Microbial Biomass Formation Research Articles

Kinetics of mass transfer-limited bacterial growth on solid PAHs.

The importance of mass transfer relative to the intrinsic microbial activity was examined in a laboratory system using Mycobacterium sp. LB501T and poorly soluble anthracene as sole carbon source. M. sp. LB501T was grown on various amounts of solid anthracene in batch cultures, and microbial biomass formation was compared to independently determined dissolution fluxes. Provision of only a few anthracene crystals (< or = 2 g L(-1)) resulted in pseudolinear growth due to low dissolution fluxes, whereas exponential growth was only obtained when high amounts of solid anthracene (30 g L(-1)) were provided. The influence of substrate bioavailability on microbial growth was predicted successfully by a dynamic, flux-based approach (Best-Equation), which combines substrate dissolution from crystals into solution, substrate uptake by microorganisms from solution, and concurrent biomass formation.

Critical sulphur concentration and sulphur requirement of microbial biomass in a glucose and cellulose-amended regosol

The critical S concentration and S requirement of the soil microbial biomass of a granitic regosol was examined. S was applied at the rate of 0, 5, 10, 20, 30 and 50 μg S as MgSO4·7H2O, together with either 3000 μg glucose-C or 3333 μg cellulose-C, 400 μg N, and 200 μg P g –1 soil and 200 μg K g–1 soil. Microbial biomass, inorganic SO42–-S, and CO2 emission were monitored over 30 days during incubation at 25 °C. Both glucose and cellulose decomposition rates responded positively to the S made available for microbial cell synthesis. The amounts of microbial biomass C and S increased with the level of applied S up to 10 μg S g–1 soil and 30 μg S g–1 soil in the glucose- and cellulose-amended soil, respectively, and then declined. Incorporated S was found to be concentrated within the microbial biomass or partially transformed into soil organic matter. The concentration of S in the microbial biomass was higher in the cellulose- (4.8–14.2 mg g–1) than in the glucose-amended soil (3.7–10.9 mg g–1). The microbial biomass C:S ratio was higher in the glucose- (46–142 : 1) than in the cellulose-amended soil (36–115 : 1). The critical S concentration in the microbial biomass (defined as that required to achieve 80% of the maximum synthesis of microbial biomass C) was estimated to be 5.1 mg g–1 in the glucose- and 10.9 mg g–1 in the cellulose-amended soil. The minimum requirement of SO42–-S for microbial biomass formation was estimated to be 11 μg S g–1 soil and 21 μg S g–1 soil for glucose- and cellulose-amended soil, respectively. The highest levels of activity of the microbial biomass were observed at the SO42–-S concentrations of 14 μg S g–1 soil and 17 μg S g–1 soil, for the glucose and cellulose amendments, respectively, and were approximately 31–54% higher during glucose than cellulose decomposition.

Isotope analysis of pyrolysis products from Sphagnum peat and dissolved organic matter from bog water

Elemental analyses (H, N, C, O, S), bulk isotope analyses ( 13C, 15N) and 13C content of pyrolysis products from Sphagnum moss, underlying peat from a bog and the bog water (Hohlohsee, Black Forest, Germany) were performed to identify humification processes in the early diagenesis of peat formation and to determine the origin of dissolved organic matter (DOM) in the bog lake. Atomic ratios of bulk elemental analysis suggest a compositional shift from carbohydrate dominated structures to phenolic polymers. Observed variations of bulk δ 15N and total nitrogen are likely due to microbial production. Combining isotopic and structural information using a coupled Py-GC/MS-IRMS system provides further information on the peat formation, e.g. biogeochemical processes of (1) biological degradation of source material, (2) selective preservation of individual compounds, and (3) formation of microbial biomass (e.g. trophic level effect). In particular, the stable isotope data helped to identify microbial processes as a source for carbohydrate pyrolysis products in deeper horizons. The comparison of pyrolysis products from peat and DOM from the bog lake indicates different sources. From the isotope ratios of pyrolysates it is suggested that DOM is formed in situ by microbial production and not simply dissolved from the peat profile. The uptake of 13C depleted carbon, e.g. respired CO 2, CO 2 from the oxidation of methane or acetic acid is proposed as an important factor in the formation of dissolved organic matter.

Nitrogen Release and Formation of Microbial Biomass from Nitrogen-15-Labeled Crop Residues in Soils under Field Condition

Nitrogen Release and Formation of Microbial Biomass from Nitrogen-15-Labeled Crop Residues in Soils under Field Condition

Mineralization and microbial biomass formation in upland soil amended with some tropical plant residues at different temperatures

Abstract A model experiment was carried out at 15, 25, and 35°C to investigate the changes in microbial biomass and the pattern of mineralization in upland soil during 8 weeks following the addition of 8 organic materials including 6 tropical plant residues, ipil ipil (Leucaena leucocephala), azolla (Azolla pinnata), water hyacinth (Eichhornia crassipes), dhaincha (Sesbania rostrata), cowpea (Vigna unguiculata), and sunhemp (Crotalaria juncea). The amounts of CO2-C evolved and inorganic N produced at 35°C were about 2 times larger than those at 15°C. At any temperature, the flush decomposition of C was observed within the first week and thereafter the rate of mineralization became relatively slow. A negative correlation was observed between inorganic N and C/N ratios of the added organic materials. The relationships between the amounts of cellulose or cellulose plus hemicellulose and the amount of mineralized N of the added organic materials were also negative. The changes in the microbial biomass were af...

Biodegradability and Microbial Activities During Composting of Poultry Litter

Poultry litter is composted to reduce odor and pathogens and to improve its quality as a soil amendment. Organic material, e.g., sawdust, is added to increase the C:N ratio to achieve optimum degradation of organic C and retention of N through microbial biomass formation. However, the relative biodegradabilities of the organic material in poultry litter and the amendment are usually not known. Furthermore, it is assumed that as microorganisms metabolize organic compounds and produce CO2, they increase in biomass and, therefore, retain N. In this study, bench-scale compost reactors were used to determine the relative contributions of poultry litter and of the amendment (sawdust) to the biodegradability of a compost mix. Approximately 29% of the volatiles lost from the poultry litter mix came from the sawdust. Fiber analyses revealed that only a small portion of cellulose was degraded. Although microbial subpopulations able to degrade selected macromolecules were present at varying levels, the overall level of microorganisms did not change markedly. Populations capable of degrading bacterial cell walls were present throughout the composting period, and microbiological assays indicated that inorganic nutrients were available to support limited microbial growth. These results suggest that N compounds and inorganic nutrients are recycled, rather than fixed during composting.

Formation of Microbial Biomass and Its Nitrogen Flow in Soil

Formation of Microbial Biomass and Its Nitrogen Flow in Soil

Biomass and activity of microorganisms in a fuel oil contaminated soil

The measurement of microbial biomass in soils contaminated by fuel oil was investigated using the CHCl 3 fumigation-extraction method. It was shown that usually no significant amounts of fuel oil were additionally made extractable by CHCl 3 fumigation. Thus, the fumigation-extraction method can be used in fuel oil contaminated soils. In the two fuel oil treatments of an incubation experiment 87% (0.5% oil-C) and 82% (1.0% oil-C) of the added C were mineralized to CO 2 in 165 days. Only 5.2% (0.5%-oil-C treatment) and 8.5% (1.0%-oil-C treatment) of the added fuel oil could be measured at the end of the experiment. The soil microbial biomass content (biomass C, biomass N and biomass ninhydrin-reactive N) of the control soil and that of the 0.5%-oil-C treatment showed some fluctuations, but no marked changes during the incubation. The microbial biomass content in the 1.0%-oil-C treatment had increased significantly by the end of the incubation. The amount of inorganic N incorporated into organic matter at the end of the incubation showed that the portion of fuel oil, not recovered as CO 2 or extracted as fuel oil residue, could be explained by the formation of microbial biomass and microbial residual mass. Significant amounts of chemically-unchanged “bound residues” are extremely unlikely at this time.

Influence of light intensity on the distribution of carbon and consequent effects on mineralization of soil nitrogen in a barley (Hordeum vulgare L.)-soil system

A pot experiment was conducted in a 14C-labelled atmosphere to study the influence of living plants on organic-N mineralization. The soil organic matter had been labelled, by means of a 200-days incubation, with 15N. The influence of the carbon input from the roots on the formation of microbial biomass was evaluated by using two different light intensities (I). Mineralization of 15N-labelled soil N was examined by following its fate in both the soil biomass and the plants. Less dry matter accumulated in shoots and roots at the lower light intensity. Furthermore, in all the plant-soil compartments examined, with the exception of rhizosphere respiration, the proportion of net assimilated 14C was lower in the low-I treatment than in the high-I treatment. The lower rates of 14C and 15N incorporation into the soil biomass were associated with less root-derived 14C. During the chamber period (14CO2-atmosphere), mineralized amounts of 15N (measured as plant uptake of 15N) were small and represented about 6.8 to 7.8% of the initial amount of organic 15N in the soil. Amounts of unlabelled N found in the plants, as a percentage of total soil N, were 2.5 to 3.3%. The low availability of labelled N to microorganisms was the result of its stabilization during the 210 days of soil incubation. Differences in carbon supply resulted in different rates of N mineralization which is consistent with the hypothesis that roots induce N mineralization. N mineralization was higher in the high-I treatment. On the other hand, the rate of mineralization of unlabelled stable soil N was lower than labelled soil 15N which was stabilized. The amounts of 15N mineralized in planted soil during the chamber period (43 days) which were comparable with those mineralized in unplanted soil incubated for 210 days, also suggested that living plants increased the turnover rate of soil organic matter.

The mineralization of N from finely or coarsely chopped crop residues: measurements and modelling

Sugar beet leaves, a mixture of sugar beet crowns and leaves, cabbage leaves or spinach leaves were either coarsely or finely chopped and mixed with either a sandy or clay soil and incubated at 20 ° C under optimal moisture conditions for 24 weeks. The release of mineral N and the formation of microbial biomass were measured at intervals during the course of the experiment.The release of mineral N was strongly dependent upon the amount of carbon and nitrogen added in the crop residues : spinach (C:N = 6) released most nitrogen and most quickly, cabbage leaves (C:N = 18) and the mixture of beet leaves and crowns (C:N = 42) released N more slowly. In most cases there was no significant difference in the decomposition rate of finely and coarsely chopped residues. An existing simulation model was able to simulate the mineralization or immobilization of N with the minimum of adjustment to its parameters using only information about the crop residues.

Mineralization of straw and formation of soil microbial biomass in a soil treated with simazine and dinoterb

Three weeks after treatment with simazine and dinoterb, 14C-labelled straw (2 mg g −1 soil) was added to an arable soil and incubated for a further 66 days. Straw mineralization was not affected by the two herbicides. In the two herbicide treatments, the soil microbial biomass measured by the fumigation-extraction method remained unchanged after the initial 20-day incubation period without straw addition. Also, the initial formation of microbial biomass was not apparently altered by simazine and dinoterb at day 5 after straw addition. However, the two herbicide treatments significantly accelerated the subsequent decline so that significantly lower microbial biomass contents were measured from day 33 after straw addition. Increased values for the metabolic coefficient q 14CO 2 indicate a less efficient use of the added substrate for microbial growth in the soil treated with simazine and dinoterb.

Turnover of root-derived material and related microbial biomass formation in soils of different texture

Wheat plants were grown on two soils of different texture, a sandy soil and a silty clay loam, in an atmosphere containing 14CO 2. The 14C and total C content of the shoots, roots, soil rhizosphere CO 2 and soil microbial biomass were measured 21, 28, 35 and 42 days after germination. There was a pronounced effect of soil texture on the turnover of root-derived C through the microbial biomass. Turnover was relatively fast and at a constant rate in the sandy soil but slowed down in the clay soil, following an initial high assimilation of root products into the microbial biomass. Four percent of the total fixed 14C was retained in the clay loam after 6 weeks compared with a corresponding value of 1.2% for the sandy soil. The proportion of fixed 14C recovered as rhizosphere CO 2 at each of the sampling times was relatively constant for the sandy soil ( ca 19%) but decreased from 17% at day 28 to 11% at day 42 in the clay soil. The proportion of total fixed 14C in the soil biomass as measured by a fumigation technique increased to a maximum value of 20% after 6 weeks in the sandy soil but decreased in the clay soil from 86% at day 21 to 26% after 42 days plant growth.