters were more affected under soil warming alone. In addition, biomass of roots increased under soil warming at stem elongation. Stable grain yield was observed under reduced precipitation amount and also under increased evaporation through soil warming. These findings provide additional evidence that barley is relatively drought tolerant, which should be taken into consideration in the context of appropriate crop selection under climate change

Tenosynovial giant cell tumors as accidental findings after episodes of distortion of the ankle: two case reports

<p>Abstract</p> <p>Introduction</p> <p>Tenosynovial giant cell tumors are benign tumors of uncertain pathogenesis. They occur in the joints, tendons and synovial bursas. Due to a high recurrence rate of up to 50%, some authors call a giant cell tumor a semimalignant tumor. To date, less than 10 cases of tenosynovial giant cell tumor of the ankle have been published in the international medical literature.</p> <p>Case presentation</p> <p>In this case report, we present two patients with localized tumors that were detected accidentally after the occurrence of ankle sprains with persisting pain in the joint. The tumors were resected by open marginal surgery and regular follow-up examinations were carried out.</p> <p>Conclusions</p> <p>We present an unusual occurrence of a tumor along with a possible follow-up strategy, which has not been previously discussed in the international literature.</p

Numerical investigations regarding a novel process chain for the production of a hybrid bearing bushing

This contribution deals with the numerical investigations to develop a novel process chain for hybrid solid components using Tailored Forming. For manufacturing a hybrid bearing bushing, co-extrusion is the first step to produce hybrid semi-finished workpieces followed by a die forging process, machining processes and hardening. Combining aluminium with steel, compounds with wear-resistant functional surfaces and reduced weight are realised. Numerical simulations are a decisive part of the process chain design, for example to determine suitable process parameters for the co-extrusion process and to predict the thickness of intermetallic phases in the joining zone using a macroscopic phenomenological model. A numerical design including a tool analysis of the die forging process was carried out taking the experimentally determined material properties and the temperature profile after inductive heating into account. Additionally, the damage and fatigue behaviour of the polycrystalline material of the joining zone are modelled at the microstructure level. Moreover, a new discretization scheme, namely the virtual element method, which is more efficient at grain level, is developed regarding a crystal plasticity framework. Numerical simulations are used to develop inductive heating strategies for the forming process and for the design of the inductive hardening of the functional surface at the end of the process chain. In order to investigate the performance of this hybrid machine element under application-oriented conditions, a contact simulation is linked with a statistical damage model to calculate the bearing fatigue. In this study, a general overview of the individual process steps is given and results of the respective models are presented. © 2020, The Author(s)

Impact of ocean acidification and high solar radiation on productivity and species composition of a late summer phytoplankton community of the coastal Western Antarctic Peninsula

The Western Antarctic Peninsula (WAP), one of the most productive regions of the Southern Ocean, is currently undergoing rapid environmental changes such as ocean acidification (OA) and increased daily irradiances from enhanced surface‐water stratification. To assess the potential for future biological CO2 sequestration of this region, we incubated a natural phytoplankton assemblage from Ryder Bay, WAP, under a range of pCO2 levels (180 μatm, 450 μatm, and 1000 μatm) combined with either moderate or high natural solar radiation (MSR: 124 μmol photons m−2 s−1 and HSR: 435 μmol photons m−2 s−1, respectively). The initial and final phytoplankton communities were numerically dominated by the prymnesiophyte Phaeocystis antarctica, with the single cells initially being predominant and solitary and colonial cells reaching similar high abundances by the end. Only when communities were grown under ambient pCO2 in conjunction with HSR did the small diatom Fragilariopsis pseudonana outcompete P. antarctica at the end of the experiment. Such positive light‐dependent growth response of the diatom was, however, dampened by OA. These changes in community composition were caused by an enhanced photosensitivity of diatoms, especially F. pseudonana, under OA and HSR, reducing thereby their competitiveness toward P. antarctica. Moreover, community primary production (PP) of all treatments yielded similar high rates at the start and the end of the experiment, but with the main contributors shifting from initially large to small cells toward the end. Even though community PP of Ryder Bay phytoplankton was insensitive to the changes in light and CO2 availability, the observed size‐dependent shift in productivity could, however, weaken the biological CO2 sequestration potential of this region in the future