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61.
Evaluation of enzyme activities in combination with taxonomic analyses may help define the mechanisms involved in microbial decomposition of orgaic amendments and biological control of soilborne pathogens. In this study, powdered pine bark was added to nematode-infested soil at rates of 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 g kg–1. Total fungal populations did not differ among treatments immediately after application of pine bark. After 7 days, fungal populations were positively correlated with increasing levels of pine bark. This increase was sustained through 14 and 21 days.Penicillium chrysogenum andPaecilomves variotii were the predominant fungal species isolated from soil amended with pine bark. Total bacterial populations did not change with addition of pine bark at 0, 7, and 14 days after treatment. At 21 and 63 days, total bacterial populations declined in soil receiving the highest rates of pine bark. Addition of pine bark powder to soil caused a shift in predominant bacterial genera fromBacillus spp. in nonamended soil, toPseudomonas spp. in amended soil. Soil enzyme activities were positively correlated with pine bark rate at all sampling times. Trehalase activity was positively correlated with total fungal populations and with predominant fungal species, but was not related to bacterial populations. The number of non-parasitic (non-stylet bearing) nematodes andMeloidogyne arenaria in soil and roots were not correlated with pine bark rate. However,Heterodera glycines juveniles in roots, and the number of cysts g–1 root, declined with increasing levels of pine bark.Journal Series Series No. 18-933598 Alabama Agricultural Experiment Station 相似文献
62.
The duckweed Lemna gibba required light and a suitable energy source such as sucrose, glucose or fructose, for maximum growth in culture. The requirement
for light was relatively unimportant and the plants grew well in a photon flux density of only 52 μmol m-2s-1 PAR. The uptake and incorporation of uniformly labelled 14C-glucose into fronds was related only to the concentration of the sugar.
When incubated with soil, labelled L. gibba behaved in a manner similar to that of labelled ryegrass roots which had been produced by a more elaborate technique using
a 14CO2 labelled atmosphere. During incubation with soil for 224 days the L. gibba material (specific activity 6133 Bq mg-1 d. wt) lost 64% of its radioactivity as 14CO2 and ryegrass (specific activity 6634 Bq mg-1 d. wt) lost 49%. Alkaline extracted humic and fulvic acids from soil had specific activities for the L. gibba incubation of 3409 and 407 Bq mg-1 solid and for ryegrass roots of 4609 and 546 Bq mg-1 solid respectively. The production of 13C or 14C-labelled L. gibba can be undertaken using only simple equipment producing material the specific radioactivity of which can be controlled by
adjusting the activity of the sugar energy source. 相似文献
63.
B. S. Griffiths 《Plant and Soil》1994,164(1):25-33
Food web studies from a range of ecosystems have demonstrated that the fauna contributes about 30% of total net nitrogen mineralization.
This results mainly from the activities of microbial-feeding microfauna (nematodes and protozoa). Microbial and microfaunal
activity is concentrated at spatially discrete and heterogeneously distributed organic substrates, including the rhizosphere.
The dynamics of microfauna and their effect on nutrient cycling and microbial processes at these sites is reviewed. The potential
manipulation of microfauna, either as an experimental tool to further understand soil microbial ecology or as a practical
means of managing nutrient flows in agroecosystems, is discussed. 相似文献
64.
Nutrient distribution in a Swedish tree species experiment 总被引:2,自引:0,他引:2
The influence of four tree species on the distribution of nutrients between different compartments of the ecosystem was examined.
In a randomized block (n=3) experiment in south-western Sweden, Ca, Mg and K were determined as exchangeable amounts in the
mineral soil and as total amounts in the O+A1 horizons (topsoil) and in the aboveground tree biomass. N contents were determined in all compartments as well as P contents
of the aboveground tree biomass and the topsoil. The four tree species planted were: silver fir [Abies alba Mill.] (AA), grand fir [Abies grandis Lindl.] (AG), Norway spruce [Picea abies L. Karst.] (PA) and Japanese larch [Larix leptolepis (Sieb. och Zucc.) Endl.] (LL). At the age of 35–36 years, the total stemwood production of the most productive species, AG,
was estimated at 471 m3 ha−1. In relation to AG, LL had produced 80%, PA 73% and AA 37%.
The system totals [aboveground tree biomass total + topsoil total + exchangeable (Ca, Mg, K) or total (N) in the mineral soil]
of Ca, K and N did not differ significantly at the 5% level between the investigated species. For Mg, the system total in
LL was significantly higher than for the other species.
There was an indication that LL and AA contained higher amounts of Ca, Mg, K and N in the topsoil but less in the biomass
than did AG and PA (partly significant). In the mineral soil, there were no significant differences in the exchangeable pools
of Ca and K, nor in the total amounts of N.
The biomass nutrient concentrations generally decreased in the order: AA > PA > AG > LL. At stem or whole-tree harvest, the
Ca export per biomass unit would more than double in the case of PA compared to LL. LL also contained less N in the biomass
than the other species. However, the N content in the biomass did not differ between the most (AG) and the least (AA) productive
species, although the production of dry weight biomass (standing + harvested) of AG had been twice that of AA. It is concluded
that the nutrient budget of a managed forest may vary considerably depending on the choice of tree species. 相似文献
65.
Iron toxicity and other chemical soil constraints to rice in highland swamps of Burundi 总被引:1,自引:0,他引:1
Iron toxicity is suspected to be a major nutritional disorder in rice cropping systems established on flooded organic soils that contain reductible iron. A pot trial was carried out to assess Fe toxicity to rice in flooded Burundi highland swamp soils with a wide range of organic carbon contents. Soil and leaf analyses were performed and total grain weight was determined. Clear Fe toxicity was diagnosed, based on leaf Fe content at panicle differentiation. Leaf Fe contents higher than 250 g g–1 dry matter induced lower Mg (and probably Mn) uptake, and a 50% total grain weight reduction. These features were associated with exchangeable Fe equivalent fractions higher than 86%. Besides, several non-Fe toxic soils exhibited an Mg-Mn imbalance. 相似文献
66.
Lipase-catalyzed alcoholysis of triglycerides for the preparation of 2-monoglycerides 总被引:11,自引:0,他引:11
Anna Millqvist Patrick Adlercreutz Bo Mattiasson 《Enzyme and microbial technology》1994,16(12):1042-1047
Rhizopus arrhizus lipase immobilized on celite was used to prepare isomerically pure 2-monoglycerides by alcoholysis of triglycerides in organic media. Reaction parameters such as choice of solvent, choice of alcohol, and alcohol concentration were studied. When 12.5 mM tripalmitin was used as substrate, methyl-tert-butyl ether was the best solvent for alcoholysis at water activity 0.11. Ethanol gave the highest yield (97%) at an optimal ethanol concentration of 200–300 mM. At higher alcohol concentrations, the enzyme activity was substantially lowered. The enzyme preparation showed high stability in repeated-batch reactions. 相似文献
67.
Effect of shock-loading of heavy metals on total organic carbon and phosphate removal in an anaerobic-aerobic activated sludge process 总被引:1,自引:0,他引:1
The effect of shock-loading of zinc, copper and cadmium ions on the removal of total organic carbon (TOC) and phosphate in an anaerobic-aerobic activated sludge process was investigated. TOC removal was not sensitive to shock-loading of Zn2+ and Cd2+ ions, and complete removal was achieved even at 20 mg Zn2+/l and 20 mg Cd2+/l. However, with over 1 mg Cu2+/1 TOC removal efficiency decreased. PO
inf4
sup3-
removal, in contrast, was extremely sensitive to these metal ions, with the threshold being 1 mg Zn2+/l and 1 mg Cd2+/l. Higher concentrations adversely affected PO
inf4
sup3-
removal. Copper again proved detrimental; no PO
inf4
sup3-
removal was achieved even at 1 mg Cu/l. These results highlight the sensitivity of the removal efficiencies of TOC and PO
inf4
sup3-
to shock loadings of these heavy metals.Y.P. Ting is with the Department of Chemical Engineering, National University of Singapore, Kent Ridge, 0511, Singapore; H. Imai and S. Kinoshita are with the Department of Chemical Process Engineering, Hokkaido University, Sapporo 060, Japan. 相似文献
68.
Four out of 187 strains, from enrichment cultures of dibenzothiophene (DBT), grew on DBT or thiophene 2-carboxylate as S sources. The four isolates, presumptively identified as Agrobacterium sp., Xanthomonas sp. and Corynebacterium spp., individually and together desulphurized DBT, producing 2-hydroxybiphenyl and sulphate.M. Constanti and A. Bordons are with the Departament de Bioquímica i Biotecnologia, and J. Giralt is with the Departament d'Enginyeria Química, both of the Universitat Rovira i Virgili, Pl. Imperial Tarraco 1, 43005 Tarragona, Catatonia, Spain 相似文献
69.
沈阳西部污灌水中有机污染物的分析刘海玲,张丽珊,姚家彪,于殿臣,朱岩,可夫,姜萍(中国科学院沈阳应用生态研究所,110015)AnalysisofOrganicPollutantsinIrrigatedsewageInWesternShenyang.... 相似文献
70.
Diurnal variations of amino acids and organic acids in xylem fluid from Lagerstroemia indica: an endogenous circadian rhythm 总被引:2,自引:0,他引:2
Diurnal variations in the concentrations of major organic compounds occurred in xylem fluid extracted from Lagerstroemia indica L. The concentration of amino acids and the N/C ratio was at a maximum and that of organic acids was at a minimum between 1230 and 2030 h. Since the concentrations of total organic nitrogen, total amino acids and most individual amino acids (but not organic acids or sugars) were also proportional to xylem tension two experiments were performed to discern whether variations in chemistry were a consequence of diurnal changes in moisture stress. In the first experiment, L. indica , exposed to variable levels of moisture stress during midday, manifested an increase in organic acids and a reduction in the N/C ratio. In the second experiment, chemical profiles of xylem fluid were collected and compared for plants exposed to a natural photoperiod, constant darkness or continuous light at noon and midnight. After 1 day amino acids increased in concentration during midday for all treatments; the variation was greatest (10-fold) for plants in constant darkness where xylem tension varied from 0.20 to 0.25 MPa. Only plants exposed to continuous light lost a diurnal rhythm after 3 days. Thus, the circadian rhythm was endogenous, terminated in continuous light and was not mediated by changes in moisture stress. Glutamine accounted for most of the diurnal variation in total amino acids, organic nitrogen and the N/C ratio in xylem fluid. 相似文献