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1.
Summary There were significant differences among pigeonpea [Cajanus cajan (L.) Millsp] Rhizobium sp. strains (IC 3506, IC 3484, IC 3195, and IC 3087) in their ability to nodulate and fix N2 under saline conditions. Pigeonpea plants inoculated with IC 3087 and IC 3506 were less affected in growth by salinity levels of 6 and 8 dS m-1 than plants inoculated with the other strains. For IC 3506, IC 3484, and IC 3195, there was a decrease in the number of nodules with increasing salinity, while the average nodule dry weight and the specific nitrogenase activity remained unaffected. However, in IC 3087, the number of nodules increased slightly with increasing salinity. Leaf-P concentrations increased with salinity in the inoculated plants irrespective of the Rhizobium sp. strain, and leaf-N concentrations decreased with increasing salinity in IC 3484 and IC 3195 only. Shoot-Na and-Cl levels were further increased in these salt-sensitive strains only at 8 dS m-1. Therefore there may be scope for selecting pigeonpea Rhizobium sp. symbioses better adapted to saline conditions. The Rhizobium sp. strains best able to form effective symbioses at high salinity levels are not necessarily derived from saline soils.Submitted as JA No. 919 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)  相似文献   

2.
The rose of an isolate of the arbuscular mycorrhizal (AM) fungusGlomus mosseae in the protection ofMedicago sativa (+Rhizobium meliloti) against salt stress induced by the addition of increasing levels of soluble salts was studied. The interactions between soluble P in soil (four levels), mycorrhizal inoculum and degree of salinity in relation to plant growth, nutrition and infective parameters were evaluated. Salt stress was induced by sequential irrigation with saline water having four concentrations of three salts (NaCl, CaCl2, and MgCl2).15N-labelled ammonium sulphate was added to provide a quantitative estimate of N2 fixation under moderate to high salinity levels. N and P concentration and nodule formation increased with the amount of plant-available P or mycorrhizal inoculum in the soil and generally declined as the salinity in the solution culture increased from a moderate to a high level. The mycorrhizal inoculation protected the plants from salt stress more efficiently than any amount of plant-available P in soil, particularly at the highest salinity level applied (43.5 dS m–1). Mycorrhizal inoculation matched the effect on dry matter and nutrition of the addition in the soil of 150 mg P kg–1. Nevertheless the highest saline solution assayed (43.5 dS m–1) affected more severely plants supplemented with phosphorus than those with the addition of mycorrhizal inoculum. Such a saline-depressing effect was 1.5 (biomass), 1.4 (N) and 1.5 (P) times higher in plants supplied with soluble phosphate than with AM inoculum. Mechanisms beyond those mediated by P must be involved in the AM-protectioe effect against salinity. The15N methodology used allowed the determination of N2 fixation as influenced by different P applications compared to mycorrhizal inoculation. A lack of correlation between nodule formation and function (N2 fixation) was evidenced in mycorrhizal-inoculated plants. In spite of the reduced activity per nodule in mycorrhizal-inoculated In spite of the reduced activity per nodule in mycorrhizal-inoculated plants, the N contents determined indicated the highest acquisition of N occurred in plants with the symbiotic status. Moreover, N and P uptake increased while Ca and Mg decreased in AM-inoculated plants. Thus P/Ca ratios and cation/anion balance in general were altered in mycorrhizal treatments. This study therefore confirms previous findings that AM-colonized plants have optional and alternative mechanisms available to satisfy their nutritive requirements and to maintain their physiological status in stress situations and in disturbed ecosystems.  相似文献   

3.
Summary Physiological and symbiotic characteristics were identified in Rhizobium fredii isolated from subtropical-tropical soils. The generation times of R. fredii Taiwan isolated-SB 357 and -SB 682 were 1.7 and 2.5 h, respectively. These strains were associated with acid production in yeast-extract mannitol medium. They were able to use hexoses, pentose, sucrose, trehalose and raffinose. Strain SB 357 can resist a high concentration of kanamycin (100 g ml–1 and penicillin (400 g ml–1). It can tolerate up to 2.34% NaCl and 1031.3 mosmol kg–1 (23.4 bars). The growth rate of R. fredii SB 357 under the concentration of approximately 450 mosmol kg–1 (10.2 bars) was not affected by salinity, but responded to osmotic pressure. Both strains (SB 357 and SB 682) isolated from subtropical-tropical soils were able to form an effective N2-fixing symbiosis with the US soybean cv Clark lanceolate leaflet.  相似文献   

4.
Summary The Rhizobium-legume symbiosis in arid ecosystems is particularly important for locations where the area of saline soils is increasing and becoming a threat to plant productivity. Legumes, which are usually present in arid ecosystems, may be adapted to fix more N2 under saline conditions than legumes grown in other habitats.Legumes are known to be either sensitive or moderately resistant to salinity. The salt sensitivity can be attributed to toxic ion accumulations in different plant tissues, which disturb some enzyme activities.Among the basic selection criteria for salt-tolerant legumes and rhizobia are genetic variability within species with respect to salt tolerance, correlation between accumulations of organic solutes (e. g., glycine betaine, proline betaine, and proline) and salt tolerance, and good relationships between ion distribution and compartmentation, and structural adaptations in the legumes.Salt stress reduces the nodulation of legumes by inhibiting the very early symbiotic events. Levels of salinity that inhibit the symbiosis between legumes and rhizobia are different from those that inhibit the growth of the individual symbionts. The poor symbiotic performance of some legumes under saline conditions is not due to salt limitations on the growth of rhizobia.Prerequisites for a successful Rhizobium-legume symbiosis in saline environments include rhizobial colonization and invasion of the rhizosphere, root-hair infection, and the formation of effective salt-tolerant nodules.The possibility of exploring the Rhizobium-legume symbiosis to improve the productivity of saline soils is reviewed in this paper.  相似文献   

5.
Summary Chickpea cultivars (Cicer arietinum L.) and their symbiosis with specific strains of Rhizobium spp. were examined under salt stress. The growth of rhizobia declined with NaCl concentrations increasing from 0.01 to 2% (w : v). Two Rhizobium spp. strains (F-75 and KG 31) tolerated 1.5% NaCl. Of the 10 chickpea cultivars examined, only three (Pusa 312, Pusa 212, and Pusa 240) germinated at 1.5% NaCl. The chickpea — Rhizobium spp. symbiosis was examined in the field, with soil varying in salinity from electrical conductivity (EC) 4.5 to EC 5.2 dSm-1, to identify combinations giving satisfactory yields. Significant interactions between strains and cultivars caused differential yields of nodules, dry matter, and grain. Four chickpea — Rhizobium spp. combinations, Pusa 240 and F-75 (660 kg ha-1), Pusa 240 and IC 76 (440 kg ha-1), Pusa 240 and KG 31 (390 kg ha-1), and Pusa 312 and KG 31 (380 kg ha-1), produced significantly higher grain yields in saline soil.  相似文献   

6.
Summary We studied the effect of three successive cuttings on N uptake and fixation and N distribution in Leucaena leucocephala. Two isolines, uninoculated or inoculated with three different Rhizobium strains, were grown for 36 weeks and cut every 12 weeks. The soil was labelled with 50 ppm KNO3 enriched with 10 atom % 15N excess soon after the first cutting. Except for the atom % 15N excess in branches of K28 at the second cutting, both the L. leucocephala isolines showed similar patterns of total N, fixed N2, and N from fertilizer distribution in different parts of the plant at each cutting. The Rhizobium strain did not influence the partitioning of 15N among the different plant parts. Significant differences in 15N enrichment occurred in different parts. Live nodules of both isolines showed the lowest atom % 15N excess values (0.087), followed by leaves (0.492), branches (0.552), stems (0.591), and roots (0.857). The roots contained about 60% of the total plant N and about 70% of the total N derived from fertilizer over the successive cuttings. The total N2 fixed in the roots was about 60% of that fixed in the whole plant, while the shoots contained only 20% of the fixed N2. We conclude that N reserves in roots and nodules constitute another N source that must be taken into account when estimating fixed N2 or the N balance after pruning or cutting plants. 15N enrichment declined up to about fivefold in the reference and the N2-fixing plants over 24 weeks following the 15N application. The proportion and the amounts of N derived from fertilizer decreased, while the amount derived from N2 fixation increased with time although its proportion remained constant.  相似文献   

7.
Summary Fifty-six isolates of Rhizobium and Bradyrhizobium spp. (Cajanus) were studied for their plasmid profile and N2-fixation efficacy. One to three plasmids were reproducibly detected in all the Rhizobium spp. strains but no plasmid was detected in the Bradyrhizobium spp. strains. Rhizobium sp. strain P-1 was mutagenized by Tn5 and three nod– and six nod+fix– were screened for symbiotic parameters. Neomycin-sensitive mutants were isolated by elevated temperatrue (40°C) from tranconjugants carrying Tn5 insertions. The high temperature cured these mutants from the single large plasmid present in the parent strain P-1. All these cured mutants were nod–, indicating that the genes for nodulation were present on this plasmid, which is readily cured at a high temperature (40°C). The high temperature in the semi-arid zones of Haryana could be responsible for the low nodulation of pigeonpea because the plasmid carrying the nodulation genes is cured at 40°–45°C giving rise to non-nodulating mutants.  相似文献   

8.
Summary N accumulation, nodulation, and acetylene reduction activity were measured at frequent intervals during the growth of two chickpea genotypes, and N2 fixation was estimated by an isotope-dilution method, using safflower as a non-N2-fixing reference. Safflower was more efficient at N uptake than both the chickpea genotypes for at least the first 50 days and thus could not be used as an accurate reference control. We recommend that further work should employ non-nodulatiog genotypes of chickpea as reference plants and use slow-release forms of 15N fertilizer. Direct genotype comparison by isotope dilution estimated that genotype K 850 fixed 16–18 kg ha–1 more N than G 130, and this difference was supported by the greater nodule mass and acetylene reduction activity in the K 850 cultivar. Inoculation with an ineffective chickpea Rhizobium sp. led to 69% nodulation on cultivar K 850 but only 33% on G 130. While nodule weight, N uptake, and acetylene reduction activity decreased with inoculation in K 850, the isotope dilutions were similar for both inoculation treatments. The lack of a significant effect on N2 fixation was ascribed to the partial success of inoculant establishment.Published as Journal Article No. JA 692 of the International Crops Research Institute for the Semi Arid Tropics, Patancheru, A.P. 502324, India  相似文献   

9.
ABSTRACT

Common bean (Phaseolus vulgaris L.) has been shown to be a poor di-nitrogen (N2) fixer and nitrogen (N) fertilizers are usually recommended in bean production. Recent research results suggest that the success of the bean/Rhizobium symbiosis may depend, in part, on the specific bean genotype. Twelve dry bean genotypes differing in growth habit, commercial class, and maturity were evaluated for N2 fixation in field experiments. Response to inoculant application was highly influenced by environmental conditions. Genotypes differed in nodule dry mass, seed yield, seed N yield, and in amount of N2 fixed. Growth habit alone was not adequate in classifying bean genotypes for N2 fixation. The actual amount of N2 fixed was low ranging from 16 kg ha?1 to 27 kg ha?1, suggesting that the symbiotic process alone may not provide adequate N for optimum seed yield in dry environments.  相似文献   

10.
Depth of root symbiont occurrence in soil   总被引：1，自引：0，他引：1  
Summary The woody legume Prosopis glandulosa (mesquite) growing in the California Sonoran Desert develops functional root symbiotic associations (N2-fixing nodules, vesicular-arbuscular mycorrhizal fungi) at depths greater than 4 m in moist soil above a seasonally stable water table. Population densities of symbiotic microorganisms are substantially greater at depth than near the surface. Inferences of plant symbiotic dependence based upon examination of surface roots and soil may be incorrect since deep roots can support the symbioses which are critical for plants utilizing deep water.  相似文献   

11.
A bradyrhizobial-fungal biofilm (i.e. Bradyrhizobium elkanii SEMIA 5019-Penicillium spp.) developed in vitro was assayed for its nitrogenase activity and was evaluated for N2-fixing symbiosis with soybean under greenhouse conditions. The biofilm showed nitrogenase activity, but the bradyrhizobial strain alone did not. Shoot and root growth, nodulation and N accumulation of soybean increased significantly with an inoculum developed from the biofilm. This study concludes that such biofilmed inoculants can improve N2-fixing symbiosis in legumes, and can also directly contribute to soil N fertility in the long term. Further studies should be conducted to investigate the performance of these inoculants under field conditions.  相似文献   

12.
Summary Variation in nodulation and N2 fixation by the Gliricidia sepium/Rhizobium spp. symbiosis was studied in two greenhouse experiments. The first included 25 provenances of G. sepium inoculated with a mixture of three strains of Rhizobium spp. N2 fixation was measured using the 15N isotope dilution method 12 weeks after planting. On average, G. sepium derived 45% of its total N from atmospheric N2. Significant differences in fixation were observed between provenances. The percentage of N derived from atmospheric N2 ranged from 26 to 68% (equivalent to 18–62 mg N plant-1) and was correlated with total N in the plant (r=0.70; P=0.05). The second experiment included six strains of Rhizobium spp. and two methods of inoculation and the plants were harvested 14,35 and 53 weeks after planting. In the first harvest significant differences were found between the number of nodules and the percentage and amount of N2 fixed. There was also a significant correlation between the number of nodules and the amount of N2 fixed (r=0.92; P=0.05). In the final harvest no correlation was observed, although there were significant differences between the number of nodules and the percentage of N derived from the atmosphere. The amount of N2 fixed increased with time (from an average of 27% at the first harvest to 58% at the final harvest) and was influenced by the Rhizobium spp. strain and the method of inoculation. It ranged from 36% for Rhizobium sp. strain SP 14 to 71% for Rhizobium SP 44 at the last harvest. Values for the percentage of atmosphere derived N2 obtained by soil inoculation were slightly higher than those obtained by seed inoculation.  相似文献   

13.
Effects of phosphorus (P) deficiency on nodulation were examined in soybean grown in nutrient solution for 7 weeks. Increasing P supply increased shoot growth of nitrogen (N2)-fixing plants from week 5 and that of nitrate-fed plant from week 4 after treatment. Nitrogen (N2)-fixing plants had a greater P requirement for maximum growth at week 5. Increasing P supply from 1 to 16 μ M increased N concentration in N2-fixing plants at week 4 but did not affect it from week 5. By contrast, P deficiency increased N concentration in nitrate-fed plants. Increasing P supply improved nodule formation from week 3. Nodule mass was affected more by P supply than nodule number, which, in turn, was affected more than plant growth. However, P supply did not decrease nodule specific N2 fixation from week 5. The results suggest that P deficiency impaired symbiotic N2 fixation through delaying onset of nodule function and decreasing nodule development.  相似文献   

14.
A laboratory incubation experiment was conducted to evaluate the effect of magnesium chloride–induced salinity on carbon dioxide (CO2) evolution and nitrogen (N) mineralization in a silty loam nonsaline alkaline soil. Magnesium chloride (MgCl2) salinity was induced at 0, 4, 8, 12, 16, 20, 30, and 40.0 dS m?1 and measured CO2 evolution and N mineralization during 30 days of incubation. Both CO2 evolution and N mineralization decreased significantly with increasing salinity. The cumulative CO2 evolution decreased from 235 mg kg?1 soil at electrical conductivity (EC) 0.65 dS m?1 to 11.9 mg kg?1 soil at 40 dS m?1 during 30 days of incubation. Similarly, N mineralization decreased from 185.4 mg kg?1 at EC 0.65 dS m?1 to 34.45 mg kg?1 at EC 40.0 dS m?1 during the same period. These results suggested that increasing magnesium chloride salinity from 4 dS m?1 adversely affect microbial activity in terms of carbon dioxide evolution and N mineralization.  相似文献   

15.
Summary Field experiments were carried out to determine the effects of single and mixed inoculations with Rhizobium and vesicular-arbuscular mycorrhiza (VAM) on nodulation, symbiotic N2 fixation and yield of soybeans in six Taiwan subtropical-tropical sites. Inoculation with Rhizobium alone significantly increased nodulation, nodule weight and nitrogenase activity of nodules in three out of six experimental fields, and affected soybean yields in the range –13% to + 134%. Inoculation with VAM fungi alone did not have a significant effect on nodulation and nitrogenase activity. Mycorrhiza inoculation affected soybean yields in the range –13% to + 65%, but only the yield increases at one out of six sites with N application were statistically significant. Mixed inoculation with Rhizobium and mycorrhiza affected yields in the range –8% to + 145% A synergistic effect from mixed inoculation of Rhizobium-mycorrhiza on soybean yields was found in one out of six experimental fields. The yield response to N application (40 kg N ha–1) in these six paddy-field trials was not significant. These results suggest that single or mixed inoculation of rhizobia can greatly assist soybean grain yields and can replace N fertilizers.  相似文献   

16.
Summary A field experiment in concrete-based plots was conducted to estimate the contribution of N derived from air (Ndfa) or biological N2 fixation in Sesbania rostrata and S. cannabina (syn. S. aculeata), using various references, by the 15N dilution method. The two Sesbania species as N2-fixing reference plants and four aquatic weed species as non-N2-fixing references were grown for 65 days after sowing in two consecutive crops, in the dry and the wet seasons, under flooded conditions. Soil previously labeled with 15N at 0.26 atom % 15N excess in mineralizable N was further labeled by ammonium sulfate with 3 and 6 atom % 15N excess. The results showed that 15N enrichment of soil NH 4 + -N dropped exponentially in the first crop to half the original level in 50 days while in the second crop, it declined gradually to half the level in 130 days. The decline in 15N enrichment, in both N2-fixing and non-fixing species, was also steeper in the first crop than in the second crop. Variations in 15N enrichment among non-fixing species were smaller in the second crop. The ratio of the uptake of soil N to that of fertilizer N in N2-fixing and non-fixing species was estimated by the technique of varying the 15N level. In the second crop, this ratio in non-fixing species was higher than that in N2-fixing species. Comparable estimates of % Ndfa were obtained by using 15N enrichment of various non-fixing species. There was also good agreement between the estimates obtained by using 15N enrichment of non-fixing species and those by using soil NH 4 + -N, particularly in the second crop. By 25 days after sowing, the first crop of both Sesbania spp. had obtained 50% of total N from the atmosphere and the second crop had obtained 75%. The contribution from air increased with the age of the plant and ranged from 70% to 95% in 45–55 days. S. rostrata fixed substantially higher amounts of N2 due to its higher biomass production compared with S. cannabina. Mathematical considerations in applying the 15N dilution method are discussed with reference to these results.  相似文献   

17.
After the toxic spill occurred at Aznalcóllar pyrite mine (Southern Spain), a wide area of croplands near the Doñana Wild Park was contaminated with 4.5 million m3 of slurries composed of acidic waters loaded with toxic metals and metalloids such as As, Sb, Zn, Pb, Cu, Co, Tl, Bi, Cd, Ag, Hg and Se. Today, 6 years after the spill, the concentration of toxic elements in these soils is still very high, in spite of the efforts to clean the zone. However, some plant species have colonised this contaminated area. Legumes possessing N2-fixing nodules on their roots represented a significant proportion of these plants. Our objective was to use the Rhizobium-legume symbiosis as a new tool for bioremediate the affected area. We have isolated about 100 Rhizobium strains, 41 of them being resistant to high concentrations of As (300 mg l−1), Cu (100 mg l−1) and Pb (500 mg l−1). Their phenotypes and bioaccumulation potentials have been characterised by their growth rates in media supplemented with As and heavy metals. The presence of the resistance genes in some strains has been confirmed by PCR and Southern blot hybridisation. Several Rhizobium were symbiotically effective in the contaminated soils. On the other hand, the first steps in nodule establishment seemed to be more affected by heavy metals than N2-fixation.  相似文献   

18.
Some of the measures suggested for amelioration of drought effects include application of N fertilizer and plant growth regulators (PGRs). Since N2-fixing bacteria produce plant growth substances (PGRs), the effect of foliar application of an active strain of Klebsiella sp. (KUPOS) on IR-50 rice was examined using three foliar sprays applied at 10-day intervals. Irrigation once every 3 days was essential for plant growth. Application of KUPOS and 40 kg N ha-1 improved grain yield of acutely water stressed plants from 330 kg ha-1 to more than 1300 kg ha-1 along with an improvement in several growth variables and yield determinants. Indole acetic acid, kinetin and GA3, in a mixture of 10-4 M of each, were less effective than KUPOS in alleviating stress effects. The adverse effects of water stress on respiration and photosynthesis as indicated by CO2 exchange were also alleviated by these treatments. While uptake of K, Mg, Ca, Fe and Mo was increased, Na content decreased, accompanied by an increase in proline content. The order of effectiveness of the treatments was 40 kg N ha-1 >KUPOS>PGRs.  相似文献   

19.
Residues from some tree species may contain allelopathic chemicals that have the potential to inhibit plant growth and symbiotic N2-fixing microorganisms. Soybean [Glycine max (L.) Merr] was grown in pots to compare nodulation and N2-fixation responses of the following soil amendments: control soil, leaf compost, red oak (Quercus rubra L.) leaves, sugar maple (Acer saccharum Marsh) leaves, sycamore (Platanus occidentalis L.) leaves, black walnut (Juglans nigra L.) leaves, rye (Secale cereale L.) straw, and corn (Zea mays L.) stover. Freshly fallen leaves were collected from urban shade trees. Soil was amended with 20 g kg-1 air-dried, ground plant materials. Nodulating and nonnodulating isolines of Clark soybean were grown to the R2 stage to determine N2-fixation by the difference method. Although nodulation was not adversely affected, soybean grown on leaf-amended soil exhibited temporary N deficiency until nodulation. Nodule number was increased by more than 40% for soybean grown on amended soil, but nodule dry matter per plant generally was not changed compared with control soil. Nonnodulating plants were severely N deficient and stunted as a consequence of N immobilization. Nodulating soybean plants grown on leaf or crop residue amended soil were more dependent on symbiotically fixed N and had lower dry matter yields than the controls. When leaves were composted, the problem of N immobilization was avoided and dry matter yield was not reduced. No indication of an allelopathic inhibition on nodulation or N2-fixation from heavy application of oak, maple, sycamore, or walnut leaves to soil was observed.  相似文献   

20.
Soybean (Glycine max L. Merr.) cvs. Akisengoku and Peking, and cowpea (Vigna unguiculata Walp.) cv. Kegonnotaki were inoculated with Bradyrhizobium japonicum AlO17, Shinorhizobium fredii USDAI93, and B. sp. Vigna MAFF03-03063, respectively and were cultured hydroponically with supply of CO2-free air, 3dm3 m-3 CO2 air, or 25 dm3 m-3 CO2 air to study the effects of the CO2 concentration in the rhizosphere on plant growth, nodulation, and nitrogen fixation. Increase of the CO2 concentration in the rhizosphere led to the increase of the plant dry weight in the symbiosis between Peking and USDAI93, and that between Kegonnotaki and MAFF03-03063. On the other hand, dry matter accumulation in the symbiosis between Akisengoku and AI017 decreased under the supply of 25 dm3 m-3 CO2 air aimed at increasing the CO2 concentration in the rhizosphere beyond the optimum CO2 concentration for growth. Nodule mass and nodule number per plant were highest in Akisengoku, followed by Kegonnotaki and lowest in Peking. Also the increase of the CO2 concentration in the rhizosphere led to the increase of the nodule mass and number in Kegonnotaki, while no changes were observed in Akisengoku and Peking. Biological nitrogen fixation (BNF) was highest in Akisengoku, followed by Kegonnotaki, and lowest or near zero in Peking. BNF in Akisengoku and Kegonnotaki showed a similar tendency to that of dry matter accumulation. BNF of Peking was especially low under the supply of CO2-free air, and it increased with the increase of the CO2 concentration in the rhizosphere. For the symbiosis of Bradyrhizobium strains with soybean and cowpea, the most suitable CO2 concentration for N2 fixation and plant growth was estimated to be about 10 dm3 m-3, while for the symbiosis of S. fredii with soybean, the value was estimated to be above 30 dm3 m-3.  相似文献   

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