Amount Of Microbial Biomass Research Articles

Significance of microbial biomass for carbon and nitrogen mineralization in soil

AbstractC and N mineralization was quantified in an incubation experiment with two samples containing different amounts of microbial biomass. The samples from two layers (0–20, 20–30 cm) of an arable luvisol from loess were fertilized with nitrate, mixed with 14C‐labelled straw and incubated for 52 days at different O2 levels. Decreasing O2 concentrations (21, 2, 1 and 0% O2) in soil conducted a decrease in C and N mineralization. More C and N were mineralized in samples with a higher initial microbial biomass. The differences in microbial biomass were still present at the end of the experiment, but more proliferation was detected in samples with the lower initial microbial biomass, leading to equal ratios between microbial biomass‐C and soil organic C in both soils.

Effectiveness of antibiotics to distinguish the contributions of fungi and bacteria to net nitrogen mineralization, nitrification and respiration

Streptomycin and cycloheximide were applied singly or in combination to an arable or a forest soil to determine their effects on N mineralization, nitrification, CO 2 evolution, and microbial biomass C and N. Only slight differences were observed in concentrations of both inorganic N forms, CO 2 evolution and amounts of microbial biomass C and N between the streptomycin-treated arable soil and the respective control. Cycloherimide singly or in combination with streptomycin stimulated N mineralization, depressed NO − 3 production as well as the increase in microbial biomass C and N observed in the untreated arable soil. The C : N ratio of soil microbial biomass fluctuated around 4 with eycloheximide singly or in combination with streptomycin during the 0–10 day incubation; the ratio was generally higher than 4.5 but never exceeded 5 in the streptomycin-treated arable soil and in the respective control. The inhibition of nitrification in the arable soil by the fungicide prompted the question concerning the relative importance of autotrophic and heterotrophic nitrification rates; the inhibition of the NO − 3 formation by nitrapyrin and the absence of stimulation by peptone indicated that the potential for autotrophic nitrification in this soil is greater than that for heterotrophic nitrification. The addition of antibiotics to the forest soil increased respiration and NH + 4-N concentration with the highest effect with both anibiotics. Both biocides singly or in combination depressed the decrease of NO − 3-N concentration observed in the control; they markedly depressed microbial biomass C and N during the early incubation period; then both microbial biomass values increased probably because surviving microorganisms utilized organic compounds released from antibiotic-killed cells.

Effects of copper on the decomposition of plant residues, microbial biomass, and β-glucosidase activity in soils

Abstract Two types of soils (Brown Lowland soil and Ando soil), which were artificially enriched with different amounts of Cu, were incubated with or without pulverized orchard grass for 12 weeks at 25°C. For both soils with and without orchard grass amendment, the amount of CO2 evolved over the 12-week period of incubation decreased by the enrichment with Cu at a concentration exceeding 1,000 mg kg−1 soil. The decrease of the mineralization of added orchard grass in the Cu-enriched soil was conspicuous especially during the initial period of incubation. The amount of microbial biomass C at the end of the incubation was significantly reduced by the Cu enrichment regardless of the amendment with orchard grass. The relative decrease of the soil microbial biomass was much greater than that of the soil respiration. The amount of biomass C was negatively correlated with the amount of 0.1 M CaCl2-extractable Cu as a logarithmic function. On the other hand, the β-glucosidase activity at the end of the incubation was not significantly affected by the presence of Cu in the soils without orchard grass amendment and increased with the increase in the amount of enriched Cu in the orchard grass-amended soils.

Microbial biomass and activity in the humus layer following burning: short-term effects of two different fires

During a 3-year study, soil microbial biomass C and N, length of the fungal hyphae, soil respiration, and the percent mass loss of needle litter were recorded in coniferous forest soil humus layers following a prescribed burning (PB) treatment or a forest fire simulation (FF) treatment (five plots per treatment). Unburned humus from adjacent plots served as controls (PC and FC, respectively). Prescribed burning was more intensive than the forest fire, and this was reflected in all the measurements taken. The amounts of microbial biomass C and N, length of fungal hyphae, and soil respiration in the PB area did not recover to their controls levels, whereas unchanged microbial biomass N and recovery of the length of the fungal hyphae to control levels were observed in the FF area. The mean microbial C/N ratio was approximately 7 in all the areas, which reflected the C/N ratio of the soil microbial community. Deviation from this mean value, as observed during the first three samplings from the PB area (3, 18, and 35 days after fire treatment), suggested a change in the composition of the microbial community. Of the two treated areas, the decrease in soil respiration (laboratory measurements) was much more pronounced in the PB area. However, when the humus samples from both areas were adjusted to 60% water holding capacity, no differences in respiration capacity were observed. The drier humus, due to higher soil temperatures, of the PB area is a likely explanation for the low soil respiration. Lower soil respiration was not reflected in lower litter decomposition rates of the PB area, since there was a significantly higher needle litter mass loss during the first year in the PB area followed by a decline to the control level during the second year. Consistently higher mass losses were recorded in the FC area than in the FF area.

Microbial biomass nitrogen and mineralization-immobilization processes of nitrogen in soils incubated with various organic materials

Abstract The effects of the addition of organic materials on the change of the pattern of microbial biomass N in soils were assessed in relation to the mineralization — immobilization processes of N. Two types of field moist soils (Udifluvent and Melanudand) amended with chicken manure, clover leaves, farmyard manure, bark compost and rice straw were incubated for 16 weeks at 25°C, and the amounts of biomass N and inorganic N were measured periodically. The chloroform fumigation-extraction method was used for measuring the soil microbial biomass N. Chicken manure was rapidly mineralized from the onset of incubation and did not result in an appreciable increase of the amount of microbial biomass N (<4.0% of the added organic N). Clover leaves showed a lag period of 2 weeks before active N mineralization commenced and the amount of microbial biomass N increased during the lag period, reaching a value of 13.6% of the added organic N, while the amount of biomass N decreased rapidly. On the other hand, the addition of farmyard manure and rice straw resulted in N immobilization from the start of incubation, and N immobilization continued up to 4 weeks for the farmyard manure-treated soils and during the entire incubation period for the rice straw-treated soils. The amount of soil microbial biomass N increased within 2 weeks (10.5–13.5% of the added organic N) by the addition of farmyard manure or rice straw and the increase was maintained throughout the immobilization phase. Bark compost induced a slight N mineralization and immobilization, and the amount of microbial biomass N increased was low (<5.8% of the added organic N). Thus the addition of organic materials resulted in the increase in the amount of microbial biomass N regardless of the soil types. However, the changes in the pattern of microbial biomass N were related to the N mineralization and immobilization processes of each organic material.

Effect of grassland management on N mineralization potential, microbial biomass and N yield in the following year.

The effect of mowing or grazing and mineral fertilizer level on N mineralization potential and microbial biomass N (N flush) was studied in 1988 on a sandy soil and a sedimentary calcareous silty loam (loam) in the Netherlands. On the loam the residual effect of the treatments on N yield and herbage dry matter accumulation in the following year was also studied. The different management practices were started in 1985 on the sandy soil and in 1986 on the loam. The amount of microbial biomass N was larger under grazing than under mowing. The increase in the amount of microbial biomass N due to grazing was larger for the loam than for the sandy soil. The N-mineralization rate was higher under grazing than under mowing. The difference in N-mineralization rates between grazed and mown fields was 20-30 % in April for both soils, but increased considerably in the sandy soil during the growing season. It was estimated that the difference in N-mineralization between mown and grazed plots under field conditions was 110 and 40 kg N/ha per year in the sandy soil and the loam, respectively. Thus the optimum N fertilizer application rate should be considerably lower under grazing conditions than under mowing conditions, especially on sandy soil. Fertilizer level had no effect on the amount of microbial biomass and rates of N-mineralization. Both grazing compared to mowing and increasing N fertilizer levels above 550 kg N/ha per year affected the N yield and dry matter accumulation in the following year (= residual effects) on the loam. These effects were greater for N yield than for dry matter accumulation. The residual effect of previous fertilizer input was probably caused by the presence of different amounts of N in roots and stubble. The residual effect on N yield under grazing exceeded that under mowing by 28%. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Microcalorimetry as a tool to detect changes in soil microbial biomass

High levels of heavy metals such as Cu, Zn and Pb have been found in soils to which composted municipal waste have been added over long periods of time. The impact of heavy metals on the endogenous microbial community was studied by measuring total microbial biomass and biomass activity in soils which contained either low or high heavy metal concentrations. Methods used were fumigation‐incubation, ATP extraction and microcalorimetry. The total amount of microbial biomass was not correlated with the total extractable amounts of heavy metals (extraction with aqua regia) nor with the NH4OAc‐EDTA extractable amounts. Neither the apparent growth rate constants of glucose‐amended soils, as estimated by microcalorimetry, nor the ATP contents were correlated with the amounts of heavy metals present. In contrast, the ratio of the heat evolved 2 hours after glucose addition to the ATP content increased with increasing concentrations of heavy metals. This ratio is a parameter which is inversely proportional to the e...

Negative relationship between microbial biomass and root amount in topsoil of a renovated grassland

Abstract A part of an orchardgrass (Dactylis glomerata L.) meadow was renovated linearly (9 cm in width and 16.5 cm in depth), and reseeded or not with perennial ryegrass (Lolium perenne L.) in autumn. The two boundaries between renovated and unrenovated soils (non-volcanic alluvial soil containing volcanic ash soil) were separated by a nylon mesh screen (ϕ25 μm) or acrylic board to change the amount of grass roots in the renovated soils. In the next spring, the topsoils (0-5 cm) were analyzed to clarify the correlation among the amount of microbial biomass, the amount of roots, and the soil- or root-derived respiration rates during a 10-day period of incubation. The soil respiration rates increased in the presence of the roots. With increasing soil respiration rates, the amount of flush-N determined by the fumigation-incubation method decreased. Under the microscope, it was found that the fungal biomass, the dominant microbial biomass, was negatively correlated (significant at p = 0.05) with the soil res...

Effects of heavy metals from past applications of sewage sludge on microbial biomass and organic matter accumulation in a sandy loam and silty loam U.K. soil

Amounts of microbial biomass were measured in soils from two different U.K. field experiments, one on a sandy loam (15% clay) at Luddington (Wick series) and the other on a silty loam soil (21% clay) at Lee Valley (Hamble series), where sewage sludges, mainly enriched with single metals, were applied 22 yr ago. No single metal (Zn, Cu, Ni and Cd) at or below current EC permitted total soil metal concentrations, or limits, decreased the amounts of soil microbial biomass. However, Cu at about two and a half times permitted metal limits decreased the amounts of biomass by about 40% at both sites and caused an increased accumulation of organic C and total N of about 30% in the sandy loam and about 13% in the silty loam soil. Zinc, at about the same concentration, decreased the biomass by about 40% in the sundy loam and 30% in the silty loam soil while soil organic matter accumulation increased by only 9–14%. Cadmium, at about twice current EC limits did not affect the amount of biomass or soil organic matter in the silty loam soil. Similarly, neither were affected by Ni at 2–3 times current metal limits. The amount of microbial biomass C as a percentage of total soil organic C was much lower (< 1.0%) in soils contaminated with Zn and Cu at about two-and-a-half times current permitted limits than in soils containing less metal. This also suggested that the metals were causing decreased microbial biomass at these metal concentrations.

Availability of mineralized N from microbial biomass and organic matter after drying and heating of grassland soils

A dwarf bamboo-type grassland soil (Thick High-humic Andosol) was nitrogen-limited for grass despite the presence of a considerable amount of microbial biomass N. By either treatments of air-drying and subsequent heating, the content of mineral N in the soil was increased by 3.7 g N and 11.7 g N m-2, respectively, after a 55-day incubation period. The efficiency of mineralized N for growth of orchardgrass was compared with nitrate-N added just before cultivation. The dry matter content of the grass increased from 81.7 g (control) to 169 g and to 337 g m-2 in the dried and in the heated soils, respectively, when N application was omitted. Of the mineral N released by air-drying and heating of the soil, 84% and 77% were absorbed by the grass, and 30% and 20% was assumed to be derived from microbial biomass, respectively. In contrast the grass apparently absorbed 54–56% of the 5 g nitrate-N m-2 added to the control and the air-dried soils. It was also noted that fungal biomass N had decreased by 1.5–1.9 g m-2 in the control soil after addition of 10 g nitrate-N m-2.

Microbial Biomass Nitrogen in Anaerobic Soil as Affected by N-Immobilization and N2-Fixation

Wet paddy soil was preincubated under anaerobic condition with glucose and either (15NH4)2SO4 or 15N2 for 4 weeks and the changes in the amount of microbial biomass N were estimated by the chloroform fumigation method, followed by submerged incubation for 4 weeks. Added 15NH4 + was actively immobilized within the first day of preincubation. 15N2 was also actively fixed within the first day, followed by a slight fixation till 3 week of preincubation. In both 15N-treatments, the contents of available N (N mineralized after chloroform fumigation during 28 days of submerged incubation) and labelled available N increased in the early stage within the first week of preincubation, then decreased until the end of the preincubation. On the other hand, the amount of labelled min-N (N mineralized in unfumigated soil during submerged incubation) remained almost constant throughout the preincubation period. Remineralized NH4 + during the 4th week of preincubation had a similar 15N abundance to that of available N in t...

Mineralization of nutrients from soil microbial biomass

Soil samples of parabrown earth and chernozem, each having a different amount of microbial biomass, were used to investigate the contribution of microbial cells to the pool of mobile plant nutrients in soils. The quantities of nutrients mobilized in soils which had been dried or fumigated were closely related to the quantities available in freshly-killed biomass. For the percent of N mineralized from dead microbial biomass in arable soil during 28 days, a “ k N-factor” (28 days) of 0.37 was suggested. In oven-dried (70°C) and air-dried (room temperature) soils, approximately 77 and 55% of the N mineralized after remoistening and incubating at 22°C for 4 weeks came from the freshly-killed biomass. The remaining 23 and 45% were derived from non-biomass organic N fractions of the soils. In fumigation experiments (CHCl 3, 24 h), the amount of P released was closely related to the P content of the soil microbial biomass. The fluctuating amounts of K available after fumigation did not correspond to the amount of biomass killed. A scheme for the transformation of dead microbial biomass-C and -N in arable soil is suggested.

THE TURNOVER OF SOIL ORGANIC MATTER IN SOME OF THE ROTHAMSTED CLASSICAL EXPERIMENTS

ABSTRACTData are assembled from the Rothamsted classical field experiments on the effects of long-continued cropping and manuring on the amount of organic matter in soil, on the age of this soil organic matter, on the amount of microbial biomass in the soil, and on the rate at which plant residues d