Improved Mineral Nutrition Research Articles

Growth Response of <i>Gliricidia sepium</i> (Jacq.)Walp to Inoculation with Different Arbuscular Mycorrhizal (Am) Fungi

This study was conducted to assess the variation in performance of four arbuscular mycorrhizal fungi (Glomus clarum, Glomus etunicatum, Glomus intraradices, and Gigaspora rosea) with and without Rhizobium inoculation in promoting growth and nutrient (N and P) uptake in Gliricidia sepium. Gliricidia seedlings were grown in sterilised (autoclaved) vermiculite and sand mixture in 2:1 (v:v). Each week, plants received 50 cm3 of nutrient solution (with N and P additions) according to the treatments. The experimental design was a 4x2 factorial arranged in a randomised complete block design. Seedlings were harvested after 12 weeks. Dry weights of plant parts, nodulation, arbuscular mycorrhizal fungal colonization, nitrogen and phosphorus concentration and content were determined. AM fungi differed in their effectiveness in enhancing growth of Gliricidia sepium. Glomus clarum was most efficient and produced statistically higher total plant dry weight than other mycorrhizal fungi. Dual inoculation with AM fungi and Rhizobium was effective in promoting host plant growth over Rhizobium- uninoculated mycorrhizal plants in terms of leaf area, shoot and root dry weights, total plant biomass and shoot-root ratio. Rhizobium-inoculated Glomus clarum treatment recorded significantly higher (approximately a third fold increase) total plant dry weight, than the similar treatments of Glomus etunicatum, Glomus intraradices and Gigaspora rosea. Shoot-root ratio was statistically greater with mycorrhizal plants inoculated with Rhizobium than the non-Rhizobium inoculated treatments due to improved mineral nutrition particularly nitrogen (through nitrogen fixation). Nodulation assessed by the number of nodules produced per plant was statistically similar between the Rhizobium- inoculated mycorrhizal treatments but significantly higher than the Rhizobium- inoculated non-mycorrhizal comparison treatment. Plants inoculated with Glomus clarum and Glomus intraradices significantly achieved higher root colonization than Glomus etunicatum and Gigaspora rosea. Rhizobium inoculation reduced root colonization with all the Glomus species except Gigaspora rosea. A highly significant (P

Effects of arbuscular mycorrhizal inoculation on cadmium accumulation by different tobacco ( Nicotiana tabacum L.) types

The effect of arbuscular mycorrhiza (AM) on cadmium (Cd) uptake by tobacco ( Nicotiana tabacum L.) was studied in a pot experiment. Three commercial varieties, Basma BEK, K326 and TN90, representing three distinct tobacco types, were each grown in a different soil with nutritional conditions matching as closely as possible their requirements for field production. Cd concentrations in these soils were within the background range. Each variety was either non-mycorrhizal or inoculated with one of five AM fungal isolates. Cd concentration in leaves was decreased by inoculation with selected isolates in the K326 and TN90 variety grown in acidic soils. In contrast, it was increased by inoculation with most isolates in the Basma BEK variety grown in a basic soil with low Cd availability. Besides, plants of all three varieties had significantly higher leaf concentrations of phosphorus and nitrogen in some inoculated treatments. The percentage of root colonisation was mostly low in the inoculated treatments. In the Basma BEK and TN90 variety, the tested AM fungal isolates differed in their ability to colonise roots, but no correlation was found between the root colonisation of an isolate and its effects on the Cd concentrations in tobacco leaves. One isolate influenced most pronouncedly Cd concentrations and improved mineral nutrition in all the three combinations of variety and soil despite its low colonisation levels. AM symbiosis probably affected Cd uptake of tobacco by indirect mechanisms such as stimulation of root growth or mycorrhizal plant mediated changes in chemical or biological soil properties.

Biochemical changes in micropropagated grape ( Vitis vinifera L.) plantlets due to arbuscular-mycorrhizal fungi (AMF) inoculation during ex vitro acclimatization

Improved establishment of mycorrhizal tissue culture derived plantlets during acclimatization (Stage IV) is commonly attributed to the enhanced vegetative growth as a resultant of different morphological and in vivo changes. These changes are early and better cuticle development, high biomass accumulation, enhanced physiological changes, improved mineral nutrition, especially phosphorus and micronutrients, etc. However, improvement in establishment of micropropagated plantlets during acclimatization may not only be limited to these mechanisms. In the present investigation, biochemical status of micropropagated grape plantlets in response to six single and a mixed strains of arbuscular-mycorrhizal fungi (AMF) during hardening were studied under glasshouse conditions. The histochemical studies revealed that the mycorrhizal inoculation resulted in accumulation of different biochemicals in the plant system such as chlorophyll, carotenoids, proline, phenol and enzymes like polyphenol oxidase (PPO) and nitrate reductase (NR). The mycorrhizal plantlets showed enhanced survival and improved tolerance against stresses experienced during weaning phase. The mycorrhizal plants also exhibited improved physiological and nutritional status and had higher relative water content (RWC) and photosynthetic rate. These plantlets also accumulated higher N, P, Mg and Fe concentrations, which may primarily be as a result of biochemical changes brought about by mycorrhizal association. Mycorrhizal plantlets also showed better hardening under glasshouse conditions. The result suggests that the biochemical changes brought about by mycorrhization were helpful in mitigating different stresses experienced by the tissue culture plants during hardening, which determine their performance later in field.

Large‐scale identification of genes in the fungus Hebeloma cylindrosporum paves the way to molecular analyses of ectomycorrhizal symbiosis

• In an attempt to advance the understanding of ectomycorrhizal symbiosis, which improves mineral nutrition and resistance to abiotic and biotic stresses of most woody plants from temperate and boreal regions, we produced a cDNA library of the ectomycorrhizal fungus Hebeloma cylindrosporum in a yeast expression vector. The library was used for functional complementation cloning and for sequencing of 4036 expressed sequence tags (ESTs). • Expression of the library in a yeast ade2 and trp1 mutant strain allowed cloning of two Hebeloma genes, HcADE2 and HcTRP1 by functional complementation. This experiment highlighted both the efficiency of the complementation strategy and the quality of the library. • All sequence data available on Hebeloma (4596) were analysed and contiged. The whole EST resource is accessible via a web interface, which allows searching and navigation through clusters and tentative contigs (TCs). • Analysis of the database revealed a low level of counterparts already identified in other ectomycorrhizal fungi. For example, it allowed identification of a large set of membrane transporters, such as phosphate, potassium, sulphate or micronutrient transporters. Thus, this EST resource provides a valuable tool for research on ectomycorrhiza and symbiotic interactions.

Calcium Analysis of Selected Western African Foods

Because mineral composition data for Western African foods are incomplete, it is essential to obtain analyses of foods in order to assess the quality of existing food as well as to estimate dietary intake of various minerals, such as calcium. Twenty-eight Western African foods were analyzed for calcium using the method described by Ferguson et al., (1993) and the Association of Official Analytical Chemists (AOAC) (Padmore, 1990). Calcium concentrations were determined using an inductively coupled plasma atomic emission spectrophotometer (ICP). Calcium recovery was 94.4% of the expected value with respect to a standard reference material (corn husk). For all foods assessed, the content of calcium ranged from 3.04 to 3630 mg/100 g dry wt. Based on dry weight, the top five foods for calcium in rank order were sorrel leaves (3630 mg/100 g), amaranth leaves (3590 mg/100 g), okra leaves (2850 mg/100 g), onion leaves (2540 mg/100 g), and baobab leaves (2240 mg/100 g). Data from this study provide calcium analyses of some commonly eaten Western African foods, which should help in planning food-based intervention programs to improve mineral nutrition.

Regulation of the germination of Aleppo pine (Pinus halepensis) by nitrate, ammonium, and gibberellin, and its role in post-fire forest regeneration

Aleppo pine (Pinus halepensis Mill.) regenerates after wildfires only by germination. This post-fire germination is controlled by temperature, light and the chemical characteristics of the ash-bed. The extremely high pH caused by the ash inhibits germination of Aleppo pine as well as of many other species. Here we report that ash extracts at neutral pH stimulate P. halepensis germination. The effects of ash extracts, nitrate, ammonium (in concentrations present in the ash) and GA 3 on the germination of P. halepensis seeds and on lipase activity at early germination were studied under controlled conditions. Sub-optimal concentrations of nitrate-and ammonium-stimulated germination and the activity of lipase in the seeds. It is proposed that nitrate increases seed sensitivity to GA 3 while ammonium directly affects lipase activity. The balance between the inhibition of germination by the high pH of ash and its stimulation by the nitrate and ammonium present in the ash determines the overall effect of the ash on post-fire germination of Aleppo pine. The pine seedlings appear in high density among the trees but because of the effects of the ash they appear in sparse stands under the projection of the burned pine canopies. These seedlings benefit from weak inter- and intra-specific competition as well as improved mineral nutrition and have good chances to grow into large trees that will form the regenerating forest; therefore, the enhancement of P. halepensis germination by nitrate and ammonium and its inhibition by high pH can he considered as ecophysiological adaptations to post-fire regeneration.

Water relations of whole strawberry plantlets in vitro inoculated with Glomus intraradices in a tripartite culture system

An in vitro tripartite culture system was used to monitor the effect of arbuscular mycorrhizal (AM) symbiosis on host plant water relations. We hypothesized that the root colonization by Glomus intraradices Schenck and Smith modifies the water’s status, the control of water losses and the osmotic relations of leaves and roots of micropropagated strawberry ( Fragaria ananassa Duch. cv. Kent) plantlets, under in vitro conditions of high humidity. Strawberry plantlets, AM or non-AM, disposed in a randomized complete block design, were assessed in order to measure relative water content (RWC) of leaf discs, roots and complete plants, leaf stomatal conductance (Gs), leaf and root osmotic potentials (Ψ πL, Ψ πR), chlorophyll fluorescence parameters Fv/Fm, fresh, dry and turgid weights and mineral content. Although Ψ πL, Ψ πR, Gs and RWC of foliar discs were not affected by the fungal inoculation, the RWC of the complete plants was 11% higher in AM colonized plantlets compared to non-AM ones. This significant increase of RWC of whole plants was not related to an improved mineral nutrition nor growth stimulation of mycorrhizal plantlets. This is the first report that AM colonization enhances the RWC of entire strawberry microplants under axenic well-watered conditions. We have concluded that this effect is related to a higher water content in AM root systems not paralleled to a dilution in the root osmotic potential, Ψ πR, suggesting that mycorrhizal roots must have a higher concentration of water soluble compounds or a different distribution in the cell compartments than non-AM roots.

Les mycorhizes des plantes actinorhiziennes

Summary As pioneer species for land revegetation, actinorhizal plants are predisposed to form with mycorrhizal fungi symbiotic associations that are as essential for plant growth as the associations they form with Frankia. As expected, mycorrhizas stimulate the development and the N2-fixing activity of the actinorhizal symbiosis by improving mineral nutrition of the host plant. In addition to mycorrhizas, actinorhizal plants are also able to form an unique type of roots called « proteoid roots » or « cluster roots » in response to the detrimental effects of nutrient deficiencies in soil. As an alternative of mycorrhizas, cluster roots are specialized roots capable of assisting plant growth in marginal, nutrient deficient soils. There is no competition between Frankia and mycorrhizal fungi for infection sites but extensive mycorrhizas can affect Frankia growth and the subsequent development of young lobes of actinorhizal nodules. By contrast, the presence of Frankia in planta has no incidence on mycorrhizal infection processus. With reference to Alnus and Allocasuarina the possible implications of Frankia and mycorrhizal fungi on the mechanisms of recognition and chemical signalisation between the host plant and these microsymbionts are discussed. Strikingly, it should be noticed that Frankia and arbuscular endomy- corrhizal fungi exhibit a number of similarities that could be taken into account for developing future research.

Implication of ectomycorrhizal fungi in the cytokinin relations of loblolly pine (Pinus taeda L.)*

SUMMARYSeven ectomycorrhizal fungi were screened by a soybean cell division bioassay to determine their potential for cytokinin synthesis. Fungal isolates of Rhizopogon roseolus (Corda) Hollos and Suillus punctipes (Peck) Sing, released significant quantities of cytokinin‐like substances into the culture medium. In contrast, Cenococcum geophilum (Fr.), Hebeloma crustuliniforme (Bull. ex. St. Amans) Qual., Pisolithus tinctorius (Pers.) Coker and Couch, Suillus granulatus (L. ex. Fr.) O. Kuntze, and Thelephora terrestris (Ehrh.) Fr. failed to elicit a positive cytokinin response in the soybean bioassay. Purification of S. punctipes culture filtrates by cation exchange, organic solvent partitioning, and separation on Sephadex LH‐20 revealed the presence of compounds with the same retention volume as zeatin and zeatin riboside. Greenhouse studies with loblolly pine (Pinus taeda L.) indicated that, together with improved plant growth and enhanced mineral nutrition, P. tinctorius mediated a significant effect on host cytokinin relations. Cytokinin activity of extracted needles increased 44 and 30% for 12‐ and 14‐month‐old seedings, respectively, following ectomycorrhizal establishment. Axenically grown seedlings colonized by 5. punctipes showed no alterations in growth, nutrition, or cytokinin concentration, compared to non‐inoculated controls, even though mycorrhizal formation exceeded 30%. The ability of ectomycorrhizal fungi to affect host cytokinins was not dependent upon an ability to synthesize cytokinins in pure culture. Results are discussed in relation to improved mineral nutrition, enhanced root growth, and increased short‐root proliferation in the ectomycorrhizal association.

Mycorrhizae Influence Tropical Succession

Most vascular plants depend to some extent on vesicular-arbuscular (V-A) mycorrhizae for mineral uptake, although a few species do not. Some mycotrophic plants cannot grow without mycorrhizae; others grow better without mycorrhizae in fertile soils, but benefit from mycorrhizae in poor soils. Thus, the mycorrhizal fungus content and the fertility of soil influence the occurrence of plant species. Because V-A mycorrhizal fungi depend on mycotrophic plants for carbon, and because they produce few spores which may survive only a short time in the lowland humid tropics, plant community composition in turn affects the mycorrhizal fungus content of soil. This influences the further course of plant succession by affecting which species of plants can subsequently occur in the community. Pool soils may favor alternate stable communities. If mycorrhizal fungi are present, obligately mycotrophic species are the best competitors and should dominate communities. They support an abundance of mycorrhizal fungi, ensuring the continued superiority of obligate mycotrophs. If mycorrhizal fungi are absent, non-mycorrhizal species will comprise the community. Even if mycorrhizal fungi are subsequently introduced, these plants will not support them, favoring persistence of the non-mycorrhizal species. On fertile soils, facultative mycotrophs are most common. They will support infection if mycorrhizal fungi are available when the soils age and fertility declines, paving the way for their replacement by obligate mycotrophs. If mycorrhizal fungi are unavailable, facultatively mycotrophic species will be replaced by non-mycorrhizal plants. Non-mycorrhizal plants may also derive competitive advantage where mycorrhizal fungi are present, from not needing to await infection to start growing. Thus, pioneer species are often non-mycorrhizal. Seral species tend to be facultative mycotrophs, and most lowland tropical forest trees tend to be obligately mycotrophic. Ectomycorrhizal individuals are likely to occur in abundance in nutrient-starved or disturbed habitats, although ectomycorrhizal species are rare in the lowland tropics. Ectomycorrhizal associates may influence tropical succession by lowering populations of V-A mycorrhizal fungi. THIS PAPER SUGGESTS how interactions between vascular plants and mycorrhizal fungi may influence succession. I discuss: 1) how plants depend on mycorrhizae to different degrees for mineral uptake; 2) how different dependence on mycorrhizae might affect the competitive success of plants in soils with different mycorrhizal fungus contents and mineral availabilities, and as a consequence, might influence plant community composition; 3) how plant communities, in turn, may affect mycorrhizal fungus populations; and 4) how further development of a plant community thereby might be influenced. There is evidence for the first three of these interactions; the fourth, consequent successional change, is based on inference. I focus on vesicular-arbuscular (V-A) mycorrhizal associations in the lowland tropics. Ectomycorrhizal associations, rare in the lowland tropics, are discussed as exceptions, because compared to V-A mycorrhizal fungi ectomycorrhizal fungi are more host-specific, disperse better, and some species may not be as dependent on their hosts. PLANTS DIFFER IN THEIR DEPENDENCE ON MYCORRHIZAE Most species of plants are capable of associating with fungi of a single zygomycetous family, the Endogonaceae, to form V-A mycorrhizae (Gerdemanin 1968). By improving mineral nutrition, especially if substrate mineral availability is low or imbalanced, V-A mycorrhizae can increase the growth of host plants (Mosse 1973b), can improve water uptake and resistance to temporary wilting (Safir, Boyer and Gerdemann 1972; Menge et al. 1978), and may improve seedling survival (Baylis 1959; Gerdemann 1965; Kleinschmidt and Gerdemann 1972; Janos 1975a, 1975b, 1977). Mycorrhizae seem to minimize the expense to the host of seeking-out minerals (Harley 1975) even though the hosts supply carbon to V-A mycorrhizal fungi (Ho and Trappe 1973). The external hyphae of mycorrhizae increase mineral uptake, especially uptake of phosphorus which is relatively immobile in soil, probably by providing a large, well-distributed absorbing surface (Mosse 1973b). The advantage of an extensive absorbing surface is diminished in fertile soils (Voigt 1971), however, and continued support of mycorrhizae in fertile soils may decrease host growth (Cooper

Cone-Induction Response of Douglas Fir to Form of Nitrogen Fertilizer and Time of Treatment

Cone production increases of 2.5, 5.0 and 1.5 times that of control were obtained the year following treatment with 400 lb nitrate nitrogen per acre (1 lb/acre = 1.12 kg/ha), applied 6 weeks before vegetative bud break, at the start of bud break, and 10 days after the midpoint of the bud break period, respectively, on 20-year-old Douglas fir (Pseudotsugamenziesii (Mirb.) Franco.). Cone counts of 15, 26, 72, 142 and 155 were obtained from 0, 200, 400, 800 and 1600 lb nitrate nitrogen per acre, applied to 13-year-old trees during early bud break. Ammonium nitrogen, applied at the same rates and times, was ineffective for stimulation of cone production on either age of tree. There were no differences in rate of accumulation of total nitrogen in buds and foliage, shoot-growth responses, or total number of buds per shoot due to form of nitrogen. Nitrate treatment enhanced cone production through a reduction in bud failure during the shoot elongation period. These results suggest responses are not primarily due to improved mineral nutrition, but to a specific chemical stimulation from critically timed changes in type of nitrogen metabolism. Possible influences of temperature and rainfall on natural cone crop periodicity and on proper timing of nitrate treatment are discussed.