Colorimetric determination of reducing sugars in soils
ABSTRACT Reducing sugars are the end products of many biological processes and enzymatic reactions in soils. They are determined in assay of several soil enzymes, including cellulase activity. Five colorimetric methods [phenol-sulfuric acid, anthrone-sulfuric acid, dinitrosalicylic acid (DNS), reaction with potassium ferric hexa-cyanide reagent (Prussian blue), and the Somogyi-Nelson (molybdenum blue) methods] were evaluated for determination of reducing sugars and total saccharides extracted from soils. Results showed that the Prussian blue and the molybdenum blue methods were the most sensitive and accurate for determination of reducing sugars in soils. Metals extracted from soils interfered with molybdenum blue color development. These metals, however, could be removed by K-saturated resin before analysis. The trace amount of metals extracted from soils did not interfere with the Prussian blue color development, but this method is too sensitive to be useful for determination of reducing sugars in soil extracts. Unlike the Prussian blue method, which is very sensitive and has 1 h color stability, the molybdenum blue method has color stability of at least 24 h. Reducing sugar values in soils increased significantly upon air-drying of field-moist soils or incubation of soils with acetate buffer (50 mM, pH 5.5) at 30°C for 24 h, suggesting enzymatic hydrolysis of the native substrates. Calibration graphs showed that the phenol-sulfuric acid, DNS, and anthrone-sulfuric acid methods are not as sensitive as the other two methods.
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ABSTRACT: The incorporation of organic amendments from pruning waste into soil may help to mitigate soil degradation and to improve soil fertility in semiarid ecosystems. However, the effects of pruning wastes on the biomass, structure and activity of the soil microbial community are not fully known. In this study, we evaluate the response of the microbial community of a semiarid soil to fresh and composted vegetal wastes that were added as organic amendments at different doses (150 and 300 t ha−1) five years ago. The effects on the soil microbial community were evaluated through a suite of different chemical, microbiological and biochemical indicators, including enzyme activities, community-level physiological profiles (CLPPs) and phospholipid fatty acid analysis (PLFA). Our results evidenced a long-term legacy of the added materials in terms of soil microbial biomass and enzyme activity. For instance, cellulase activity reached 633 μg and 283 μg glucose g−1 h−1 in the soils amended with fresh and composted waste, respectively. Similarly, bacterial biomass reached 116 nmol g−1 in the soil treated with a high dose of fresh waste, while it reached just 66 nmol g−1 in the soil amended with a high dose of composted waste. Organic amendments produced a long-term increase in microbiological activity and a change in the structure of the microbial community, which was largely dependent on the stabilization level of the pruning waste but not on the applied dose. Ultimately, the addition of fresh pruning waste was more effective than the application of composted waste for improving the microbiological soil quality in semiarid soils.Applied Soil Ecology 05/2015; 89. DOI:10.1016/j.apsoil.2014.12.009 · 2.21 Impact Factor
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ABSTRACT: This study focuses on the soil- and water-borne plant pathogen Phytophthora cinnamomi Rands and the phenomenon of P. cinnamomi suppressive soil. In particular, this thesis reports on the outcome of field surveys and glasshouse assays undertaken to locate P. cinnamomi suppressive soils and to confirm the involvement of biological processes in suppression. The potential role of cellulase and laminarinase in suppression was investigated and a molecular technique known as length heterogeneity PCR (LH-PCR) was used to analyse the structure and diversity of bacterial and fungal communities in avocado orchard soils that were suppressive and conducive to P. cinnamomi. Four avocado orchards with P. cinnamomi suppressive soils were identified and soils were γ-irradiated to destroy their suppressive capacity, thus confirming biological suppression. Suppression was also partially transferred to γ-irradiated and conducive soils by mixing with 10% suppressive avocado soils. Cellulase and laminarinase activities measured in avocado orchard soils inoculated with P. cinnamomi were not associated with disease severity in lupin seedlings during glasshouse assays involving the same soil samples. In addition, reduced disease severity in avocado seedlings grown in sterile and conducive soils mixed with 10% suppressive soils and inoculated with P. cinnamomi was not associated with cellulase or laminarinase activities in these treatments. When cellulase and laminarinase were added to sterile sand inoculated with P. cinnamomi, disease severity in lupins did not decrease, and the enzyme solutions appeared to have a phytotoxic effect on the plants. Neither suppressive nor conducive soils had characteristic bacterial or fungal community LH-PCR profiles. In addition, LH-PCR indicated that bacterial and fungal community diversity was moderate to high in both suppressive and conducive soils (bacterial Shannon index H′ = 2.99 – 3.01; fungal Shannon index H′ = 3.5 – 3.7). However, minor shifts in bacterial and fungal community structure were observed in response to mixing conducive and irradiated soils with suppressive soils. This was associated with decreased disease severity in avocado seedlings in these treatments. The shift in bacterial community structure was partially determined by the appearance and increased abundance of several bacterial 16S rDNA sequences, which were unique to the suppressive soils, in the mixed soil treatments. At least one fungal ITS2 sequence was abundant in the suppressive soils, less abundant in the conducive soil and increased in the conducive and irradiated soils after they were mixed with suppressive soils. It is suggested that the bacteria and fungi from which these sequences originated may be involved in suppression and further work should be undertaken to determine their identity and confirm their potential role in the development and maintenance of P. cinnamomi suppressive soils.07/2006, Degree: Doctor of Philosophy (Microbiology), Supervisor: Dr Tony Vancov, Dr Alison McInnes, Dr Percy Wong
Aerobiologia 01/2015; DOI:10.1007/s10453-015-9369-3 · 1.20 Impact Factor