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Nitrogen sources of oligoporus placenta and trametes versicolor evaluated in a 2³ experimental plan
(2012)
Four full-factorial 2³ experimental plans were applied to evaluate the nitrogen (N) sources of Oligoporus placenta and Trametes versicolor and their interaction with the atmospheric N2-assimilating bacterium Beijerinckia acida. The effects of N from peptone, of sapwood and of N from gaseous N2 on fungal, bacterial and fungal–bacterial activity were investigated. The activities were determined by quantification of biomass, formation of CO2, consumption of O2 and laccase activity. The significance of each effect was tested according to t-test recommendation.
The activity of both fungi was enhanced by peptone rather than sapwood or gaseous N2. Nevertheless, comparative studies under an N2-free gas mixture as well as under air revealed that the presence of N2 affected bacterial growth and bacterial–fungal cocultivations. Elemental analysis isotope ratio mass spectrometry (IRMS) of the bacterial and fungal biomass enabled estimation of N transfer and underlined gaseous N2 as requisite for fungal–bacterial interactions. Combining full-factorial experimental plans with an analytical set-up comprising gas chromatography, IRMS and enzymatic activity allowed synergistic effects to be revealed, fungal N sources to be traced, and symbiotic fungal–bacterial interactions to be investigated.
As a glacier retreats, it leaves behind it a forefield that has a natural gradient of soil formation age. We systematically sampled the Damma glacier forefield (Switzerland) along a temporal gradient of soils deglaciated between 1956 and 2002. A significant change in organic carbon content, sulfate concentration, pH, water and nucleic acid content was observed along the forefield chronosequence. Based on 16S rRNA gene based fingerprinting, the structure of the bacterial community also shifted along the forefield. Shifts in the structure of the bacterial community were significantly correlated to changes of pH, soil water content and soil age. To test the impacts of an array of environmental variables including soil age, soil water content, and different anions on the structure of the bacterial community we incubated different glacier forefield soils under specific treatment conditions for 30 days at 25 °C. The incubation of recently deglaciated soils resulted into an increase of bacteria from the family Methylocystaceae and from the class Betaproteobacteria while the community composition from matured soil changed to a lesser extent. The total nitrogen concentration in matured soil doubled during incubation, whereas the nitrogen concentrations in recently deglaciated soil stayed constant. This suggested that the microbial ecosystem functioned differently in the mature versus the recently deglaciated soils. Only soil age and soil water content could be singled out as having significant effects on the structure and composition of the bacterial community, despite the fact that bacterial communities in glacier forefields are exposed to other steep environmental gradients.
Isotope ratio mass spectrometry (IRMS) is an advanced method to investigate carbon (C) and nitrogen (N) in organic samples. In particular, the N content, its isotope signature and the C/N ratio reveal important facts of nutrient cycling, niche separation and ecological food webs. In this study, the characteristics of N turnover of wood decomposing microorganisms were investigated.
The growth of the white rot causing basidiomycete Trametes versicolor is enhanced after addition of ammonia or urea, whereas the brown rot causing Oligoporus placenta is not accelerated. In addition, an interaction of each fungus with atmospheric N2 assimilating (diazotrophic) bacteria was investigated. Cultivation experiments with a gas mixture of 15N2/O2 and subsequent IRMS analysis of dry biomass of the diazotrophs Azotobacter croococcum, Beijerinckia acida and Novosphingobium nitrogenifigens revealed that they assimilated up to 12% of their N from N2. The experiments reflected N availability as a prerequisite for efficient growth of decomposing basidiomycetes and diazotrophs. Fungal–bacterial co-cultivation experiments showed that depending on the growth characteristics and bacterial N2 assimilation activity N is transferred from certain bacteria into fungal biomass. Thus, the experiments gave a first indication of an interaction between wood decomposing basidiomycetes and diazotrophs, which is a novel pathway of fungal N acquisition.