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51.
Root,shoot and soil parameters required for process-oriented models of crop growth limited by water or nutrients 总被引:2,自引:0,他引:2
A review is given of the prospects for using process-oriented models of water and nutrient uptake in improving integrated agriculture. Government-imposed restrictions on the use of external inputs will increase the likelihood of (temporary) nutrient or water stress in crop production in NW Europe and thus a better understanding is required of shoot-root-soil interactions than presently available. In modelling nutrient and water uptake, three approaches are possible: 1) models-without-roots, based on empirically derived efficiency ratios for uptake of available resources, 2) models evaluating the uptake potential of root systems as actually found in the field and 3) models which also aim at a prediction of root development as influenced by interactions with environmental factors. For the second type of models the major underlying processes are known and research can concentrate on model refinement on the one hand and practical application on the other. The main parameters required for such models are discussed and examples are given of practical applications. For the third type of models quantification of processes known only qualitatively is urgently needed. 相似文献
52.
The chemical and biological characteristics of humus within the Ah horizon (Calcic-Luvisol) have been studied. Attention was paid to variation in the NMR spectra of humic fractions and 13C values and to how these changes are related to different biological humic fraction activities.The chemical changes in particular involve the decrease of the aromatic component and the increase of the non-aromatic component within the horizon and the different 13C value not only within the horizon but also among the humic fractions distinctive of different molecular sizes.An attempt has been made to explain the vertical chemical changes in terms of processes affecting the biological characteristics of the high and low molecular size humic fractions. The main conclusions are that the low molecular size humic fractions, in the upper part of the horizon, are of greater importance with respect to the other humic fractions in influencing the enzyme activities linked to growth metabolism. The biological role of the high molecular size humic fractions characterised by a relevant content of peptidic- and carbohydratic-C is also presented. 相似文献
53.
Summary The role of tubular mastigonemes in the reversal of thrust of the anterior flagellum ofPhytophthora cinnamomi was analysed using mastigoneme-specific monoclonal antibodies and immunoflu-orescence and video microscopy. Exposure of live zoospores ofP. cinnamomi to the mastigoneme-specific Zg antibodies caused alterations in the arrangement of mastigonemes on the flagellar surface and at Zg concentrations above 0.3 /ml, mastigonemes became detached from the flagellum. As a consequence of antibody binding to the mastigonemes there were concentration-dependent perturbations in zoospore swimming behaviour and anterior flagellum beat pattern. With increasing antibody concentration zoospores swam more slowly and other parameters of their swimming pattern, such as the wavelength of the swimming helix and the frequency of rotation, were also reduced. The effects of Zg antibodies were specific at two levels: control immunoglobulins or antibodies that bound to other flagellar surface components did not have an effect on motility, and Zg antibodies did not interfere with the motility of zoospores of oomycete species to which they did not bind. The effects of antibody-induced disruption of mastigoneme arrangement strongly support previous hypotheses that tubular mastigonemes are responsible for thrust reversal by the anterior flagellum, enabling it to pull the cell through the surrounding medium. 相似文献
54.
杉木,火力楠纯林及混交林细根周转的研究 总被引:87,自引:13,他引:74
系统研究了杉木、火力楠纯林及混交林细根生物量、生产力及年周转率。结果表明,杉木、火力楠纯林及混交林活细根生物量分别为880、3035和1560kg.ha^-1;死细根生物量为235、398和565kg.ha^-1;细根年周转率为1.29、1.42和1.40;年生产量为1137、4318和2179kg.ha^-1;年死亡量为497.595和1149kg.ha^-1,分别相当于林分枯枝落叶年凋落量为3 相似文献
55.
用奎吖咽(quinacrine)作荧光指标剂,测定玉米(ZeamaysL.)根尖微粒体(MIC)膜囊泡的H~+-泵活性,结果表明1mmol/LNaN_3仅抑制该泵活性约8%,而0.8mmol/L钒酸盐(Van)则可抑制其活性达80%,说明MIC制剂中H~+-泵活性主要由质膜(PM)H~+-ATPase产生。此泵活性严格需要Mg~(2+),二价阳离子作用大小的顺序为Mg~(2+)>Mn~(2+)>Zn~(2+)>Ca~(2+)=0;阴离子作用大小的1顺序为Br~->Cl~->NO_3~->SO_4~(2-),并初步证实当质膜同侧发生电子传递时,没有跨膜H~+梯度(△μH~+)生成。 相似文献
56.
Sandra Irene Pitta-Alvarez Ana María Giulietti 《In vitro cellular & developmental biology. Plant》1995,31(4):215-220
Summary
Brugmansia candida hairy roots, obtained by infection withAgrobacterium rhizogenes LBA 9402, exhibit, after subculturing in liquid media, a tendency towards dedifferentiation. It has been found that the following
strategies can be applied to inhibit this dedifferentiation and preserve normal root morphology: (a) lowering both the mineral
and sucrose concentration in the media employed so as to diminish osmotic stress (a condition to which these roots appear
to be particularly susceptible); (b) employing antiauxins in appropriate concentrations; and (c) maintaining the hairy roots
on solid media prior to use in production processes in liquid media. The first strategy suggested does not favor alkaloid
productivity, but in this case a two-step method could be attempted: biomass with normal root morphology could be obtained
in a first stage using low sucrose concentrations, and in a second stage, sucrose could be increased in order to achieve higher
productivity. In all the clones ofB. candida obtained, alkaloid production was biased towards scopolamine. 相似文献
57.
A simple classification of the complex parts of vascular plants 总被引:1,自引:0,他引:1
GERARD CUSSET F.L.S. 《Botanical journal of the Linnean Society. Linnean Society of London》1994,114(3):229-242
Four operational morphological units are defined to characterize 'typical' stems, leaves, roots and hairS. Any complex part can be classified among these OMUs by a graphical representation or by a quadruplet suitable for computer-aided analyses. Thirty-nine examples are given, suggesting a continuous view of plant morphology. 相似文献
58.
59.
60.
Rhizosphere, fine-root and needle chemistry were investigated in a 28 year old Norway spruce stand in SW Sweden. The uptake and allocation pattern of plant nutrients and aluminium in control plots (C) and plots repeatedly treated with ammonium sulphate (NS) were compared. Treatments started in 1988. Current year needles, one-year-old needles and cylindrical core samples of the LFH-layer and the mineral soil layers were sampled in 1988, 1989 and 1990. Compared to the control plots, pH decreased significantly in the rhizosphere soil in the NS plots in 1989 and 1990 while the SO4-S concentration increased significantly. Aluminium concentration in the rhizosphere soil was generally higher in the NS plots in all soil layers, except at 0–10 cm depths, both in 1989 and 1990. Calcium, Mg and K concentrations also increased after treatment with ammonium sulphate. Ammonium ions may have replaced these elements in the soil organic matter. The NS treatment significantly reduced Mg concentrations in fine roots in all layers in 1990. A similar trend was found in the needles. Ca concentrations in fine roots were significantly lower in the NS plots in the LFH layer in 1990 and the same pattern was found in the current needles. The N and S concentrations of both fine roots and needles were significantly higher in the NS plots. It was suggested that NS treatment resulted in displacement of Mg, Ca and K from exchange sites in the LFH layer leading to leaching of these cations to the mineral soil. Further application of ammonium sulphate may damage the fine roots and consequently adversely affect the water and nutrient uptake of root systems. 相似文献