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Microbial N (microbial + n)
Selected AbstractsBacterial immobilization and remineralization of N at different growth rates and N concentrationsFEMS MICROBIOLOGY ECOLOGY, Issue 1 2005Per Bengtson Abstract An experiment was designed to resolve two largely unaddressed questions about the turnover of N in soils. One is the influence of microbial growth rate on mobilization and remineralization of cellular N. The other is to what extent heterotrophic immobilization of is controlled by the soil concentration of . Bacteria were extracted from a deciduous forest soil and inoculated into an aqueous medium. Various N pool dilution/enrichment experiments were carried out to: (1) calculate the gross N immobilization and remineralization rates; (2) investigate their dependence on concentrations; (3) establish the microbial preference for depending on the concentration ratio. Remineralization of microbial N occurred mainly at high growth rates and concentrations. There was a positive correlation between immobilization and remineralization rates, and intracellular recycling of N seemed to be an efficient way for bacteria to withstand low inorganic N concentrations. Thus, extensive remineralization of microbial N is likely to occur only when environmental conditions promote high growth rates. The results support previous observations of high immobilization rates, especially at low concentrations, but was also immobilized at high NH4 concentrations. The latter can be understood if part of the microbial community has a preference for . [source] The use of endogenous nitrogen for microbial crude protein synthesis in the rumen of growing bullsJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 5 2000H. Kluth Summary The objective of this study was to quantify endogenous nitrogen (N) recycled for microbial protein synthesis in the rumen. Four growing bulls (Schwarzbuntes Milchrind; bodyweight: 240,310 kg) with duodenal T-shaped cannulas were fed diets containing four levels of crude protein content (200, 156, 102 and 63 g/kg dry matter, respectively). The diets were based on wheat, barley, tapioca meal, soybean extracted meal, dried beet pulp, meadow hay and straw. The diets had an energy level of 11.1, 10.9, 10.2 and 9.6 MJ metabolizable energy/kg dry matter. Faeces and urine were collected in four 7-day balance periods. Duodenal flow rate was estimated by TiO2, pelleted with grain, as a marker. The relationship between urine N excretion, the amount of microbial N reaching the duodenum, ruminal N balance and N retention were examined and the amount of endogenous N available for microbial protein synthesis without negative effects on the N retention was determined. It can be concluded that up to 16% of the microbial N supply could be covered by recycled endogenous N, but N retention should not be decreased by more than 1.5 residual standard deviations of maximal N retention. [source] Vertical distribution of soil properties under short-rotation forestry in Northern GermanyJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2010Petra Kahle Abstract Short-rotation forestry (SRF) on arable soils has high potentials for biomass production and leads to long-term no-tillage management. In the present study, the vertical distributions of soil chemical and microbial properties after 15 y of SRF with willows and poplar (Salix and Populus spp.) in 3- and 6-year rotations on an arable soil were measured and compared to a pertinent tilled arable site. Two transects at different positions in the relief (upper and lower slope; transect 1 and 2) were investigated. Short-rotation forestry caused significant changes in the vertical distribution of all investigated soil properties (organic and microbial C, total and microbial N, soil enzyme activities), however, the dimension and location (horizons) of significant effects varied. The rotation periods affected the vertical distribution of the soil properties within the SRF significantly. In transect 1, SRF had higher organic-C concentrations in the subsoil (Bv horizon), whereas in transect 2, the organic-C concentrations were increased predominantly in the topsoil (Ah horizon). Sufficient plant supply of P and K in combination with decreased concentrations of these elements in the subsoil under SRF pointed to an effective nutrient mobilization and transfer from the deeper soil horizons even in the long term. In transect 1, the microbial-C concentrations were higher in the B and C horizons and in transect 2 in the A horizons under SRF than under arable use. The activities of ,-glucosidases and acid phosphatases in the soil were predominantly lower under SRF than under arable use in the topsoil and subsoil. We conclude, that long-term SRF on arable sites can contribute to increased C sequestration and changes in the vertical distribution of soil microbial biomass and soil enzyme activities in the topsoil and also in the subsoil. [source] Understorey plant and soil responses to disturbance and increased nitrogen in boreal forestsJOURNAL OF VEGETATION SCIENCE, Issue 2 2009O.H. Manninen Abstract Question: How do N fertilization and disturbance affect the understorey vegetation, microbial properties and soil nutrient concentration in boreal forests? Location: Kuusamo (66°22,N; 29°18,E) and Oulu (65°02,N; 25°47,E) in northern Finland. Methods: We conducted a fully factorial experiment with three factors: site (two levels), N fertilization (four levels) and disturbance (two levels). We measured treatment effects on understorey biomass, vegetation structure, and plant, soil and microbial N and C concentrations. Results: The understorey biomass was not affected by fertilization either in the control or in the disturbance treatment. Fertilization reduced the biomass of deciduous Vaccinium myrtillus. Disturbance had a negative effect on the biomass of V. myrtillus and evergreen Vaccinium vitis-idaea and decreased the relative proportion of evergreen species. Fertilization and disturbance increased the biomass of grass Deschampsia flexuosa and the relative proportion of graminoids. The amount of NH4+ increased in soil after fertilization, and microbial C decreased after disturbance. Conclusions: Our results suggest that the growth of slow-growing Vaccinium species and soil microbes in boreal forests are not limited by N availability. However, significant changes in the proportion of dwarf shrubs to graminoids and a decrease in the biomass of V. myrtillus demonstrate the susceptibility of understorey vegetation to N enrichment. N enrichment and disturbance seem to have similar effects on understorey vegetation. Consequently, increasing N does not affect the rate or the direction of recovery after disturbance. Moreover, our study demonstrates the importance of understorey vegetation as a C source for soil microbes in boreal forests. [source] Sequestration of soil nitrogen as tannin,protein complexes may improve the competitive ability of sheep laurel (Kalmia angustifolia) relative to black spruce (Picea mariana)NEW PHYTOLOGIST, Issue 1 2009G. D. Joanisse Summary ,,The role of litter tannins in controlling soil nitrogen (N) cycling may explain the competitive ability of Kalmia relative to black spruce (Picea mariana), although this has not been demonstrated experimentally. ,,Here, the protein-precipitation capacities of purified tannins and leaf extracts from Kalmia and black spruce were compared. The resistance to degradation of tannin,protein precipitates from both species were compared by monitoring carbon (C) and N dynamics in humus amended with protein, purified tannins or protein,tannin precipitates. The purity of the precipitates was verified using solid-state 13C nuclear magnetic resonance (NMR) spectra. The ability of mycorrhizal fungi associated with both species to grow on media amended with tannin,protein complexes as the principal N source was also compared. ,,The protein precipitation capacity of Kalmia tannins was superior to those of black spruce. Humus amended with protein increased both mineral and microbial N, whereas humus amended with tannin,protein precipitates increased dissolved organic N. Mycorrhizal fungi associated with Kalmia showed better growth than those associated with black spruce when N was provided as tannin,protein precipitates. ,,These data suggest that Kalmia litter increases the amount of soil N sequestered as tannin,protein complexes, which may improve the competitive ability of Kalmia relative to black spruce by favouring N uptake by mycorrhizas associated with the former. [source] | |||||||||||||