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Spatial and temporal distribution of water and nitrogen supply affects soil-borne nitrous oxide (N2O) emissions. In this study, the effects of different irrigation technologies (no irrigation, sprinkler irrigation and drip irrigation) and nitrogen (N) application types (broadcasted and dissolved in irrigation water) on N2O emissions and the potentially underlying, genetically determined microbial processes were investigated over an entire season in potato cropping. N2O fluxes were highest during the first half of the season and mostly affected by the applied water volume rather than the N application types. The comparison of the different water application types revealed that nitrifier denitrification might potentially be the dominant source of N2O emissions, especially under sprinkler irrigation. The type of N fertilizer supply, broadcasted application or dissolved in irrigation water, showed only minor differences in the potential microbial community functionality. N2O production in both treatments was most likely also dominated by nitrifier denitrification, while the process of denitrification might be feasible too. Even though the current agronomic management measures generally meet the crop demand of water and N, it might be recommendable to adapt the time of application considering that potatoes mainly require N at later growth stages which could also reduce N2O emissions at the same time. [ABSTRACT FROM AUTHOR]

Free-living nematodes harbor and disseminate various soil-borne bacterial pathogens. Whether they function as vectors or environmental reservoirs for the aquatic L. pneumophila, the causative agent of Legionnaires' disease, is unknown. A survey screening of biofilms of natural (swimming lakes) and technical (cooling towers) water habitats in Germany revealed that nematodes can act as potential reservoirs, vectors or grazers of L. pneumophila in cooling towers. Consequently, the nematode species Plectus similis and L. pneumophila were isolated from the same cooling tower biofilm and taken into a monoxenic culture. Using pharyngeal pumping assays, potential feeding relationships between P. similis and different L. pneumophila strains and mutants were examined and compared with Plectus sp., a species isolated from a L. pneumophila-positive thermal source biofilm. The assays showed that bacterial suspensions and supernatants of the L. pneumophila cooling tower isolate KV02 decreased pumping rate and feeding activity in nematodes. However, assays investigating the hypothesized negative impact of Legionella's major secretory protein ProA on pumping rate revealed opposite effects on nematodes, which points to a species-specific response to ProA. To extend the food chain by a further trophic level, Acanthamoebae castellanii infected with L. pneumphila KV02 were offered to nematodes. The pumping rates of P. similis increased when fed with L. pneumophila-infected A. castellanii, while Plectus sp. pumping rates were similar when fed either infected or non-infected A. castellanii. This study revealed that cooling towers are the main water bodies where L. pneumophila and free-living nematodes coexist and is the first step in elucidating the trophic links between coexisting taxa from that habitat. Investigating the Legionella–nematode–amoebae interactions underlined the importance of amoebae as reservoirs and transmission vehicles of the pathogen for nematode predators. [ABSTRACT FROM AUTHOR]

• Nematode communities were shaped by environmental filtering. • Tree type, ground cover and resources were drivers in the organic layer. • Abiotic conditions (water content, soil type) impacted the mineral soil most. • Specific nematode families correlated with forest stand age and density. • Management practice increasing deadwood had no effects. A key to forest productivity is structure and function of the biotic microbiome in the soil, which determines nutrient mineralisation and consequently tree growth and fitness. Soil nematodes are a dominant part of these assemblages, with an important role in the associated micro-food web. However, nothing is known about how forest management and soil properties affect soil nematodes. This study investigated the nematode communities in the organic layer and mineral soil of 150 forests located in three different German regions. Fifty forest stands each were studied in Schwäbische Alb (ALB), Hainch-Dün (HAI) and Schorfheide-Chorin (SCH). The effect of forest management (forest management index – ForMI, silvicultural management intensity indicator – SMI), soil properties (total C, N, S, P, organic C, inorganic C, pH, water content) and microbial food source (phospholipid fatty acids - PLFA) on nematode density, community and ecological indices were assessed. The nematode density in the organic layer of the forests was with a mean of 290 individuals g−1 DW comparable across all three regions, while in the mineral soil nematode density was significant lower in SCH. Here, dry sandy soils are frequently stocked with intensively managed pine forests, and the associated fungal-based decomposition is reflected in a greater proportion of fungal-feeding nematodes and a higher Channel Index. Effects of region and soil layer were mirrored by the structure of the nematode community. Organic layer and mineral soil differed distinctly, while in the latter SCH separated from ALB and HAI. The nematode community was predominantly affected by region, soil properties and resources, with microbial diet as driving factor in the organic layer, whereas soil parameters were more important in mineral soil. In comparison, the influence of forest management was low, with ForMI and SIM together explaining 8% (organic layer) and 4% (mineral soil) of the overall variation. Most remarkable, the nematode community in HAI, a region dominated by broad-leaf forests, was resilient to management intensity in the organic layer. On the other hand, management practice had family-specific impact: In the organic layer of ALB, the density of the bacterial-feeding Teratocephalidae and the fungal-feeding Aphelenchoididae increased with higher Inonat (indicates non-natural tree species) and higher SMIr (addresses stand age and species selection related to the risk of stand loss). In sum, the structure and function of nematode communities were driven by both, biotic factors such food source (i.e. the soil layer inhabited) and abiotic factors such as soil type and climate (i.e. region). Furthermore, forest management can affect nematode communities, mainly by the selected tree species, but also by stand age and density. [ABSTRACT FROM AUTHOR]

Ecological communities in forests have been shown to be strongly affected by forest management but a detailed understanding of how different components of management affect insect communities directly and indirectly via environmental variables, how management influences functional trait diversity and composition, and whether these results can be transferred to other functional groups besides insects (e.g. bacteria or nematodes) is still missing. To address these questions we used water-filled tree holes, which provide habitats for insect larvae and other aquatic organisms in forests, as a model system. We mapped all water-filled tree holes in 75 forest plots (1 ha) under different management intensity in three regions of Germany. We measured structural and climatic conditions at different spatial scales, sampled insect communities in 123 tree holes and bacterial and nematode communities in a subset of these. We found that forest management in terms of harvesting intensity and the proportion of non-natural tree species (species not part of the natural vegetation at the sites) negatively affected tree-hole abundance. An increased proportion of non-natural tree species had a positive direct effect on insect richness and functional diversity in the tree holes. However, a structural equation model showed that increasing management intensity had negative indirect effects on insect abundance and richness, operating via environmental variables at stand and tree-hole scale. Functional diversity and trait composition of insect communities similarly responded to changes in management-related variables. In contrast to insects, bacterial and nematode richness were not directly impacted by forest management but by other environmental variables. Our results suggest that forest management may strongly alter insect communities of tree holes, while nematodes and bacteria seem less affected. Most effects in our study were indirect and negative, indicating that management has often complex consequences for forest communities that should be taken into account in forest management schemes., (Copyright © 2019 Elsevier B.V. All rights reserved.)