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1.
Tetrahymena pyriformis cultures were maintained when transferred serially in solutions containing 105 to 107Klebsiella pneumoniae cells.ml?1, bacterial numbers that were observed to persist in the presence of protozoa. The number of cells of one strain of K. pneumoniae surviving predation in solution was essentially the same in the absence of an alternative prey as in the presence of a second K. pneumoniae strain. Toxins deleterious to protozoa did not appear as the animal consumed the bacteria. T. pyriformis reduced the abundance of Escherichia coli from about 108 to 106.ml?1. but the latter number persisted for 15 days; however, in solutions containing chloramphenicol, the abundance of E. coli fell to 590 cells. ml?1 in 15 days. In solutions containing the antibiotic, T. pyriformis reduced the Rhizobium sp. population from more than 106 to less than 103 cells in 10 days and K. pneumoniae from more than 108.ml?1 to zero in 18 days. An appreciable decline in abundance of these bacteria did not occur in the antibiotic-amended liquid free of protozoa. T. pyriformis did not greatly reduce Rhizobium sp. numbers when both were added to irradiated soil, but the predator caused the bacterial population to decline from 4 × 108 to fewer than 105.g?1 in 16 days in chloramphenicol-treated soil. Colpoda sp. inoculated with Rhizobium sp. into soil sterilized by autoclaving only reduced the prey abundance from 109 to 108.g?1, but the protozoan caused the bacterial population to fall to about 100.g?1 in 15 days in the presence of the antibiotic. The population of Rhizobium sp. added to nonsterile soil dropped from in excess of 108 to 6 × 106.g?1 in 29 days. but it declined to 550. g?1 in the same period when chloramphenicol was also introduced. It is concluded that the ability of these bacteria to maintain themselves in solution and in soil is governed by their capacity to reproduce and replace the cells consumed by predation. 相似文献
2.
《Soil biology & biochemistry》1987,19(3):247-252
Chickpea Rhizobium populations in soil samples from research stations and farmers' fields in different geographic regions of India ranged from <10 to > 104 rhizobia g−1 soil. Fields on research stations with a known history of chickpea cropping had more rhizobia (calc. 103 to 105 rhizobia g1̄ soil) than the majority of farmers' fields (calc. < 10 to 103 rhizobia g−1 soil). In the absence of chickpea in the cropping pattern, soils generally had < 102 rhizobia g1̄ and crops in such fields nodulated poorly. However, poor nodulation was also observed when populations of rhizobia were high, indicating that other factors were also important for nodulation. There was no obvious consistent correlation of Rhizobium population with pH, electrical conductivity and nitrate-nitrogen status of the soil.Rhizobium populations declined with soil depth and were highest (about 104 rhizobia g−1 soil) in the top 30 cm of the profile and lowest, but still present (calc. 103–103 rhizobia g'1 soil), at 90–120 cm—a depth where no nodules are found. Populations fluctuated most in the top 5 cm, being reduced during periods of high soil temperature in summer and recovering after rains. Rhizobium populations were at a maximum after chickpea but survived well under pigeonpea, groundnut and maize. When rice followed an inoculated chickpea crop, there was about a 100-fold decrease in the Rhizobium population. 相似文献
3.
A salinity-tolerant strains of Rhizohium able to grow and fix nitrogen in symbiosis with lentil (Lens esculenta) in saline soil was derived frorn effective Rhizobium strain RL 5. A forced mutation with the mutagen nitrosoguanidine resulted in the isolation of five different mutant strains. The salinity tolerance, streptomycin resistance, growth, nodulation behaviour and relative efficiency of symbiotic N2-fixation of these strains were studied. Among the five mutants and parent, LM 4 and LM 1 successfully tolerated 200 μ g ml?1 streptomycin and 1.5%NaCl. These two mutants also significantly increased number and dry weight of nodules per plant, dry matter yield of the crop and N2-fixation. Between the two, LM 4 seemed generally the better. 相似文献
4.
Isolates of Rhizobium phaseoli resistant to spergon (2,3,5,6-tetrachloro-l,4-benzoquinone), Rhizobium meliloti resistant to thiram (tetramethylthiuram disulfide) and of a cowpea Rhizobium resistant to phygon (2,3-dichloro-l,4-naphthoquinone) were obtained by culturing the bacteria in media with increasing concentrations of these fungicides. The cultures grew in media with 200 μg thiram ml?1, 150 μg spergon ml?1 or 400 μg phygon ml?1. Spergon-tolerant R. phaseoli was sensitive to thiram, and thiram-tolerant R. meliloti was sensitive to spergon. The dry weights of beans, alfalfa and cowpeas and the amount of N2 fixed were the same for plants inoculated with the fungicide-resistant or the sensitive parent rhizobia. However, when the three parent Rhizobium strains were applied to seeds treated with the three fungicides, the plants that developed were stunted, chlorotic, grew poorly and fixed little or no N2. By contrast, beans, alfalfa or cowpea plants derived from seeds coated with spergon, thiram or phygon and inoculated with the resistant rhizobia grew as well and fixed as much N2 as legumes derived from seeds not treated with the pesticides. These findings provide the basis for a simple method for simultaneously allowing for N2 fixation and seed protection of legumes. 相似文献
5.
The average number of survivors of fast-growing medic rhizobia (3 strains), fast-growing Rhizobium leguminosarum types (6 strains) and slow-growing species (9 strains) following desiccation of sandy soil inoculated with 106 bacteria·g?1 soil was 727, 795 and 15,682 bacteria·g?1 soil, respectively. Survival in desiccated sandy soil was not influenced by the degree of extracellular polysaccharide production in strains of R. trifolii, nor was it influenced by growth of R. meliloti and slow-growing species in media of low water activity before desiccation in sandy soil.A progressive increase in numbers of fast-growing bacteria surviving desiccation was observed in sandy soil amended with increasing concentrations of powdered montmorillonite, but not with mont-morillonite added as a suspension to the soil. The clay had either a detrimental effect or no effect on the survival of the slow-growing rhizobia. Maltose, sucrose and polyvinylpyrrolidonc provided a greater degree of protection to both fast- and slow-growing rhizobia than was obtained with montmorillonite. The effect of polyethylene glycol 6000 was similar to the effect of montmorillonite, as the polymer only protected the fast-growing rhizobia and not the slow-growing species. 相似文献
6.
The usage of sewage sludge on agricultural lands is an effective and inexpensive practice that provides nutrients for crops. A successful legume crop also depends on the survival of Rhizobium in the soil environment. The number of R. japonicum (USDA 110) in treatment groups containing various soil-to-sludge ratios (control, 13:1, 9:1 and 5:1) during incubation for 1, 21 and 42 days was investigated. The control group contained soil without sludge. Mecklenburg clay and Enon sandy loam soils (both are fine, mixed, thermic, ultic Hapludalfs) were used. All treatments were adjusted to pH 6.7 and brought to 75% of field capacity with 1 ml inoculum (9 × 108 cells ml? 1) and distilled water. Samples were incubated at 25 C and monitored periodically for the number of surviving R. japonicum (USDA 110) organism by the plant infcction-MPN method. Strains were identified by gel-immunodiffusion. Recovery of rhizobia from both soils was < 1% in all treatment groups after 42 days. However, for control, 13:1, 9:1 and 5:1 groups, the percentage recovery was higher in Enon sandy loams (7.9, 2.3, 2.3 and 2.3%, respectively) at 21 days. Recovery of rhizobia in the 5:1 group from both soils was 7.9% after 1 day, whereas control values were 92%. A decline in rhizobial populations in higher sludge soils may be due to the heavy metals present and available during mineralization of sludge in soils. However, the number of R. japonicum that survived to 21 days was 1.7 × 105g?1 and 1.7 x 106g?1 for Mecklenburg clay and Enon sandy loam soils with highest sludge, respectively. 相似文献
7.
Sudan is the fourth largest exporter of groundnuts in the world, yet little is known concerning the plant-rhizobial symbiosis. A study was made on the abundance of groundnut-nodulating rhizobia in the soils of Sudan as related to soil properties and the duration since groundnuts were last planted. Also, physiological, serological and nitrogen-fixing characteristics of Sudanese rhizobia are reported. All but one of 32 sites contained more than 300 rhizobia g?1 soil capable of forming nodules on siratro (Macroptilium atropurpureum). Several of these soils had never been planted to groundnut. A correlation matrix indicated no relationship was present between soil rhizobial populations and any of the measured soil properties, or between soil rhizobial populations and the time since groundnuts were last planted in the rotation. Individual isolates of Rhizobium from six legumes: groundnut (Arachis hypogaea), mung bean (Vigna radiata), lubia (Dolichos lablab), cowpea (Vigna unguiculata), pigeonpea (Cajanus cajan) and bambara groundnut (Voandzeia subterranea) were obtained from four locations in Sudan. All isolates were able to nodulate each of the six legumes when grown in sterile vermiculite. The isolates grew in 0.1% NaCl-amended media, but growth was variable in 2.0% amended media. Most isolates grew after exposure to moist heat for 15 min at 50°C. Optimum pH for growth was, in general, between pH 6 and 8. Agglutination reactions indicated isolates from groundnuts, as well as isolates from other legumes, belonged to several serological groupings. Some isolates formed a large number of nodules on a Sudanese groundnut cultivar, whereas other isolates formed only few nodules. 相似文献
8.
Field pea (Pisum sativum L.) is widely grown in South Australia (SA), often without inoculation with commercial rhizobia. To establish if symbiotic factors are limiting the growth of field pea we examined the size, symbiotic effectiveness and diversity of populations of field pea rhizobia (Rhizobium leguminosarum bv. viciae) that have become naturalised in South Australian soils and nodulate many pea crops. Most probable number plant infection tests on 33 soils showed that R. l. bv. viciae populations ranged from undetectable (six soils) to 32×103 rhizobia g−1 of dry soil. Twenty-four of the 33 soils contained more than 100 rhizobia g−1 soil. Three of the six soils in which no R. l. bv. viciae were detected had not grown a host legume (field pea, faba bean, vetch or lentil). For soils that had grown a host legume, there was no correlation between the size of R. l. bv. viciae populations and either the time since a host legume had been grown or any measured soil factor (pH, inorganic N and organic C). In glasshouse experiments, inoculation of the field pea cultivar Parafield with the commercial Rhizobium strain SU303 resulted in a highly effective symbiosis. The SU303 treatment produced as much shoot dry weight as the mineral N treatment and more than 2.9 times the shoot dry weight of the uninoculated treatment. Twenty-two of the 33 naturalised populations of rhizobia (applied to pea plants as soil suspensions) produced prompt and abundant nodulation. These symbioses were generally effective at N2 fixation, with shoot dry weight ranging from 98% (soil 21) down to 61% (soil 30) of the SU303 treatment, the least effective population of rhizobia still producing nearly double the growth of the uninoculated treatment. Low shoot dry weights resulting from most of the remaining soil treatments were associated with delayed or erratic nodulation caused by low numbers of rhizobia. Random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) fingerprinting of 70 rhizobial isolates recovered from five of the 33 soils (14 isolates from each soil) showed that naturalised populations were composed of multiple (5-9) strain types. There was little evidence of strain dominance, with a single strain type occupying more than 30% of trap host nodules in only two of the five populations. Cluster analysis of RAPD PCR banding patterns showed that strain types in naturalised populations were not closely related to the current commercial inoculant strain for field pea (SU303, ≥75% dissimilarity), six previous field pea inoculant strains (≥55% dissimilarity) or a former commercial inoculant strain for faba bean (WSM1274, ≥66% dissimilarity). Two of the most closely related strain types (≤15% dissimilarity) were found at widely separate locations in SA and may have potential as commercial inoculant strains. Given the size and diversity of the naturalised pea rhizobia populations in SA soils and their relative effectiveness, it is unlikely that inoculation with a commercial strain of rhizobia will improve N2 fixation in field pea crops, unless the number of rhizobia in the soil is very low or absent (e.g. where a legume host has not been previously grown and for three soils from western Eyre Peninsula). The general effectiveness of the pea rhizobia populations also indicates that reduced N2 fixation is unlikely to be the major cause of the declining field pea yields observed in recent times. 相似文献
9.
Soils from a pastoral farm that had received large amounts of heavy metal contaminated sewage sludge 6-10 years previously were investigated to determine the impact of heavy metals on Rhizobium. The 8 ha application area was originally divided into five different-sized blocks (blocks 1-5), which received sludge at different times between 1991 and 1994. The response of a lux biosensor based on R. leguminosarum bv. trifolii (Rhizotox-C), was compared with more traditional techniques for measuring the presence of effective strains of Rhizobium (MPN) and nitrogen fixation (δ15N natural abundance). Although population size (MPNs), nitrogen fixation and biosensor response varied between treatment blocks, linear regression analysis determined that this block effect could not be directly linked to soil heavy metal concentrations, but was probably due to biological, physical, chemical and environmental compounding factors at the site. In this type of uncontrolled field application, the lux bioassay may provide the most useful information as it measures toxicity to any microorganism exposed to the soil solution, for example, the free living rhizobia. 相似文献
10.
Different strains of Rhizobium (isolates from Glycine max, Phaseolus mungo and Vigna unguiculuta) adapted to tetramethylthiuram disulfide (thiram, TMTD) 30 μg ml?1). The number of transfers (5–19) and days of incubation (20–95) during which different strains of Rhizobium developed resistance varied. The results of reversion experiments show that the developed resistance was stable. The rates of growth was faster in resistant strains but their final cell numbers were less than those of sensitive strains. Dehydrogenase activity decreased with the development of resistance except in strain D-338. With the development of resistance total lipids and phospholipids increased, glycolipids decreased and neutral lipids varied. The presence of compounds stimulating lipid production in cells increased the total lipids of the strains and their resistance to TMTD. 相似文献
11.
The acid tolerance of Sinorhizobium meliloti in culture media and in soils is considered a useful criteria to select for strains with improved survival in agricultural acidic soils. Using a glass tube system with gamma-irradiated soil at different pH values, we analysed the survival of two different alfalfa-nodulating rhizobia: S. meliloti (pHlimit for growth 5.6–6.0) and the acid-tolerant Rhizobium sp. LPU83, closely related to the strain Rhizobium sp. Or191 (pHlimit for growth below 5.0). Although the acid-tolerant rhizobia showed a slightly better survival during the first months in acid soil (pH=5.6), none of the strains could be detected 2 months after inoculation (bacterial counts were below 103 colony-forming units (cfu)/30 g of soil). The inclusion of two alfalfa plants/glass tube with soil, however, supported the persistence of both types of rhizobia at pH 5.6 for over 2 months with counts higher than 9×106 cfu/30 g of soil. Remarkably, in the presence of alfalfa the cell densities reached by S. meliloti were higher than those reached by strain LPU83, which started to decline 1 week after inoculation. Although more acid-sensitive in the culture medium than the Or191-like rhizobia, in the presence of the host plant the S. meliloti strains showed to be better adapted to the free-living condition, irrespective of the pH of the soil. 相似文献
12.
An examination of 85 strains of bacteria from five species of rhizobia (Rhizobium sp., R. japonicum, R. lupini, R. meliloti and R. trifolii), using a new semi-quantitative assay procedure, disclosed wide diversity among the strains in their requirement for, and response to, vitamins, carbon sources, and nitrogen sources. Approximately half of the strains in the first four species grew as well without vitamins as they did when supplied with a vitamin mixture or with yeast extract, but the other strains showed considerable variation in their requirements. Some strains were inhibited by yeast extract, or showed best growth in basic media supplemented with only one vitamin. The strains within the species differed widely in their utilization of gluconate, mannitol and arabinose as C-sources; there was less diversity in their use of glutamine, histidine, NH4+-N and NO3?-N as N-sources. The significance of these observations in the culture of rhizobia in the laboratory, in their ecological adaptation to particular environments, and in their ability to form an effective symbiosis with particular host legumes, is discussed. 相似文献
13.
Three fast-growing rhizobia (Rhizobium meliloti isolated from Medicago saliva, R. trifolii from Trifolium subterraneum, and Rhizohium sp. from Leucaena leucocephala) and three slow-growing rhizobia R. japonicum from Glycine max, Rhizobium spp from Centrosema pubescens and Crotolaria anagyroides) were grown in defined media. The mean generation times of the fast-growing and slowgrowing strains were 3.8 h and 8.6 h respectively. Slow-growing organisms raised the initial pH of the defined medium while the fast-growing organisms lowered it. Rates of oxygen consumption tended to be higher in the slow-growing organisms.UMKL 19 (isolated from L. leucocephala) possessed all the normal reactions of fast-growing rhizobia but had a single sub-polar flagellum, similar to the three slow-growing strains studied.Certain combinations of amino acids and sugars (e.g. glutamine and galactose) induced an acidic reaction in the fast-growing organisms while the slow-growing ones changed the media to alkaline. Fast-growing organisms utilized more galactose for growth compared to slow-growing ones. Both types of organisms synthesized and released a wide range of amino acids into the medium.We suggest that pH changes produced by rhizobia growing on yeast-extract mannitol media are caused by the preferential utilization of sugars by fast-growing organisms and nitrogenous compounds by slow-growing ones. 相似文献
14.
192 sites covering the main soil types in Northern Ireland were analysed for numbers and effectiveness of clover and Lotus rhizobia, and chemical properties. Peat sites were generally highly acid (pH <5.5) and mineral sites near neutral (pH 5.5–7.8). Clover rhizobia were generally absent from peat sites and present in mineral sites as large populations (> 106 g?1 dry soil). 79% of isolates were effective on T. repens var. Grasslands Huia. Lotus rhizobia were generally absent from peat sites, less often present than clover rhizobia in mineral sites, and as smaller populations. They were mainly effective on L. pedunculatus var. G4705 and were all of the slow-growing type belonging to the genus Bradyrhizobium. Numbers of clover rhizobia were significantly correlated with soil pH, exchangeable Ca, base saturation and Al saturation, but effectiveness of clover rhizobia and numbers of Lotus rhizobia were not correlated with any soil chemical property. 相似文献
15.
L.E. Casida 《Soil biology & biochemistry》1983,15(5):551-555
Myxobacter strain 8 is one component of a sequence of three predatory bacteria that develop in soil when Micrococcus luteus host cells are added to the soil. The survival of strain 8 in the presence and absence of added host cells in natural soil not allowed to dry out was examined. Strain 8 vegetative cells died relatively rapidly in unamended soil. Death was faster and occurred to a greater extent in acidic than in neutral pH soil. However, in both cases death was accompanied by formation of sonication-resistant myxospores so that they comprised the ultimate population. These myxospores survived for prolonged periods in both acidic and neutral pH soils.Vegetative cells added in high numbers to soil did not multiply under any of the conditions tested. They did multiply, however, when they were added in low numbers to soil (including acidic soil) receiving sequential (additive) amendments of heart infusion broth or living M. luteus cells. This multiplication produced strain 8 cell numbers approximating those in the above experiments receiving high strain 8 cell number inoculations. Possibly, this represents a maximum vegetative cell number for soil.Germination of the myxospores in soil, followed by growth, seemed to require an approximately neutral pH and the presence of a proper host organism. Germination occurred with M. luteus as host, but not with Escherichia coli. A delayed germination occurred when sequential amendments of heart infusion broth, instead of M. luteus host cells, were made, but this could reflect a growth response by some indigenous components of the soil microflora that then served as host cells for germination. 相似文献
16.
The behaviour of Rhizobium strains introduced separately into soil from a contaminated site with high concentrations of heavy metals (mainly Zn and Hg), and the role of plasmids in the ecology of these rhizobia strains were studied. Six Rhizobium leguminosarum biovar trifolii strains, from different sources and with different plasmid contents, were selected. Two of them were isolated from nodules of subterranean clover plants (Trifolium subterraneum) grown in the contaminated soil and four were from an uncontaminated soil. After inoculation with approximately 107 cells g−1 soil, of each strain, survival and plasmid stability were assessed over a period of 12-18 months. Differences in survival of Rhizobium strains were only detected more than 12 months after inoculation. After 18 months it was clear that survival in contaminated soil was greatest in the two strains originally isolated from that contaminated soil, and also by two of the strains originally isolated from uncontaminated soil. The latter two strains were also the only ones that showed changes in their plasmid profiles. The remaining isolates had the lowest populations, and their plasmid profiles were unchanged and similar to the parent strains. 相似文献
17.
《Applied soil ecology》2003,22(3):211-223
A legume introduced into a new area will only form nodules and fix nitrogen if compatible rhizobia are present in the soil. Using 25 (60 in the case of Sesbania sesban) soils sampled from tropical areas of Africa, Asia and Latin America, we examined the nodulation of four agroforestry tree species (Calliandra calothyrsus, Gliricidia sepium, Leucaena leucocephala and S. sesban), their symbiotic interactions with the native rhizobial populations, and some of the ecological indicators of rhizobial population dynamics. Rhizobial population sizes estimated by the legume species ranged from undetectable numbers to 3.16×104 cells per g of soil depending on the trap host species. Although C. calothyrsus had the highest nodulation rate in the soils used, inoculation tests showed L. leucocephala to be the most promiscuous species while G. sepium had the most effective symbiosis. S. sesban was the most specific for both nodulation and symbiotic effectiveness. Symbiotic effectiveness did not bear any close relationship with specific soil parameters, but rhizobial numbers were highly correlated with soil acidity, particle size and exchangeable bases. Soil acidity was also the main factor that was highly correlated with genetic diversity among the rhizobial populations. 相似文献
18.
E.B. Roslycky 《Soil biology & biochemistry》1982,14(2):87-92
Limited information on the effect of glyphosate (N-phosphonomethylglycine) on soil microorganisms justified an inquiry into the response of soil actinomycetes, bacteria and fungi in terms of their respiration, and sensitivity of isolates. Low concentrations of glyphosate had little effect on total populations of these organisms during the 214-day experiment, while high concentrations initially increased actinomycete and bacterial numbers by 2 and 1 logs, respectively. The stimulation was followed by a decline and fluctuation showing a gradual increase in numbers. The respiration rates of the soil microbiota in soil suspensions, showed some irregular stimulation and retardation with up to 10 μg glyphosate ml?1. In contrast high doses suppressed O2 uptake by the microbiota. Fungi were the least affected. Pronounced inhibition of actinomycete and bacterial respiration was in agreement with the results from isolate replication. The results indicated both stimulation and inhibition of O2 uptake by some organisms within these groups. In contrast to some reports of limited, short-term inquiries these results showed considerable effects of glyphosate on soil microorganisms. 相似文献
19.
Displacement of native rhizobia nodulating chickpea (Cicer arietinum L.) by an inoculant strain through soil solarization 总被引：1，自引：0，他引：1
Summary Soil solarization greatly reduced the native chickpea Rhizobium population. With inoculation, it was possible to increase the population of the Rhizobium in solarized plots. In the 1st year, 47% nodulation was obtained with chickpea inoculant strain IC 59 when introduced with a cereal crop 2 weeks after the soil solarization and having a native Rhizobium count of <10 g-1 soil, and only 13% when introduced 16 weeks after solarization at the time the chickpeas were sown, with 2.0×102 native rhizobia g-1 soil. In the non-solarized plots inoculated with 5.6×103 native rhizobia g-1 soil, only 6% nodulation was obtained with the inoculant. In the succeeding year, non-inoculated chickpea was grown on the same plots without any solarization or Rhizobium inoculation. The treatment that showed good establishment of the inoculant strain in year 1 formed 68% inoculant nodules. Other treatments indicated a further reduction in inoculant success, from 1%–13% to 1%–9%. Soil solarization thus allowed an inoculant strain to successfully displace the high native population in the field and can serve as a research tool to compare strains in the field, irrespective of competitive ability. In year 1, Rhizobium inoculation of chickpea gave increased nodulation and increased plant growth 20 and 51 days after sowing, and increased dry matter, grain yield, and grain protein yield at maturity. These beneficial effects of inoculation on plant growth and yield were not measured in the 2nd year.Submitted as Journal Article No. JA 945 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru, Andhra Pradesh 502 324, India 相似文献
20.
We compared the uptake of nitrogen, potassium and phosphorus (as well as 14C-labelled mannitol, 3H-labelled glutamate, and 32P-labelled phosphate) in three fast- and three slow-growing rhizobia. The fast-growing strains used were Rhizobium meliloti (isolated from Medicago sativa), R. trifolii (from Trifolium subterraneum), and Rhizobium spp from Leucaena leucocephala, while the slow-growing strains were R. japonicum (Glycine max), and two Rhizobium spp (from Centrosema pubescens and Crotolaria anagyroides). Slow-growing organisms preferentially utilized glutamate in the medium. Both fast- and slow-growing strains took up more NH+4-N than NO?3-N on a per cell basis. In the presence of mannitol, fast-growing strains can cause either acid or alkaline reactions, an effect that is dependent only on the N-source (NH+4 or NO?3). Uptake preferences of the fast-growing Leucaena isolate (UMKL 19) resembled those of the slow-growing rhizobia, further strengthening the argument that this organism (and others like it) may be intermediate between the normal fast- and slow-growing groups. Generally, the efficiency of uptake of N (either as NH+4 or NO?3), P, and therefore K, was greater in the fast-growing organisms. 相似文献