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101.
102.
103.
The effect of two Bradyrhizobium japonicum strains (D344 and Urbana), on the frequency and intensity of infection by a VAM fungal Glomus sp. and the effect of VAM on biomass production by nodulating plants were tested in soybean growing in a soil containing low levels of accessible P and N. During the initial stage of vegetative growth, mycorrhiza frequency in roots inoculated with the two rhizobial strains did not differ. However, during flowering it was 178% higher in roots with the strain D344 than in the presence of the strain Ubrana. At final harvest (green pods) the VAM frequency did not differ in the presence of either strain. VAM positively affected biomass production, foliar concentrations of P, Zn and Cu, and number and dry matter yield of pods, but did not increase concentrations of total N and K. In nonmycorrhizal plants total nitrogenase activity (not nodule mass) and growth were higher with the rhizobial strain Urbana. The greatest nitrogenase activity, growth and yield occurred in the presence of the VAM fungus, and did not differ for plants with different strains of rhizobia. 相似文献
104.
Simon R. Mortimer 《植被学杂志》1992,3(5):665-673
Abstract. The use of root / shoot ratios to describe allocation of dry weight to structures for capturing soil resources and light is limited due to other functions of the root and shoot such as support and storage. The ratio of fine-root length to leaf area (RLA) provides a better expression of the relative sizes of above-and below-ground exchange surfaces. Dry matter partitioning, leaf area and root lengths were determined for five species of chalk grassland perennial (Carex flacca, Cirsium acaule, Festuca ovina, Leontodon hispidus and Scabiosa columbaria) by extraction of soil cores from an intact sward. The forb species had a greater proportion of their dry matter below-ground. Interspecific variation in values of RLA was considerable, mean values ranging from 137 m/m2 in Cirsium acaule to ca. 27 000 m/m2 for Festuca ovina. The implications of this interspecific variation in RLA for the competitive interactions in infertile calcareous grasslands are discussed in relation to phenology and internal nutrient cycling. 相似文献
105.
Dissolved and suspended mercury. species in the Wabigoon River (Ontario,Canada): seasonal and regional variations 总被引:1,自引:1,他引:0
Jackson T. A. Parks J. W. Jones P. D. Woychuk R. N. Sutton J. A. Hollinger J. D. 《Hydrobiologia》1982,91(1):473-487
Seasonal and regional variations in the speciation, sediment-water partitioning, and dynamics of mercury (Hg) were studied
at selected sites along the Hg-polluted Wabigoon River, and at unpolluted headwater and tributary sites, during April–September,
1979. ‘Dissolved’ and ‘particulate’ forms of Hg in the water were separated by continuous-flow centrifugation in the field.
The Hg and other pollutants such as wood chips and salt had been discharged from a chlor-alkali plant and paper mill at Dryden,
Ontario.
Concentrations and loadings of particulate methyl mercury (CH3Hg+) and total particulate Hg (and loadings of total ‘dissolved’ Hg) were greatest during the spring flood (April-May) owing
to accelerated resuspension and transport of sediments. Concentrations of ‘dissolved’ CH3Hg+, however, were highest in the summer (July–September), probably reflecting stimulation of microbial methylating activity
by elevated temperatures, together with factors such as reduced levels of metal-scavenging particulates and minimal dilution
by runoff. Total dissolved Hg concentrations were relatively high in September at polluted sites only, possibly because of
desorption from sediments due to elevated concentrations of Cl− ions. Loadings of dissolved CH3Hg+ tended to be high in the summer but were generally depressed (suggesting sorption by suspended particles) during the major
spring-flood episode in May.
During July–August dissolved CH3Hg+ was a function of total dissolved Hg, suggesting rapid biomethylation of desorbed inorganic Hg; but in general dissolved
and suspended CH3Hg+ levels depended on environmental variables and were unrelated to total Hg concentrations. In the summer only, total dissolved
Hg was a function of dissolved Cl−. Hg species in particulates were associated with sulfides, hydrated Fe and Mn oxides, organic matter (notably high molecular
weight humic and humic-Fe components), and selenium (Se); but CH3Hg+ and total Hg differed in their specific preferences for binding agents, implying that binding sites discriminate between
CH3Hg+ and Hg2+ ions. CH3Hg+ was associated with sulfide and (in the spring only) with Fe oxides, whereas total Hg was associated with organic matter
and Se and with DTPA- and NaOH-extractable Fe in the spring but with Mn oxide and NaOH-extractable organics in the summer.
Sulfides were most abundant in May, indicating that they were eroded from bottom sediments, but Fe and Mn oxides were most
abundant in the summer, probably owing to activities of filamentous iron bacteria and other micro-organisms.
Particulate Hg was 98–100% nonextractable by mild solvents such as Ca acetate, CaCl2, dilute acetic acid, and (at polluted sites only) DTPA solutions, suggesting that the particulate Hg mobilized in the spring
may not be readily available to organisms; association with Se and high molecular weight humic matter also supports this hypothesis.
Hg probably becomes more bio-available in the summer, as suggested by the upsurge in dissolved CH3Hg+ and total dissolved Hg levels, and by increases in the solubility of particulate Hg in acetic acid, DTPA, H2O2, and NaOH solutions, as well as an increase in the relative importance of lower molecular weight fractions of NaOH-extractable
Hg (in September).
Regional variations in Hg speciation and partitioning reflected a gradient in sediment composition from wood chips near Dryden
to silt-clay mud further downstream. Hg in silt-clay mud relatively far (> 35 km) downstream from the source of pollution
or in unpolluted areas appeared to be more readily solubilized by Cl− ions or chelators such as DTPA, more readily methylated (as indicated by downstream increases in dissolved CH3Hg+ levels and CH3Hg+/total Hg ratios), and was to a greater degree organically bound (H2O2-extractable), and thus was probably more bio-available, than Hg in wood-chip deposits. Possible explanations include weaker
binding of Hg by the mud, the more finely divided state of the mud, and improved microbial growth at lower concentrations
of toxic pollutants. Owing to enrichment in sulfides and Fe oxides, resuspended wood-chip sediments were especially efficient
scavengers of CH3Hg+.
The results indicate that in any pollution abatement plan aimed at lowering the Hg levels in the biota of lakes fed by the
Wabigoon River, immobilization, removal, or detoxification of dissolved as well as particulate forms of Hg in the river would
probably have to be considered. Possibly, Hg species could be ‘scrubbed’ from the river water by increasing the suspended
load and by sedimentation and treatment with Hg-binding agents in special receiving basins. 相似文献
106.
Summary Autoclaved or natural field soil amended with 0.1 to 5.0 per cent (W/W) of margosa cake, rice husk and sawdust with or without supplemental nitrogen were tested for lytic activity and bacterial numbers. Generally, non-amended autoclaved soil caused little or no lysis of mycelium ofF. oxysporum f. sp.udum; non-amended natural soil caused more lysis. Amendment of soil with margosa cake, rice husk or saw-dust with or without supplemental nitrogen greatly enhanced its lytic effect on the fungus. The degree of lysis depended on the dosage of amendment used and the stage of its decomposition in the soil. The extent of lysis increased as the bacterial population increased. Amongst bacteria,Bacillus subtilis was very common in most lytic zones. 相似文献
107.
Summary Living cells ofSerratia marcescens, uniformly labelled with15N, were added to samples of maple (Acer saccharum) and black spruce (Picea mariana) forest soils. After different periods of incubation from zero time to 100 days, the soils were subjected to alkali-acid and phenol extraction to provide humic acid, fulvic acid, humin and humoprotein fractions. Significant amounts of the cell nitrogen were recovered in the humic and fulvic acids immediately after addition. After incubation, less cell, nitrogen appeared in the humic acid and more in the fulvic acid. The amount of cell nitrogen recovered in the humin fraction increased with incubation. Roughly 5 to 10 per cent of the added cell nitrogen was found as amino acid nitrogen from humoprotein in a phenol extract of the humic acid. The data are consistent with the occurrence of co-precipitation of biologically labile biomass nitrogen compounds with humic polymers during the alkaline extraction procedure involved in the humic-fulvic fractionation. 相似文献
108.
Summary Results of numerous tests of tropical and temperate legume hosts and Rhizobium strains accumulated between 1952 and 1966 were examined for a relation between N percent (y) and dry weight per plant (x). The data fitted the equation y=A–be–cx. The most effective Rhizobium strains can be selected on the basis of dry matter yields of whole plants or plant tops only, without the need for N analyses, using statistical analyses. A previously proposed method which employs the linear relation between N-yield and dry matter yield was shown to apply only when data for strains which are not fully effective are excluded.It is postulated that symbiotically fixed N forms a different compound from that resulting from applied mineral N and that this compound cannot be remobilised before flowering.deceased 相似文献
109.
Summary Mineralization of soil nitrogen studies with two acid sulfate soils under anaerobic and aerobic incubation at 30°C for 2 weeks showed that the mineral N was released and accumulated entirely as NH
4
+
in both soils. Nitrification did not occur in either of the soils under conditions that stimulate nitrification. The acid sulfate soils studied release good amounts of mineralizable N, and, because of lack of nitrifying activity, denitrification may not be a serious problem in these soils. 相似文献
110.
Effect of heating on properties of some soils from Southern Nigeria and growth of rice 总被引:3,自引:0,他引:3
Summary The effect of heating on the properties of Apomu (Psammentic Usthorthent), Egbeda (Oxic Paleustalf) and Gambari (Typic Plinthustalf) surface soils were studied under laboratory conditions. Heating at low temperatures (100°C) have no detrimental effects on soil properties, on the contrary it increased the soil extractable P, Mg, Fe, Mn and Zn levels. Pronounced reductions in total N, Org. C, Org. P and extractable Ca and Mg levels and marked increases in extractable P, Zn, Mn and Fe were observed by heating to 200°C. Heating to 500° had an adverse effect on soil chemical and physical properties.Plant height and dry matter yeild of rice plants were higher when grown on Egbeda soil previously heated to 100°C. With addition of N, P and K there was no observed beneficial effect of the heating treatment. Rice plants grown on Egbeda soil previously heated to 200°C showed high uptake of Mn. Plants grew badly in soil previously heated to 500°C. 相似文献