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1.
Martin Wood 《Plant and Soil》1987,97(3):303-314
Summary Laboratory data for the loss of root material by barley and field data for the growth of barley plants in Syria and in England
have been combined to predict the amount of material lost by barley roots during a season, and to predict the resulting microbial
biomass in the rhizosphere. The predicted microbial biomass C in the rhizosphere ranged from 10–34% of the total plant biomass
C depending mainly upon the value used for rate of loss of root material. Total loss of root material predicted during a season
in England constituted 7.7–25.4 percent of C fixed by photosynthesis. The major assumptions made in these calculations are
considered, and the predicted values discussed in relation to reported values for soil microbial biomass, CO2 fluxes from soil and associative nitrogen fixation. 相似文献
2.
Citric acid excretion and precipitation of calcium citrate in the rhizosphere of white lupin (Lupinus albus L.) 总被引:14,自引:0,他引:14
Abstract. White lupin ( Lupinus albus L.) was grown for 13 weeks in a phosphorus (P) deficient calcareous soil (20% CaCO3 , pH(H2 O)7.5) which had been sterilized prior to planting and fertilized with nitrate as source of nitrogen. In response to P deficiency, proteoid roots developed which accounted for about 50% of the root dry weight. In the rhizosphere soil of the proteoid root zones, the pH dropped to 4.8 and abundant white precipitates became visible. X-ray spectroscopy and chemical analysis showed that these precipitates consisted of calcium citrate. The amount of citrate released as root exudate by 13-week-old plants was about 1 g plant−1 , representing about 23% of the total plant dry weight at harvest. In the rhizosphere soil of the proteoid root zones the concentrations of available P decreased and of available Fe, Mn and Zn increased. The strong acidification of the rhizosphere and the cation/anion uptake ratio of the plants strongly suggests that proteoid roots of white lupin excrete citric acid, rather than citrate, into the rhizosphere leading to intensive chemical extraction of a limited soil volume. In a calcareous soil, citric acid excretion leads to dissolution of CaCO3 and precipitation of calcium citrate in the zone of proteoid roots. 相似文献
3.
Three axenic and rhizosphere microorganism-inoculated shortgrass steppe plant species were evaluated for possible differences in residual organic carbon and nitrogen present as sugars, organic acids and amino acids. IntroducedAgropyron cristatum was compared toA. smithii andBouteloua gracilis, which are dominant species in the native shortgrass steppe. These plants, grown for 90 days in root growth chambers, showed differences in residual organic carbon and nitrogen per gram of root, and rhizosphere microbe presence resulted in additional changes in these compounds. The root biomass ofB. gracilis was significantly increased with microbes present. TheAgropyron species had significantly lower amino acid levels with microbes present, while under the same conditions, theB. gracilis showed significant decreases in residual sugars. Based on the amino acids, sugars and organic acids, the C/N ratio of the sterileA. cristatum was higher than forB. gracilis. Rhizosphere microbe presence did not result in changes in these C/N ratios. These results suggest thatA. cristatum, with microbes present, will have lower levels of amino acids present, whileB. gracilis, with a lower C/N ratio, will have sugars used to a greater extent by the rhizosphere microbes. This resulted in the higher levels of residual soluble organic C and N in the rhizosphere ofB. gracilis, in comparison with the introducedA. cristatum. These differences may be critical in influencing the course of nutrient accumulation and plant competition in short-grass steppe communities, and in understanding basic aspects of plant-rhizosphere microorganism interactions. 相似文献
4.
Summary Four inbred lines ofZea mays (33.16, B 68, N 7B, B 77) were grown in nutrient solution to which K2Cr2O7 was added to give final concentration of 5 mg/l Cr (VI). The most evident differences in metal tolerance were observed between the B 68 and 33.16 line: in fact, even though the level of Cr (VI) was almost the same in the root tissues of both lines after 6 d of treatment, in the B 68 line, Cr induced marked alterations of nuclear structure and a progressive arrest of the cell cycle in G 1. In the 33.16 line, on the contrary, the integrity of the nuclei was well preserved and the progression of the cell cycle was only barely affected.Abbreviations Cr
(VI) hexavalent chromium
- CRBC
chick red blood cells
- DAPI
4,6-diamidino-2-phenylindole
- FCM
Flow cytometry
- FM
Fluorescence microscopy
- TEM
Transmission electron microscopy
- Tris
10 mM Tris(hydroxymethyl)aminomethane 相似文献
5.
Curt Leben 《Plant and Soil》1986,91(1):139-142
Summary Survival ofPseudomonas syringae pv.lachrymans with seedling cucumber roots, root washings, rhizosphere soil, and nonrhizosphere soil was determined 7–8 days after the soil surface was watered with a cell suspension of the bacterium. Plants were in pots in the green-house and soil was not sterilized. Survival was best with roots and root washings, next best in rhizosphere soil, and poor in nonrhizosphere soil. 相似文献
6.
Summary
Lolium perenne was grown in solution culture with either ample or deficient phosphate supply (high-P and low-P plants). The concentration in the roots of phosphorus as water-soluble compounds, phospholipid and insoluble residue was measured. A supplementary experiment showed that the concentration of each component in the roots of low-P plants was similar to that in plants grown in P-deficient soil. The time-course of the decline of each P component was determined in roots detached from the shoot and left hanging in solution. During the three weeks residue P concentration in the roots declined little. In contrast, both types of root lost about three-quarters of their lipid P in the first week. Low-P roots lost little of their water-soluble P. High-P roots contained much more water-soluble P and lost much of it during the first two weeks. By the end of three weeks their water-soluble P content was levelling out at a value similar to that in low-P roots, suggesting a non-labile pool. The rapid loss of lipid P from low-P roots comprised more than half of their total loss, and the possible ecological significance of this is discussed. 相似文献
7.
Genotypical differences among graminaceous species in release of phytosiderophores and uptake of iron phytosiderophores 总被引:1,自引:0,他引:1
Graminaceous species can enhance iron (Fe) acquisition from sparingly soluble inorganic Fe(III) compounds by release of phytosiderophores (PS) which mobilize Fe(III) by chelation. In most graminaceous species Fe deficiency increases the rate of PS release from roots by a factor of 10–20, but in some species, for example sorghum, this increase is much less. The chemical nature of PS can differ between species and even cultivars.The various PS are similarly effective as the microbial siderophore Desferal (ferrioxamine B methane sulfonate) in mobilizing Fe(III) from a calcareous soil. Under the same conditions the synthetic chelator DTPA (diaethylenetriamine pentaacetic acid) is ineffective.The rate of Fe(III)PS uptake by roots of graminaceous species increases by a factor of about 5 under Fe deficiency. In contrast, uptake of Fe from both synthetic and microbial Fe(III) chelates is much lower and not affected by the Fe nutritional status of the plants. This indicates that in graminaceous species under Fe deficiency a specific uptake system for FePS is activated. In contrast, the specific uptake system for FePS is absent in dicots. In a given graminaceous species the uptake rates of the various FePS are similar, but vary between species by a factor of upto 3. In sorghum, despite the low rate of PS release, the rate of FePS uptake is particularly high.The results indicate that release of PS and subsequent uptake of FePS are under different genetic control. The high susceptibility of sorghum to Fe deficiency (lime-chlorosis) is most probably caused by low rates of PS release in the early seedling stage. Therefore in sorghum, and presumably other graminaceous species also, an increase in resistance to lime chlorosis could be best achieved by breeding for cultivars with high rates of PS release. In corresponding screening procedures attention should be paid to the effects of iron nutritional status and daytime on PS release as well as on rapid microbial degradation of PS. 相似文献
8.
Summary Polyclonal antibodies directed against polypeptide epitopes of conglutin , a glycosylated lectin in lupin seed, have been used to identify and quantify this protein in root extracts of germinating lupins. The highest conglutin content was found in protein extracts of root elongation zones after 5 to 7 days germination. Root conglutin showed the same subunit composition, glycosylation pattern, isoelectric point, and lectin activity as the cotyledonary one. Immunolocalization experiments on root thin sections demonstrated that conglutin is chiefly present in the intercellular spaces of the cortical parenchyma, where it forms large aggregates. Labelling of the Golgi complexes and the area between the plasmalemma and cell wall revealed the conglutin pathway from post-synthetic processing to excretion via the secretory system.Abbreviations EDTA
ethylene diamino tetraacetic acid
- IEF
isoelectric focusing
- LRW
London resin white
- NC
nitrocellulose
- PAGE
polyacrylamide gel electrophoresis
- pI
isoelectric point
- Pi
inorganic phosphate
- SDS
sodium dodecylsulphate
- TEM
transmission electron microscopy 相似文献
9.
Role of proteinaceous amino acids released in root exudates in nutrient acquisition from the rhizosphere 总被引:1,自引:1,他引:0
The role of proteinaceous amino acids in rhizosphere nutrient mobilization was assessed both experimentally and theoretically. The degree of adsorption onto the soil's solid phase was dependent on both the amino acid species and on soil properties. On addition of amino acids to both soil and freshly precipitated Fe(OH)3, no detectable mobilization of nutrients (K, Na, Ca, Mg, Cu, Mn, Zn, Fe, S, P, Si and Al) was observed, indicating a very low complexation ability of the acidic, neutral and basic amino acids. This was supported by results from a solution equilibria computer model which also predicted low levels of amino acid complexation with solutes present in the soil solution. On comparison with the Fe(OH)3 and equilibria data obtained for the organic acid, citrate, it was concluded that amino acids released into the rhizosphere have a limited role in the direct acquisition of nutrients by plants. The effectiveness of root exudates such as amino acids, phytosiderophores and organic acids in nutrient mobilization from the rhizosphere is discussed with reference to rhizosphere diffusion distances, microbial degradation, rate of complexation and the root's capacity to recapture exudate-metal complexes from the soil. 相似文献
10.
Summary The cortical cell membranes of maize and marrow roots grown at normal, or chilling, temperatures have been studied by freeze-fracture electron microscopy. Using computer-assisted methods to analyse intramembraneous particle (IMP) frequencies, diameters and distribution, no significant trends in differences between normal and chilled roots were found. While this result does not correspond with the findings from similar experiments on microorganisms, it is compatible with contemporary ideas concerning temperature-induced phase transitions in the lipids of higher plant cell membranes. The cortical cell membranes of barley roots that had been subjected to cold osmotic shock also showed no differences from untreated roots as demonstrable in freeze-fracture replicas.IMPs were found to cluster around plasmodesmata after chilling but the physiological significance of this, if any, remains to be investigated further.While these negative results only indirectly help towards understanding how cell membranes react to chilling, the techniques described open the way for more detailed analyses of IMP characteristics in plant cell membranes. 相似文献