לוח שנה משולב

TBA

Fears of global climate change and its potential outcomes have stimulated intensive efforts to update current climate models. Nevertheless, most of the existing models lack inputs specific to peatlands and/or to microorganisms. Peatlands store up to 30% of the world’s soil carbon and contribute up to 30% of atmospheric methane, thus their response to climate change is of special interest. Peatlands are mostly found at northern high latitudes where nutrient poor conditions foster Sphagnum as a keystone plant species. My studies focus on understanding the response of peatland ecosystems to climate change at the Marcell Experimental Forest (MEF) in northern Minnesota, USA. At MEF, the U.S. DOE has created a unique multi-faceted large scale climate manipulation experiment known as SPRUCE (Spruce and Peatland Response Under Climatic and Environmental Change), initiated in June 2014. From June 2014 to June 2015, we evaluated the responses of microbial communities, both in structure and metabolic potential, to 5 soil warming treatments (+0°C; +2.25°C; +4.5°C; +6.75°C; +9°C). Methane flux was correlated with temperature in the treatments, suggesting that increases in soil temperature apparently drive the emission response. However, multiple lines of evidence, including laboratory incubations, indicate that CH4 emission increased due to surface processes and not degradation of deep carbon. Characterization of in situ microbial communities indicated no significant effect of temperature or time on community composition or function. Specifically, the potential activity of extracellular lignin oxidative enzymes showed that one year of soil warming had a limited effect on microbial activity. While the physiology and ecology of Sphagnum have been well-studied, the structure, function and response of their microbiome to climate change is less understood. Sphagnum-associated, nitrogen-fixing bacteria are thought to play a major role in plant functioning and the peatland nitrogen cycle. Therefore, we conducted intensive sampling of the S. magellanicum phyllosphere-associated microbial communities. Our results revealed a significant geographical effect on general and nitrogen-fixing microbial communities. Interestingly, the nitrogen-fixing core-microbiome contained only 2 members, taxonomically affiliated with Nostoc azollae (symbiotic Cyanobacteria) and Methyloferula stellate (an obligate methanotroph). Potentially synergistic interactions between these nitrogen-fixing bacteria not only provide the plant with sufficient nitrogen, but may also reduce methane emission from peatlands. Our observations of evolutionary conserved nitrogen-fixing bacteria among representative peatland sites further knowledge of the benefits of the microbiome to Sphagnum host fitness and to ecosystem function.

Clusters – in particular those of transition metals – may act like surfaces of limited size, this analogy being recognized long time ago [1,2]. We have studied the C-H bond activation of various organic molecules by naked transition metal clusters before [3], and it became mandatory to switch to simpler systems. By virtue of our tandem cryo ion trap instrument we study the adsorption kinetics of clusters under single collision conditions as well as the Infrared Multiple Photon Dissociation (IR-MPD) by application of optical parametric oscillator/amplifier (OPO/OPA) photon sources, one and two colour investigations of metal organic complexes by such technique being published [4].

Our ongoing studies of N2 and H2 cryo adsorption on Fe, Co, and Ni clusters and alike [5] revealed clearly discernible mono layer like adsorbate shells. Beyond such mere kinetics – though interesting in themselves – we recorded IR-MPD spectra of dinitrogen stretching vibrations within such [Mn(N2)m]+ cluster surface – adsorbate layer complexes by variation of their stoichiometry, n and of m alike, and in conjunction with electronic structure modelling (by DFT), and with synchrotron X-ray based studies of spin and orbital contributions to the total magnetic moments of the isolated clusters [6].

This invited presentation shall elucidate the current state of cluster adsorbate studies under cryo conditions and in isolation. It aims to put into perspective the findings from adsorption kinetics, IR spectroscopy, DFT modelling and magnetic spectroscopy. It concludes with an outlook onto the road ahead.

This research originates from a long standing support by the DFG through the transregional collaborative research center SFB/TRR 88 3MET.de