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Abstract The herbicide Roundup (and glyphosate, its active ingredient) is extensively used for weed control on a worldwide scale. It is absorbed after foliar application and quickly translocated inside the plant. In this study, we investigated the effects of Roundup speed, a commercial glyphosate formulation, on the structural composition (dominance of microbial groups, phospholipid fatty acid analysis - PLFA) and functional diversity (use of carbon sources, Multiple Substrate Induced Respiration - MSIR) of soil microorganisms. We specifically aimed at understanding the potential impact of biotic interactions on herbicide effects and included plants, earthworms, and endomycorrhizal fungi in the experimental setup. For this, we grew clover (Trifolium repens) in the greenhouse and added mycorrhizal inoculum (Glomus mosseae) and earthworms (Lumbricus terrestris) to the pots. Two weeks after foliar Roundup application and subsequent plant death, the pots were destructively sampled. The application resulted in a significant increase of microbial respiration (SIR) by approximately 30%. A multivariate analysis of the MSIR data exhibited small but significant differences between the microbial communities of treated and untreated pots, while no significant difference was apparent for the PLFA data. Bacterial PLFAs generally decreased following herbicide application, while mycorrhizal and fungal PLFAs were not affected. We did not find a consistent difference between the fatty acid markers of gram negative and gram positive bacteria. For all investigated parameters, there were highly significant differences between the upper (0–5 cm depth) and lower (5–10 cm) soil layers. The fact that rooting density differed by a factor of 3.5 between the two layers indicated that herbicide effects were especially pronounced in the clover rhizosphere and were likely due to changes in root exudate composition. We found significant, though very small, interactions between Roundup and other experimental factors (especially mycorrhizal inoculum). Highlights • Foliar application of Roundup increased soil microbial respiration (SIR) by 30%. • The application decreased gram+ and gram- bacterial PLFAs, but not that of saprotrophic fungi. • Roundup had small, but significant, impacts on the functional diversity (MSIR) of soil microbiota. • There were very weak interactions between Roundup and soil depth, mycorrhiza, and earthworms. [ABSTRACT FROM AUTHOR]

Microorganisms in forest soils provide essential ecosystem services, such as decomposition of organic matter and nutrient mineralization. However, microbial community structure and function can be affected by environmental conditions, such as regional climate and soil properties and, moreover, by human activity through forest management. We examined the biomass and composition of microbial assemblages in 150 forest stands in the organic layer (Oi, Oe, Oa) and upper mineral soil (0–10 cm) in three regions across Germany (Schwäbische Alb, Hainich-Dün, Schorfheide-Chorin) by phospholipid fatty acid (PLFA) analysis. Different explanatory environmental variables (total C, N, S, P, organic C, inorganic C, pH, water content) were identified. The intensity of land use was characterized with the Forest Management Intensity Index (ForMI). The total amount of PLFAs, as measure for microbial biomass, was different among the three regions both in the organic layer and mineral soil. In the organic layer, total PLFAs decreased from Schwäbische Alb over Hainich-Dün to Schorfheide-Chorin, with the latter comprising a fourfold and twofold lower amount in fungal and bacterial PLFAs, respectively. In contrast, in the mineral soil the forests in the Hainich-Dün showed the highest microbial biomass. Discriminant function analysis of PLFA pattern indicated that Gram-positive bacteria and fungi accounted mainly for the regional differences in the organic layer, whereas in the mineral soil additionally Gram-negative and actinobacteria were important. Redundancy analysis showed that PLFA profiles were predominantly affected by sampling site and environmental variables, with the water content in the organic layer and the soil texture in the mineral soil explaining most of the variability in microbial communities between the three regions. Additionally, forest stands were classified into four management groups (conifer; deciduous with low, medium, and high intensity) based on the ForMI. In the mineral soil, forest management accounted for a small proportion of the observed regional differences. Within regions, fungal biomass in the organic layer decreased with management intensity at the Schwäbische Alb and increased in the mineral soils of Hainich-Dün region. Microbial community structure discriminated coniferous and deciduous forests in all three regions, and moreover showed a separation based on forest management intensity in the Schorfheide-Chorin. In conclusion, microbial biomass and community composition in forest organic layer and mineral soil were more influenced by regional conditions, including environmental properties such as moisture, soil texture, C/N ratio and pH, than by forest management intensity. However, within given environments, microbial assemblages can be influenced by forest management, in particular through changes in the tree species composition. [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]

The decomposition of plant litter is an important mechanism in regard to energy and nutrient dynamics of ecosystems. Silicon concentration of plant tissue can affect these processes by changing litter quality, i.e. nutrient stoichiometry and cellulose and phenols content. To determine which group of microbial decomposers benefits from high Si content in plants and how this impacts on animal decomposers, a batch experiment was conducted with reed leaf litter ( Phragmites australis ) differing in Si content in the presence/absence of invertebrate shredders ( Gammarus pulex ). Lipid concentration of G. pulex , in reed litter and fine particulate matter (FPOM) were examined. High Si concentration in reed resulted in a decline of gram positive bacteria in the heterotrophic biofilm and of gram negative bacteria in FPOM. The lipid composition in the next trophic level, the decomposer G. pulex , changed too, indicating a diet shift in favor of bacteria and algae with increasing litter Si concentration. Thus, basal decomposers were affected by the Si availability in plant resources, and these effects likely persist along the food chain, as FPOM is a dominant food supply for other groups, e.g. collectors. This impact of Si content on plant substrate quality for decomposer food webs may have global relevance, due to related modifications in carbon and nutrient cycling during litter decomposition. [ABSTRACT FROM AUTHOR]