Adenylate energy charge and ATP-to-microbial biomass C ratio in soils differing in the intensity of disturbance

We carried out an 8-days' incubation experiment with three different intensities of soil disturbance to analyse the effects on the ATP-to-microbial biomass C ratio and on the adenylate energy charge (AEC=(ATP+0.5×ADP)/(AMP+ADP+ATP). Single mixing of soil at 50% water holding capacity with a spatula during weighing of the samples into extraction jars at the end of the 8-days' incubation or 8-times repeated daily mixing for 2 min triggered the immediate formation of ATP, increasing both AEC and the ATP-to-microbial biomass C ratio. The energy for this extra ATP produced seems to be mainly derived from an accelerated turnover of C within the microbial biomass. In contrast, 8-days' continuous mixing led to a significant decrease in AEC and ATP-to-microbial biomass C ratio.     

Reaction of microorganisms to rewetting in continuous cereal and legume rotation soils of semi-arid Sub-Saharan Africa

A 20-day incubation experiment with continuous cereal (CC) versus cereal legume (CL) rotation soils of two semi-arid Sub-Saharan sites (Fada-Kouaré in Burkina Faso, F, and Koukombo in Togo, K) were carried out to investigate the effects of rewetting on soil microbial properties. Site- and system-specific reactions of soil microorganisms were observed on cumulative CO₂ production, adenylates (ATP, ADP, and AMP), microbial biomass C and N, ergosterol, muramic acid and glucosamine. Higher values of all parameters were found in the CL rotation soils and in both soils from Fada-Kouaré. While the inorganic N concentration showed only a system-specific response to rewetting, the adenylate energy charge (AEC) showed only a site-specific response. ATP recovered within 6 h after rewetting from ADP and AMP due to rehydration of microorganisms and not due to microbial growth. Consequently, no N seemed to be immobilized by microorganisms and all NO₃ in the soil was immediately available to the plants. The fungal cell-membrane component ergosterol was three (CC) and five (CL) times larger at Fada than in the respective soils at Koukombo. The concentrations of the bacterial cell-wall component muramic acid were by 20% and of mainly fungal glucosamine by 10% larger in the CL rotation soils than in the CC soils. This indicates long-shifts in the microbial community structure.     

Microbial reaction in activity, biomass, and community structure after long-term continuous mixing of a grassland soil

Long-term continuous mixing at 40% water holding capacity (WHC) or as slurry at 400% WHC should result in increased soil organic matter decomposition rates in comparison to a control treatment at 40% WHC, but may have strong impacts on soil microbial indices for activity, biomass, and community structure. The amount of extractable inorganic N (NO₃-N+NH₄-N) accumulated in the soil solution after 40 weeks of incubation at 25 °C was 3% of total N in the control treatment and 4% in the two continuous mixing treatments. However, in the treatment mixing at 40% WHC, this 33% increase compared to the control treatment might be explained solely by the decrease in microbial biomass N. In the control treatment, microbial indices decreased in the order microbial biomass C (−10%), microbial biomass N (−40%), ergosterol (−45%) and ATP (−60%). In the treatment mixing at 40% WHC, all four microbial biomass indices were significantly lower than the respective index in the control treatment. This was especially true for microbial biomass N. In the treatment mixing as slurry, only the contents of microbial biomass C and ATP were significantly lower in comparison to the control treatment. The correspondence analysis ordination biplot of the phospholipid fatty acid (PLFA) profiles showed distinct clusters for the three treatments at the end of the incubation. The strongest relative decline of 64% was observed for the fungi-specific PLFA 18:3ω6 in the treatment mixing as slurry in comparison to the control treatment. The content of total bacterial PLFA decreased only by 23%. The differences between the control treatment and the treatment mixing at 40% WHC were less apparent. Fungi represent on average 21% of total microbial biomass C at the end of the incubation if the ergosterol content is recalculated into fungal biomass C. In accordance with this percentage, 22% of the group-specific PLFA could be attributed to fungi.     

Influence of sulphur supply on glucose and ATP concentrations of inoculated broad beans (Vicia faba minor L.)

In the present study, the influence of S supply on S concentrations, N₂ fixation, available amounts of glucose and adenylates of Vicia faba minor L. were weekly investigated, starting 6 weeks after sowing. Glucose was determined photometrically in shoots, roots and nodules and in ATP, ADP and AMP by bioluminescence in roots, mitochondria and bacteroids. Sulphur deficiency resulted in significantly lower S concentrations of shoots, roots and nodules, in a reduced N₂ fixation as well as in significantly lower amounts of glucose in shoots and nodules. In roots and bacteroids, S deficiency resulted in lower ATP concentrations, while the influence of S supply on ADP and AMP was less pronounced. With optimum S supply, the available amounts of glucose and ATP were strongly influenced by flower formation and seed development. Dedicated to Prof. Dr. Dr. h.c. W. Werner on the occasion of his 75th birthday.