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In bog ecosystems, vegetation controls key processes such as the retention of carbon, water and nutrients. In northern hemispherical bogs, a shift from Sphagnum- to vascular plant-dominated vegetation is often traced back to Climate Change and increased anthropogenic nitrogen deposition and coincides with substantially reduced capacities in carbon, water and nutrient retention. In southern Patagonia, bogs dominated by Sphagnum and vascular plants coexist since millennia under similar environmental settings. Thus, South Patagonian bogs may serve as ideal examples for the long-term effect of vascular plant invasion on carbon, water and nutrient balances of bog ecosystems. The contemporary balances of carbon and water of both a bog dominated by Sphagnum and vascular plants are determined by CO2- H2O and CH4 flux measurements and an estimation of lateral water losses as well as losses via dissolved organic and inorganic carbon compounds. The high time resolution of simultaneous eddy covariance measurements of CO2 and H2O in both bog types and the strong interaction between climatic variables and the physiology of bog plants allow for direct comparisons of carbon and water fluxes during cold, warm, dry, wet, cloudy or sunny periods. By the combination with leaf-scale measurements of gas exchange and fluorescence, plant-physiological controls of photosynthesis and transpiration can be identified. Long-term peat accumulation rates will be determined by carbon density and age-depth profiles including a characterization of peat humification characteristics. A reciprocal transplantation experiment with incorporated shading, liming and labeled N addition treatments is conducted to explore driving factors affecting competition between Sphagnum and vascular plants as well as the interactions between CO2-, CH4-, and water fluxes and decisive plant functional traits affecting key processes for carbon sequestration and nutrient cycling. Decomposition rates and driving below ground processes are analyzed with a litter bag field experiment and an incubation experiment in the laboratory.
Salinity reduces the productivity of cucumber (Cucumis sativus L.) through osmotic and ionic effects. For given atmospheric conditions we hypothesize the existence of an optimal canopy structure at which water use efficiency is maximal and salt accumulation per unit of dry matter production is minimal. This canopy structure optimum can be predicted by integrating physiological processes over the canopy using a functional-structural plant model (FSPM). This model needs to represent the influence of osmotic stress on plant morphology and stomatal conductance, the accumulation of toxic ions and their dynamics in the different compartments of the system, and their toxic effects in the leaf. Experiments will be conducted to parameterize an extended cucumber FSPM. In in-silico experiments with the FSPM we attempt to identify which canopy structure could lead to maximum long-term water use efficiency with minimum ionic stress. The results from in-silico experiments will be evaluated by comparing different canopy structures in greenhouses. Finally, the FSPM will be used to investigate to which extent the improvement of individual mechanisms of salt tolerance like reduced sensitivity of stomatal conductance or leaf expansion can contribute to whole-plant salt tolerance.
In subsoils, organic matter (SOM) concentrations and microbial densities are much lower than in topsoils and most likely highly heterogeneously distributed. We therefore hypothesize, that the spatial separation between consumers (microorganisms) and their substrates (SOM) is an important limiting factor for carbon turnover in subsoils. Further, we expect microbial activity to occur mainly in few hot spots, such as the rhizosphere or flow paths where fresh substrate inputs are rapidly mineralized. In a first step, the spatial distribution of enzyme and microbial activities in top- and subsoils will be determined in order to identify hot spots and relate this to apparent 14C age, SOM composition, microbial community composition and soil properties, as determined by the other projects within the research unit. In a further step it will be determined, if microbial activity and SOM turnover is limited by substrate availability in spatially distinct soil microsites. By relating this data to root distribution and preferential flow paths we will contribute to the understanding of stabilizing and destabilizing processes of subsoil organic matter. As it is unclear, at which spatial scale these differentiating processes are effective, the analysis of spatial variability will cover the dm to the mm scale. As spatial segregation between consumers and substrates will depend on the pore and aggregate architecture of the soil, the role of the physical integrity of these structures on SOM turnover will also be investigated in laboratory experiments.
When released into surface waters, engineered inorganic nanoparticles (EINP) can be subject to multiple transformations. The objectives of MASK are to understand under which conditions EINP in aquatic systems will attach to suspended matter, under which conditions and in which time scale EINP are coated by NOM present in freshwater systems, how these coated colloidal particles are stabilized in the aquatic system and to which extent the aquatic aging processes are reversible. Homo-aggregation, coating changes, biological interactions and hetero-aggregation are hypothesized as key processes governing EINP aging in water bodies. In process orientated laboratory incubation experiments (50 ml to 6 l) with increasing complexity, MASK unravels the relevance and the interplay of inorganic colloids, aquagenic and pedogenic organic matter and solution physicochemistry for stability of EINP. These systems will successively approach situations in real waters. MASK thus provides information on EINP fluxes in the aquatic compartment, their time scales, reversibility and relative relevance. EINP will be analysed by standard light scattering techniques, ICP-MS, ESEM/EDX, WetSTEM and AFM. A method coupling hydrodynamic radius chromatography (HDC) with ICPMS recently developed by K. Tiede for nAg0 will be optimized and developed for further EINP analysis, MASK is further responsible for the virtual subproject ANALYSIS, the development and optimization of joint research unit methods of EINP analysis, sample preparation and sample storage, the exchange of methods and coordinates the joint analyses and the central EINP database.
In the context of global change, marine organisms are subjected not only to gradual changes in abiotic parameters, but also to an increasing number of extreme events, such as heatwaves. However, we still know little about the influence of heatwaves on the structure of marine communities, and experimental studies are needed to test the impact of heatwaves alone, and in combination with other environmental drivers. Here, we conducted a mesocosm experiment and applied an integrated multiple driver design to assess the potential impact of heatwaves under ambient and future environmental conditions on natural coastal plankton communities. To represent future environmental conditions, temperature and pH were manipulated based on the Representative Concentration Pathway 8.5 proposed by the IPCC for 2100, and dissolved N:P ratios were increased to simulate the conditions expected in European coastal zones. Throughout the experiment, we measured abiotic conditions as well as the abundance of bacterioplankton, phytoplankton, and microzooplankton.
We experimentally manipulated the presence of light and light intensity (F = 36.7 μmol m⁻² s⁻¹; D = 0 μmol m⁻² s⁻¹; L = 4.8 μmol m⁻² s⁻¹; M = 21.4 μmol m⁻² s⁻¹) and tested their effects on the vertical positioning of the freshwater jellyfish (Craspedacusta sowerbii) medusae. For the experiments, approximately 100 C. sowerbii medusae were collected in August 2017 in two lakes (Haager Weiher and Leitner Weiher) in Bavaria, Germany. Testing was carried out at Seeon Limnological Station in close vicinity to the collection site. The experimental columns were 7.4 cm in diameter and 170 cm high and were marked with horizontal lines every 5 cm for visual position estimation. Four replicates run in parallel. One C. sowerbii medusa was used in each experimental column. Data cover three light treatments, each run twice: 1) 16:8 h full light (F)–dark (D) light intensity cycles (nF = 716, nD = 428), 2) 16:8 h full light (F)–full dark (D) light intensity cycles complemented with low (L) and medium (M) light intensities (nF = 96, nM = 96, nL = 48, nD = 288), and 3) altered light intensities in approximately 2-hour periods randomly among dark, low, medium, and full light intensities (nF = 96, nM = 76, nL = 72, nD = 336). Results show that light alone was sufficient to trigger a vertical position change of jellyfish towards the water surface, especially high light.
We conducted a mesocosm experiment with an integrated multiple driver design to assess the impact of future global change scenarios on plankton, a key component of marine food webs. The experimental treatments were based on the RCP 6.0 and 8.5 scenarios developed by the IPCC, which were Extended (ERCP) to integrate the future predicted changing nutrient inputs into coastal waters. The mesocosm experiment was conducted over three weeks in late-summer (August-September) 2018. Seawater containing a natural plankton community was collected from the coastal North Sea. At the onset of the experiment, CO2 saturated seawater was added to the ERCP scenario mesocosms to adjust pCO2 and pH levels for each scenario. To create a realistic environment, we also manipulated the atmospheric pCO2 in the enclosed mesocosm tanks throughout the experiment. Seawater temperature was adjusted daily according to the current North Sea temperature measured at the Helgoland Roads for the Ambient, and 1.5°C and 3.0°C warmer for the ERCP 6.0 and ERCP 8.5 scenarios, respectively. Dissolved nutrient concentrations were determined at the onset of the experiment and adjusted to reach the desired N:P ratios. Samples were taken in an interval of 1-3 days depending on the phytoplankton bloom development, and community composition, except for the large mesozooplankton, was monitored throughout the experiment period.
LA-ICP-MS data from three different experiments including five foraminiferal species: Ammonia confertitesta (Bourgenuf, France), Bulimina marginata, Cassidulina laevigata (Gullmard Fjord, Sweden), Amphistegina lessonii and Operculina ammonoides (Eilat, Israel). Foraminifera were cultured at different oxygen concentrations (30% and 100% oxygen saturation). Element to calcium ratio (E/Ca) and partition coefficients (D) of Mg, Mn and Sr are noted for individual laser ablation measurements per specimen.
Changes in agroecosystem management (e.g. landscape diversity, management intensity) affect the natural control of pests. The effects of agricultural change on this ecosystem service, however, are not universal and the mechanisms affecting it remain to be understood. As biological control is effectively the product of networks of interactions between pests and their natural enemies, food web analysis provides a versatile tool to address this gap of knowledge. The proposed project will utilize a molecular food web approach and examine, for the first time, how changes in plant fertilisation and landscape complexity affect quantitative aphid-parasitoid-hyperparasitoid food webs on a species-specific level to unravel how changes in food web interactions affect parasitoid aphid control. Based on the fieldderived data, cage experiments will be conducted to assess how parasitoid diversity and identity affect parasitoid interactions and pest control, complementing the field results. The work proposed here will take research on parasitoid aphid control one step further, as it will provide a clearer understanding of how plant fertilization affects whole aphid-parasitoid food webs in both simple and complex landscapes, allowing for further improvements in natural pest control.
Arsenic-contaminated ground- and drinking water is a global environmental problem with about 1-2Prozent of the world's population being affected. The upper drinking water limit for arsenic (10 Micro g/l) recommended by the WHO is often exceeded, even in industrial nations in Europe and the USA. Chronic intake of arsenic causes severe health problems like skin diseases (e.g. blackfoot disease) and cancer. In addition to drinking water, seafood and rice are the main reservoirs for arsenic uptake. Arsenic is oftentimes of geogenic origin and in the environment it is mainly bound to iron(III) minerals. Iron(III)-reducing bacteria are able to dissolve these iron minerals and therefore release the arsenic to the environment. In turn, iron(II)-oxidizing bacteria have the potential to co-precipitate or sorb arsenic during iron(II)- oxidation at neutral pH followed by iron(III) mineral precipitation. This process may reduce arsenic concentrations in the environment drastically, lowering the potential risk for humans dramatically.The main goal of this study therefore is to quantify, identify and isolate anaerobic and aerobic Fe(II)-oxidizing microorganisms in arsenic-containing paddy soil. The co-precipitation and thus removal of arsenic by iron mineral producing bacteria will be determined in batch and microcosm experiments. Finally the influence of rhizosphere redox status on microbial Fe oxidation and arsenic uptake into rice plants will be evaluated in microcosm experiments. The long-term goal of this research is to better understand arsenic-co-precipitation and thus arsenic-immobilization by iron(II)-oxidizing bacteria in rice paddy soil. Potentially these results can lead to an improvement of living conditions in affected countries, e.g. in China or Bangladesh.
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