Divergent composition but similar function of soil food webs of individual plants: plant species and community effects.

Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity restoration experiment we first compared the soil nematode communities of 228 individual plants belonging to eight herbaceous species. We included grass, leguminous, and non-leguminous species. Each individual plant grew intermingled with other species, but all plant species had a different nematode community. Moreover, nematode communities were more similar when plant individuals were growing in the same as compared to different plant communities, and these effects were most apparent for the groups of bacterivorous, carnivorous, and omnivorous nematodes. Subsequently, we analyzed the composition, structure, and functioning of the complete soil food webs of 58 individual plants, belonging to two of the plant species, Lotus corniculatus (Fabaceae) and Plantago lanceolata (Plantaginaceae). We isolated and identified more than 150 taxa/groups of soil organisms. The soil community composition and structure of the entire food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants and are strongly influenced by the species identity of the plant. However, the ecosystem functions these food webs provide are determined by the identity of the entire plant community.

Two bacterial strains isolated from a Zn-polluted soil enhance plant growth and mycorrhizal efficiency under Zn-toxicity.

In this study we investigated the interactions among plant, rhizosphere microorganisms and Zn pollution. We tested the influence of two bacterial strains isolated from a Zn-polluted soil on plant growth and on the symbiotic efficiency of native arbuscular mycorrhizal fungi (AMF) under Zn toxicity. The two bacterial strains exhibited Zn tolerance when cultivated under increasing Zn levels in the medium. However, strain B-I showed a higher Zn tolerance than strain B-II at the two highest Zn levels in the medium (75 and 100 mg l(-1) Zn). Molecular identification placed the strain B-I within the genus Brevibacillus. Our results showed that bacterial strain B-I consistently enhanced plant growth, N and P accumulation, as well as nodule number and mycorrhizal infection which demonstrated its plant-growth promoting (PGP) activity. This strain B-I has been shown to produce IAA (3.95 microg ml) and to accumulate 5.6% of Zn from the growing medium. The enhanced growth and nutrition of plants dually inoculated with the AMF and bacterium B-I was observed at three Zn levels assayed. This effect can be related to the stimulation of symbiotic structures (nodules and AMF colonization) and a decreased Zn concentration in plant tissues. The amount of Zn acquired per root weight unit was reduced by each one of these bacterial strains or AMF and particularly by the mixed bacterium-AMF inocula. These mechanisms explain the alleviation of Zn toxicity by selected microorganisms and indicate that metal-adapted bacteria and AMF play a key role enhancing plant growth under soil Zn contamination.

Impact of microbial inoculation on biomass accumulation by Sulla carnosa provenances, and in regulating nutrition, physiological and antioxidant activities of this species under non-saline and saline conditions.

Bacteria (Pseudomonas sp. and Bacillus sp.) and/or the arbuscular mycorrhizal (AM) fungus Rhizophagus intraradices were able to improve growth, physiological and biochemical characteristics of four Sulla carnosa Desf. provenances (Sidi khlif, Thelja, Kalbia and Kerker) from Tunisia under both saline and non-saline conditions. S. carnosa is a salt-tolerant legume plant, native from North Africa. The intrinsic bacterial characteristics evidenced the fitness of these bacteria to support salt stress and to stimulate plant growth. Bacillus sp. produced more indol acetic acid (IAA) than Pseudomonas sp. and showed a great surviving capacity under salt conditions supporting its capacity to improve plant growth under stress conditions. The microorganisms applied also have a different potential to increase the nutritional and related plant growth parameters. It is noticeable that some provenances reached the highest level of growth when inoculated with Bacillus sp. in Sidi khlif or by Bacillus plus AMF in Kalbia, which increased shoot by 318% and root by 774%. In contrast, in Thelja and Kerker the impact of the test microorganisms was mainly evidenced at increasing nutritional and physiological functions. Salinity reduced some growth and physiological variables as stomatal conductance, photosynthetic pigments and photosynthetic efficiency and increased electrolyte leakage. However, the microbial inoculants compensated these detrimental effects in a degree depending on the S. carnosa provenance. These microorganisms also orchestrate antioxidant activities involved in adaptative responses in S. carnosa provenances. The intrinsic ability of inoculants allow us to select the provenance/microorganism combination which maximizes S. carnosa growth, nutrition and physiological/biochemical responses under salt and non-salt conditions. The results obtained support that the target microbial inocula are beneficial for the ecological stability if this Mediterranean legume.

Application of Aspergillus niger-treated agrowaste residue and Glomus mosseae for improving growth and nutrition of Trifolium repens in a Cd-contaminated soil.

The microbial transformation of sugar beet (SB) agrowaste with or without rock-phosphate (RP) has utility for the improvement of plant growth in a Cd (5 microg g-1) artificially contaminated soil, particularly when the soil is co-inoculated with arbuscular mycorrhizal (AM) fungus Glomus mosseae isolated from a Cd-polluted area. Under such Cd-polluted conditions, the limited growth, mineral nutrition, symbiotic developments (nodulation and AM-colonization) and soil enzymatic activities were stimulated using SB or SB+RP as soil amendments and G. mosseae as inoculant. G. mosseae enhanced plant establishment in a higher extent in amended soil; it is probably due to the interactive effect increasing the potential fertility of such compounds and its ability for decreasing Cd transfer from soil to plant. The amount of Cd transferred from soil solution to biomass of AM-colonized plants ranged from 0.09 microg Cd g-1 (in SB+RP-amended soil) to 0.6 microg Cd g-1 (in non-amended soil). Nodule formation was more sensitive to Cd than AM-colonization, and both symbioses were stimulated in amended soils. Not only AM-colonization but also amendments were critical for plant growth and nutrition in Cd-polluted soil. The high effectiveness of AM inoculum increasing nutrients and decreasing Cd in amended soil indicated the positive interaction of these treatments in increasing plant tolerance to Cd contamination.

Interactive effect of Brevibacillus brevis and Glomus mosseae, both isolated from Cd contaminated soil, on plant growth, physiological mycorrhizal fungal characteristics and soil enzymatic activities in Cd polluted soil.

The interaction between two autochthonous microorganisms (Brevibacillus brevis and Glomus mosseae) isolated from Cd amended soil increased plant growth, arbuscular mycorrhizal (AM) colonization and physiological characteristics of the AM infection (measured as SDH or ALP activities). The enhanced plant Cd tolerance after coinoculation with native microorganisms seemed to be a consequence of increased P and K acquisition and, simultaneously, of decreased concentration of Cd, Cr, Mn, Cu, Mo, Fe and Ni in plant tissue. Autochthonous microbial strains were more efficient for nutrient uptake, to immobilize metals and decrease their translocation to the shoot than reference G. mosseae (with or without bacteria). Indole acetic acid produced by B. brevis may be related to its ability for improving root growth, nodule production and AM fungal intra and extraradical development. Dehydrogenase, phosphatase and beta-glucosidase activities, indicative of microbial metabolism and soil fertility, were maximized by the coinoculation of autochthonous microorganisms in cadmium polluted conditions. As a consequence, the use of native microorganisms may result very efficient in bioremediation.

VESICULAR-ARBUSCULAR MYCORRHIZA IMPROVE BOTH SYMBIOTIC N2 FIXATION AND N UPTAKE FROM SOIL AS ASSESSED WITH A 15 N TECHNIQUE UNDER FIELD CONDITIONS.

A technique using 15 N-labelled inorganic fertilizer was applied to estimate N2 fixation by the forage legume Hedysarum coronarium L. and to ascertain the role of vesicular-arbuscular (VA) mycorrhizas in plant N nutrition throughout a growing season under field conditions. The absence of the specific Rhizobium for the forage legume in the test soil allowed us the use of 15 N methodology with the same legume as reference 'non-fixing' crop. At the first harvest, mycorrhizal inoculation behaved similarly to the phosphate addition in improving the percentage (70 %) and the total amount of N derived from fixation. But thereafter, mycorrhizal inoculation not only enhanced dry matter yield, N concentration and total N yield but also the amount of N derived from soil and from fixation, as compared with either phosphate-added or control plants. This indicated that mycorrhizas acted both by a P-mediated mechanism to improve N2 fixation and by enhancing N uptake from soil. The latter agrees with recent findings by others that VA mycorrhizal hyphae can translocate and assimilate ammonium, a fact of physiological and ecological interest.

Selective interactions between different species of mycorrhizal fungi and Rhizobium meliloti strains, and their effects on growth, N2 -fixation (15 N) and nutrition of Medicago sativa L.

Three isolates of vesicular-arbuscular (VA) mycorrhizal fungi, belonging to the species Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, G. fasciculatum (Taxter sensu Gerd.) Gerd, and Trappe, and G. caledonium (Nicol. and Gerd.) Trappe and Gerd, were inoculated in dual combinations with six strains of Rhizobium meliloti with the aim of testing these combinations for functional compatibility with their common host plant, the legume Medicago sativa L. Symbiotic efficiency (promotion of plant growth and N and P nutrition) was found to be dependent on the particular combination of Rhizobium strain and Glomus species indicating selective and specific compatibilities between strains and isolates of the two types of microsymbiont, but also between them and the common host plant. Observed effects on plant growth were in general, though not always, related to the extent of VA mycorrhizal colonization. Although the different mycorrhizal and/or rhizobial treatments produced different effects on plant growth, the rate of nodule formation on M. sativa roots remained constant. Most mycorrhizal treatments increased the concentration and/or content of N in plant shoots but effectiveness was in the order: G. fasciculatum > G. mosseae > G. caledonium. In some cases, this increase in N-content may be a consequence of a P-mediated stimulation of N2 -fixation by VA mycorrhiza, as ascertained using 15 N. In other instances, however, the increase seems to reflect a VA mycorrhizal-mediated enhancement of N-uptake from soil. VA mycorrhizal inoculation decreased the concentration of Ca and Mg in plant shoots and a buffering effect of VA mycorrhiza in situations of nutrient excess in soil is proposed.

The use of isotopic dilution techniques to evaluate the interactive effects of Rhizobium genotype, mycorrhizal fungi, phosphate-solubilizing rhizobacteria and rock phosphate on nitrogen and phosphorus acquisition by Medicago sativa.

A pot experiment was designed to evaluate the interactive effects of multiple microbial inoculation treatments and rock phosphate (RP) application on N and P acquisition by alfalfa plants using 15 N and 32 P isotopes. The microbial inocula consisted of a wild type (WT) Rhizobium meliloti strain, its genetically modified (GM) derivative, which had an enhanced competitiveness, the arbuscular mycorrhizal (AM) fungus Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, and a phosphate-solubilizing rhizobacterium (Enterobacter sp.). Inoculated micro-organisms became established in the root tissues and/or in the rhizosphere soil of alfalfa plants (Medicago sativa L.). The GM Rhizobium strain did not interfere with AM formation. Inoculated phosphate-solubilizing rhizobacteria established in the alfalfa rhizosphere, but the level of establishment was lower where the natural population of phosphate-solubilizing bacteria was stimulated by AM inoculation and RP application. The stimulation of these indigenous bacteria was also greater in the rhizosphere of alfalfa nodulated by the GM Rhizobium. Improvements in N and P accumulation in alfalfa corroborate beneficial effects of the improved GM Rhizobium on AM performance, in RP-amended plants. Inoculation with Enterobacter did not improve the AM effect on N or P accumulation in the RP-added soil, but it did in the non RP-amended controls. Measurements of the 15 N∶14 N ratio in plant shoots indicated enhanced N2 fixation rates in Rhizobium-inoculated AM-plants, over that achieved by the same Rhizobium strain in non-mycorrhizal plants. Regardless of the Rhizobium strain and of whether or not RP was added, AM-inoculated plants showed a lower specific activity (32 P∶31 P) than did their comparable non-mycorrhizal controls, suggesting that the plant was using otherwise unavailable P sources. The phosphate-solubilizing, AM-associated, microbiota could in fact release phosphate ions, either from the added RP or from the indigenous 'less-available' phosphate. Deficiency in Ca concentration in soil solution in the neutral test soil might benefit P solubilization. The proportion of plant P derived either from the labelled soil P (labile P pool) or from RP was similar for AM inoculated and non-mycorrhizal controls (without Enterobacter inoculation) for each Rhizobium strain, but the total P uptake, regardless of the P source, was far higher in AM-plants. Enterobacter inoculation seems to improve the use of RP in the rhizosphere of non-mycorrhizal plants inoculated with the WT Rhizobium.

Interactions between plant-growth-promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi and Rhizobium spp. in the rhizosphere of Anthyllis cytisoides, a model legume for revegetation in mediterranean semi-arid ecosystems.

Arbuscular mycorrhizal (AM) fungi, Rhizobium bacteria and plant-growth-promoting rhizobacteria (PGPR) were isolated from a representative area of a desertified semi-arid ecosystem in the south-east of Spain. Microbial isolates were characterized and screened for effectiveness by a single-inoculation trial in soil microcosms. Anthyllis cytisoides L., a mycotrophic pioneer legume, dominant in the target mediterranean ecosystem, was the test plant. Several microbial cultures from existing collections were also included in the screening process. Two AM fungi (Glomus coronatum, native, and Glomus intraradices. exotic), two Rhizobium bacteria (NR4 and NR9, both native) and two PGPR (A2, native, and E, exotic) were selected. A further screening for the appropriate double and triple combinations of microbial inoculants was then performed. The parameters evaluated were biomass accumulation and allocation, N and P uptake, N2 -fixation (15 N) and specific root length. Overall, G. coronatum, native in the field site was more effective than the exotic G. intraradices in co-inoculation treatments. In general, our results support the importance of physiological and genetic adaptation of microbes to the whole environment, thus local isolates must be involved. Many microbial combinations were effective in improving either plant development, nutrient uptake, N2 -fixation or root system quality. Selective and specific functional compatibility relationships in plant response between the microbial inoculants, were observed. Despite the difficulty of selecting a multifunctional microbial inoculum, appropriate microbial combinations can be recommended for a given biotechnological input related to improvement of plant performance. This could be exploited in nursery production of target plant species endowed with optimized rhizosphere/mycorrhizosphere systems that can be tailored to help plants to establish and survive in nutrient-deficient, degraded habitats. The relevance of this microbial-based approach in the context of a reclamation strategy addressed to environmental sustainability purposes is discussed.

Application of an encapsulated filamentous fungus in solubilization of inorganic phosphate.

Spores of Aspergillus niger were encapsulated in agar, calcium alginate and k-carrageenan and further applied in citric acid production during six repeated batch cultivations. Rock phosphate (RP) at concentrations of 3 g l-1 and 7 g l-1 was supplemented to the culture medium to test encapsulated-fungus solubilizing capability. The highest average citric acid productivity of 0.15 g l-1 h-1 was reached with alginate-bead-encapsulated A. niger on RP-free culture medium while agar seemed to be the most suitable carrier on RP-supplemented medium. Accordingly, the highest average soluble P concentration of 0.20 g l-1 batch-1 was obtained with agar-cell beads as compared with other encapsulated systems.

Symbiotic efficiency of autochthonous arbuscular mycorrhizal fungus (G. mosseae) and Brevibacillus sp. isolated from cadmium polluted soil under increasing cadmium levels.

The effect of inoculation with indigenous naturally occurring microorganisms (an arbuscular mycorrhizal (AM) fungus and rhizosphere bacteria) isolated from a Cd polluted soil was assayed on Trifolium repens growing in soil contaminated with a range of Cd. One of the bacterial isolate showed a marked PGPR effect and was identified as a Brevibacillus sp. Mycorrhizal colonization also enhanced Trifolium growth and N, P, Zn and Ni content and the dually inoculated (AM fungus plus Brevibacillus sp.) plants achieved further growth and nutrition and less Cd concentration, particularly at the highest Cd level. Increasing Cd level in the soil decreased Zn and Pb shoot accumulation. Coinoculation of Brevibacillus sp. and AM fungus increased shoot biomass over single mycorrhizal plants by 18% (at 13.6 mg Cd kg(-1)), 26% (at 33.0 mg Cd kg(-1)) and 35% (at 85.1 mg Cd (kg(1)). In contrast, Cd transfer from soil to plants was substantially reduced and at the highest Cd level Brevibacillus sp. lowered this value by 37.5% in AM plants. Increasing Cd level highly reduced plant mycorrhization and nodulation. Strong positive effect of the bacterium on inocula, are important in plant Cd tolerance and development in Cd polluted soils.

Drought tolerance and antioxidant activities in lavender plants colonized by native drought-tolerant or drought-sensitive Glomus Species.

This study compared the effectiveness of four arbuscular mycorrhizal (AM) fungal isolates (two autochthonous presumably drought-tolerant Glomus sp and two allochthonous presumably drought-sensitive strains) on a drought-adapted plant (Lavandula spica) growing under drought conditions. The autochthonous AM fungal strains produced a higher lavender biomass, specially root biomass, and a more efficient N and K absorption than with the inoculation of similar allochthonous strains under drought conditions. The autochthonous strains of Glomus intraradices and Glomus mosseae increased root growth by 35% and 100%, respectively, when compared to similar allochthonous strains. These effects were concomitant with an increase in water content and a decline in antioxidant compounds: 25% glutathione, 7% ascorbate and 15% H(2)O(2) by G. intraradices, and 108% glutathione, 26% ascorbate and 43% H(2)O(2) by G. mosseae. Glutathione and ascorbate have an important role in plant protection and metabolic function under water deficit; the low cell accumulation of these compounds in plants colonized by autochthonous AM fungal strains is an indication of high drought tolerance. Non-significant differences between antioxidant activities such as glutathione reductase (GR), catalase (CAT) and superoxide dismutase (SOD) in colonized plants were found. Thus, these results do not allow the generalization that GR, CAT and SOD were correlated with the symbiotic efficiency of these AM fungi on lavender drought tolerance. Plants colonized by allochthonous G. mosseae (the less efficient strain under drought conditions) had less N and K content than those colonized by similar autochthonous strain. These ions play a key role in osmoregulation. The AM symbiosis by autochthonous adapted strains also produced the highest intraradical and arbuscular development and extraradical mycelial having the greatest fungal SDH and ALP-ase activities in the root systems. Inoculation of autochthonous drought tolerant fungal strains is an important strategy that assured the greatest tolerance water stress contributing to the best lavender growth under drought.

An indigenous drought-tolerant strain of Glomus intraradices associated with a native bacterium improves water transport and root development in Retama sphaerocarpa.

The effects of interactions between Bacillus thuringiensis, a drought-adapted bacterium, and two isolates of Glomus intraradices, an arbuscular mycorrhizal (AM) fungus, on Retama sphaerocarpa, a drought-adapted legume, were investigated. The fungal isolates were an indigenous drought-tolerant and a nonindigenous drought-sensitive isolate. Shoot length and root growth, symbiotic parameters, water transport (in terms of percent relative plant water uptake), and volumetric soil moisture and soil enzymatic activities in response to microbial inoculations were evaluated. Retama plants colonized by G. intraradices plus Bacillus possessed similar shoot length after 30 days from sowing compared with noninoculated Retama plants after 150 days. Inoculation with drought-adapted bacterium increased root growth by 201%, but maximum root development was obtained by co-inoculation of B. thuringiensis and the indigenous G. intraradices. Nodules were formed only in plants colonized by autochthonous AM fungi. Relative water uptake was higher in inoculated than in noninoculated Retama plants, and these inoculants depleted soil water content concomitantly. G. intraradices-colonized Retama reached similar shoot length irrespective of the fungal origin, but there were strong differences in relative water uptake by plants colonized by each one of the fungi. Indigenous G. intraradices-colonized roots (evaluated as functional alkaline phosphatase staining) showed the highest intensity and arbuscule richness when associated with B. thuringiensis. The interactive microbial effects on Retama plants were more relevant when indigenous microorganisms were involved. Co-inoculation of autochthonous microorganisms reduced by 42% the water required to produce 1 mg of shoot biomass. This is the first evidence of the effectiveness of rhizosphere bacterium, singly or associated with AM fungus, in increasing plant water uptake, which represents a positive microbial effect on plants grown under drought environments.

Effectiveness of autochthonous bacterium and mycorrhizal fungus on Trifolium growth, symbiotic development and soil enzymatic activities in Zn contaminated soil.

AIMS: This study investigates how autochthonous micro-organisms [bacterium and/or arbuscular mycorrhizal (AM) fungi] affected plant tolerance to Zn contamination. METHODS AND RESULTS: Zinc-adapted and -nonadapted Glomus mosseae strains protected the host plant against the detrimental effect of Zn (600 microg g(-1)). Zn-adapted bacteria increased root growth and N, P nutrition in plants colonized by adapted G. mosseae and decreased the specific absorption rate (SAR) of Cd, Cu, Mo or Fe in plants colonized by Zn-nonadapted G. mosseae. Symbiotic structures (nodule number and extraradical mycelium) were best developed in plants colonized by those Zn-adapted isolates that were the most effective in increasing plant Zn tolerance. The bacterium also increased the quantity and quality (metabolic characteristics) of mycorrhizal colonization, with the highest improvement for arbuscular vitality and activity. Inocula also enhanced soil enzymatic activities (dehydrogenase, beta-glucosidase and phosphatase) and indol acetic acid (IAA) accumulation, particularly in the rhizosphere of plants inoculated with Zn-adapted isolates. CONCLUSIONS: Glomus mosseae strains have a different inherent potential for improving plant growth and nutrition in Zn-contaminated soil. The bacterium increased the potential of mycorrhizal mycelium as inoculum. SIGNIFICANCE AND IMPACT OF THE STUDY: Mycorrhizal performance, particularly that of the autochthonous strain, was increased by the bacterium and both contributed to better plant growth and establishment in Zn-contaminated soils.

Brevibacillus brevis isolated from cadmium- or zinc-contaminated soils improves in vitro spore germination and growth of Glomus mosseae under high Cd or Zn concentrations.

In this study we investigated the saprophyte growth of two arbuscular-mycorrhizal fungi (Glomus mosseae isolate) under increasing Cd or Zn levels and the influence of a selected bacterial strain of Brevibacillus brevis. Microorganisms here assayed were isolated from Cd or Zn polluted soils. B. brevis increased the presymbiotic growth (germination rate growth and mycelial development) of Glomus mosseae. Spore germination and mycelial development of both G. mosseae isolate were reduced as much as the amount of Cd or Zn increased in the growth medium. In medium supplemented with 20 microg Cd mL(-1), the spore germination was only 12% after 20 days of incubation, but the coinoculation with B. brevis increased this value to 40% after only 15 days. The addition of 20 microg Cd mL(-1) to the growth medium drastically inhibited hyphal development, but the presence of the bacterium increased hyphal growth of G. mosseae from 195% (without Cd) until 254% (with 20 microg Cd mL(-1)). The corresponding bacterial effect increasing micelial growth ranged from 125% (without Zn) to 232% (200 microg Zn mL(-1)) in the case of G. mosseae isolated from Zn-polluted soil. Mycelial growth under 5 microg Cd mL(-1) (without bacterium) was similarly reduced from that produced at 15 microg Cd mL(-1) in the presence of the bacteria. As well, 50 microg Zn mL(-1) (without bacterium) reduced hyphal growth as much as 200 microg Zn mL(-1) did in the presence of B. brevis. The bacterial effect on the saprophytic growth of G. mosseae in absence of metal may be due to the involvement of indole acetic acid (IAA) produced by these bacteria. The Cd bioaccumulation ability exhibited (76%) by Cd-adapted B. brevis reduced the Cd damage on G. mosseae in Cd-contaminated medium. These capabilities of B. brevis isolates partially alleviate the inhibitory effects of Cd or Zn on the axenic growth of G. mosseae.

Production of Plant Growth-Regulating Substances by the Vesicular-Arbuscular Mycorrhizal Fungus Glomus mosseae.

Glomus mosseae, a representative species of Endogonaceae (Phycomycetes) able to form vesicular-arbuscular mycorrhiza, was investigated for phytohormone production. Spores of G. mosseae were axenically germinated in water, and the resultant mycelial growth was assayed by standard procedures for extracting plant hormones from microbial cultures. Paper partition chromatography and specific bioassays were used to separate and identify plant growth-regulating substances. The microorganism synthesized at least two gibberellin-like substances, one with R(f) corresponding in position to authentic gibberellic acid, and four substances with the properties of cytokinins.

Inoculation of woody legumes with selected arbuscular mycorrhizal fungi and rhizobia to recover desertified mediterranean ecosystems.

Revegetation strategies, either for reclamation or for rehabilitation, are being used to recover desertified ecosystems. Woody legumes are recognized as species that are useful for revegetation of water-deficient, low-nutrient environments because of their ability to form symbiotic associations with rhizobial bacteria and mycorrhizal fungi, which improve nutrient acquisition and help plants to become established and cope with stress situations. A range of woody legumes used in revegetation programs, particularly in Mediterranean regions, were assayed. These legumes included both exotic and native species and were used in a test of a desertified semiarid ecosystem in southeast Spain. Screening for the appropriate plant species-microsymbiont combinations was performed previously, and a simple procedure to produce plantlets with optimized mycorrhizal and nodulated status was developed. The results of a 4-year trial showed that (i) only the native shrub legumes were able to become established under the local environmental conditions (hence, a reclamation strategy is recommended) and (ii) biotechnological manipulation of the seedlings to be used for revegetation (by inoculation with selected rhizobia and mycorrhizal fungi) improved outplanting performance, plant survival, and biomass development.