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Mesocosm experiment on the influence of heatwave on plankton

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.

The iron-snow regime in Fe-FeS cores: a numerical and experimental approach

In the Earth, the dynamo action is strongly linked to core freezing. There is a solid inner core, the growth of which provides a buoyancy flux that drives the dynamo. The buoyancy in this case derives from a difference in composition between the solid inner core and the fluid outer core. In planetary bodies smaller than the Earth, however, this core differentiation process may differ - Fe may precipitate at the core-mantle boundary (CMB) rather than in the center and may fall as iron snow and initially remelt with greater depth. A chemical stable sedimentation zone develops that comprises with time the entire core - at that time a solid inner core starts to grow. The dynamics of this system is not well understood and also whether it can generate a magnetic field or not. The Jovian moon Ganymede, which shows a present-day magnetic dipole field, is a candidate for which such a scenario has been suggested. We plan to study this Fe-snow regime with both a numerical and experimental approach. In the numerical study, we use a 2D/3D thermo-chemical convection model that considers crystallization and sinking of iron crystals together with the dynamics of the liquid core phase (for the 3D case the influence of the rotation of the Fe snow process is further studied).The numerical calculations will be complemented by two series of experiments: (1) investigations in metal alloys by means of X-ray radioscopy, and (2) measurements in transparent analogues by optical techniques. The experiments will examine typical features of the iron snow regime. On the one hand they will serve as a tool to validate the numerical approach and on the other hand they will yield important insight into sub-processes of the iron snow regime, which cannot be accessed within the numerical approach due to their complexity.

Origin and fate of dissolved organic matter in the subsoil

Dissolved organic matter (DOM) is one major source of subsoil organic matter (OM). P5 aims at quantifying the impact of DOM input, transport, and transformation to the OC storage in the subsoil environment. The central hypotheses of this proposal are that in matric soil the increasing 14C age of organic carbon (OC) with soil depth is due to a cascade effect, thus, leading to old OC in young subsoil, whereas within preferential flowpaths sorptive stabilization is weak, and young and bioa-vailable DOM is translocated to the subsoil at high quantities. These hypotheses will be tested by a combination of DOC flux measurements with the comparative analysis of the composition and the turnover of DOM and mineral-associated OM. The work programme utilizes a DOM monitoring at the Grinderwald subsoil observatory, supplemented by defined experiments under field and labora-tory conditions, and laboratory DOM leaching experiments on soils of regional variability. A central aspect of the experiments is the link of a 13C-leaf litter labelling experiment to the 14C age of DOM and OM. With that P5 contributes to the grand goal of the research unit and addresses the general hypotheses that subsoil OM largely consists of displaced and old OM from overlying horizons, the sorption capacity of DOM and the pool size of mineral-associated OM are controlled by interaction with minerals, and that preferential flowpaths represent 'hot spots' of high substrate availability.

Contribution of ectomycorrhizal fungi to the formation and mobilization of soil organic matter (SOM)

In forest ecosystems ectomycorrhizal fungi are responsible for the mobilization of mineral nutrients from soil organic matter (SOM) resulting in a marked increase in productivity of their symbiotic host plants. In return the fungi obtain a significant amount of photosynthetic products from these plants, allowing the formation of an extensive hyphal system. These hyphae constitute a major part of soil biomass and, ultimately, a major source for SOM formation. While plant-fungal nutrient exchange has been analyzed extensively, this proposal is focused on the fungal contribution to SOM formation and on the processes leading to the acquisition of nutrients by the fungi. These two processes will be studied separately and in a quantitative way using isotopic labeling in soil bioreactors. Analysis of the fate of 13C labeled fungal material (Laccaria bicolor) in soil bioreactors will tell how fast and to what extent the various fractions of hyphal biomass are transformed into non-living SOM. As potential molecular or structural markers for SOM formation from fungal hyphae we will analyze characteristic remnants of fungal hyphae in SOM using scanning electron microscopy, DNAfragments using a PCR approach for the fungal rRNA internal transcribed spacerregions and biochemical markers like fatty acids and ergosterol. The impact of ectomycorrhizal mycelia supported by Pinus sylvestris plantlets on 13C- and 15N-labeled SOM and on microbial biomass will be analyzed in separate soil bioreactor experiments.

Light effects on the vertical positioning of the freshwater jellyfish (Craspedacusta sowerbii Lankester, 1880)

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.

openSenseMap: Sensor Box experimenta Forum #2

Dies ist die SenseBox vor dem Forum der experimenta. Kommt gerne vorbei und schaut euch auch die anderen Citizen Science Projekte in unserem Welterforscher im Forum an.

Effect of agricultural intensification on cereal aphid-primary parasitoid-hyperparasitoid food web structures and interactions

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.

Immobilisation of arsenic in paddy soil by iron(II)-oxidizing bacteria

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.

Quantification of the influence of current use fungicides and climate change on allochthonous Organic MATer decomposition in streams (QUANTOMAT)

The decomposition of terrestrial organic material such as leaf litter represents a fundamental ecosystem function in streams that delivers energy for local and downstream food webs. Although agriculture dominates most regions in Europe and fungicides are applied widely, effects of currently used fungicides on the aquatic decomposer community and consequently the leaf decomposition rate are largely unknown. Also potential compensation of such hypothesised adverse effects due to nutrients or higher average water temperatures associated with climate change are not considered. Moreover, climate change is predicted to alter the community of aquatic decomposers and an open question is, whether this alteration impacts the leaf decomposition rate. The current projects follows a tripartite design to answer these research questions. Firstly, a field study in a vine growing region where fungicides are applied in large amounts will be conducted to whether there is a dose-response relationship between the exposure to fungicides and the leaf decomposition rate. Secondly, experiments in artificial streams with field communities will be carried out to assess potential compensatory mechanisms of nutrients and temperature for effects of fungicides. Thirdly, field experiments with communities exhibiting a gradient of taxa sensitive to climate change will be used to investigate potential climate-related effects on the leaf decomposition rate.

Ecological valuation of crop pollination in traditional Indonesian homegardens

Traditional Indonesian homegardens harbour often high crop diversity, which appears to be an important basis for a sustainable food-first strategy. Crop pollination by insects is a key ecosystem service but threatened by agricultural intensification and land conversion. Gaps in knowledge of actual benefits from pollination services limit effective management planning. Using an integrative and agronomic framework for the assessment of functional pollination services, we will conduct ecological experiments and surveys in Central Sulawesi, Indonesia. We propose to study pollination services and net revenues of the locally important crop species cucumber, carrot, and eggplant in traditional homegardens in a forest distance gradient, which is hypothesized to affect bee community structure and diversity. We will assess pollination services and interactions with environmental variables limiting fruit maturation, based on pollination experiments in a split-plot design of the following factors: drought, nutrient deficiency, weed pressure, and herbivory. The overall goal of this project is the development of 'biodiversity-friendly' land-use management, balancing human and ecological needs for local smallholders.

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