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21.
Leaching losses of nitrogen from a clay soil under grass and cereal crops in Finland 总被引:1,自引:0,他引:1
Antti Jaakkola 《Plant and Soil》1984,76(1-3):59-66
Summary A 16-plot experimental field was established in 1975 on a clay soil in Jokioinen, Finland. The water discharge through tile drains was measured and its ammonium and nitrate N contents determined for each plot separately. The surface runoff was also measured and analysed. The annual runoff and the N leached from the surface of moderately fertilized (100 kg/ha/y N) cereal plots varied during 1976–1982 from 21 to 301 mm and from 2 to 7 kg/ha, respectively. The discharge of water and leaching of N through subdrains varied from 65 to 225 mm and from 1 to 38 kg/ha, respectively. The highest leaching was probably caused by a previous fallow. The annual N uptake by the crop varied between 41 and 122 kg/ha.Of the fertilizer-N used for cereals, 20% of that applied in the autumn was lost, but only 1 to 4 per cent was lost when applied in the spring. There was much less N leaching from ley than from barley plots, although the former was given twice as much N. The rate of N fertilization had only a very slight effect on N leaching from both ley and barley plots.The results were compared with those obtained in lysimeters filled with clay, silt, sand and peat soils. No definite conclusions can be drawn because the lysimeter experimental data are only for the first year. 相似文献
22.
Toby Passioura Bhaskar Bhushan Anthony Tumber Akane Kawamura Hiroaki Suga 《Bioorganic & medicinal chemistry》2018,26(6):1225-1231
The combination of genetic code reprogramming and mRNA display is a powerful approach for the identification of macrocyclic peptides with high affinities to a target of interest. We have previously used such an approach to identify a potent inhibitor (CP2) of the human KDM4A and KDM4C lysine demethylases; important regulators of gene expression. In the present study, we have used genetic code reprogramming to synthesise very high diversity focused libraries (>1012 compounds) based on CP2 and, through affinity screening, used these to delineate the structure activity relationship of CP2 binding to KDM4A. In the course of these experiments we identified a CP2 analogue (CP2f-7) with ~4-fold greater activity than CP2 in in vitro inhibition assays. This work will facilitate the development of more potent, selective inhibitors of lysine demethylases. 相似文献
23.
Dynamic role of “illite-like” clay minerals in temperate soils: facts and hypotheses 总被引:2,自引:0,他引:2
Analysis of new data and reinterpretation of published information for clay minerals found in temperate climate soil profiles
indicates that there is often a gradient of “illite-like” clay minerals with depth. We used the term “illite-like” because
these observations are based on X-Ray Diffractogram patterns and not on layer charge measurements which allow to define properly
illite. It appears that “illite-like” layers are concentrated in the upper, organic - rich portion of the soil profile both
under grassland and forest vegetation. “Illite-like” layer quantity seems directly related to soil potassium status. Indeed,
intensive agriculture practises without potassium fertilization reduce “illite-like” content in surface soils, whereas several
years of potassic fertilization without plant growth can increase “illite-like” content. The potassic soil clay mineral, illite,
is particularly important in that it can be the major source of readily available potassium for plants. Spatial and temporal
dynamics of clay minerals should be related to the potassium cycle. We propose that the frequently observed general trend
of increasing exchangeable potassium in the top soil can be correlated with an increase in “illite-like” in the clays and
that the decrease of potassium caused by intensive agricultural practices leads to “illite-like” layer destabilization. This
vision of “illite-like” layer as a potassium reservoir refueled by plants and emptied by intensive cropping renews the concept
of potassium availability and indicates a need to be discussed as well in natural ecosystems as in cultivated ecosystems. 相似文献
24.
Influence of suspended clay on phosphorus uptake by periphyton 总被引:1,自引:0,他引:1
We investigated the effect of suspended clay upon the phosphorus uptake rate exhibited by lotic periphyton communities. Suspended
inorganic clays and periphyton are common to aquatic environments, and both can strongly influence physical and chemical water
conditions. We used replicated artificial stream channels to test the prediction that suspended clay particles would affect
the uptake of soluble reactive phosphorus (SRP) by periphyton. Commercially available kaolinite and bentonite clays were characterized
for their aqueous suspension behavior and affinities for SRP. Periphyton was grown in a recirculating stream system and subjected
to simultaneous suspended clay and SRP additions. SRP removal from solution, both in the presence and absence of suspended
clays, was used to quantify SRP uptake parameters by periphyton. Clay type and concentrations of 20, 80, and 200 mg l−1 had no significant effect upon SRP uptake rate exhibited by periphyton during three 90-min experiments. Less than 1% of SRP
removal was attributable to the suspended clay load or artificial stream construction materials, based on clay isotherm data
and material sorption studies, indicating that 99% of SRP removal was attributable to biotic uptake. Removal of SRP (as KH2PO4) was described by a first-order equation with rate constants ranging between 0.02 and 0.14 min−1. Our results suggest that high turbidity conditions caused by suspended mineral clays have little immediate effect upon SRP
removal from the water column by periphyton.
Handling editor: D. Ryder 相似文献
25.
Éric Armynot du Châtelet Viviane Bout-Roumazeilles Armelle Riboulleau Alain Trentesaux 《Revue de Micropaléontologie》2009,52(1):75
The paleoecological interpretation of fossil foraminiferal assemblages depends on an understanding of the ecological processes operating at the present. This study investigates both the quality of organic matter (OM) by elemental analysis as well as the sediment grain size and clay mineralogy to understand their relative influence on distribution and abundance of benthic foraminifera. This study is carried out on 15 samples regularly spaced from the mudflat to the tidal marsh. The results indicate that grain size is the most limiting parameter. Living (stained) benthic foraminiferal density and species richness are both very low within coarser sediments. OM is the second limiting factor. The density of foraminifera is the lowest and the species richness is the highest with the lowest organic carbon (Corg) contents and C/N < 12. Conversely, when the Corg is very high and C/N > 12, the density is high and the species richness medium. A high smectite proportion within the clay-size fraction seems to favor the development of Miliammina fusca. Trochammina inflata and Jadammina macrescens are both favored by an increase of organic carbon proportion but Trochammina inflata preferentially feeds on algal-derived OM when compared with Jadammina macrescens. 相似文献
26.
Siderophores are low molecular weight organic ligands exuded by some aerobic organisms and plants to acquire Fe under Fe-limited
conditions. The hydroxamate siderophores may sorb to aluminosilicate clays through a variety of mechanisms depending upon
the nature of the clay and of the siderophore along with solution conditions such as pH, ionic strength, and presence of metal
cations. They may also affect metal binding to clays. Here, we review previous studies of siderophore sorption to aluminosilicate
clays; briefly discuss how the techniques of X-ray diffractometry, Fourier-transform infrared spectroscopy, and X-ray absorption
spectroscopy may be applied to such studies; review effects of siderophores on metal sorption to clays; and highlight some
areas for future research. 相似文献
27.
The objectives of the present survey were to formulate a zoocenological analysis of the gastropod communities in clay pit
ponds, as well as to determine the relationships between the gastropods and their environments, and to evaluate the water
habitats in terms of their ecological-conservation value. The physical and chemical parameters of water, gastropod species
and macrophytes occurring in the ponds indicate mesotrophic conditions. Principal Component Analysis (PCA) reveals a correlation
between gastropod density and nitrates, a correlation between gastropod density and alkalinity, and additionally shows a correlation
between gastropod density and chlorides. The pond surface area, nitrates, chlorides concentrate, alkalinity, and substratum
have all affected these gastropod communities. The occurrence of the first permanent population of Ferrissia clessiniana (Jickeli, 1882) was recorded in Poland. Valvata naticina Menke 1845 has become a critically rare species (CR) due to the pollution of water environments. Five other species, e.g.
Anisus vorticulus (Troschel, 1834) and Planorbis carinatus O.F. Müller, 1774 are recorded on the Polish Red List of Species. The clay pit ponds of the Ciechanowska Upland, because
of their distinctive environmental features, provide a refuge where a number of rare, threatened and alien gastropod species
live. 相似文献
28.
IMOGEN POOLE FLS HAZEL P. WILKINSON FLS 《Botanical journal of the Linnean Society. Linnean Society of London》2000,133(1):1-26
Small diameter pyritized axes, commonly referred to as 'twigs', of fossil vitaceous and menispermaceous wood from the Lower Eocene, London Clay Formation of south-east England are described here for the first time. The vitaceous twigs, which represent the earliest known occurrence of fossil Vitaceae wood, are characterized by large diameter, solitary vessels, tall wide rays which dilate in the phloem region, scalariform intervessel pits and simple perforation plates. The wood anatomy supports a close relationship to the Vitaceae and in particular the genus Rhoicissus Planch. The menispermaceous twigs are characterized by medium to moderately large vessels, simple perforation plates, alternate intervascular pitting and very broad and high rays. The anatomical characters support a close relationship to the Menispermaceae and in particular the genera Tinomiscium Miers and Coscinium Colebr. However, as these fossil twigs are not exactly similar to any particular genus they have been placed in the organ genus, Vitacexoylon Wheeler and LaPasha and Menispermoxylon Vozenin-Serra, Privé-Gill & Ginsburg, with which, respectively, they have the greatest similarity. These specimens were studied using reflected light- and scanning electron microscopy. 相似文献
29.
P. V. Coveney J. L. W. Griffin M. Watkinson A. Whiting E. S. Boek 《Molecular simulation》2013,39(3):295-316
We report the synthesis and qualitative testing of a novel class of clay nanocomposite meterials made by the in situ copolymerisation of small intercalating monomer molecules using combinatorial-style diversity methods. Initial screening was undertaken by treating montmorillonite clay films with combinations of selected additives in aqueous solution. The treated films were assessed for their stability in a qualitative manner based on their response to water. The mechanical stength of these films was also assessed qualitatively. Promising “lead” formulations showed no signs of water-induced swelling and/or exfoliation, while also being flexible and hard. In addition, the interlamellar d-spacings in the treated clay films were measured using X-ray diffraction, where possible; the value of the d-spacing in the treated clays was found to vary significanlty, from 12.7–17.7?Å. The lead formulations were then tested on bulk montmorillonite clay, confirming that the thin film behaviour was representative of that of the bulk. Direct analysis of the treated clays by mass spectrometry using both FAB and MALDITOF did not provide any useful information. However, when the clays were subjected to extraction using chloroform, clear evidence of higher relative moleclar mass species was forthcoming, confirming that polymersation of the additives was occurring. Further supporting evidence was obtained by solid-state NMR anlaysis of treated iron-free (laponite) clay samples, which also revealed extensive polymerisation of the monomers used. Comparison of these data with the results of some simple molecular modelling studies indicates that polymerisation is indeed occurring within the clay galleries. 相似文献
30.
The extent of decline in the population density of Rhizobium sp. exposed to Bdellovibrio was markedly reduced in the presence of montmorillonite, kaolinite or vermiculite but not by a soil clay fraction. Increasing levels of montmorillonite reduced the numbers of vibrios that appeared in a two-membered culture and allowed for greater survival of the rhizobia. Bdellovibrio and not Rhizobium sp. was retained when mixed with the three clay minerals, but no appreciable retention was evident with the soil clay fraction. Suspensions of colloidal soil organic matter protected the hosts from parasitism, although aqueous extracts of soil did not affect the relationship. Cells from old Rhizobium sp. cultures were attacked only after a lag phase, but rhizobia that had been stored were more rapidly lysed than cells tested immediately after removal from the growth medium. The possible significance of these findings to the survival of rhizobia in soils containing Bdellovibrio is discussed. 相似文献