Browsing by Subject "Bodenmikroorganismus"

Now showing 1 - 3 of 3
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    Hidden miners – the roles of cover crops and soil microorganisms in phosphorus cycling through agroecosystems
    (2019) Hallama, Moritz; Pekrun, Carola; Lambers, Hans; Kandeler, Ellen
    Background Phosphorus (P) is a limiting nutrient in many agroecosystems and costly fertilizer inputs can cause negative environmental impacts. Cover crops constitute a promising management option for sustainable intensification of agriculture. However, their interactions with the soil microbial community, which is a key driver of P cycling, and their effects on the following crop, have not yet been systematically assessed. Scope We conducted a meta-analysis of published field studies on cover crops and P cycling, focusing on plant-microbe interactions. Conclusions We describe several distinct, simultaneous mechanisms of P benefits for the main crop. Decomposition dynamics, governed by P concentration, are critical for the transfer of P from cover crop residues to the main crop. Cover crops may enhance the soil microbial community by providing a legacy of increased mycorrhizal abundance, microbial biomass P, and phosphatase activity. Cover crops are generally most effective in systems low in available P, and may access ‘unavailable’ P pools. However, their effects on P availability are difficult to detect by standard soil P tests, except for increases after the use of Lupinus sp. Agricultural management (i.e. cover crop species selection, tillage, fertilization) can improve cover crop effects. In summary, cover cropping has the potential to tighten nutrient cycling in agricultural systems under different conditions, increasing crop P nutrition and yield.
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    Soil microorganisms as hidden miners of phosphorus in soils under different cover crop and tillage treatments
    (2022) Hallama, Moritz; Kandeler, Ellen
    Phosphorus (P) is one of the most limiting plant nutrients for agricultural production. The soil microbial community plays a key role in nutrient cycling, affecting access of roots to P, as well as mobilization and mineralization of organic P (Porg). This thesis aimed to better understand the potential of cover crops to enhance plant-soil-microbe interactions to improve the availability of P. This dissertation consists of a meta-analysis of and two field experiments. The used methods showed that microbial P, the activity of P-cycling enzymes and PLFAs increased under cover crops, indicating an enhanced potential for organic P cycling. Gram- positive and Gram-negative bacteria, and to a lesser extent also arbuscular mycorrhizal fungi, increased their abundance with cover crops. However, saprotrophic fungi could benefit most from the substrate input derived from cover crop roots or litter. Enzyme-stable Porg shifted towards pools of a greater lability in the active soil compartments (rhizosheath and detritusphere). The effects of agricultural management, such as cover crop species choice and tillage, were detectable, but weaker compared to the effect of the presence of cover crops. With the obtained results, the research aims of this thesis could be successfully addressed. We were able to confirm that cover crops have the potential to improve main crops’ access to P. Furthermore, we presented and discussed three pathways of P benefit. In the plant biomass pathway, P is cycled through cover crop biomass and becomes available for the main crop upon litter decomposition. The microbial enhancement pathway describes how the cover crop’s interaction with soil microbes increases their abundance and activity, thereby increasing the availability of Porg. Some cover crop species seem to be capable of utilizing a biochemical modification pathway, where changes in the sorption capacity of the soil result in a greater quantity of plant-available phosphate. However, the latter pathway was apparently not important in the crop rotations used in our field experiments. The data also allowed us to characterize ways in which plant-soil-microbe interactions under cover crops affected the relationship of soil microbial functions to the enzymatic availability of Porg pools. Cover crops increased the abundance and activity of microbes, especially fungi, as well as microbial P. This enhancement in P-cycling potential shifted Porg toward pools of greater availability to added enzymes. However, the relation between enzymes and Porg pools is complex and is possibly affected by soil P composition and other site characteristics, indicating the need for further research in this area. Finally, we elucidated how the choice of cover crop species and agricultural management can shift the relative importance of the pathways for the P benefit of the main crop, while site-specific management allows farmers to adapt to local conditions and to optimize the functions of their agroecosystems. In conclusion, our results indicate that the pathways of cover crop derived P benefit take place simultaneously. We confirmed the potential of cover crop biomass for the cycling of P, and we suggest that our observed increases in the availability of soil Porg are related to microbial abundance and activity. The interactions of cover cropping and tillage indicate also that P benefit can be optimized by management decisions. Finally, these new insights into soil phosphorus cycling in agroecosystems have the potential to support further development of more sustainable agricultural systems.
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    The importance of soil microorganisms and cover crops for copper remediation in vineyards
    (2014) Mackie, Kathleen; Kandeler, Ellen
    The historical use of copper fungicides, as a plant protection agent, has moderately polluted agricultural topsoils across Europe. Organic agriculture, in particular, continues to be limited to the use of copper fungicides due to a lack of permitted alternative plant protection agents. In recent years, the effects of copper accumulation in the soil have been observed. Studies on the negative effects of copper in agricultural soils show a decrease in ecosystem services, which rely on macro- and micro-organisms. Thus, there is the question of how to remediate copper polluted crop fields. Although this topic has more recently been investigated in the laboratory, currently, there are no experiments available in the field. Viticulture is one of the largest perennial crops in Europe that utilize copper fungicides. Therefore, this dissertation was designed to investigate copper remediation strategies in vineyards, in order to best understand potential solutions for a growing problem, as well as their effect on ecosystem services. Understanding the reaction of and support by soil microorganisms will help determine which strategy has the best potential. The main project was implemented using two field experiments, each of which analyzed copper availability, microbial abundance, function and community composition to determine the overall outcome of copper remediation. The dissertation is presented in four papers. The first paper is a review on copper in vineyards, which focused specifically on cutting-edge remediation strategies currently being studied. This paper also provided information on knowledge gaps in the literature. The second paper showed the spatial distribution of copper and soil microorganisms at the plot scale, providing a better understanding of copper and microbial distribution as well as a foundation for subsequent papers. The third paper analyzed copper phytoextraction by single species and mixed species cover crop plots and the microbial community that may support it. The fourth paper was aimed at observing the ability of biochar and biochar-compost to immobilize copper and improve ecosystem services. The studies utilized classic soil biological methods (enzyme activities, microbial C and N, ergosterol) and modern molecular techniques (quantitative polymerase chain reaction (qPCR) of 16S rRNA and taxa specific bacteria genes and phospholipid fatty acid analysis (PLFA)) as well as determination of chemical soil properties and copper fractions.