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Peat soils can be strong sources of atmospheric nitrous oxide (N2O), but at the same time act as sinks for the greenhouse gas N2O. However, the role of N2O reduction to dinitrogen (N2) here is still not fully understood. In particular, this applies to pristine or weakly disturbed fen mires. These types of peatland ecosystems are characterised by anoxic soil conditions and special N dynamics restricted to ammonium (NH4+) turnover and very low nitrate (NO3−) availability. N2O and N2 fluxes from intact soil cores from three weakly disturbed fen mire types and two soil habitats (tussocks and hollows) were investigated using the helium (He) incubation approach. Ambient air in headspaces were first substituted with a He-O2 trace gas mixture to quantify N2O and N2 exchanges under prevailing soil oxygen (O2) conditions, and then with an anoxic He trace gas mixture (99.9% He) for establishing the maximum possible denitrification rate. Changing from the He-O2 mixture to a pure He trace gas mixture led to strong increase of N2 fluxes (up to 2916 μg N m−2 h−1) and negative N2O fluxes of up to −72 μg N m−2 h−1. Whilst small differences in N gas fluxes were found between all types of fen mires, an analysis of the denitrifier abundance based on nirK, nirS and nosZ genes indicated respectively more pronounced variation. The structure of denitrifier communities exhibited a strong plot specificity driven by water-filled pore space, soil organic matter and soil pH. This short-term He incubation experiment revealed that weakly disturbed fen mires act as considerable N2O sinks under anoxic conditions and improved our knowledge of the original N dynamics in this peatland ecosystem.

Worldwide excessive use of chemical pesticides with harmful side effects to environment and humans has increased the call for a pesticide-free agriculture. Biological control of plant pathogens by antagonistic microorganisms may be an alternative. These should also include plant-associated pseudomonads. They are adapted to live on and inside plants due to their diverse metabolic and ecological abilities. Many Pseudomonas strains exhibit a diverse spectrum of antagonistic traits enabling them to suppress various phytopathogens by direct antibiosis and/or by triggering defence responses in the host plants. Although a certain proportion of strains within the indigenous populations of pseudomonads on and inside plants are able to do so, the spread of these bacteria in the field is rather restricted and individuals with antagonistic activity are unevenly and patchily distributed. Natural biological control of fungal and bacterial plant diseases by pseudomonads possibly supported by adapted management systems therefore, seems unlikely. However, selected Pseudomonas strains can be artificially introduced into the soil–plant ecosystem and have proven to be promising microbial antagonists. But, more substantial in-depth studies to improve the efficacy and survival of biocontrol agents are needed to use them in pesticide-free agriculture on a field scale. Potential biocontrol strains have to undergo a targeted selection process that also takes into account their mode of action. Their application in consortia of multiple strains or with other microbial taxa that are complementary in their action may have advantages in biocontrol efficiency compared to single strains. Biotechnological solutions have to ensure both efficient antagonistic performance and sufficient persistence of the introduced bacteria in the field. With today's knowledge, seed inoculation seems to be a practicable approach to exploit the biocontrol potential of pseudomonads in crop farming.

The community composition of epiphytic heterotrophic bacteria on leaves of beech and oak, which were either damaged by lepidopterous larvae or remained undamaged, was investigated. In addition, the ability of these bacteria to utilize inorganic nitrogen was studied. The bacteria were isolated on nutrient agar and systematically identified with biochemical and physiological tests. Rarefaction plots and the Shannon-Wiener function revealed that species diversity was significantly higher on leaves of damaged beech compared to undamaged leaves, but no differences were found on leaves of oak. The portion of bacterial isolates showing a strong response to ammonia and nitrate was significantly larger on leaves of oak than on those of beech. Furthermore, significantly more isolates with a high capability to assimilate both nitrogen compounds were found on leaves attacked by the folivorous larvae compared to those not attacked on oak. It is suggested that the changes in the microbial community in response to folivorous insects might affect the extent of nutrient cycling exceeding eventually the scale of a leaf.

Comparing different methods of grassland management, the microbial community of grasses was analysed throughout the growing season. The quantitative development of heterotrophic bacteria, yeasts, filamentous fungi, streptomycetes and Listeria has been investigated. Furthermore, the community structure of heterotrophic bacteria was analysed by identifying isolated strains by means of classical biochemical and morphological examination supported by an application of multitest systems based on enzymatic reactions (Biolog, API). The population of heterotrophic bacteria and filamentous fungi was influenced by the age of plant material as well as by the density in the field. Thus, bacteria and fungi reached significantly larger numbers on plants of the late cut utilization (first cut at the beginning of July) in comparison with the regrowth of conventional cutting in mid May. These higher densities of micro-organisms exceeded threshold values that has been fixed for feedstuff s and therefore suggest an affect on the forage quality of this material. The population of yeasts neither showed a continual development over the season nor seemed to be influenced by any kind of management. Streptomycetes were only determined in larger numbers at the beginning of sampling in April, followed by a sporadical occurrence in the following course of investigation. Species of the genera Listeria have not been found at any time of sampling. The community structure of heterotrophic bacteria was numerically predominated by the genera Pseudomonas, Stenotrophomonas, Pantoea, Clavibacter and Curtobacterium . Generally, the population was characterized by low diversity. An influence of management on the composition of bacteria did not become obvious.

A total of 256 strains of lactic acid bacteria isolated from forage grasses were screened for antagonistic activities under conditions where the effects of organic acids and hydrogen peroxide were minimised. Thirty seven strains were shown to inhibit the growth of other lactic acid bacteria in the agar spot test with viable cells. Cell free supernatants from 16 of these strains, most of them belonging to the species Lactobacillus plantarum and Enterococcus faecium , exhibited inhibitory activity against indicator strains. Crude protein extracts containing different bacteriocin-like substances were made from cell free supernatants of Lactobacillus plantarum P1331, Enterococcus faecium P5977 and Leuconostoc mesenteroides P6007, and sensitivity to these extracts of 53 strains of lactic acid bacteria and 25 strains of other phylloplane bacteria were tested. Forty four strains of lactic acid bacteria, and all but one strain of the Gram-positive heterotrophic aerobic bacteria tested were inhibited by at least one of the antagonists. All Gram-negative strains tested were resistant. Inhibitory activity against sensitive indicators was also detected when the strains P1331, P5977 and P6007 grew on “phylloplane agar”, a medium which simulates the low level nutrient conditions found on the phylloplane, in a temperature range between 4 and 37°C. It therefore seems to be likely that strains of lactic acid bacteria able to produce bacteriocin-like substances can influence the development of the population of lactic acid bacteria on plants.