Fluorescein Diacetate Hydrolysis Activity Research Articles

Impact of irrigation water quality on soil nitrifying and total bacterial communities

Disturbance induced by two contrasting irrigation regimes (groundwater versus urban wastewater) was evaluated on a sandy agricultural soil through chemical and microbial analyses. Contrary to wastewater, groundwater displayed very high nitrate contents but small amounts of ammonium and organic matter. Despite these strong compositional shifts, soil organic carbon and nitrogen, nitrate and ammonium contents were not significantly different in both types of irrigated plot. Moreover, neither microbial biomass nor its activity, determined as fluorescein diacetate hydrolysis activity, was influenced by irrigation regimes. Bacterial community structure, assessed by denaturing gradient gel electrophoresis (DGGE) of 16S ribosomal DNA fragments, was also weakly impacted as molecular fingerprints shared an overall similarity of 85%. Ammonia-oxidizing bacterial community (AOB) was monitored by DGGE of the functional molecular marker amoA gene (alpha subunit of the ammonia monooxygenase). Surprisingly, no amoA signals were obtained from plots irrigated with groundwater, whereas signal intensities were high in all plots under wastewater. Among the last, compositional shifts of the AOB community were weak. Overall, impact of irrigation water quality on soil chemistry could not be evidenced, whereas effects were low on the total bacterial compartment but marked on the AOB community.

Non‐enzymatic hydrolysis of fluorescein diacetate (FDA) in a Mediterranean oak (Quercus ilex L.) litter

SummaryWe show the presence of interfering substances when the total microbial activity in litter samples is measured with fluorescein diacetate (FDA), and we propose some methodological modifications to avoid such interference. Three distinct litter layers (the OhLn, the OhLv and the OhLf) of evergreen oak (Quercus ilex L.) were characterized by 13C CPMAS NMR and the spectra show that the recalcitrant aromatic and phenolic compounds increase with the degree of degradation of litter. A wide range of sources of interference in the hydrolysis of FDA was found. To understand the origin of this interference, sterilized litter materials (i.e. γ‐irradiated or autoclaved) and a wide range of organic substances (i.e. amino acids, glucose, sorbitol and organic humic acids) were investigated. Insignificant differences on the FDA hydrolysis activity (FDA activity) were found in the γ‐irradiated and non‐irradiated OhLn litter, indicating that γ‐irradiation does not destroy enzymes. Conversely, after heat‐sterilization of litter, samples showed FDA activity corresponding to 60, 34.8 and 30.8% (in the OhLn, the OhLv and the OhLf layers, respectively) of that of control litters. This indicates the presence of non‐enzymatic interfering substances in the FDA assays. As the humification and litter depth increased, hydrolysis of FDA due to interferences decreased, indicating degradation and/or chelation of interfering substances. We hypothesize that lysine, arginine, histidine and cysteine are mainly responsible for the hydrolysis of FDA. We suggest that the use of phosphate buffer (50 mm, pH 7.0) with incubation < 30 minutes, in combination with a temperature between 30 and 40°C, produces insignificant interference in the determination of the final FDA activity in litter samples.

Accumulation of heavy metals in dietary vegetables and cultivated soil horizon in organic farming system in relation to atmospheric deposition in a seasonally dry tropical region of India

Increasing consciousness about future sustainable agriculture and hazard free food production has lead organic farming to be a globally emerging alternative farm practice. We investigated the accumulation of air-borne heavy metals in edible parts of vegetables and in cultivated soil horizon in organic farming system in a low rain fall tropical region of India. The factorial design of whole experiment consisted of six vegetable crops (tomato, egg plant, spinach, amaranthus, carrot and radish) x two treatments (organic farming in open field and organic farming in glasshouse (OFG)) x seven independent harvest of each crop. The results indicated that except for Pb, atmospheric deposition of heavy metals increased consistently on time scale. Concentrations of heavy metals in cultivated soil horizon and in edible parts of open field grown vegetables increased over time and were significantly higher than those recorded in OFG plots. Increased contents of heavy metals in open field altered soil porosity, bulk density, water holding capacity, microbial biomass carbon, substrate-induced respiration, alkaline phosphatase and fluorescein diacetate hydrolytic activities. Vegetable concentrations of heavy metal appeared in the order Zn > Pb > Cu > Ni > Cd and were maximum in leaves (spinach and amaranths) followed by fruits (tomato and egg plant) and minimum in roots (carrot and radish). Multiple regression analysis indicated that the major contribution of most heavy metals to vegetable leaves was from atmosphere. For roots however, soil appeared to be equally important. The study suggests that if the present trend of atmospheric deposition is continued, it will lead to a destabilizing effect on this sustainable agricultural practice and will increase the dietary intake of toxic metals.

Side effects of pencycuron on nontarget soil microorganisms in waterlogged soil: Field experiment

Field experiments with waterlogged rice were conducted during the wet seasons (June–October) of 2002 and 2003, in an alluvial clay loam soil treated with and without decomposed cow manure (DCM) at field rate (FR), 2-times FR (2FR) and 10-times FR (10FR) as foliar spray. Soil microbial biomass-C (MBC), ergosterol content and fluorescein diacetate hydrolyzing activity (FDHA) declined in all the treatment combinations including the control till day 30, when the field was waterlogged. After crop harvest at day 70, when the experimental plots became aerobic, the soil microbial parameters increased remarkably with all the treatment combinations. The microbial metabolic quotient (qCO 2) and microbial respiration quotient ( Q R) under different treatment combinations showed distinct increasing trend up to day 30 followed by a sharp decrease at day 70 irrespective of DCM amendment. Thus, the toxic effect of pencycuron on microbiological parameters persisted till the field was submerged. After withdrawal of submergence at crop harvest, the microbial parameters measured in the present study improved remarkably. Present work thus demonstrated that pencycuron application might not cause any permanent detrimental effect on the studied soil microbiological parameters.

Características biológicas do solo indicadoras de qualidade após dois anos de aplicação de biossólido industrial e cultivo de milho

A utilização agrícola de biossólidos tem sido muito incentivada, mas, como esses resíduos apresentam composição química variada, o valor agronômico e os efeitos sobre características indicadoras de qualidade do solo precisam ser avaliados caso a caso, a fim de estabelecer normas de segurança para uso desses materiais. Neste trabalho foram avaliadas características biológicas, após a aplicação, por dois anos consecutivos, de doses crescentes (0, 6, 12, 18 e 24 t ha-1 base seca) de um biossólido gerado por uma indústria de fibras e resinas PET e da adubação mineral completa no cultivo de milho, em um Cambissolo distrófico, comparados aos de uma área adjacente, sob Brachiaria sp. e sem cultivo nos últimos 10 anos, usada como referência. Os valores de C e N da biomassa microbiana, a respiração basal e as atividades das enzimas urease e beta-glicosidase e da hidrólise do diacetato de fluoresceína (FDA) aumentaram, enquanto a atividade da fosfatase ácida diminuiu com a elevação das doses de biossólido, porém estas não tiveram efeito sobre o quociente metabólico (qCO2). A diminuição da atividade da fosfatase se deveu ao aumento da disponibilidade de P no solo, não caracterizando efeito adverso da aplicação do biossólido. Com aplicação de 12 t ha-1 de biossólido (recomendação agronômica), a respiração e a hidrólise da FDA foram maiores e a atividade da fosfatase foi menor que a obtida no solo com adubação mineral, mas as demais características avaliadas não diferiram entre estes tratamentos. A colonização micorrízica de Brachiaria sp. não diferiu entre plantas de crescimento espontâneo nas parcelas anteriormente cultivadas com milho e aquelas da área adjacente. Apesar do menor número de esporos, verificou-se enriquecimento de espécies de fungos micorrízicos arbusculares (FMAs) nas parcelas cultivadas. O carbono orgânico (Corg) e a biomassa microbiana apresentaram alta correlação com os demais parâmetros avaliados, indicando que as alterações na quantidade e qualidade da matéria orgânica, promovidas pela aplicação do biossólido, refletiram na dinâmica da microbiota e influenciaram positivamente os parâmetros biológicos de qualidade do solo.

Effect of novaluron on microbial biomass, respiration, and fluorescein diacetate-hydrolyzing activity in tropical soils

The aim of this study was to assess the potential harmful effects of novaluron on soil microbiological parameters in clay loam alluvial soil (Typic udifluvent) and coastal saline soil (Typic endoaquept) under controlled laboratory tests. The applications of novaluron were made at or above the recommended rates, which includes field rate (FR), two times (2FR), and ten times (10FR) the FR. The laboratory incubation study was carried out at 60% of maximum water holding capacity of soils and at 30°C. Novaluron application rate even up to 10FR resulted in a short-lived and transitory toxic effect on soil microbial biomass C and fluorescein diacetate-hydrolyzing activity. Microbial metabolic quotient changed but for a short period. It can be concluded that novaluron had a transient and negligible harmful effect on the soil microbiological parameters studied at higher rates than those usually used in the field.

Enzymatic evaluation of decomposition in mosaic landscapes of a tidal flat ecosystem

Organic matter decomposition is an important ecological function in tidal flat ecosystems, and extracellular hydrolytic enzyme activities can be used as indices of this process. In this study, the spatial and temporal variations of enzyme activities were determined to establish easily measured variables that could be used to assess wetland functions. Seven sampling sites belonging to the hydrogeomorphic subclasses estuary, foreshore, and lagoon were selected in the intertidal zone of the Obitsu River Delta and the Banzu Tidal Flat in Tokyo Bay, Japan. Ten field surveys were conducted between June 2001 and April 2003. In each survey triplicate sediment samples were collected from each sampling site. For each sample, fluoresceindiacetate hydrolysis (FDH), β-glucosidase (GLU), and β-acetylglucosaminidase (AGA) activities were measured. Among the 210 samples, the means and standard deviations were 0.018 ± 0.011 unit g−1 h−1 for FDH, 0.074 ± 0.043 mmol kg−1 h−1 for GLU, and 0.043 ± 0.041 mmol kg−1 h−1 for AGA. According to analysis of variance, sampling time, site location, and their interaction significantly influenced FDH activity. Both the sampling time and sampling location affected GLU and AGA activities, although no significant interaction was found. GLU and AGA activities were higher in the estuary sites than in the foreshore sites and the lagoon site. GLU and AGA activities differed among the estuary sites, although there were no significant differences in GLU and AGA activities among the foreshore beach sites. We recorded significant temporal changes of GLU and AGA activities, and seasonal changes differed across the three years of the study.

Long-term application of compost influences microbial biomass and enzyme activities in a tropical Aeric Endoaquept planted to rice under flooded condition

In a field study, long-term application of compost to a tropical Aeric Endoaquept under continuous rice growing in a rice–rice–fallow sequence resulted in the stimulation of microbial biomass and select soil enzyme activities. Mean seasonal soil microbial biomass-C (C mic) increased by 42%, 39% and 89% in inorganic fertilizer, compost and compost+inorganic fertilizer treatments, respectively, over the unamended control. C mic content was also influenced by the rice crop growth stage and was highest at maximum tillering stage irrespective of treatments and declined thereafter. Soil organic C (C org) content showed highly significant positive correlation with dehydrogenase, urease, cellulase, β-glucosidase and fluorescein di-acetate (FDA) hydrolysis activity, and a positive but not significant correlation with invertase and amidase activity. C/N ratio which was lowest in unamended control plots showed a significant positive relationship with only the enzymes involved in C cycle. Stepwise regression analysis revealed that for prediction of both total organic C and total N, FDA hydrolysis activity contributed significantly for the variance and explained up to 85–96% variability. Results demonstrated that microbial biomass and soil enzyme activity is sensitive in discriminating between long-term organic residue amendment practices.

Effect of Pencycuron on Microbial Parameters of Waterlogged Soil

A laboratory study was conducted to monitor the effect of pencycuron [1-(4-chlorobenzyl)-1-cyclopentyl-3-phenylurea] on microbial parameters of alluvial (AL) soil (Typic udifluvent) and coastal saline (CS) soil (Typic endoaquept) under waterlogged condition. Pencycuron at field rate (FR), 2FR and 10FR affected the microbial biomass C (MBC), soil ergosterol content and fluorescein diacetate hydrolyzing activity (FDHA) differentially. The DCM amendment did not seem to have any counteractive effect on the toxicity of pencycuron on the microbial variables. The change in microbial metabolic quotient (qCO2) and microbial respiration quotient (QR), indicated pencycuron induced disturbance at 10FR. Present study revealed that the metabolically activated microbial population was more suppressed compared to the dormant population.

Microbial activities in soils of a former sawmill area

To find out microbial metabolic functioning and toxicity in a former sawmill area, carbon dioxide evolution, methane oxidation potential, 10 hydrolytic enzyme activities, Vibrio fischeri test, fluorescein diacetate hydrolysis activity (FDA), soil pH, carbon, nitrogen and pentachlorophenol (PCP) content were measured at four sites. The area is contaminated with aged chlorophenols. Chlorophenol content of soil was analyzed with a novel HPLC-MS technique, which allowed to measure chlorophenols without derivatization. The sites had a pollution gradient from 0.5 to 15 microg PCP g dw of soil(-1). Endogenous carbon dioxide evolution, methane oxidation potential, butyrate-esterase, acetate-esterase, sulphatase and aminopeptidase activities were lower at the site 2 than 3, although the site 2 and 3 had similar content of carbon and nitrogen. The soil was toxic in V. fischeri test at the site 2, which had high content of PCP (3.93+/-1.00 microg PCP g dw of soil(-1)). The results indicated that endogenous carbon dioxide evolution, methane oxidation potential, butyrate-esterase, acetate-esterase, sulphatase and aminopeptidase activities were sensitive to PCP in the soil. The results indicated that alpha-glucosidase, beta-glucosidase, beta-xylosidase, beta-cellobiosidase, phosphomonoesterase, N-acetyl-glucosaminidase activity and FDA hydrolysis activity were not sensitive to PCP in the soil. Soil processes involved in the cycling of carbon, nitrogen, sulphur and phosphorus were only slightly vulnerable in the former sawmill area and most sensitive microbial species were probably replaced with more tolerant ones to maintain and recover functioning of the former sawmill soils.

Influence of soil properties on fluorescein diacetate hydrolyzing activity under different agro-ecosystems

Fluorescein diacetate hydrolyzing activity (FDHA) of soils, both in field moist and air dried, of different agro-ecosystems in alluvial soil was studied. Field moist soils recorded higher values than in air-dried soils, but they showed significant positive correlation (0.93**). FDHA in both soil pretreatments showed positive correlation with organic matter (0.98** for field moist soil and 0.92** for air-dried soil) and clay content (0.85** for field moist soil and 0.82* for air-dried soil) of the soils. Multiple regression analysis showed that the stabilization of FDHA in the studied soils was due to organic matter-enzyme complex. Among the organic matter fractions, humus C plays dominating role to control the FDHA of the soils.

Biochemical parameter changes in urban-waste compost used as biofilter for pesticide decontamination

Urban-waste compost (UWC) can be used as a biofilter filling to reduce the effects of pesticide spills. Here, water that was contaminated by three different pesticides, the insecticide chlorpyrifos (Chl), the fungicide metalaxyl (Meta) and the herbicide glyphosate (Gly), was percolated through 2 kg of UWC material. The pesticide residues in the leached water and the modifications induced in some of the UWC biochemical and microbiological parameters (including microbial biomass carbon (MBC) and nitrogen (MBN), and fluorescein diacetate (FDA) hydrolysis, alkaline monophosphatase (AMP) and dehydrogenase (DH) activities) were investigated over 2 months of incubation at 20°C. The UWC showed a good retention capacity towards the three pesticides tested, with the highest efficiency for Gly. Chl caused an initial detrimental effect on the MBC content and a decrease in the FDA hydrolysis capacity, while Meta and Gly increased the MBC content throughout the incubation. The results demonstrate that UWC can be successfully used as a biofilter to reduce pesticide spills and to clean up water contaminated with pesticides. The evaluation of the modifications induced on the UWC MBC and MBN, and FDA hydrolysis, AMP and DH activities suggest different biodegradation potentials of the UWC micro-organisms vs. the three pesticides studied.

Microbial biomass and its activities in salt-affected coastal soils

Seasonal fluctuations in salinity are typical in coastal soils due to the intrusion of seawater in the groundwater. We studied the effect of salinity on the microbial and biochemical parameters of the salt-affected soils of the coastal region of Bay of Bengal, Sundarbans, India. The average pH values and average organic C (OC) contents of soils from nine different sites cultivated with rice (Oryza sativa) ranged from 4.8 to 7.8 and from 5.2 to 14.1 g kg−1, respectively. The average electrical conductivity of the saturation extract (ECe) during the summer season was about five times higher than that during the monsoon season. Within the nine sites, three soils (S3, S4, and S5) were the most saline. The average microbial biomass C (MBC), average basal soil respiration (BSR), and average fluorescein diacetate hydrolyzing activity (FDHA) were lowest during the summer season, indicating a negative influence of soil salinity. About 59%, 50%, and 20% variation in MBC/OC, FDHA/OC, and BSR/MBC (metabolic quotient, qCO2), respectively, which are indicators of environmental stress, could be explained by the variation in ECe. The decrease in MBC and microbial activities with a rise in salinity is probably one of the reasons for the poor crop growth in salt-affected coastal soils.

Organic soil amendments: Impacts on snap bean common root rot ( Aphanomyes euteiches) and soil quality

Common root rot (causal agent Aphanomyes euteiches) is a major disease of commercially grown snap bean ( Phaseolus vulgaris L.). Organic amendments hold potential to suppress plant diseases, which may be due to changes in soil biology and other soil properties. The objective of this study was to determine the potential of paper-mill residual by-products to suppress common root rot of snap bean in relation to soil properties. The study was done on soil (Plainfield sandy loam, Hancock, WI) from a field trial comparing annual applications of fresh paper-mill residuals (0, 22 or 33 dry Mg ha −1) or composted paper-mill residuals (0, 38 or 78 dry Mg ha −1). Soil was removed from each treatment that had been in place 3 years in April 2001 (1 year after last amendment) and on September 2001 (4 months after last amendment) and brought to the laboratory. Soils were incubated at field moisture content (25 °C) and periodically bioassayed with bean seedlings (9, 44, 84, 106, 137, 225 or 270 days after removal from the field) for snap bean root rot. Soils were sampled on the same day as the root rot bioassay and assayed for β-glucosidase, arylsulfatase and fluorescein diacetate hydrolysis activities (FDA), microbial biomass-C (MB C) (by chloroform fumigation), water stable aggregation, and total C. There were large differences in snap bean root rot incidence between the field amendment treatments. The unamended field soil had high levels of disease incidence throughout the experiment but disease incidence tended to decrease over time in amended soils. The disease was suppressed by both fresh and composted paper-mill residuals, but the composted residuals at high rates had the lowest disease incidence (<40%) and produced healthiest plants. Root rot severity was strongly negatively correlated with total C (0.001 ≤ p) and arylsulfatase activity (0.001 ≤ p). β-Glucosidase activity was negatively correlated (0.05 ≤ p) with disease severity while soil MB C showed inconsistent negative correlations with disease severity over the incubation sampling periods. Arylsulfatase activity was the best indicator for reflecting disease suppression. The amendments improved soil quality, which was exemplified by improved aggregation.

Assay for fluorescein diacetate hydrolytic activity: Optimization for soil samples

With the increased interest in integrated soil bioecosystem studies, there is a need to have a method of measuring overall microbial activity potential. Hydrolysis of fluorescein diacetate [3′,6′-diacetylfluorescein (FDA)] has been suggested as a possible method because the ubiquitous lipase, protease, and esterase enzymes are involved in the hydrolysis of FDA. Following hydrolysis of FDA, fluorescein is released and can be measured spectrophotometrically. Our objective was to optimize the assay for FDA hydrolytic activity in soil samples and determine the kinetic parameters involved in this reaction. The optimized method involves extraction and quantitative measurement of the fluorescein released when 1.0 g of soil is incubated with 50 ml of 60 mM Na–phosphate solution (buffered at pH 7.6) at 37 °C for 3 h. Results showed that FDA hydrolysis was optimum at buffer pH 7.6 and the soil enzymes were denatured at temperatures above 60 °C. Three soils were used to optimize this method: Heiden clay, Raub silt loam, and Cecil sandy loam. This procedure is simple, precise, and can be used in commercial soil testing laboratories to determine general microbial activity and as a soil quality indicator.

Pencycuron application to soils: Degradation and effect on microbiological parameters

Clay loam soil from agricultural fields of alluvial (AL) soil (typic udifluvent) and coastal saline (CS) soil (typic endoaquept) were investigated for the degradation and effect of pencycuron application at field rate (FR), 2-times FR (2FR) and 10-times FR (10FR) with and without decomposed cow manure (DCM) on soil microbial variables under laboratory conditions. Pencycuron degraded faster in CS soil and in soil amended with DCM. Pencycuron spiking at FR and 2FR resulted in a short-lived (in case of 10FR slightly longer) and transitory toxic effect on soil microbial biomass-C (MBC), ergosterol content and fluorescein diacetate hydrolyzing activity (FDHA). Amendment of DCM did not seem to have any counteractive effect of the toxicity of pencycuron on the microbial variables. The ecophysiological status of the soil microbial communities as expressed by microbial metabolic quotient ( q CO 2 ) and microbial respiration quotient ( Q R) changed, but for a short period, indicating pencycuron induced disturbance. The duration of this disturbance was slightly longer at 10FR. Pencycuron was more toxic to the metabolically activated soil microbial populations, specifically the fungi. It is concluded that side effects of pencycuron at 10FR on the microbial variables studied were only short-lived and probably of little ecological significance.

Cover crop, tillage, and herbicide effects on weeds, soil properties, microbial populations, and soybean yield

A field study was conducted during 1997 to 2001 on a Dundee silt loam soil at Stoneville, MS, to examine the effects of rye and crimson clover residues on weeds, soil properties, soil microbial populations, and soybean yield in conventional tillage (CT) and no-tillage (NT) systems with preemergence (PRE)-only, postemergence (POST)-only, and PRE plus POST herbicide programs. Rye and crimson clover were planted in October, desiccated in April, and tilled (CT plots only) before planting soybean. Both cover-crop residues reduced density of barnyardgrass, broadleaf signalgrass, browntop millet, entireleaf morningglory, and hyssop spurge but did not affect yellow nutsedge at 7 wk after soybean planting (WAP) in the absence of herbicides. Densities of these weed species were generally lower with PRE-only, POST-only, and PRE plus POST applications than with no-herbicide treatment. Total weed dry biomass was lower when comparing CT (1,570 kg ha−1) with NT (1,970 kg ha−1), rye (1,520 kg ha−1) with crimson clover (2,050 kg ha−1), and PRE plus POST (640 kg ha−1) with PRE-only (1,870 kg ha−1) or POST-only (1,130 kg ha−1) treatments at 7 WAP. Soils with crimson clover had higher organic matter, NO3–N, SO4–S, and Mn, and lower pH compared with rye and no–cover crop soils. Total fungi and bacterial populations and fluorescein diacetate hydrolytic activity were higher in soil with crimson clover, followed by rye and no cover crop. Soybean yields were similar between CT (1,830 kg ha−1) and NT (1,960 kg ha−1), no cover crop (2,010 kg ha−1) and rye (1,900 kg ha−1), and rye and crimson clover (1,790 kg ha−1), but they were higher in PRE plus POST (2,260 kg ha−1) than in PRE-only (1,890 kg ha−1) or POST-only (1,970 kg ha−1) treatments.

Biodegradation of linear alkylbenzene sulfonates in sulfate-leached soil mesocosms

Aromatic sulfonates (R–SO 3 −) can be used as sulfur sources by sulfate-starved bacteria in laboratory cultures and the corresponding phenols are excreted from the cells. The present study was conducted to demonstrate whether such desulfonation reactions also occur in sulfate-leached agricultural soil, where desulfonation of organic sulfur compounds may have agronomic importance as a S source for plants. Xenobiotic linear alkylbenzene sulfonates (LAS) were added to nominal concentrations of 0, 10 and 100 mg kg −1 dry weight in a sandy soil that was depleted in sulfate by leaching the soil with water (sulfate depletion, ∼75%). The soil was incubated at 20 °C in duplicate 3-dm 3 mesocosms for 8 weeks. Primary degradation of LAS was rapid with half-lives of 1–4 days. Sulfophenylcarboxylates were identified and quantified as intermediates, whereas linear alkylphenols (the expected primary desulfonation products) were not detected by high-pressure liquid chromatography coupled with both fluorescence and electrospray ionization-mass spectrometry. Thus, LAS was used by the bacteria as a source of energy and carbon, rather than as a source of sulfur. Measurements of soil pH, fluorescein diacetate (FDA) hydrolysis and arylsulfatase activity showed that stable microbial conditions prevailed in the soil mesocosms. FDA hydrolysis (a measure of total microbial activity) was transiently inhibited at the highest LAS concentrations. Arylsulfatase activity (i.e., hydrolysis of aromatic sulfate esters) was not significantly affected by the soil incubation, although arylsulfatases may be upregulated in sulfate-starved bacteria. However, an increased production of arylsulfatase may be difficult to detect due to the background of extracellular arylsulfatases stabilised in the soil. Therefore, the present data does not exclude a regulatory response to sulfate depletion by the soil microorganisms. However, the importance of desulfonation reactions in natural environments still needs to be demonstrated.

Soil microbial biomass and fluorescein diacetate hydrolytic activity in Japanese acidic tea field soils

The soil microbial biomass (SME) content and fluorescein diacetate (FDA) hydrolytic activity in 21 acidic tea field soils in Japan were determined. SM 3 content in the tea field soils was quantitatively similar to that in 13 arable soils with neutral soil pH previously reported. However, the ratio of the SMB content to organic matter content in the tea field soils classified as red-yellow soil, brown forest soil, and lithosol was clearly lower than that in the neutral arable soils classified as non-volcanic ash soil. FDA hydrolytic activity in the tea field soils was higher than the activity in various soils with neutral soil pH and showed a negative relationship with the soil pH.

Loss of soil organic matter and related soil properties under long-term sugarcane production on two contrasting soils

The effects of increasing periods under sugarcane monoculture (managed with preharvest burning) on soil organic matter content and related soil properties were investigated in the 0- to 10-cm layer of a sandy coastal Ochric Cambisol (Glenrosa soil) and a red Rhodic Ferralsol (Hutton soil) from the sugar belt of the South African province of KwaZulu-Natal. The organic C content at both sites under undisturbed vegetation was between 40 and 50 g C kg(-1). This declined exponentially with increasing years under sugarcane. For the Glenrosa site it reached a new equilibrium level after about 3040 years. After 20 30 years of sugarcane, organic C content had declined to about 33 g kg(-1) for the Hutton soil and 17 g kg-1 for the Glenrosa soil. The higher organic matter content maintained at the Hutton site was attributed mainly to clay protection of organic matter since the clay content of the Hutton soil was 62% compared to 18% for the Glenrosa soil. For the same reason, aggregate stability was also generally higher in the Hutton than Glenrosa soil. The loss of soil organic matter under sugarcane resulted in a concomitant decline in soil microbial biomass C, percentage of organic C present as microbial biomass, basal respiration, fluorescein diacetate hydrolytic activity and aggregate stability. At the Glenrosa site, the natural delta(13)C abundance in soils was used to calculate the loss of forest-derived, native soil C and the concomitant input of sugarcane-derived C. Sugarcane-derived organic C increased over time until it accounted for about 61% of organic C in the surface 10 cm in soils that had been under sugarcane for greater than 50 years. It was concluded that sugarcane production can cause a large decline in soil organic matter content and that practices such as green cane harvesting, zero tillage and use of green crops should be promoted to help ameliorate the problem.