Methane dynamics in vegetated habitats in inland waters: quantification, regulation, and global significance

Freshwater ecosystems, including lakes, wetlands, and running waters, are estimated to contribute over half the natural emissions of methane (CH4) globally, yet large uncertainties remain in the inland water CH4 budget. These are related to the highly heterogeneous nature and the complex regulation of the CH4 emission pathways, which involve diffusion, ebullition, and plant-associated transport. The latter, in particular, represents a major source of uncertainty in our understanding of inland water CH4 dynamics. Many freshwater ecosystems harbor habitats colonized by submerged and emergent plants, which transport highly variable amounts of CH4 to the atmosphere but whose presence may also profoundly influence local CH4 dynamics. Yet, CH4 dynamics of vegetated habitats and their potential contribution to emission budgets of inland waters remain understudied and poorly quantified. Here we present a synthesis of literature pertaining CH4 dynamics in vegetated habitats, and we (i) provide an overview of the different ways the presence of aquatic vegetation can influence CH4 dynamics (i.e., production, oxidation, and transport) in freshwater ecosystems, (ii) summarize the methods applied to study CH4 fluxes from vegetated habitats, and (iii) summarize the existing data on CH4 fluxes associated to different types of aquatic vegetation and vegetated habitats in inland waters. Finally, we discuss the implications of CH4 fluxes associated with aquatic vegetated habitats for current estimates of aquatic CH4 emissions at the global scale. The fluxes associated to different plant types and from vegetated areas varied widely, ranging from−8.6 to over 2835.8 mg CH4 m−2 d−1, but were on average high relative to fluxes in non-vegetated habitats. We conclude that, based on average vegetation coverage and average flux intensities of plant-associated fluxes, the exclusion of these habitats in lake CH4 balances may lead to a major underestimation of global lake CH4 emissions. This synthesis highlights the need to incorporate vegetated habitats into CH4 emission budgets from natural freshwater ecosystems and further identifies understudied research aspects and relevant future research directions

BAFF, a Novel Ligand of the Tumor Necrosis Factor Family, Stimulates B Cell Growth

Members of the tumor necrosis factor (TNF) family induce pleiotropic biological responses, including cell growth, differentiation, and even death. Here we describe a novel member of the TNF family, designated BAFF (for B cell activating factor belonging to the TNF family), which is expressed by T cells and dendritic cells. Human BAFF was mapped to chromosome 13q32-34. Membrane-bound BAFF was processed and secreted through the action of a protease whose specificity matches that of the furin family of proprotein convertases. The expression of BAFF receptor appeared to be restricted to B cells. Both membrane-bound and soluble BAFF induced proliferation of anti-immunoglobulin M–stimulated peripheral blood B lymphocytes. Moreover, increased amounts of immunoglobulins were found in supernatants of germinal center–like B cells costimulated with BAFF. These results suggest that BAFF plays an important role as costimulator of B cell proliferation and function

APRIL, a New Ligand of the Tumor Necrosis Factor Family, Stimulates Tumor Cell Growth

Members of the tumor necrosis factor (TNF) family induce pleiotropic biological responses, including cell growth, differentiation, and even death. Here we describe a novel member of the TNF family designated APRIL (for a proliferation-inducing ligand). Although transcripts of APRIL are of low abundance in normal tissues, high levels of mRNA are detected in transformed cell lines, and in human cancers of colon, thyroid, and lymphoid tissues in vivo. The addition of recombinant APRIL to various tumor cells stimulates their proliferation. Moreover, APRIL-transfected NIH-3T3 cells show an increased rate of tumor growth in nude mice compared with the parental cell line. These findings suggest that APRIL may be implicated in the regulation of tumor cell growth

N-glycosylation of mouse TRAIL-R and human TRAIL-R1 enhances TRAIL-induced death.

APO2L/TRAIL (TNF-related apoptosis-inducing ligand) induces death of tumor cells through two agonist receptors, TRAIL-R1 and TRAIL-R2. We demonstrate here that N-linked glycosylation (N-glyc) plays also an important regulatory role for TRAIL-R1-mediated and mouse TRAIL receptor (mTRAIL-R)-mediated apoptosis, but not for TRAIL-R2, which is devoid of N-glycans. Cells expressing N-glyc-defective mutants of TRAIL-R1 and mouse TRAIL-R were less sensitive to TRAIL than their wild-type counterparts. Defective apoptotic signaling by N-glyc-deficient TRAIL receptors was associated with lower TRAIL receptor aggregation and reduced DISC formation, but not with reduced TRAIL-binding affinity. Our results also indicate that TRAIL receptor N-glyc impacts immune evasion strategies. The cytomegalovirus (CMV) UL141 protein, which restricts cell-surface expression of human TRAIL death receptors, binds with significant higher affinity TRAIL-R1 lacking N-glyc, suggesting that this sugar modification may have evolved as a counterstrategy to prevent receptor inhibition by UL141. Altogether our findings demonstrate that N-glyc of TRAIL-R1 promotes TRAIL signaling and restricts virus-mediated inhibition

Linking Carbon Dynamics in Stream Ecosystems to Dissolved Organic Matter Quality

Stream ecosystems form an active component of the carbon (C) cycle, and are identified as “hotspots” for carbon dioxide (CO2) emissions. However, the mechanisms driving CO2 emissions from streams are not completely understood. Beside the input of C in the form of CO2 from groundwater, streams receive organic matter from aquatic and terrestrial origins which is partly mineralized to inorganic nutrients and CO2. Future predictions suggest enhanced input of terrestrial organic matter into streams. As such, surrounding land use may highly influence dissolved organic matter (DOM) composition and turnover in streams. The quality, i.e. bioavailability or lability, of aquatic and terrestrial organic matter, as well as which quality feature provides which bioavailability, is controversially discussed and the research is still in its infancy. Thus, the main goal of my thesis is to enhance the understanding of the role of organic matter quality as a potential driver for organic matter turnover in stream ecosystems. A further goal is to shed light on C dynamics with main focus on CO2 of streams surrounded by different land use. The presented work is based on an experimental approach in the laboratory, supported by seasonal field studies and a developed model in order to explore C dynamics and the corresponding drivers in stream ecosystems. The underlying mechanisms and the importance of DOM quality as a main driver was assessed on the small scale in laboratory experiments. The C emissions from streams were quantified and the influence of DOM quality was examined on a stream reach scale by investigating two stream types with different organic matter quality inputs. By developing a process-based model, the understanding of the daily and seasonal scale of C turnover in stream ecosystems was amplified. The results from the experiment under controlled conditions demonstrate that DOM quality governs microbial metabolism (i.e. respiration and bacterial protein production). Moreover, I revealed significant quality differences between two terrestrial DOM sources, while respiration and bacterial protein production increased with the available proportion of the labile DOM source. The molecular weight of DOM was the strongest predictor of bacterial protein production and respiration, while among others, the concentration of low molecular weight substances was another highly influential predictor. The importance of molecular size/weight and DOM quality for microbial metabolism was further confirmed on the stream reach scale where we demonstrated among others a significant linkage between molecular size of DOM and pCO2 across agricultural and forest streams. Moreover, agricultural streams contained significantly higher pCO2 compared to forest streams during all seasons. However, CO2 emissions measured with the powerful drifting chamber method were not significantly different between the stream types. Modeled dissolved oxygen (O2) and CO2 dynamics calibrated with field data resulted in respiratory quotients (RQ = mole of CO2 produced per mole of O2 consumed), which are intimately linked to the elemental composition of the respired compounds across four seasons and two stream types. RQ values were not related to adjacent land use or season. Nevertheless, I found significant relationships between RQ values and DOM quality indicators, such as fluorescing component characteristic for higher plant material and molecule size of DOM in agricultural streams. In conclusion, this thesis demonstrates that DOM quality is an important driver for organic matter turnover in streams. Consequently, my results indicate that ongoing and future land use change and enhanced terrestrial DOM input into streams may influence CO2 emissions, and underline the status of streams as C turnover “hotspots”. Thus, my thesis contributes to the mechanistic understanding of organic matter cycling in stream ecosystems and their role in the regional and global C cycle. Therefore, organic matter quality should be considered in future models and studies with respect to C cycling

Zusammenhänge von Kohlenstoffdynamiken und der Qualität von gelöstem organischen Material in Bachökosystemen

Stream ecosystems form an active component of the carbon (C) cycle, and are identified as “hotspots” for carbon dioxide (CO2) emissions. However, the mechanisms driving CO2 emissions from streams are not completely understood. Beside the input of C in the form of CO2 from groundwater, streams receive organic matter from aquatic and terrestrial origins which is partly mineralized to inorganic nutrients and CO2. Future predictions suggest enhanced input of terrestrial organic matter into streams. As such, surrounding land use may highly influence dissolved organic matter (DOM) composition and turnover in streams. The quality, i.e. bioavailability or lability, of aquatic and terrestrial organic matter, as well as which quality feature provides which bioavailability, is controversially discussed and the research is still in its infancy. Thus, the main goal of my thesis is to enhance the understanding of the role of organic matter quality as a potential driver for organic matter turnover in stream ecosystems. A further goal is to shed light on C dynamics with main focus on CO2 of streams surrounded by different land use. The presented work is based on an experimental approach in the laboratory, supported by seasonal field studies and a developed model in order to explore C dynamics and the corresponding drivers in stream ecosystems. The underlying mechanisms and the importance of DOM quality as a main driver was assessed on the small scale in laboratory experiments. The C emissions from streams were quantified and the influence of DOM quality was examined on a stream reach scale by investigating two stream types with different organic matter quality inputs. By developing a process-based model, the understanding of the daily and seasonal scale of C turnover in stream ecosystems was amplified. The results from the experiment under controlled conditions demonstrate that DOM quality governs microbial metabolism (i.e. respiration and bacterial protein production). Moreover, I revealed significant quality differences between two terrestrial DOM sources, while respiration and bacterial protein production increased with the available proportion of the labile DOM source. The molecular weight of DOM was the strongest predictor of bacterial protein production and respiration, while among others, the concentration of low molecular weight substances was another highly influential predictor. The importance of molecular size/weight and DOM quality for microbial metabolism was further confirmed on the stream reach scale where we demonstrated among others a significant linkage between molecular size of DOM and pCO2 across agricultural and forest streams. Moreover, agricultural streams contained significantly higher pCO2 compared to forest streams during all seasons. However, CO2 emissions measured with the powerful drifting chamber method were not significantly different between the stream types. Modeled dissolved oxygen (O2) and CO2 dynamics calibrated with field data resulted in respiratory quotients (RQ = mole of CO2 produced per mole of O2 consumed), which are intimately linked to the elemental composition of the respired compounds across four seasons and two stream types. RQ values were not related to adjacent land use or season. Nevertheless, I found significant relationships between RQ values and DOM quality indicators, such as fluorescing component characteristic for higher plant material and molecule size of DOM in agricultural streams. In conclusion, this thesis demonstrates that DOM quality is an important driver for organic matter turnover in streams. Consequently, my results indicate that ongoing and future land use change and enhanced terrestrial DOM input into streams may influence CO2 emissions, and underline the status of streams as C turnover “hotspots”. Thus, my thesis contributes to the mechanistic understanding of organic matter cycling in stream ecosystems and their role in the regional and global C cycle. Therefore, organic matter quality should be considered in future models and studies with respect to C cycling.Bäche und Flüsse stellen eine aktive Komponente des Kohlenstoffkreislaufes dar und wurden als „Hotspots“ für Kohlendioxid (CO2) Emissionen identifiziert. Die Mechanismen, welche die CO2 Emissionen aus Bächen steuern, sind bisher aber noch nicht vollständig verstanden. Zusätzlich zum Grundwassereintrag von Kohlenstoff in Form von CO2, wird in Bäche organisches Material aquatischen und terrestrischen Ursprungs eingetragen, welches teilweise zu anorganischen Nährstoffen und CO2 mineralisiert wird. Studien weisen auf einen derzeitig erhöhten Eintrag von terrestrischem organischem Material in Bächen hin, der in naher Zukunft weiter ansteigen soll. Es ist daher zu vermuten, dass die Landnutzung in der unmittelbaren Umgebung der Bäche, die Zusammensetzung und Umsetzung des gelösten organischen Materials in den Bächen stark beeinflusst. Die Qualität des organischen Materials aquatischer und terrestrischer Herkunft, also die Bioverfügbarkeit oder Labilität, sowie welches Qualitätsmerkmal welchen Grad an Bioverfügbarkeit darstellt, wird bisher noch kontrovers diskutiert. Die Forschung zu diesen Aspekten befindet sich noch am Anfang. Daher ist das Hauptziel meiner Doktorarbeit, das Verständnis zur Rolle der Qualität des organischen Materials als potentiell kontrollierenden Faktor für die Umsetzung von organischem Material in Bachökosystemen, zu erhöhen. Ein weiteres Ziel ist es, die Kohlenstoffdynamik, hauptsächlich CO2 Dynamiken, in verschiedenen Bächen mit unterschiedlichen Einflüssen durch die umgebende Landnutzung näher zu untersuchen. Die vorliegende Arbeit basiert dabei auf einem experimentellen Ansatz im Labor, ergänzt durch saisonale Feldstudien und der Entwicklung eines Models, um Kohlenstoffdynamiken sowie deren entsprechende kontrollierenden Mechanismen in Bachökosystemen zu untersuchen. Die Mechanismen und die Bedeutung der Qualität des gelösten organischen Materials als Einflussfaktor wurden im kleinen Maßstab untersucht. In einem Vergleich zweier Bachtypen mit unterschiedlichen Einträgen von organischem Material auf Bach-Abschnitts Ebene, wurden Kohlenstoffemissionen quantifiziert sowie der Einfluss der Qualität des organischen Materials untersucht. Die Entwicklung eines prozessbasierten Modells, ermöglichte ein besseres Verständnis der Kohlenstoffumsätze in Bachökosystemen auf täglicher und jahreszeitlicher Ebene. Die Ergebnisse aus dem Experiment mit kontrollierten Bedingungen zeigen, dass die Qualität des gelösten organischen Materials den mikrobiellen Metabolismus, also Atmung und bakterielle Produktion, reguliert. Darüber hinaus konnte ich erhebliche Qualitätsunterschiede zwischen zwei gelösten organischen Kohlenstoffquellen terrestrischer Herkunft aufzeigen. Die Intensität der Respiration und bakteriellen Produktion nahm dabei mit dem verfügbaren Anteil an labilem gelöstem organischen Material zu. Das Molekulargewicht des gelösten organischen Materials war der stärkste Einflussfaktor für die Respiration und bakterielle Produktion. Die Konzentration der niedermolekularen Substanzen stellte einen weiteren sehr einflussreichen Faktor dar. Die Bedeutung von Molekülgrösse/-gewicht des gelösten organischen Materials und dessen Qualität für den mikrobiellen Metabolismus wurde in der Feldstudie bestätigt. Dort habe ich unter anderem auch einen signifikanten Zusammenhang zwischen der Molekülgrösse des gelösten organischen Materials und dem Partialdruck von CO2 gefunden, der sich unabhängig von der umgebenden Landnutzung (Landwirtschaft oder Wald) gezeigt hat. Des Weiteren wiesen landwirtschaftliche Bäche im Vergleich zu Waldbächen signifikant höhere CO2 Partialdrücke zu allen Jahreszeiten auf. Im Gegensatz dazu zeigten die CO2 Emissionen, gemessen mit der zuverlässigen Methode der driftenden Kammer, keine signifikanten Unterschiede zwischen den beiden Bachtypen. Modellierte Dynamiken von gelöstem Sauerstoff und CO2, die mit Felddaten kalibriert wurden, resultierten in Respirationsquotienten (RQ = Verhältnis von Mol CO2 produziert per Mol Sauerstoff konsumiert), welche eng mit der Elementarzusammensetzung der respirierten Komponenten zusammenhängen, in zwei Bachtypen (Landwirtschaft und Wald) zu allen vier Jahreszeiten. Die RQ-Werte zeigten jedoch keinen Zusammenhang mit angrenzender Landnutzung oder der Jahreszeit. Ich konnte dennoch signifikante Zusammenhänge zwischen RQ- Werten und einigen Qualitätsindikatoren von gelöstem organischen Material, wie zum Beispiel einer Fluoreszenz-Komponente, welche für höhere Pflanzen charakteristisch ist oder der Molekülgrösse vom gelösten organischen Material in landwirtschaftlichen Bächen, nachweisen. Abschließend lässt sich sagen, dass meine Arbeiten die Rolle der Qualität des gelösten organischen Materials als wichtigen Einflussfaktor für die Kohlenstoffumsätze innerhalb von Bächen hervorheben. Meine Arbeiten zeigen, dass die derzeitigen und zukünftigen Landnutzungsänderungen und die erhöhten Einträge terrestrischen Materials einen großen Einfluss auf die CO2 Emissionen darstellen können. Die Rolle der Bäche als „Hotspots“ von Kohlenstoffumsätzen konnte in meinen Untersuchungen bestätigt werden. Meine Dissertation trägt daher zu einem besseren mechanistischen Verständnis dieser Umsätze und der Rolle der Bäche in regionalen und globalen Kohlenstoffkreisläufen bei. Folglich sollte die Qualität des eingetragenen Materials in zukünftigen Modellen und Untersuchungen zum Kohlenstoffkreislauf berücksichtigt werden

Analysis of Dairy Cow Behavior during Milking Associated with Lameness

The detection of lame cows is a challenging and time-consuming issue for dairy farmers. Many farmers use the milking time to monitor the condition of their animals. Because lame cows often show increased stepping when standing to relieve pressure on aching claws, we investigated whether lame cows showed increased activity in the milking parlor. On 20 Swiss dairy farms, 647 cows were scored on lameness with a five-point locomotion score and categorized as clinical lame and non-lame cows in order to see if there are differences in behavior between these two groups (non-lame = scores 1 and 2; lame = scores 3, 4, and 5). During one evening milking, the behavior of the cows was analyzed. A three-dimensional accelerometer, attached to the milking cluster, detected the hind leg activity indirectly via the movements of the milking unit. Additionally, head movements, as well as weight shifting and the number of steps with the front legs, were analyzed from video recordings. Owing to a high percentage of false positive hind leg activities in some milkings measured by the sensor, only 60% of the collected data were evaluated for behavior (356 cows/milkings on 17 farms). Twenty-seven percent of the investigated cows were classified as lame. The lameness prevalence was increasing with increasing parity. Lame cows showed a higher hind leg activity during milking as well as a higher frequency of front steps and weight shifting events during their stay in the milking parlor than non-lame cows. No relation between the status of lameness and the number of head movements could be seen. Observation of increased stepping and weight shifting of individual animals during milking by the farmer could be used as an additional indicator to detect lame cows, but further investigations are required

Flow and Turbulence driven Water Surface Roughness and Gas Exchange Velocity in Streams

Gas exchange velocity in streams and rivers controls fluxes of atmospheric gases across the air-water interface and is commonly related to the turbulence at the water side. Similarly, river flow hydraulics influences the water surface roughness, which is frequently used (in terms of surface flow types) for eco- and morphological mapping of spatial variations of hydraulic conditions. We investigated the relationships between gas exchange velocity, water surface roughness and flow hydraulics for different surface flow types in a low-mountain stream. We used the flux chamber-method to estimate exchange velocity, a freely floating sphere (equipped with acceleration sensors) to measure water surface roughness, as well as a field-particle image velocimetry system for flow and turbulence measurements. The results demonstrate that the gas exchange velocity in smooth and rippled flows followed the same universal dependence on turbulent dissipation rates (with an empirical scaling coefficient at the upper limit) as observed in wind-driven systems. More rough flows were anisotropic and gas exchange velocity was stronger related to vertical components of turbulence parameters. We further explored the potential of using surface flow type evaluations and water surface roughness measurements for estimating gas exchange velocities at the reach scale and beyond

Collaborative Projects: Unleashing Early Career Scientists’ Power

Collaborative research projects exclusively targeted to early career researchers (ECRs) have been initiated in Europe. So far, the first two collaborative projects have united more than 80 ECRs. We describe the structure and benefits of such initiatives for the ECRs and highlight the positive influence on the whole scientific community