Effect of inoculum rate on the performance of chickpea (Cicer arietinum L.) Rhizobium strains in the field

Summary The influence of three inoculum rates on the performance of three chickpea (Cicer arietinum L.) Rhizobium strains was examined in the field on a Mollisol soil. Increasing amounts of inoculum improved the performance of the strains. A normal dose (10⁴ cells per seed) applied at different intervals gave non-significant increases in nodulation, nitrogenase activity (acetylene reduction assay), nitrogen uptake and grain yield. A ten-fold increase in inoculum increased nodule number, shoot dry weight, nitrogenase activity (ARA) and grain yield, but increases over the control were significant only for nodule dry weight and nitrogen uptake by shoot and grain. The highest level of inoculum (100 × normal) significantly increased nodule dry weight, grain yield, total nitrogenase activity (ARA) and nitrogen uptake by shoot and grain. Strain TAL 620 was more effective than the other two. Combined nitrogen (60 kg N ha^–1) suppressed nodulation and nitrogenase activity (ARA).Research paper No. 4345 from the Experiment Station, G. B. P. U. A. & T., Pantnagar, Nainital, U. P.     

Establishment and persistence of Rhizobium trifolii in western australian soils

Large scale experiments with inoculated and drill sown Trifolium subterraneum, T. hirtum, and T. cherleri showed that recent isolates of Rhizobium trifolii from healthy plants in problem pastures were superior to the strains used in commercially available inoculants. The new rhizobia are also shown to persist in the soil longer than the commercial strains. Evidence was obtained of different levels of performance by R. trifolii strains on different soils. Following the inclusion of one of the superior isolates in commercial peat inoculants, a number of farmer-sown pastures were examined for strain persistence. The new isolates showed much improved persistence over the older inoculant strains.     

Characterization of rhizobia from <Emphasis Type="Italic">Sesbania</Emphasis> species native to seasonally wetland areas in Uruguay

Naturally growing Sesbania species with tolerance to unfavourable habitats are widely distributed in non-cultivated seasonally wetland areas in Uruguay. We investigated the relative abundance, diversity and symbiotic efficiency of Sesbania punicea and S. virgata rhizobia in three ecologically different undisturbed and water-logged sites in Uruguay. Numbers of native-soil rhizobia infective on S. punicea or S. virgata were low, with higher numbers associated with the presence of S. virgata. Plants of S. virgata inoculated with soil suspension showed aerial and nodule biomass greater than that obtained with S. punicea. The rhizobia nodulating Sesbania species in water-logged lands in different regions of Uruguay were diverse differing in growth rates, acid production, growth at 39°C and in LB medium, host range and symbiotic efficiency. Seventeen representative strains clustered into four groups on the basis of phenotypic characteristics, ARDRA and DNA fingerprinting (GTG₅-PCR). Partial sequence of 16S rRNA from eight of these strains classified them into at least two genera with four species: Azorhizobium doebereinerae, Rhizobium sp. related to R. etli and two different Rhizobium sp.-Agrobacterium. Our results confirm the presence of the specie Azorhizobium doebereinerae as microsymbionts of S. virgata in South America. No strain of Rhizobium etli has previously been reported as a microsymbiont of Sesbania, though R. etli like organisms have also been recovered from Dalea purpurea and Desmanthus illinoensis. Significant increases in dry matter production were obtained with S. virgata plants inoculated with selected rhizobial strains under growth chamber conditions.     

Biological control of Rhizoctonia sp. root rot of Casuarina equisetifolia seedlings by Frankia spp. strains

Seventy Frankia spp. strains (nodulating N₂-fixing actinomycetes) were isolated from root nodules of Casuarina equisetifolia from different localities of Tamil Nadu state, India. From these, four strains (UMCe12, UMCe23, UMCe35, and UMce55) were selected. Their potential use as biological control agents for Rhizoctonia solani root rot disease of C. equisetifolia seedlings and their relative efficiency in nodule production were investigated. Between the two inoculum broadcast systems tested, seed-coating with Frankia spp. cell suspension was superior to the soil application of cells as sand-vermiculite-basal ammonium propionate inoculum. UMCe12 was the promising strain, offering the highest level of disease protection (81.1%) and nodule production (88.1%) in the R. solani-infested soil, followed by UMCe23 (60.3 and 65.5% of disease protection and nodule production, respectively), UMCe55 (53.5 and 58.2%), and UMCe35 (45.4 and 44.5%). Further, a significant positive correlation was observed between the dose of Frankia spp. and efficiency in both disease control and nodule production.     

The natural aging-related biochemical changes in the seeds of two legume varieties stored for 40 years

Abstract

This study was carried out to evaluate the effect of long-term natural aging on germinability and several biochemical characteristics regarding antioxidative response of both dry and germinating two different clover (Trifolium repens and Trifolium pratense) seeds stored for 40 years. The percent germination of the seeds was monitored for 7 days. The activities of catalase, peroxidase, superoxide dismutase, lipid peroxidation, H₂O₂ levels, and phenolic matter content were tested on 0, 1st, 3rd, and 7th days of germination. On the 7th day of germination, the germination ratios of the old T. repens and T. pratense seeds were 32 and 17%, while freshly harvested seeds showed 99 and 96% germination on the 4th day, respectively. The long-term aging caused an important increase in lipid peroxidation levels of the old dry seeds. Total phenolic content was high in the old dry seeds of T. repens compared with those of T. pratense. Remarkably, the long-term aging caused an important decrease in H₂O₂ content and the activities of catalase and peroxidase enzymes, but an increase in activity of superoxide dismutase in both the old dry seeds. The decreases in germinability of the old legume seeds were well correlated with the increasing level of lipid peroxidation and the decreasing activities of peroxidase and catalase. During the germination of the legume seeds, a noticeable increase was determined only in peroxidase activity in two types of the old seeds, while catalase activity decreased. However, the other biochemical parameters studied did not significantly change between the germinating old seeds and their freshly harvested controls.     

Competition between Winged Bean Psophocarpus tetragonolobus (L) D.C. Rhizobium Strains for Nodulation

The competitiveness of several effective winged bean Rhizobium strains for nodulation was assessed in a glass house experiment with paired and multi-strain inoculations. The strains varied in their competitive abilities when applied as mixed inocula. The strains KUL-BH, KUL-Z₃, KUL-JN and KUL-GP were more competitive than the strain RRIM 56. The strain KUL-GP was more competitive than the strain KUL-JN. The strains KUL-BH and KUL-GP had relatively high competitiveness. The multi-strain inoculum consisting of Rhizobium strains RRIM 56, KUL-BH, KUL-JN, KUL-GP and KUL-Z₃ was equally effective as the single strain inoculations and thus the multi-strain inoculum could be used in field practice. The broth and the peat multi-strain inocula were equally effective.     

Potassium uptake of rye-grass (Lolium perenne) and red clover (Trifolium pratense) as related to root parameters

Summary Rye-grass (Lolium perenne) is known to be a strong competitor to red clover (Trifolium pratense) for soil K⁺ under conditions of low K availability in the soil. The objective of this study was to clarify whether this competitive behaviour of the two species can be explained by root morphology. Total K⁺ uptake ofL. perenne andT. pratense was studied under field conditions in relation to root fresh weight, root density, root cation exchange capacity, root surface and root length. The soil was an Alfisol, Udalf. All root parameters, when calculated per unit soil surface (M²), were higher inL. perenne than inT. pratense. In addition,L. perenne had longer root hairs and a denser root hair system thanT. pratense. The greatest difference in root morphology between species was root length, withL. perenne roots averaging 4–6 times longer than those ofT. pratense.Significant correlations were found between the total K⁺ uptake and all root parameters examined, with highest correlationsforroot fresh weight (r,0.92***T. pratense; 0.94***L. perenne) and root length (r, 0.91***T. pratense;r, 0.93***L. perenne). Potassium uptake per unit root fresh weight, root surface and root length were all significantly higher forT. pratense than for L. perenne. Differences in the rate of K⁺ uptake between species were particularly high when expressed per unit root length. Because of its greater root length and surface area,L. perenne can take up more soil K⁺ thanT. pratense, particularly where there is a low K^– supply in the soil. Under such conditionsL. perenne will be a particularly strong competitor toT. pratense.     

Competitive interaction among strains of Rhizobium leguminosarum bv. phaseoli in the nodulation of kidney beans (Phaseolus vulgaris L.)

We examined the competitiveness of five effective Rhizobium leguminosarum biovar phaseoli strains in the nodulation of kidney beans (Phaseolus vulgaris L.), either alone or in pairwise combination, against the indigenous strains. The results showed that the introduced Rhizobium sp. strains (B2, B17, B36, T2, or CIAT 652) occupying 64–79% of the total nodules (as single inocula) were more competitive in nodulation than the native rhizobia. However, the competitiveness of the individual Rhizobium sp. strain either increased or decreased when used in a pairwise combination of double-strain inocula. For example, strain B17, although quite competitive against the indigenous population (68% nodule occupancy), became poorly competitive in the presence of strain B2 (reduced from 68 to 2.5%). A similar reduction in nodule occupancy by strain B17 was observed in the presence of B36 or CIAT 652, indicating that two competitive strains may not always be compatible. These results suggest that it is important to co-select competitive as well as compatible rhizobia for multistrain inoculant formulation.     

Regulated modulation of Trifolium subterraneum inoculated with bacteriocinproducing strains of Rhizobium trifolii

When a bacteriocin-sensitive and a bacteriocin-resistant strain of Rhizobium were added together to plant-tubes, containing Trifolium subterraneum cv. Dwalganup seedlings, the bacteriocinresistant strain occupied less than 10% of the nodules sites. But when a bacteriocin-producer was added with the inoculum, the bacteriocin-resistant strain occupied 75% of the nodule sites. In a replicate experiment, using a different bacteriocin-sensitive strain, the proportion of the nodules formed by the bacteriocin-resistant strain was increased from 17%, in the absence of the bacteriocin-producer, to 100% in its presence.Similar experiments were set up in non-sterile soil that contained ineffective, bacteriocin-sensitive rhizobia. When an effective bacteriocin-resistant strain was inoculated with a bacteriocin-producing strain, the proportion of nodules formed by the effective strain was greater than in the absence of the bacteriocin-producer. This was because nodulation by the indigenous rhizobia was reduced in the presence of the bacteriocin-producer.Such experiments suggest that bacteriocin-producing strains of R. trifolii that reduce the nodulation success of competing bacteriocin-sensitive strains could be used to increase the proportion of nodules formed by a desired bacteriocin-resistant strain.     

Colonization of rhizospheres and nodulation of two Vigna species by rhizobia inoculated onto seed: Influence of soil

Changes in the populations of Rhizobium strains CB756str, CB985 and CB1024strspc in the rhizospheres of cowpea (Vigna unguiculata) and black gram (V. mungo) grown at three sites were evaluated. The population dynamics of the three rhizobia varied with soil type but the strain responses on the two legumes were generally similar. Most noticeable was the ability of CB756str to grow in the sandy soil (Beerwah) but not in the heavy clays (Narayen and Emerald). In contrast, the levels of CB1024strspc and CB985 generally increased in the clay soils.Nodulation (% due to the inoculum strain) did not always reflect events within the rhizosphere. Although not suited to Narayen, CB756str formed a similar proportion of the nodule population of black gram as CB1024strspc but this may have been due to higher seed inoculum levels of CB756str. At Emerald nodulation by all three strains of rhizobia was poor regardless of the success in colonization of the rhizosphere. Successful competition for nodule sites by native rhizobia may contribute to this discrepancy between Narayen and Emerald although lower seed inoculum levels at Emerald may also have been important.Nodule decay was consistently associated with a large increase in the number of rhizobia per root system. This is likely to be important in the survival of strains into the following season.Comparisons of nodulation by parent and mutant rhizobia suggested that resistance to antibotics may have slightly reduced nodule forming ability for CB1024strspc on black gram at Emerald.     

Competitiveness of Rhizobium leguminosarum bv. phaseoli strains in relation to environmental stress and plant defense mechanisms

Summary Six Rhizobium leguminosarum bv. phaseoli strains (Ciat 151, Ciat 895, Ciat 899, CE3, H2C, Kim5s) were tested for nodule occupancy in different bean cultivars at two field sites (one fertile, one acid tropical soil) and in the greenhouse. The effects of several environmental factors such as low pH, high temperature, Al and Mn toxicity, iron deficiency, bean tannins, and bean phytoalexins were tested in vitro. Strain Kim5s was competitive under all tested conditions while strains CE3 and H2C had consistently low nodule occupancy levels. Strain Ciat 151 was superior to the other inoculant strains in the acid soil but competed poorly in the fertile soil. Strain Ciat 895 was more competitive in the fertile soil. There was a decline in nodule occupancy for all strains tested from the first trifoliate leaf stage to the pod-filling stage. No plant genotype effect on nodule occupancy was observed. There were significant (P<0.05) plant genotype and location effects, but no significant strain effect on acetylene reduction activity, plant dry weight, and nodule number. The greenhouse experiments confirmed, at least partially, the results from the field trials. In Leonard jars with an acid soil, strains Ciat 151 and Kim5s were amongst the most competitive strains. In coinoculation experiments, Kim5s was the most competitive strain, followed by Ciat 899 and Ciat 895. The competitiveness of a given strain was affected by the coinoculant strain. Tolerance in vitro to low pH, high growth temperature, Al or Mn toxicity, or Fe limitation was not related to competitiveness of the inoculum strains. The sensitivity of the strains towards bean tannins or bean phytoalexins also was not correlated with their competitiveness.     

Inoculation responses of perennial forage legumes grown in fresh hill‐land ultisols as affected by soil acidity‐related factors

A growth chamber experiment was initiated with two field moist, marginal and acidic (pH 5.1–5.2) soils of the Lily series (Typic Hapludults) in order to determine the need for improved legume‐rhizobia symbioses for forage species of current, or potential, use in the renovation of Appalachian hill‐land pastures. One soil was from an abandoned pasture having broomsedge (Andropogon virginicus L.) as the predominant vegetation, whereas the other was from a minimally‐managed pasture dominated by orchardgrass (Dactylis glomerata L.). Treatments included inoculation (or no inoculation) and the addition of aluminum, nil, or lime to provide a range of soil acidities. Both soils contained effective populations of naturalized rhizobia for white clover (Trifolium repens L.) and red clover (Trifolium pratense L.), but low and/or ineffective naturalized populations of rhizobia for alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), bigflower vetch (Vicia grandiflora Scop.), and flatpea (Lathyrus sylvestris L.). Seed inoculation, by lime‐pelleting, was highly beneficial in establishing effective symbioses for all these latter species. The addition of low levels of aluminum or lime (1.5 and 2.0 cmol/kg soil, respectively) had little effect on any of the symbioses, with the exception of those for alfalfa. Thus, an improved legume rhizobia symbiosis would not seem to be a prerequisite for renovating pastures established on chemically similar ultisols with the forage legume species examined in this study, especially if the pasture has at least some history of management.     

The nature of non-protein nitrogen accumulation in Trifolium subterraneum root nodules

Non-protein nitrogen accumulated in nodules formed on Trifolium subterraneum cv. Tallarook by Rhizobium trifolii strain NA30, but not in nodules formed by strain TA1. Studies with six R. trifolii strains and four T. subterraneum cultivars indicated that the accumulation of non-protein nitrogen was a characteristic of certain strains and that it was accompanied by a greater development of nodule tissue. With normal symbiotic associations, approximately 6 per cent of the total plant nitrogen was located in the nodule system whereas nodules accumulating non-protein nitrogen contained, on average, 12 per cent of the total nitrogen in the plant.The principal component of the accumulating non-protein nitrogen was identified as “bound” γ-aminobutyric acid. Moderate to high concentrations of γ-aminobutyric acid (0.3–1.7 mmoles/g nodule dry weight) were found in nodules formed by 10 strains (of 36 examined) on Tallarook. With two “accumulating” strains, higher concentrations of γ-aminobutyric acid were found in nodules formed on the cultivar Clare (2.0 mmoles/g nodule dry weight) than in nodules formed on Tallarook or Yarloop (1 1.4 mmoles). No γ-aminobutyric acid was found in cultured cells of either an accumulating strain (NA30) or a nonaccumulating strain (TA1) of R. trifolii.The accumulation of non-protein nitrogen as γ-aminobutyric acid, and the accompanying increase in nodule tissue, each resulting in the export of a lower proportion of the nitrogen fixed to the host, is considered to be a factor causing a lower degree of symbiotic effectiveness.     

Diversity of rhizobia nodulating Lotus corniculatus grown in northern and southern regions of Uruguay

Diversity of rhizobia nodulating Lotus corniculatus grown in geographical regions with different rainfall regimes in northern and southern Uruguay, was estimated using 168 root nodule isolates. ERIC-PCR analysis revealed no correlation between observed fingerprints and the geographical origin of isolates. Despite the commercial strain U510 has been used for decades to inoculate L. corniculatus, none of the isolates corresponded to this strain. Phylogenetic analyses using 16S rRNA and atpD genes, and ITS sequences clustered all the isolates within genus Mesorhizobium. A great majority of the isolates likely belong to the species M. huakuii, as does the commercial strain U510. The remaining isolates were closely related to either M. septentrionale or M. caraganae. Although no M. loti-like bacteria were identified, all isolates carried symbiotic genes closely related to M. loti and other narrow host range Lotus rhizobia. A significant portion of the Uruguayan isolates were as efficient as the reference strain U510 in symbiosis with L. corniculatus. A few of the isolates were also capable of nitrogen fixation in symbiosis with L. uliginosus, albeit with lower efficiency than reference strains. Our results indicate that rhizobia nodulating L. corniculatus in Uruguay are genetically and phenotypically diverse, and that the commercial strain U510 is probably not adapted to survive the Uruguayan edaphoclimatic conditions.     

Legume cover crops as a nitrogen source for pecan

Crimson clover (Trifolium incarnatum L.) plus hairy vetch ( Vicia villosa Roth), red clover (Trifolium pratense L.), white clover (Trifolium repens L.), red clover plus white clover, and bermudagrass (Cynodon dactylon [L.] Pers.) were evaluated as cover crops for pecans. Crimson clover plus hairy vetch supplied the equivalent of 101 to 159 kg nitrogen (N)/ha. Red clover plus white clover supplied up to 132 kg N/ha. Either white clover or red clover alone were less effective in supplying N than when grown together. Soil Kjeldahl‐N was usually not affected or increased using the legumes compared to fertilized bermudagrass sod. Soil nitrate (NO₃) concentrations during October were occasionally higher in unfertilized legume plots than in bermudagrass plots with March‐applied N.     

Interaction Effects of Nitrogen and Phosphorus on Nodulation in Red Clover (Trifolium pratense L.)

Red clover (Trifolium pratense L.) is one of the most important plants in forage production, especially in northern areas. Fertilisation practices are focused on high yield and forage quality but effects of nutrients on nodulation and N₂ fixation are poorly understood. The aim of this work was to study how nitrogen (N) and phosphorus (P) separately as well as in combination affected nodulation. Red clover plants were grown in pots with gravel in a greenhouse for 11 weeks. To resemble field conditions the root temperature was kept lower than the shoot temperature. Plants were given five different combinations of N and P concentrations during growth. The result showed that at high N concentrations P had a counteracting effect on the N inhibition. The N₂-fixation parameters, nodule number, nodule dry matter and specific nitrogenase activity, were six times higher in plants grown with high N and high P than in plants with high N and low P. When the N₂-fixation parameters and the dry matter of roots and shoots were related to total plant dry matter, there was a stronger effect of P on nodulation parameters than on roots and shoots. This indicates that P has a direct effect on the N₂-fixation parameters, rather than an indirect effect via increased plant growth. These results demonstrate the importance to studying the effects of more than one nutrient at a time.     

Effects of Multiple Reference Plants,Season, and Irrigation on Biological Nitrogen Fixation by Pasture Legumes using the Isotope Dilution Method

Abstract

The popular and widely used ¹⁵nitrogen (N)–isotope dilution method for estimating biological N fixation (BNF) of pasture and tree legumes relies largely on the ability to overcome the principal source of error due to the problem of selecting appropriate reference plants. A field experiment was conducted to evaluate the suitability of 12 non‐N₂‐fixing plants (i.e., nonlegumes) as reference plants for estimating the BNF of three pasture legumes (white clover, Trifolium repens L.; lucerne, Medicago sativa; and red clover, Trifolium pratense L.) in standard ryegrass–white clover (RWC) and multispecies pastures (MSP) under dry‐land and irrigation systems, over four seasons in Canterbury, New Zealand. The ¹⁵N‐isotope dilution method involving field ¹⁵N‐microplots was used to estimate BNF. Non‐N₂‐fixing plants were used either singly or in combination as reference plants to estimate the BNF of the three legumes. Results obtained showed that, on the whole, ¹⁵N‐enrichment values of legumes and nonlegumes varied significantly according to plant species, season, and irrigation. Grasses and herb species showed higher ¹⁵N‐enrichment than those of legumes. Highest ¹⁵N‐enrichment values of all plants occurred during late summer under dry‐land and irrigation conditions. Based on single or combined non‐N₂‐fixing plants as reference plants, the proportion of N derived from the atmosphere (% Ndfa) values were high (50 to 90%) and differed between most reference plants in the MSP pastures, especially chicory (Cichorium intybus), probably because it is different in phenology, rooting depth, and N‐uptake patterns compared to those of legumes. The percent Ndfa values of all plants studied also varied according to plant species, season, and irrigation in the MSP pastures. Estimated daily amounts of BNF varied according to pasture type, time of plant harvest, and irrigation, similar to those shown by percent Ndfa results as expected. Irrigation increased daily BNF more than 10‐fold, probably due to increased dry‐matter yield of pasture under irrigation compared to dry‐land conditions. Seasonal and irrigation effects were more important in affecting estimates of legume BNF than those due to the appropriate matching of N₂‐fixing and non‐N₂‐fixing reference plants.     

Delayed inoculation and competition of Rhizobium meliloti in annual Medicago species

Seed inoculation is frequently essential for annual Medicago establishment in Mediterranean dryland farming systems. As post-planting soil inoculation is often practiced when seed inoculation fails, the effect of delayed inoculation was investigated. Roots of Medicago rigidula (L.). All selection 716, and Medicago rotata Boiss. selection 2132, were initially pre-exposed to Rhizobium meliloti strains. Subsequently, roots were exposed to a secondary inoculum after 6, 48 and 168 h to simulate delayed inoculation. and subsequent establishment of others strains in the nodules were investigated. Combinations of highly effective and host compatible ICARDA strains (M15 and M53) and effective-ineffective strains (M15 and M28) were used to evaluate proportional nodulation responses. Plants were harvested after 6 weeks of growth. Nodules were assessed for distribution in the root system and for occupancy based on their differential resistance to kanamycin and streptomycin, and, in the case of ICARDA M28, on nodule characteristics. The strain ICARDA M15 was a better competitor than ICARDA M53 when applied in equal density in M. rotata, at zero time. While forming nodules with M. rigidula, ICARDA M53 was equally competitive under the same conditions. With ICARDA M15 as the primary inoculum, and ICARDA M53 delayed for 6, 48 and 168 h, the incidence of ICARDA M15 nodules increased on M. rigidula from 43% (at zero time) to 86, 94, and 97% and, on M. rotata, from 78% (at zero time) to 88%, 95%, and 98% for the three time delays, respectively. Pre-exposure of 2-day old M. rigidula seedlings to the ineffective strain ICARDA M28 as the primary inoculant was followed by significant nodule number increases (P 0.01) as compared with ICARDA M15. Nonetheless, when ICARDA M15 was the primary inoculum, M28 was able to produce about 35% of the nodules when applied at the 6 and 48 h time delays. However, with ICARDA M28 as the primary inoculum, followed by ICARDA M15, nodule occupancy of ICARDA M28 in M. rigidula increased from 40 (at zero time) to 75%, 80%, and 95% for the three time delays, respectively. The percentage of total nodulation by M28, applied at the three delay times, was markedly lower (10%, 5% and 1%, respectively) when M. rotata was pre-exposed to ICARDA M15. This suggested a host preference for ICARDA M15, even if applied as a late inoculum. Results indicate that the early events in the nodulation process of annual medics coupled with host-specificity factors are perhaps the most critical for competition among R. meliloti strains for nodule formation.     

Influence of a vesicular-arbuscular mycorrhizal fungus on the competitive ability of Bradyrhizobium spp. for nodulation of cowpea Vigna unguiculata (L.) Walp in non-sterilized soil

Summary We examined the influence of a vesicular-arbuscular (VAM) fungus (Glomus pallidum Hall) on the competitive ability of introduced and native Bradyrhizobium strains to nodulate cowpeas [Vigna unguiculata (L) Walp]. Our experiments in non-sterilized soil revealed that in the presence of VAM fungus, introduced Bradyrhizobium spp. strains become more competitive than native rhizobia. For example, strain JRC29 occupied 59.2% of the total nodules when inoculated alone, but this figure increased to 71.2% when JRC29 was used in dual inoculations with VAM fungus. A similar pattern of enhanced competitiveness for nodule formation was observed with the two other strains in the presence of the VAM fungus. Our results suggest that the competitiveness of rhizobia can be enhanced by co-inoculating with a selected strain of a VAM fungus.     

Differential effect of arbuscular mycorrhizal fungal communities from ecosystems along management gradient on the growth of forest understorey plant species

Arbuscular mycorrhizal fungi (AMF) are important functional components of ecosystems. Although there is accumulating knowledge about AMF diversity in different ecosystems, the effect of forest management on diversity and functional characteristics of AMF communities has not been addressed. Here, we used soil inoculum representing three different AM fungal communities (from a young forest stand, an old forest stand and an arable field) in a greenhouse experiment to investigate their effect on the growth of three plant species with contrasting local distributions - Geum rivale, Trifolium pratense and Hypericum maculatum. AM fungal communities in plant roots were analysed using the terminal restriction fragment length polymorphism (T-RFLP) method. The effect of natural AMF communities from the old and young forest on the growth of studied plant species was similar. However, the AMF community from the contrasting arable ecosystems increased H. maculatum root and shoot biomass compared with forest inocula and T. pratense root biomass compared to sterile control. According to ordination analysis AMF inocula from old and young forest resulted in similar root AMF communities whilst plants grown with AM fungi from arable field hosted a different AMF community from those grown with old forest inocula. AMF richness in plant roots was not related to the origin of AMF inoculum. G. rivale hosted a significantly different AM fungal community to that of T. pratense and H. maculatum. We conclude that although the composition of AM fungal communities in intensively managed stands differed from that of old stands, the ecosystem can still offer the ‘symbiotic service’ necessary for the restoration of a characteristic old growth understorey plant community.