Showing papers in "Soil Biology & Biochemistry in 1983"
TL;DR: This paper is re-evaluated in the light of subsequent studies that allow the principle of separation of variables to be tested and lends further credence to the linear relationship proposed between soil respiration and water content.
Abstract: The interaction of soil microbes with their physical environment affects their abilities to respire, grow and divide. One of these environmental factors is the amount of moisture in the soil. The work we published almost 25 years ago showed that microbial respiration was linearly related to soil-water content and log-linearly related to water potential. The paper arose out of collaboration between two young researchers from different areas of soil science, physics and microbiology. The project was driven by not only our curiosity but also the freedom to operate without the constraints common to the current system of science management. The citation history shows three peaks, 1989, 1999 and from 2002 to the present day. Interestingly, the annual citation rate is as high as it has ever been. The initial peak is due to the application of the work to studies on microbial processes. The second peak is associated with the rise of simulation modelling and the third with the relevance of the findings to climate change research. In this article, our paper is re-evaluated in the light of subsequent studies that allow the principle of separation of variables to be tested. This re-evaluation lends further credence to the linear relationship proposed between soil respiration and water content. A scaled relationship for respiration and water content is presented. Lastly, further research is suggested and more recent work on the physics of gas transport discussed briefly.
871 citations
TL;DR: In this article, the 15 N-labelled fertilizer dilution technique provides a method of obtaining estimates of biological N 2 -fixation in the field over the growing season, which explains these errors and allows a more rational choice of non-fixing control.
Abstract: The 15 N-labelled fertilizer dilution technique provides a method of obtaining estimates of biological N 2 -fixation in the field over the growing season. Field estimates of fixation obtained using peas, french beans, field beans and clover depended on the non-fixing control used. Differences in the N uptake patterns of the legume and control combinations, together with a decrease in the enrichment of plant available soil N with time, were major factors causing this dependency. A simple model of plant N accumulation at decreasing soil enrichment is presented, which explains these errors and allows a more rational choice of non-fixing control. The use of gypsum pelleted 15 N fertilizer, or any other treatment which leads to a more stable soil enrichment, reduces errors caused by mismatched N uptake patterns in the two crops.
264 citations
TL;DR: In this paper, the production and persistence of microbial biomass and also urease, phosphate and casein-hydrolysing activities were investigated when either glucose or ryegrass were added, as energy sources, with 15 NO 3 − to a clay-loam soil.
Abstract: The production and persistence of microbial biomass and also urease, phosphate and casein-hydrolysing activities were investigated when either glucose or ryegrass were added, as energy sources, with 15 NO 3 − to a clay-loam soil. Both direct count and fumigation methods were used to determine soil microbial biomass. Microbial biomass and enzyme activities increased after the addition of energy sources. Increases in phosphatase and urease activities coincided mainly with increases in bacterial biomass and with the rapid immobilization of labeled N. Conversely, the increase in casein-hydrolysing activities preceded the phase of net mineralization that occurred during the later period of incubation. Although microbial biomass and the biochemical activities tested increased in the soils treated with energy supplies, they eventually decreased to the level of the control soil. Even the increases in biomass and enzyme activities present at zero time, as a result of the addition to the soil of exogenous microorganisms and enzymes with the ryegrass, were not maintained after extensive incubation. The influence of homeostatie mechanisms which tend to maintain a stable biological composition in the soil microbial population is discussed. A possible relationship between the available “active” or “biological” space, total microbial biomass and total enzyme activity in soil is suggested.
211 citations
TL;DR: It is suggested that Gram-negative bacteria arc more metal-tolerant than Gram-positivc organisms and, in soils containing comparatively low levels of metal pollution, may be able to function without the need for plasmid-mediatedMetal-tolerance.
Abstract: The toxicity of several metals towards bacterial populations from natural and metal-polluted soils could be described either partially by a single exponential equation or completely by the sum of two exponential functions. Bacterial populations from both soils contained two subgroups, one of which could tolerate metals over a greater range of concentrations than the other. Most bacteria comprising the more mctal-tolerant subgroup were Gram-negative and were multiple drug resistant. Exceptions were organisms, tentatively identified as coryncforms, isolated on nickel-supplemented medium. It is suggested that, in general, Gram-negative bacteria arc more metal-tolerant than Gram-positivc organisms and, in soils containing comparatively low levels of metal pollution, may be able to function without the need for plasmid-mediated metal-tolerance.
181 citations
TL;DR: Evidence that ungrazed legume residues, incorporated in amounts commonly found in southern Australian wheat growing regions, contribute only a little to soil available N and to crop N uptake, even in the first year of their decomposition is supported.
Abstract: Ground 15N-labelled legume material (Medicago littoralis) was mixed with topsoils in confined microplots in the field, and allowed to decompose for 7 and 5 months in successive years (1979, 1980) before sowing wheat. The soil cropped in 1979 (and containing 15N-labelled wheat roots and legume residues) was cropped again in 1980. The results support evidence that ungrazed legume residues, incorporated in amounts commonly found in southern Australian wheat growing regions, contribute only a little to soil available N and to crop N uptake, even in the first year of their decomposition. Thus mature first crops of wheat, although varying greatly in dry matter yield (2.9-fold) and total N uptake (2.4-fold), took up only 27.8 and 20.2% of the legume N applied at 48.4 kg ha−1, these corresponding to 6.1 and 10.8% of the N of the wheat crops. The availability of N from medic residues to a second wheat crop declines to The proportional contributions of medic N to soil inorganic N, N released in mineralization tests, and to wheat crop N, differed between seasons and soils, but for a given crop did not significantly differ between tillering, flowering and maturity. In both years, grain accounted for 52–65% of the total 15N of first crops, roots for
163 citations
162 citations
TL;DR: In this paper, a balsam fir forest floor soil was fractionated in an attempt to identify the compounds responsible for the inhibition of nitrification in a highly active Al horizon.
Abstract: Nitrification in a highly active Al horizon of a balsam fir forest floor soil can be greatly inhibited by an aqueous methanol extract of the forest floor. This extract was fractionated in an attempt to identify the compounds responsible for the inhibition. Condensed tannins, smaller molecular weight phenolics, and their distribution on particulate matter in the extract were the most important inhibiting components of the extract. When all phenolic material was removed from the extract, the remaining solution stimulated nitrification.
162 citations
TL;DR: The effects of different grazing intensities of the millipede Glomeris marginata on a variety of forest organic substrates show that the animals amplified existing patterns of nutrient release.
Abstract: Decomposing oak litter was incubated in laboratory microcosms and the effects of adding a variety of soil animals upon nitrogen and cation release were monitored. Various groups of macrofauna caused a marked increase in ammonium release with smaller increases in calcium, potassium and sodium leaching. Microfauna also had significant but much less marked effects upon nitrogen and cation release. The effects of different grazing intensities of the millipede Glomeris marginata on a variety of forest organic substrates show that the animals amplified existing patterns of nutrient release.
152 citations
TL;DR: The emission of nitrous oxide (N2O) from soil under grass was measured, following applications of cow slurry and NH4NO3 fertilizer, through April to August as mentioned in this paper.
Abstract: The emission of nitrous oxide (N2O) from soil under grass was measured, following applications of cow slurry and NH4NO3 fertilizer. The N2O-flux from untreated soil averaged 0.58 mg Nm−2 day−1 through April to August. Application of slurry at the end of April and at the middle of July caused increases in the daily N2O-flux of up to 40-fold, compared to untreated grass. Applications of NH4NO3 increased the N2O-flux up to 5 times during the same period. The N2O-flux often showed marked diurnal fluctuations. These fluctuations are not solely associated with change in temperature, but may also be related to grass root activity and to photosynthesis.
139 citations
TL;DR: In this article, a series of experiments designed to determine the causes for lack of NO−3 production in the forest floor of balsam fir forests is described. But the experiments showed that denitrification was not important and that autotrophic nitrifiers were present.
Abstract: Previous work has shown that nitrification is negligible in floors of subalpine balsam fir forests but proceeds vigorously in the Al horizon beneath the forest floor. This paper describes a series of experiments designed to determine the causes for lack of NO−3 production in the forest floor. These experiments showed that denitrification was not important and that autotrophic nitrifiers were present. Increases in pH, essential nutrients and inoculum did not enhance nitrification, indicating that an inhibitor rather than a limiting factor was involved. Analysis of forest floor and Al showed that aluminum was present at concentrations greater than those found to inhibit nitrification in culture. Since the Al was actively nitrifying, it seemed unlikely that aluminum was responsible for nitrification inhibition in the forest floor. Finally, a methanol extract of polyphenols from the forest floor was added to the Al significantly reducing nitrification. These experiments suggest that the higher phenolic concentrations are responsible for inhibition of nitrification in the forest floor.
115 citations
TL;DR: In this article, seven soils were examined for their contents of p-hydroxybenzoic, vanillic, p-coumaric and ferulic acids, and vanillin, and water-soluble forms, both free and bound, of each compound also occurred in roots associated with six of the soils, and in beech litter associated with the seventh.
Abstract: Seven soils were examined for their contents of p-hydroxybenzoic, vanillic, p-coumaric and ferulic acids, p-hydroxybenzaldehyde and vanillin. Water-soluble forms, both “free” and “bound” of the phenolic compounds accounted for less than 0.7% of the total amount of each acid or aldehyde as determined by extraction of the soil with 2 M NaOH. In most instances, more than 50% of the water-soluble compounds were in the bound form, which was estimated after conversion to the free form by treatment of the water extract with NaOH. Water-soluble forms, both free and bound, of each compound also occurred in roots associated with six of the soils, and in beech litter associated with the seventh.
TL;DR: In this paper, the effect of N on the disappearance of C from a wheat straw system, and the response of the biomass to N additions, was simulated using microbial growth and maintenance terms derived from the literature.
Abstract: The behavior of added carbon as crop residues and nitrogen in agricultural ecosystems is most often quantitatively described by empirically derived first-order rate reactions. A mechanistic approach may be more precise for describing interrelations between C, N and microbial populations during short periods of active decomposition. The effect of N on the disappearance of C from a wheat straw system, and the response of the biomass to N additions, was simulated using microbial growth and maintenance terms derived from the literature. Results of the simulation were compared with microbial growth and wheat straw decomposition measurements made with an electrolytic respirometer. Straw decomposition rate was shown to be strongly dependent on available C and N during initial decomposition. When N is limiting, excess available C apparently is immobilized as polysaccharides.
TL;DR: In this article, the relationship between intensity of phosphatase activity and soil properties at two depths in some Lake District woodland soils have been examined, and significant relationships were found with soil organic matter, moisture, clay + silt, total nitrogen, isotopically-exchangeable phosphorus, extractable magnesium contents and soil pH.
Abstract: The relationships between intensity of phosphatase activity and soil properties at two depths in some Lake District woodland soils have been examined. Significant relationships were found with soil organic matter, moisture, clay + silt, total nitrogen, isotopically-exchangeable phosphorus, extractable magnesium contents and soil pH. When data from all soils, both 0–5 and 10–15 cm depths, were pooled 66% of the total variation in intensity of phosphatase activity could be accounted for by these soil properties. However, covariance analysis showed that regressions between intensity of phosphatase activity and soil properties differed with soil depth, soil type, season, vegetation type and underlying rock type. When the effects of these interactions were taken into account, up to 99% of the variation in the intensity of phosphatase activity could be accounted for. The relative importance of these interactive factors appeared to be rock type = vegetation type > soil type = season > soil depth. The effects of the soil properties and the interacting factors on the intensity of phosphatase activity in these woodland soils are discussed.
TL;DR: In this paper, the authors used two commonly used incubation methods: open-system and closed-system to study the mineralization of soil in three Canadian Prairie soils and found that little mineralization or a net immobilization of sulfur (from 1.4 to 1.3 m g SO 2m 4n-S g m1nsoil) was observed in a closed system where the soils were left undisturbed throughout incubation.
Abstract: Net mineralization of sulfur and nitrogen was studied in three Canadian Prairie soils using two commonly used incubation methods. In the open system technique, where the soils were leached periodically II.3n11.8 m g SO 2m 4n-S g m1nsoil was mineralized in 17 weeks. Little mineralization or a net immobilization of sulfur (from 1.4 to 1.3 m g SO 2m 4-S g m1nsoil) was observed in a closed system where the soils were left undisturbed throughout incubation. Changes in the specific activity ofn 35S-labelled soil solution sulfate during the closed incubation indicated that mineralization-immobilization processes were occurring simultaneously resulting in minimal net changes in CaCl 2-extractable SO 2m 4nconcentrations. The amounts of mineralized nitrogen (32.6n57.8 mg N g m1nsoil) were found to be independent of the incubation method employed.
TL;DR: Chlamydospores and conidia of several naturally occurring isolates and induced biotypes of Trichoderma spp were abundantly produced on a variety ofSolid substrates moistened with liquid nutrients or water, preferably at pH 4.
Abstract: Isolates of Trichoderma spp grew and produced chlamydospores as well as conidia in molasses-corn steep liquor (M-CSL), sucrose nitrate (SN), and glucose tartrate (GT) media. In M-SCL, isolates of T. hamatum, T. viride, and T. harzianum formed 10.4, 5.9 and 1.1 × 108 chlamydospores g−1 dry weight of mycelium. Fewer chlamydospores formed in SN and GT. Although T. harzianum formed the least number of chlamydospores, it produced the highest number of conidia in all three media. Molasses-corn steep liquor was superior to SN or GT in supporting development of both spore types. Spore production was not influenced by initial pH of the media or by continuous maintenance of the media at pH 4 or 7. Equal numbers of chlamydospores were formed in liquid media incubated in shake or static culture. Conidia formation, however, was stimulated in static culture. Chlamydospores and conidia of several naturally occurring isolates and induced biotypes of Trichoderma spp were abundantly produced on a variety of solid substrates moistened with liquid nutrients or water, preferably at pH 4. Bran, cornmeal, and peanut hull meal were better than eight other solid substrates for production of chlamydospores and conidia. A u.v.-induced, benomyl-resistant biotype of T. viride (T-1-R9) formed 22 × 107 and 18 × 108 chlamydospores and conidia, respectively, g−1 of bran-SN. The ratio of conidia to chlamydospores was always greater in solid than liquid media. In solid media, 10 times more conidia than chlamydospores were formed, whereas in liquid only two or three times more were formed. Chlamydospores from liquid and solid fermentations were viable (ca 80%) and fresh chlamydospores germinated well (ca 75%) on nutrient agar. Although dried chlamydospores were viable, as determined with tetrazolium bromide, their germination on agar was poor (ca 8%).
TL;DR: Soil respiration of a desert soil was measured at the New Mexico State University Ranch in Southern New Mexico as mentioned in this paper, which was used to estimate soil organic matter turnover which was 54 yr using summer data and 20 yr using both summer and winter data.
Abstract: Soil respiration of a desert soil was measured at the New Mexico State University Ranch in Southern New Mexico. Respiration rates were highest during late July and August after summer rains. Soil respiration data were used to estimate soil organic matter turnover which was 54 yr using summer data and 20 yr using both summer and winter data. The long turnover estimate for summer measurements resulted from temperatures above optimum in June and July. Diurnal soil respiration was also measured after a simulated 2.54 cm rain event. For both wetted and dry soils, temperature controlled the patterns of soil respiration with an optimum of near 41°C. Activation energy values decreased from 84.91 to 39.5 kJ mol −1 when the soil was wetted. A light-dark container method was tested as a possible means of estimating algal uptake of CO 2 , however, the method was not feasible for desert soils.
TL;DR: The percentage of root length infected was closely correlated with concentrations of soluble carbohydrates within roots irrespective of the treatment used to vary these concentrations, and small additions of phosphorus to severely deficient plants increased the percentageRoot length infected possibly by stimulating the growth of the mycorrhizal fungus.
Abstract: The effect of phosphorus supply on concentrations of soluble carbohydrate within roots and on the development of mycorrhizas on subterranean clover was examined in two glasshouse experiments. Where increasing phosphorus supply decreased the percentage of root length converted to mycorrhizas, it also decreased the concentrations of soluble carbohydrates within roots. Shading, defoliation and low root temperatures also decreased both the percentage of root length infected and concentrations of soluble carbohydrate within roots. The percentage of root length infected was closely correlated with concentrations of soluble carbohydrates within roots irrespective of the treatment used to vary these concentrations. Small additions of phosphorus to severely deficient plants increased the percentage root length infected possibly by stimulating the growth of the mycorrhizal fungus.
TL;DR: In this article, the fraction of total P associated with organic matter and the organic carbon content were determined in fertilized and unfertilized plots of ten Chilean allophanic soils and it was hypothesized that these effects are related to the high biochemical activity of these soil environments which are dominated by actinomycetes and fungal species.
Abstract: In fertilized and unfertilized plots of ten Chilean allophanic soils the fraction of total-P associated with organic matter and the organic carbon content were determined. Cultivation with P fertilization for 40 yr or more increased the organic C and organic P in most of the soils. It is hypothesized that these effects are related to the high biochemical activity of these soil environments which are dominated by actinomycetes and fungal species as well as to the chemical and physical properties of the soils. It appears that, following its fast adsorption onto active allophanic surfaces, added-P is subjected to reactions resulting in the formation of organic matter-P associations or complexes possibly through Al bridges. The humus-P complexes compose the major portion of total-P in these soils and may be viewed as a P sink in the overall P-cycling process. There is a need for further research on the specific mechanisms by which plant roots utilize P-sinks as sources of P. Based on microbial activity a model of the P-cycle operating in these soils is hypothesized.
TL;DR: In both manured and unmanured soils, D NB organisms were predominant in the bacterial communities on organic debris and the rice roots throughout most of the entire period of rice cultivation, although a transient decrease in the proportion of DNB organisms was observed immediately after an application of manure.
Abstract: The distribution of heterotrophic bacteria on organic debris and roots of rice plants in a paddy field were studied. The heterotrophic bacteria consisted of two main groups: those which grew on full-strength nutrient broth (NB) and those which did not grow on NB but on a 100-fold dilution of NB (DNB). The latter group was called ‘DNB organisms’ and were considered to be oligotrophic. In both manured and unmanured soils, DNB organisms were predominant in the bacterial communities on organic debris and the rice roots throughout most of the entire period of rice cultivation, although a transient decrease in the proportion of DNB organisms was observed immediately after an application of manure. Morphological and physiological characteristics of DNB isolates from organic debris and rice roots were studied: five types of cell shape were observed, (1) regular rods, (2) filament-forming rods, (3) irregular rods, (4) prosthecate organisms and (5) large oval cells. Regular rods (42% of the total DNB isolates) and irregular rods (46%) were abundant. The ecological roles of DNB organisms in paddy soil are discussed in relation to their physiological characteristics.
TL;DR: In this article, a method was developed for measuring adenosine 5'-triphosphate (ATP), adenosines 5'-diphosphate(ADP), and adenosin 5'-monophosphate) in soil extracts by the firefly luciferin-luciferase system.
Abstract: A method was developed for measuring adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP) and adenosine 5'-monophosphate (AMP) in soil. All three adenine nucleotides were extracted from soil with a solution of trichloroacetic acid, paraquat and phosphate. ATP was measured in the neutralised (pH 7.4) soil extracts by the fire-fly luciferin-luciferase system. ADP was measured as ATP after incubating the neutralised extracts with pyruvate kinase (PK) and phosphoenolpyruvate (PEP) to convert ADP to ATP. AMP was converted to ATP by incubation with the coupled PK-PEP-myokinase system and measured as ATP. The quantities of nucleotides present in the extracts were corrected for incomplete extraction from soil by measuring the percentage recovery of added ATP, ADP and AMP. The adenylate energy charge (AEC) was calculated from the formula AEC = [[ATP] + 0.5[ADP]]/[[ATP] + [ADP] + [AMP]]. Measurements were made on (1) fresh soil, extracted as soon as possible after field sampling (2) soil stored air-dry at 5°C for 18 days and (3) soil stored air-dry at 5°C for 57 days and then rewetted to the original field moisture content and incubated aerobically for 2.5 h at 10°C before extraction.
In moist soil the biomass maintains both ATP and AEC at levels close to those of activity growing cells, even though little of the biomass in soil can be in active growth at any given time. ATP accounted for 77% of the total adenine nucleotides (AT) in the fresh soil, with an AEC of 0.85 (a value comparable to that found in microorganisms undergoing active growth in vitro. In contrast, ATP only accounted for 28% of AT in the air-dried soil, with an AEC of 0.46. When the air-dried soil was rewetted, ATP increased to 66% of AT and the AEC increased to 0.76. However, AT in the air-dried soil (7.65 nmol g−1 soil) was of the same order as that in rewetted soil (6.70 nmol g−1) even though the AEC's were very different.
These results show that the soil microbial biomass does not maintain a high AEC when air-dried. Once remoistened, the population tends to restore its AEC to the original value. This restoration occurs so rapidly that it cannot be due to the formation of a new biomass.
TL;DR: In many of the publications concerning the measurement of phosphatase activities in soils, the basic rules governing enzyme assays have, at best, been only partially obeyed as mentioned in this paper.
Abstract: In many of the publications concerning the measurement of phosphatase activities in soils, the basic rules governing enzyme assays have, at best, been only partially obeyed. This review article concentrates on the measurement of phosphatase activity, draws attention to the wide discrepancies in its measurement found in the literature and urges the adoption of a more uniform technique obeying the rules governing simple enzyme kinetics.
TL;DR: In this paper, Nitrogen mineralization and immobilization were investigated in two soils incubated with ammonium sulphate or pig slurry over a range of temperatures and moisture contents, and it was found that the rate of immobilization increased with increasing moisture content, though the period of nett immobilization was shorter.
Abstract: Nitrogen mineralization and immobilization were investigated in two soils incubated with ammonium sulphate or pig slurry over a range of temperatures and moisture contents. A reduction in the mineralization of soil organic N was observed in soils incubated with 100 μg NH 4 + -Ng −1 soil as ammonium sulphate at 30°C but not at lower temperatures. Addition of 100 μg NH 4 + -N g −1 soil as pig slurry resulted in a period of nett immobilization lasting up to 30 days at 5°C. Although the length of the immobilization phase was shorter at higher temperatures the total N immobilized was similar. The subsequent rate of mineralization in slurry-treated soils was not significantly greater ( P = 0.05) than in untreated soils. There was no evidence of any subsequent increased mineralization arising from the immobilized N or slurry organic N for up to 175 days. The rate of immobilization was found to increase with increasing moisture content, though the period of nett immobilization was shorter, so that the amount of N immobilized was similar over a range of moisture contents from 10 to 40%. Approximately 40% of the NH 4 + -N in the slurry was immobilized under the incubation conditions used.
TL;DR: The effects of four treatments upon the N content of rice crop and soil in 1m2 irrigated microplots were compared and incorporating S. rostrata as green manure resulted in a grain yield increase of 372 g m−2 (3.72t ha−1).
Abstract: The effects of four treatments upon the N content of rice crop and soil in 1m2 irrigated microplots were compared: (1) PK fertilization + Sesbania rostrata (inoculated stems) ploughed in as green manure when it was 52 days old. (2) PK fertilization + S. rostrata (non-inoculated stems) ploughed in as green manure. (3) PK fertilization + ammonium sulphate (60kg N ha−1). (4) PK fertilization alone (control).
The application of chemical N fertilizer (treatment 3) increased the grain yield by 169 g m−2 (1.69t ha−1). whereas incorporating S. rostrata as green manure resulted in a grain yield increase of 372 g m−2 (3.72t ha−1). N2 fixed by S. rostrata was estimated to be at least 26.7 g m−2 (267kg N ha−1), one third being transferred to the crop and two thirds to the soil.
TL;DR: The effects of sterilizing a silt loam by γ-irradiation or autoclaving on direct counts of bacteria, CO 2 production, and mineral nitrogen content during storage at 5° C for 98 days were studied.
Abstract: The effects of sterilizing a silt loam by γ-irradiation or autoclaving on direct counts of bacteria, CO 2 production, and mineral nitrogen content during storage at 5° C for 98 days were studied. After autoclaving, 55% of the bacterial population lysed rapidly and by 56 days only 10% of the initial population could be seen. Irradiated bacteria remained intact for longer, with over 70% being visible after 98 days. CO 2 production increased after irradiation and then declined to a stable rate after 21 days. Autoclaving reduced CO 2 production to near zero. The irradiated soil responded to the addition of glucose but there was no response from the autoclaved soil. There was a flush of NH 4 + -N production after both autoclaving and irradiation. The concentration of NH 4 + -N increased in the irradiated soil throughout the 98 days' storage, but remained constant in the autoclaved soil. NO 3 − -N was reduced by both means of sterilizing. The time needed for the soil to stabilize after sterilizing is discussed.
TL;DR: The results suggest that N availability might result in a change in the growth yield of the microbial population, which is primarily limited by available C rather than available N after only 240 h incubation.
Abstract: The effect of N on the disappearance of C from 1.5 g wheat ( Triticum aestivum L. var. “Nugaines”) straw decomposing in sand and the response of the biomass to addition of N (adequate to bring the C:N ratio to 48:1) and C (200 mg of glucose-C) were determined. A concept was used that assumed the change in the microbial biomass was proportional to the change in acid hydrolyzable amino acid-N. Microbial respiration (CO 2 evolution and O 2 uptake) and growth were stimulated by the initial addition of N (which brought the original C:N ratio from 150:1 to 48:1), but the addition of the same amount of N to the system at 240 h that had received no N initially resulted in slight if any increase in respiration or microbial growth. The response of the microflora to the 200 mg of glucose-C additions after 240 h indicated the microbial populations were primarily limited by available C rather than available N after only 240 h incubation, even though about 95% of the original straw residue-C plus biomass C remained in the system. Respiratory quotients indicated a qualitative shift over time in the average oxidation state of the substrates being metabolized. It is postulated that the RQ shift resulted, at least in part, from death of the population rather than totally from the availability of the straw substrate. The initial addition of N resulted in 3.8 times the net amino acid production, but only 1.6 times the CO 2 -C production over 240 h compared with the control without added N. These results suggest that N availability might result in a change in the growth yield of the microbial population.
TL;DR: The relative sensitivities of pathogens to fluctuating soil temperatures were similar at both sites and the most sensitive were the nematodes, and the fungi V. dahliae, S. cepivorum and S. minor, while F. oxysporum, P. irregulare and P. brassicae were the least sensitive.
Abstract: The effect of covering soil with transparent polyethylene sheets, known as soil solarization, on the viability of plant pathogens was determined. The treatment was tested in mid-summer on sandy loams in N.W. and S. Victoria. Columns of moist soil were inoculated with one of a variety of pathogens, viz. Fusarium oxysporum, Pythium irregulare, Plasmodiophora brassicae, Sclerotium cepivorum, S. rolfsii, Sclerotinia minor, Verticillium dahliae and the nematodes Macroposthania xenoplax, Meloidogyne javanica, Pratylenchus penetrans and Tylenchulus semipenetrans . Columns were placed vertically in soil, and then treated either for 4 weeks in N.W. Victoria, or 6 weeks in S. Victoria. Preliminary laboratory tests showed that pathogens were killed by temperatures within the range 38–55°C. The relative sensitivities of pathogens to fluctuating soil temperatures were similar at both sites. The most sensitive were the nematodes, and the fungi V. dahliae, S. cepivorum and S. minor , while F. oxysporum, P. irregulare and P. brassicae were the least sensitive. In N.W. Victoria treatment effects were apparent to 26 cm and most pathogens were not recovered from 0 to 11 cm. In S. Victoria treatment effects were apparent to a depth of 16cm and most pathogens were not recovered from 0 to 6cm.
TL;DR: A simple method to measure soil ATP by the luciferin-luciferase system is described in this paper, where ATP is extracted from the soil by vigorous shaking with a sulfuric acid-phosphate solution for 15 min.
Abstract: A simple method to measure soil ATP by the luciferin-luciferase system is described The ATP is extracted from the soil by vigorous shaking with a sulfuric acid-phosphate solution for 15 min An aliquot of the soil suspension is neutralized with a Tris-EDTA solution and mixed with a special ATP releasing reagent (NRB) ATP is measured after a 10 s exposure to the NRB reagent, followed by addition of luciferin-luciferase and integration over 10 s in a Lumacounter M 2080 The ATP content in soils which had been stored at 5°C for 90 days and then incubated at 25°C for 5 days, ranged from 037 to 752 μg ATP g−1 dry wt, with standard deviations less than 10% There was a close (r = 096) linear relationship between ATP content and biomass C determinated by fumigation for this group of soils The soil biomass contained 42–71 μg ATP mg−1 biomass C The ATP content of the biomass declined during storage at 5°C for 210 days
TL;DR: The theoretical relationship between microclimate, temperature and moisture in decaying branchwood is considered and methods of expressing moisture content discussed in this paper, where field measurements were obtained over a 1-yr period.
Abstract: The theoretical relationship between microclimate, temperature and moisture in decaying branchwood is considered and methods of expressing moisture content discussed. Field measurements were obtained over a 1-yr period. The annual pattern of branch temperature and moisture contents consisted of a cold wet winter period when branch moisture contents are at or above saturation, low temperatures and high rainfall prevent drying. When temperatures rise in spring the trend is for branches to begin gradually to dry. During the summer months moisture contents are not constant and vary considerably from day to day with fairly rapid drying following periods of wetting. Moisture contents only rarely fell below the fibre saturation point. With the approach of autumn and winter the overall trend is for a gradual increase in moisture content but with periods of slow drying occurring whilst temperatures are still high enough to allow this.
TL;DR: The effects of naphthalene (arthropod exclusion) and simulated throughfall (N, P, K, Ca and Mg) additions on the decomposition and mineralization of dogwood litter were studied by using a field microcosm approach in a southeastern United States deciduous forest.
Abstract: The effects of naphthalene (arthropod exclusion) and simulated throughfall (N, P, K, Ca and Mg) additions on the decomposition and mineralization of dogwood (Cornus florida L.) litter were studied by using a field microcosm approach in a southeastern United States deciduous forest. Treatments without microarthropods decayed more slowly than litter with microarthropods. Simulated throughfall additions alone had no effect on litter decay rates. Fauna, simulated throughfall, and fauna plus simulated throughfall treatments increased the nutrient concentrations of decomposing litter; the treatment with both microarthropods and simulated throughfall generally exhibited the highest nutrient concentrations. Simulated throughfall also significantly increased microarthropod densities in litter. Litter immobilization of elements in throughfall was insignificant in litter with microarthropods; naphthalene-treated litter immobilized up to 8% of the elements contained in simulated throughfall.
TL;DR: The results of this study show that N 2 O evolution from soils is likely to be greater under fluctuating moisture conditions than under either continuously well-aerated conditions, or continuously excess-moisture conditions.
Abstract: The effect of several anaerobic and aerobic cycles of varying duration on N 2 O emission and labelled N loss was investigated in ( 15 NH 4 ) 2 SO 4 amended soil suspensions. No N 2 O was evolved from the continuously-anaerobic treatment. The continuously-aerobic treatment produced approximately 0.8 μg N 2 O-N g −1 dry soil in 56 days. Alternate anaerobic-aerobic cycles increased the net N 2 O evolution with 7.2 μg N 2 O-N g −1 dry soil produced in 56 days from the 7-day anaerobic, 7-day aerobic treatment. The net N 2 O evolution increased further when the duration of the anaerobic and aerobic periods was increased from 7-7 days to 14-14 days (15.7μg N 2 O-N g −1 dry soil in 56 days), although the total 15 N loss from the system was approximately the same for the two treatments. The results of this study show that N 2 O evolution from soils is likely to be greater under fluctuating moisture conditions than under either continuously well-aerated conditions, or continuously excess-moisture conditions.