The detritusphere is an excellent model to study microbial-physicochemical interactions during degradation of the herbicide MCPA. Whereas during the first phase of SPP 1315 we focused on bacterial and fungal abundance at the soil litter interface and carbon flow between different compartments, the second phase will be devoted to elucidating complex regulation mechanisms of MCPA degradation in the detritusphere: (1) At the cellular level, co-substrate availability and laccase abundance might be important regulators, (2) at the community level, bacteria harbouring different classes of tfdA genes might control degradation of MCPA and (3) at the microhabitat level, interaction between MCPA degraders and organo-mineral surfaces as well as transport processes might be important regulators. The concept of hierarchical regulation of MCPA degradation will be included into the modelling of small-scale microbial growth, MCPA transport and MCPA degradation near the soil-litter interface.
Biogeochemical interfaces shape microbial community function in soil. On the other hand microbial communities influence the properties of biogeochemical interfaces. Despite the importance of this interplay, basic understanding of the role of biogeochemical interfaces for microbial performance is still missing. We postulate that biogeochemical interfaces in soil are important for the formation of functional consortia of microorganisms, which are able to shape their own microenvironment and therefore influence the properties of interfaces in soil. Furthermore biogeochemical interfaces act as genetic memory of soils, as they can store DNA from dead microbes and protect it from degradation. We propose that for the formation of functional biogeochemical interfaces microbial dispersal (e.g. along fungal networks) in response to quality and quantity of bioavailable carbon and/or water availability plays a major role, as the development of functional guilds of microbes requires energy and depends on the redox state of the habitat.To address these questions, hexadecane degradation will be studied in differently developed artificial and natural soils. To answer the question on the role of carbon quantity and quality, experiments will be performed with and without litter material at different water contents of the soil. Experiments will be performed with intact soil columns as well as soil samples where the developed interface structure has been artificially destroyed. Molecular analysis of hexadecane degrading microbial communties will be done in vitro as well as in situ. The corresponding toolbox has been successfully developed in the first phase of the priority program including methods for genome, transcriptome and proteome analysis.
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.
The nature of the microbial communities inhabiting the deeper soil horizons is largely unknown. It is also not clear why subsurface microorganisms do not make faster use of organic compounds under field conditions. The answer could be provided by a reciprocal soil transfer experiment studying the response of transferred soils to fluctuations in microclimate, organic inputs, and soil biota. The subproject P9 will be responsible for the establishment of reciprocal transfer experiments offering a strong link between subgroups interested in organic matter quality, transport of organic substances, as well as functions of the soil microbial community. A single, high molecular weight substrate (13C labelled cellulose) will be applied at two different levels in the pre-experiment to understand the dose-dependent reaction of soil microorganisms in transferred surface and sub-soils. Uniformly 13C labelled beech roots - representing complex substrates - will be used for the main reciprocal soil transfer experiment. We hypothesize that transferring soil cores between subsoil and surface soil as well as addition of labelled cellulose or roots will allow us to evaluate the relative impact of surface/subsurface habitat conditions and resource availability on abundance, function, and diversity of the soil microbial community. The second objective of the subproject is to understand whether minerals buried within different soil compartments (topsoil vs. subsoil) in the field contribute to creation of hot spots of microbial abundance and activity within a period of two to five years. We hypothesize that soil microorganisms colonize organo-mineral complexes depending on their nutritional composition and substrate availability. The existence of micro-habitat specific microbial communities could be important for short term carbon storage (1 to 6 years). The third objective is to understand the biogeography and function of soil microorganisms in different subsoils. Parent material as well as mineral composition might control niche differentiation during soil development. Depending on size and interconnectedness of niches, colonization and survival of soil microbial communities might be different in soils derived from loess, sand, terra fusca, or sandstone. From the methodological point of view, our specific interest is to place community composition into context with soil microbial functions in subsoils. Our subgroup will be responsible for determining the abundance, diversity, und function of soil microorganisms (13C microbial biomass, 13C PLFA, enzyme activities, DNA extraction followed by quantitative PCR). Quantitative PCR will be used to estimate total abundances of bacteria, archaea and fungi as well as abundances of specific groups of bacteria at high taxonomic levels. We will apply taxa specific bacterial primers because classes or phyla might be differentiated into ecological categories on the basis of their life strategies.
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.
Dairy farming across Germany displays diverse production systems. Factor endowment, management, technology adoption as well as competitive dynamics in the local or regional land, agribusiness and dairy processing sectors contribute to this differentiation on farm level. These differences impact on the ability of dairy farms and regional dairy production systems to successfully respond to pressures arising from future market and policy changes. The overall objective of the research activities of which this project is a part of, is to develop a thorough understanding of the processes that govern the spatial dynamics of dairy farm development in different regions in Germany. The central hypothesis of this research project is that management system and technological choices differ systematically across local production and market conditions. The empirical approach will focus on the estimation of farm specific nonparametric cost functions for dairy farms located in across Germany differentiated by time and location. A spatially differentiated data base with information on input use, resource availability, as well as local market conditions for land and output markets will be compiled. The nonparametric approach is specifically suited to disclose a more accurate representation of dairy production system heterogeneity across locations and time compared to parametric concepts as it provides the necessary flexibility to accommodate non-linearities relevant for a wide domain of explanatory variables. The methodology employed goes beyond the state of the art of the literature as it combines kernel density estimation with a Bayesian sampling approach to provide theory consistent parameters for each farm in the data sample.The specific methodological hypothesis is that the nonparametric approach is superior to current parametric techniques and this hypothesis is tested using statistical model evaluation. Regarding the farm management and technological choices, we hypothesize that land suitability for feed production determines the farm intensity of dairy production and thus management and technological choices. With respect to the ability of farms to successfully respond to market pressures we hypothesize that farms at the upper and lower tail of the intensity distribution both can generate positive returns from dairy production. These last two hypotheses will be tested using the estimated spatially differentiated farm specific costs and marginal costs.The expected outcomes are of relevance for the agricultural sector and the food supply chain economy as a whole as fundamental market structure changes in the dairy sector are ongoing due to the abolition of the quota regulation in the years 2014/2015. Thus, exact knowledge about differences and development of dairy cost heterogeneity of farms within and between regions are an important factor for the actors involved in the market as well as the political support of this process.
Calcium supply in tropical soils is variable and frequently low. In spite of the heterogeneous Ca supply, some plant species, such as figs, maintain high Ca concentrations in their tissues. Figs are keystone species with more than proportional importance for the functioning of a tropical rain forest. High Ca concentrations in fig fruits may render them particularly attractive for frugivorous vertebrates. We propose to study the whole Ca cycling from soil through a selected fig species, Ficus insipida Willd. and frugivorous bats, their main dispersers, back to soil. The study will be conducted in Panama on sites differing in soil Ca status to assess the importance of soil Ca availability for fig fruit content and bat reproduction. We will quantify aboveground Ca fluxes for 16 trees along a gradient of Ca availability in soil. We will determine (1) Ca concentrations in soils, figs and leaves, (2) nutritional quality of fig and other bat-dispersed fruits and their importance for Ca balance in relation to reproduction of fruit-eating bats, (3) Ca fluxes with litterfall, throughfall, stemflow, bat pellets and faeces, (4) the importance of the contribution of bats to the Ca cycle of individual fig trees, and (5) the effect of fig trees on soil Ca concentrations.
Biochar has a great potential to ameliorate arable soils, especially those that are low in organic matter due to intensive use or erosion. Biochar is carbonised organic material with high porosity that brings about changes in physical, chemical and biological soil functions. Biochar amended soils show a higher water and cation exchange capacity with reduced leaching and enhanced availability of plant nutrients. The microbial biomass in biochar amended soils is enhanced and more diverse. Biochar is stabilised organic material, which is likely to remain for hundreds of years in the soil. Photosynthetically fixed atmospheric CO2 stabilised in biochar may thus act as a direct carbon sink and help to mitigate climate change. As feedstock and production conditions produce different biochar qualities predictions of effects in soil need to consider biochar and soil properties case by case. To date biochar has been approved to ameliorate highly weathered tropical soils with positive effects on crop growth and yield. Distinct microbial groups were reported to be enhanced in soils but if this depends on the particular soil or biochar or a combination of both is an open question, especially in temperate climates. Likewise, it is not known if microorganisms colonising biochar surfaces are responsible for its mineralization or if they just use the new niches provided. The aim of the proposed project is to investigate the influence of two biochar types on soil-plant systems by determining i) soil nutrient availability, plant growth and nutrient uptake, ii) structure and function of soil microbial communities, iv) the decomposition and fate of biochar in soils. We will use two loessial soils from the well-known DOK-trial with different soil organic matter content. Other soils from the region will be selected to provide a wider range of soil quality, in particular pH. The biochars will be produced by pyrolysis and hydrothermal carbonization (HTC) from the C4-plant Miscanthus gigantea. Pyrolysis derived material has bigger pore sizes due to the evaporating gasses and is commonly alkaline, whereas the HTC derived biochar has a finer pore size, a much higher oxygen content and more acidic functional groups.
This project proposes to explore the potential of sedimentary sequences from arid Southern Levant to record past environmental and climate changes that can be compared with the evolution of human societies during the Holocene. The Levant, crucible of history, actually possesses very few archives of past climate change in its most arid parts, which restricts the possibility to compare, on a regional scale, environmental variation and the evolution of human communities through time. The region is characterised by contrasted bioclimatic conditions, from Mediterranean-type to arid. Most of the known records of environmental change are located in the moister, Mediterranean zones of the region, where increased water availability permits the presence - or the better preservation - of high-resolution and continuous archives of past climates. However, the potential of the arid environments of the Southern Levant (roughly corresponding to modern Israel, Palestine, and Jordan) to harbour records of Holocene (last ca. 11,500 years) climate change, is far from being exploited to its full extend. Following the unique discovery of Holocene organic, peat-like deposits in the rain-shadow of the Dead Sea area in Jordan, this project proposes to investigate the potential of this currently arid region to record past environmental and climate change. The organic sequences present in the mountain slopes East of the Dead Sea have been shown to contain very good pollen information. Results from a preliminary pollen study provided in particular evidence for the periodic extension of Mediterranean-type forest vegetation, from the upper Mediterranean plateaus down to the study area. These organic sequences can be further exploited to generate more precisely dated (mainly through radiocarbon techniques) and higher-resolution records of climate and environmental change for the Holocene. Pollen data will be complemented by a series of other proxies: charcoal studies indicating recurrent fires, spores and fungi revealing past grazing activities, diatom assemblages showing changes in the water quality, increased detrital content marking periods of enhanced erosion. All these results can then be integrated into dynamic models of local environmental changes and vegetation response. Furthermore, the same area contains multiple sequences of spring carbonates (tufa / travertine) waiting to be studied. The stable isotopic (oxygen and carbon) composition of spring carbonates can provide a good record of past climate change, as it registers variations in environmental factors such as temperature, parent-water composition (itself related to the source and amount of rainfall), and evaporation. The presence of carbonate sequences near organic sequences on the edge of the Dead Sea, offers an unprecedented occasion to directly compare the isotopic variations of carbonate series with environmental variations recorded in the peaty archives.
The increasing specialization and intensification of the agricultural food production in the North China Plain is leading to restrictions in nutrients and production cycles at farm and regional levels. As a result, livestock production in the North China Plain is entailing serious environmental negative impacts related to manure surpluses and recycling of nutrients, mainly leading to problems associated with water, soil and air pollution. On the other side higher nutrient demands in the local crops is leading to the purchase of chemical or mineral fertilizers when local or on-farm nutrients are not available. Therefore, the efficient use of organic fertilizers not only depends on their availability in the farms, but also on their nutritional composition. Likewise, soil nutrient requirements and plant physiological needs have to be taken into consideration. Indeed, the closer the nutrient cycles and the lower the environmental negative impacts and farm losses are, the greater the chances for a more sustainable resource use in the North China Plain. In the context of the IRTG, aspects of livestock farming in production systems in terms of widely closed nutrients cycles will be integrated. The material flows in different animal husbandry systems will be analysed and the environmental impacts dependent on livestock farming techniques, farms operability and their respective management will be investigated. The applicability and effectiveness of the technical and organizational measures for the reduction of material losses and, the environmental burdens caused by livestock and manure mismanagement in the North China Plain will be reviewed. The benefits and profits for the local cropping systems as result of the application of organic fertilizers originated from livestock farming will be both, ecologically and economically, evaluated as an alternative to replace the use of mineral fertilizers.
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