Mycorrhizal Formation Research Articles

Establishment of Sweet Birch on Surface Mine Spoil as Influenced by Mycorrhizal Inoculation and Fertility

Abstract Induced mycorrhization of sweet birch (Betula lenta L.) by Pisolithus tinctorius (Pers.) Coker & Couch, as influenced by substrate fertility, was evaluated for its effects on seedling growth and physiology. Following a brief period in seed flats, seedlings were transplanted to mine spoil where they resided for 30 months, and three nutrition regimes were imposed throughout the study by application of differing nutrient solution concentrations. High fertility suppressed mycorrhizal formation by P. tinctorius but promoted that of other mycobionts. Pisolithus mycorrhization induced substantial aboveground and belowground growth as indicated by dimensions and mass for the former and mass and length for the latter but favoring root over shoot growth overall. Furthermore, these mycorrhizae were frequently able to compensate for the growth stimulation of higher nutrient additions. Measurements of xylem pressure potential and soil water potential indicated that water uptake was enhanced by P. tinctorius during simulated drought episodes of two durations and in subsequent recovery periods. Inoculated seedlings had higher foliar concentrations of critical nutrients, especially N, and lower concentrations of potentially phytotoxic metallic elements, particularly Mn, than uninoculated seedlings, although the latter response was absent in high fertility. Spoil analyses clearly revealed the influence of the nutrition regimes but also the effects of seedling uptake on substrate chemistry, and reinforced the findings of the foliar analysis concerning suppression of metal uptake by P. tinctorius. Collectively, these results suggest that P. tinctorius can provide sweet birch an array of physiological benefits that will permit this tree species to flourish on harsh substrates such as surface mine spoils without heavy application of chemical fertilizers.

Ectomycorrhizal Formation in Herbicide-Treated Soils of Differing Clay and Organic Matter Content

Herbicides are commonly used on private timberlands in the western United States for site preparation and control of competing vegetation. How non-target soil biota respond to herbicide applications, however, is not thoroughly understood. We tested theeffects of triclorpyr, imazapyr, and sulfometuron methyl on ectomycorrhizal formation in a greenhouse study. Ponderosa pine, Douglas-fir, and white fir seedlings were grown in four forest soils ranging in clay content from 9 to 33% and organic matter content from 3 to 17%, and treated with commercial formulations of each herbicide at 0, 1.0, and 2.0 times the recommended field rate. Many of the possible herbicide-soil combinations resulted in reduced seedling growth. Root development was particularly sensitive to the three herbicides, with an average of 51% fewer root tips compared to the control treatment. The ability of mycorrhizal fungi to infectthe remaining root tips, however, was uninhibited. Mycorrhizal formation was high, averaging 91% of all root tips, regardless of herbicide, application rate, soil type, or conifer species. In agreement, soil microbial biomass and respiratory activity were unaffected by the herbicide treatments. The results show that these herbicides do not alter the capability of mycorrhizal fungi to infect roots, even at concentrations detrimental to seedling growth.

Arbuscular mycorrhizal formation of crucifer leaf mustard induced by flavonoids apigenin and daidzein

Flavonoids from legume root secretion may probably act as signal molecules for expression of Rhizobial “nod” nodulation genes and AM fungal symbiotic gene. Leaf mustard is a non-mycorrhizal plant; it does not contain flavonoids and other signal molecules. AM fungi could not infect the roots of leaf mustard and form a symbiont in nature, when it was treated with flavonoids (apigenin or daidzein). The results of trypan blue staining showed that two kinds of AM fungi (G intraradices and G. mosseae) successfully infected the roots of non-mycorrhizal plant leaf mustard. AM fungi grew towards and colonized the roots of leaf mustard, producing young spores and completing the course of life. AM fungi are the only one kind of fungi with ALP activity. The result of ALP staining has also proved that AM fungi infected successfully the roots of leaf mustard. AM fungi (G intraradices and G. mosseae) that existed in the roots of non-mycorrhizal plant leaf mustard were probed by nested PCR and special molecular probes. The above-mentioned proof chains have fully proved that flavonoids induced AM fungi (G intraradices and G. mosseae) to infect non-mycorrhizal plant and establish symbiotic relationship.

Interactive Effects of Mycorrhization and Fertilization on Growth, Nutrition, and Water Relations of Sweet Birch

Pisolithus tinctorius(Pers.) Coker & Couch was evaluated as an ectomycorrhizal associate of sweet birch (Betula lentaL.). Sand culture and mine soil growth media were employed, and three fertilization treatments were imposed by application of differing Hoagland's nutrient solution #2 concentrations. The high fertilization treatment suppressed mycorrhizal formation by P. tinctoriusin both growth media, while the medium rather than the low treatment induced the most extensive colonization by this mycobiont. Seedlings with induced P. tinctoriusmycorrhization exhibited enhanced above— and below-ground growth according to shoot dimensions and dry weight and root weight and length. However, these responses were frequently absent with high fertilization, especially in the mine soil. Inoculated seedlings had higher foliar N, P, and K concentrations overall but lower Ca, Mg, and S concentrations than uninoculated seedlings. Those with P. tinctoriusalso had lower concentrations of several potentially phytotoxic trace elements, specifically Zn, B, Mo, and Al. Furthermore, xylem pressure and soil water potentials measured during a simulated drought episode indicated that water uptake was enhanced by these mycorrhizae. Again, however, the above physiological responses were often compromised by high fertilization. Collectively, these results indicate that P. tinctoriusis a viable mycobiont for the inoculation of sweet birch, and when substrate fertility is not excessive, can avail this host of physiological benefits that result in substantial growth enhancement.

Calluna vulgaris root cells show increased capacity for amino acid uptake when colonized with the mycorrhizal fungus Hymenoscyphus ericae.

• Ericoid mycorrhizas are believed to improve N nutrition of many ericaceous plant species that typically occur in habitats with impoverished nutrient status, by releasing amino acids from organic N forms. Despite the ubiquity of mycorrhizal formation the mechanisms and regulation of nutrient transport in mycorrhizal associations are poorly understood. • We used an electrophysiological approach to study how amino acid transport characteristics of Calluna vulgaris were affected by colonization with the ericoid mycorrhiza fungus Hymenoscyphus ericae . • Both the V max and K m parameters of amino acid uptake were affected by fungal colonization in a manner consistent with an increased availability of amino acid to the plant. • The ecophysiological significance of altered amino acid transport in colonized root cells of C. vulgaris is discussed.

Characterization of an Aux/IAA cDNA upregulated in Pinus pinaster roots in response to colonization by the ectomycorrhizal fungus Hebeloma cylindrosporum.

• In an attempt to determine whether fungal auxin affects host plant gene expression during mycorrhizal formation, an auxin upregulated cDNA, Pp-iaa88, was isolated by differential screening of a cDNA library made from auxin-treated Pinus pinaster roots. • Pp-iaa88 codes for a polypeptide that shares extensive homology to auxin-inducible Aux/IAA proteins, which are supposed to act as transcription factors. Cycloheximide did not inhibit auxin-induced mRNA accumulation, indicating that Pp-iaa88 upregulation is a primary (direct) auxin response. • The level of Pp-iaa88 transcripts in roots increased following inoculation with either an indoleacetic acid-overproducing mutant or a wild-type strain of the ectomycorrhizal fungus Hebeloma cylindrosporum. With both strains, mRNA accumulation was detectable as soon as fungal hyphae reached the root and it increased during differentiation of symbiotic structures. The kinetics of Pp-iaa88 transcript accumulation was closely connected with the dynamics of symbiosis establishment and was more rapid with the mutant than with the wild-type strain. • As a putative transcription factor expressed at the very early stages of symbiosis establishment, Pp-iaa88 could play a key role in mycorrhizal formation.

The effects of nitrogen fertilization and soil properties on mycorrhizal formation of Salix viminalis

The effects of nitrogen fertilization (100, 200 kg N ha −1 per year) and soil properties on mycorrhizal formation on Salix viminalis were investigated at three short rotation plantations on Gleysols and Cambisols (Abbachhof (ABB) and Wildeshausen (WIL) in Germany, Ultuna (ULT) in Sweden). During 3 years the ectomycorrhizal colonization, the composition of ectomycorrhizal morphotypes and the VAM spore density in the soil were analyzed. The ectomycorrhizal colonization was significantly altered due to N-fertilization at all sites. The quality and magnitude of the fertilization effects on mycorrhizal formation on Salix viminalis varied due to the soil properties, i.e. soil texture, soil N content and pH. The WIL site was characterized by sandy soil (low pH, high soil N content), whereas the ABB site was characterized by clayey soil (high pH, low N content). The ULT site was characterized by clayey soil (high pH, high N content). In the unfertilized control plots (C), ectomycorrhizal colonization was higher at WIL than at ABB. Fertilization reduced the ectomycorrhizal colonization at WIL but increased it at ABB. The distribution of the ectomycorrhizal morphotypes was very heterogeneous within the treatments, therefore significant differences were rare. Sporocarps were collected at ABB during one growing period. The sporocarps were mostly from saprophytic species, with exception of the ectomycorrhizal species Inocybe glabripes. Significant effects of N-fertilization on VAM spore density were observed at two of the three plantations. The pattern in VAM spore density was similar to the pattern seen for ectomycorrhizal colonization. Thus, VAM spore density was increased by fertilization at ABB (low soil N) and decreased at ULT (high soil N). The soil properties have been shown to modify the effects of fertilization on ectomycorrhizal colonization and VAM spore density. Therefore, in management practice of short rotation plantations, the benefit of N-fertilization should be evaluated keeping secondary effects caused by changed mycorrhizal formations in mind.

Tillage and farming system affect AM fungus populations, mycorrhizal formation, and nutrient uptake by winter wheat in a high-P soil

AbstractWe conducted a field study at the Rodale Institute Experimental Farm, Kutztown, Pennsylvania, in a high-P soil to examine the interaction of farming system and tillage on the potential functioning of arbuscular mycorrhizal (AM) fungi. Plots under conventional and low-input systems were either chisel-disked or no-tilled. Winter wheat was planted following the harvest of soybean, and shoots and roots were collected at tillering, jointing, heading, and ripening. Spores of AM fungi were isolated from soil collected at the beginning and end of the growing season. Spore populations and colonization of winter wheat roots by AM fungi were higher under low-input than conventional agriculture. Mycorrhizal fungus colonization occurred at low levels in the tillering stage and increased with plant development. Colonization during the jointing stage was higher in the low-input, no-tilled than in low-input, chisel-disked plots. Spore populations of theGlomus occultum-type group were more numerous in no-tilled than in tilled soil. The nutrient-use efficiency (g of plant biomass per g of plant N or P) of winter wheat depended on plant developmental stage, with a tendency for higher efficiency of the low-input plants at early growth stages, and of conventionally managed plants at more mature stages. Overall, plants grown in chisel-disked plots had higher N and P utilization efficiencies than plants grown in no-tilled plots. Final yield of grain was significantly greater in conventional than low-input plots, especially for no-till, despite the larger population of AM fungi.

Influence of adverse soil conditions on the formation and function of Arbuscular mycorrhizas

The majority of plants have mycorrhizal fungi associated with them. Mycorrhizal fungi are ecologically significant because they form relationships in and on the roots of a host plant in a symbiotic association. The host plant provides the fungus with soluble carbon sources, and the fungus provides the host plant with an increased capacity to absorb water and nutrients from the soil. Adverse conditions are a pervasive feature in both natural and agronomic soils. The soil environment is constantly changing with regard to moisture, temperature and nutrient availability. In addition, soil properties are often manipulated to improve crop yields. In many cases, soils may be contaminated through disposal of chemicals that are toxic to plants and microorganisms. The formation and function of mycorrhizal relationships are affected by edaphic conditions such as soil composition, moisture, temperature, pH, cation exchange capacity, and also by anthropogenic stressors including soil compaction, metals and pesticides. Arbuscular mycorrhizal fungi are of interest for their reported roles in alleviation of diverse soil-associated plant stressors, including those induced by metals and polychlorinated aliphatic and phenolic pollutants. Much mycorrhizal research has investigated the impact of extremes in water, temperature, pH and inorganic nutrient availability on mycorrhizal formation and nutrient acquisition. Evaluation of the efficacy of plant–mycorrhizal associations to remediate soils contaminated with toxic materials deserves increased attention. Before the full potential benefits of arbuscular mycorrhizal fungi to reclaim contaminated soils can be realized, research advances are needed to improve our understanding of the physiology of mycorrhizae subjected to adverse physical and chemical conditions. This paper will review literature and discuss the implications of soil contamination on formation and function of arbuscular mycorrhizal associations.

Specific Features of Mycorrhizal Symbiosis Formation in the Ontogeny of Orchids of the Temperate Zone

The study of relationships between symbiotic fungi and germinating seeds of the Orchidaceae showed that the effect of a fungus on germination depends on the presence of seed dormancy and its pattern. The specificity of symbiosis varies widely. The development of symbiotic sprouts in situand in vitro differs only in the rate, whereas the morphogenesis of asymbiotic sprouts is characterized by several anomalies.

Induction of Ltp (lipid transfer protein) and Pal (phenylalanine ammonia-lyase) gene expression in rice roots colonized by the arbuscular mycorrhizal fungus Glomus mosseae.

The expression of a lipid transfer protein (LTP) gene is regulated in Oryza sativa roots in response to colonization by the mycorrhizal fungus Glomus mosseae. Transcript levels increased when the fungus forms appressoria and penetrates the root epidermis and decreased at the onset of the intercellular colonization of the root cortex. The analysis of histochemical GUS staining in transgenic rice plants carrying the Ltp/Gus construct confirm the induction of LTP: gene associated with fungal appressoria formation and penetration area. The induction of Ltp gene expression coincided in time with a transient increase in the expression of a phenylalanine ammonia-lyase (PAL:) gene and a transient accumulation of salicylic acid (SA) in the mycorrhizal roots. The expression of LTP: and PAL: was induced in rice roots after treatment with SA and Pseudomonas syringae indicating that both genes could be implicated in the plant defence response. The exogenous application of SA to rice interacting with the mycorrhizal fungus did not affect appressoria formation but, instead, resulted in a transient delay of root mycorrhization. Nevertheless, although LTP: maintained a prolonged SA-induced expression level, mycorrhizal formation could still proceed.

Effects of nitrogen and phosphorus fertilization on mycorrhizal formation of two poplar clones (Populus trichocarpa and P. tremula x tremuloides)

Mineral fertilization is a common management practice in short rotation forestry. The mycorrhizal formation of trees can be affected by fertilizer applications, however, very little is known on such effects in arable soils. The effects of a nitrogen (N) and phosphorus (P) fertilization on mycorrhizal formation of two poplar clones (Populus trichocarpa and P. tremula x tremuloides) were investigated at the plantation Abbachhof (South Germany). We determined the ectomycorrhizal colonization and the abundance of VAM spores in the soil during three years, and the species richness of sporocarps during one growing season. Approximately 26 to 73% of the fine roots of P. trichocarpa and 41 to 82% of the fine roots of P. tremula x tremuloides were colonized with ectomycorrhizal fungi. The percentage of ectomycorrizal colonization on P. tremula x tremuloides was significantly reduced after both fertilization treatments. On P. trichocarpa only the P-fertilization reduced the ectomycorrhizal colonization. The composition of ectomycorrhizal morphotypes was significantly affected by the N and P fertilization on P. tremula x tremuloides, but not on P. trichocarpa. Sporocarps of 12 ectomycorrhizal fungi species were found at the plantation. Cortinarius uliginosus, Lactarius controversus and Krombholziella aurantiaca produced sporocarps only on control plots, whereas Cortinarius croceocaeruleus, Inocybe umbrina, Laccaria tortilis, Paxillus involutus and Rhizopogon roseolus produced sporocarps only on fertilized plots. Inocybe geophylla, I. glabripes, Laccaria laccata and Tuber borchii produced sporocarps on both control and fertilized plots. The density of VAM spores was lower in the rooting zone of Populus trichocarpa than under P. tremula x tremuloides. In an efficient management of these short rotation plantations mineral fertilizer applications must be low enough to avoid undesired suppressions of mycorrhizal formation. Auswirkungen von Stickstoff- und Phosphordüngung auf die Mykorrhizierung von zwei Pappelklonen (Populus trichocarpa und P. tremula x tremuloides) Mineralische Düngung ist ein gängiger Bestandteil der Kurzumtriebsbewirtschaftung. Die Mykorrhizaausbildung der Bäume kann durch Düngung beeinflusst werden. Bisher ist jedoch wenig über die Auswirkungen dieser Maßnahme auf landwirtschaftlichen Böden bekannt. Auf der Schnellwuchsplantage Abbachhof (Süddeutschland) wurde die Wirkung von Stickstoff- und Phosphordüngung auf die Mykorrhizierung zweier Pappelklone (Populus trichocarpa und P. tremula x tremuloides) auf einem zuvor landwirtschaftlich genutzten Boden untersucht. Die Ektomykorrhizierungsrate und die Anzahl der VAM Sporen im Boden wurden über drei Jahre und das Auftreten von Fruchtkörpern ektomykorrhizierender Pilzarten wurde während einer Vegetationsperiode erfasst. Zwischen 26 bis 73% der Feinwurzeln von Populus trichocarpa und 41 bis 82% der Feinwurzeln von P. tremula x tremuloides waren ektomykorrhiziert. Die Ektomykorrhizierungsrate von P. trichocarpa war in beiden Düngungsvarianten reduziert, während an P. trichocarpa nur die P-Düngung eine Reduktion der Ektomykorrhizierungsrate bewirkte. Die Zusammensetzung der morphologischen Mykorrhizierungstypen wurde von beiden Düngungsvarianten nur an P. tremula x tremuloides beeinflusst. Zwölf ektomykorrhizierende Pilzarten bildeten Fruchtkörper in den Pappelbeständen. Cortinarius uliginosus, Lactarius controversus und Krombholziella aurantiaca bildeten Fruchtkörper nur auf den Kontrollparzellen, wogegen Fruchtkörper von Cortinarius croceocaeruleus, Inocybe umbrina, Laccaria tortilis, Paxillus involutus und Rhizopogon roseolus nur auf gedüngten Parzellen erschienen. Inocybe geophylla, I. glabripes, Laccaria laccata und Tuber borchii bildeten Fruchtkörper sowohl auf den Kontroll- als auch auf den Düngungsparzellen. Die VAM Sporendichte war unter Populus trichocarpa geringer als unter P. tremula x tremuloides. Bei effizienter Bewirtschaftung von Schnellwuchsplantagen sollte die Düngermenge so gering bemessen werden, dass eine unbeabsichtigte Reduktion der Mykorrhizierung verhindert wird.

Effects of nitrogen and phosphorus fertilization on mycorrhizal formation of two poplar clones(Populus trichocarpa andP. tremula x tremuloides)

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Efficacy of ectomycorrhizal basidiomycetes on Japanese larch seedlings assessed by ergosterol assay

Five fungal species, Suillus grevillei, Boletinus cavipes, Inocybe kobayasii, Lactarius pominsis and Gomphidius maculatus were examined for ergosterol content during mycorrhizal formation. Ergosterol assay was a suitable method for monitoring establishment of 5 ectomycorrhizal fungi on roots. Ergosterol contents were positively correlated to biomass of each of 5 ectomycorrhizal basidiomycetes growing on Melin-Norkrans medium, ranging 1.78–2.36 μg mg-1 dry mycelia. These fungi formed ectomycorrhizae with Japanese larch seedlings in container-grown axenic culture. There were significant correlations between overall mycorrhizal density and seedling growth such as root length and shoot height at 6 mo. Mycorrhizal seedlings accumulated more mass in the root system and mycorrhizae compared with nonmycorrhizal seedlings.

Efficacy of Ectomycorrhizal Basidiomycetes on Japanese Larch Seedlings Assessed by Ergosterol Assay

Five fungal species, Suillus grevillei, Bole- tinus cavipes, Inocybe kobayasii, Lactarius porninsis and Gomphidius maculatus were examined for ergos- terol content during mycorrhizal formation. Ergos- terol assay was a suitable method for monitoring es- tablishment of 5 ectomycorrhizal fungi on roots. Er- gosterol contents were positively correlated to bio- mass of each of 5 ectomycorrhizal basidiomycetes growing on Melin-Norkrans medium, ranging 1.78- 2.36 iig mg-' dry mycelia. These fungi formed ecto- mycorrhizae with Japanese larch seedlings in contain- er-grown axenic culture. There were significant cor- relations between overall mycorrhizal density and seedling growth such as root length and shoot height at 6 mo. Mycorrhizal seedlings accumulated more mass in the root system and mycorrhizae compared with nonmycorrhizal seedlings.

The role of seed reserves in arbuscular mycorrhizal formation and growth of Leucaena leucocephala (Lam.) de Wit. and Zea mays L.

We show here that seed reserves in Leucaena leucocephala (Lam.) de Wit. and Zea mays L. (maize) are important for mycorrhizal formation and seedling growth. Seed reserve removal reduced mycorrhizal formation markedly in Leucaena but not in maize, except at 15 and 45 days after seed reserve removal. Partial or total removal of seed reserves decreased plant growth and tissue nutrient concentrations in both hosts. Nodule number in Leucaena, which was related positively to plant biomass and mycorrhizal infection levels, was reduced when one or both cotyledons were severed. Leucaena seedlings without or with partial seed reserves had higher nutrient use efficiencies throughout seedling growth. But such an effect was observed only initially in maize. Seed reserve removal increased the specific absorption rates of nutrients in both hosts. Phosphorus absorption rate was significantly and positively related to root infection levels in both Leuceana and maize. Though the growth rates of plants without seed reserves were low initially, these plants had higher growth rates during later stages. We conclude that seed reserves are not only important for seedling growth, but also for mycorrhizal formation and nodulation.

Alterations in the plasma membrane polypeptide pattern of tomato roots (Lycopersicon esculentum) during the development of arbuscular mycorrhiza

Changes induced by arbuscular mycorrhizal (AM) formation in the plasma membrane polypeptide pattern of tomato roots have been assessed by 2D-PAGE analysis. Plasma membrane fractions were isolated by aqueous two-phase partitioning from control and mycorrhizal tomato root microsomes. Analysis of 2D-PAGE gels revealed that AM colonization induces at the plasma membrane level two major changes in protein synthesis: down-regulation of some constitutive polypeptides and synthesis of new polypeptides or endomycorrhizins. A comparison of changes induced by two different levels of AM colonization showed that 16 polypeptides were differentially displayed at both AM colonization stages, while some others were transiently regulated. Five of the differentially displayed plasma membrane polypeptides at both AM colonization stages were selected for N-terminal amino acid sequencing. Reliable sequences were obtained for two of the selected spots. Sequence alignment search indicated that one of the sequenced polypeptides showed 75% identity to the N-terminal sequence of the 69 kDa catalytic subunit of the vacuolar type H(+)-ATPase of several plants. The possible significance of these findings is discussed in relation to the functioning of the AM symbiosis.

Effects of previous crops on arbuscular mycorrhizal formation and growth of maize under various soil moisture conditions

The effects of previous crops on arbuscular mycorrhizal (AM) formation and growth of succeeding maize (Zea mays L.) were examined at different soil moisture levels. Maize was grown in pots filled with soils (Andosol) from the plots, where mycorrhizal (sunflower, maize, soybean, kidney bean, adzuki bean, potato, wheat) and non-mycorrhizal (mustard, radish, sugar beet, and buckwheat) crops were cultivated in the previous season. Soil water potential was adjusted to around -10 (wet: W), -50 (moist: M), < -63 kPa (dry: D) from 11 d after sowing. The soils after cultivation of mycorrhizal plants in the previous season contained more AM spores than those after cultivation of non-mycorrhizal plants. The influence of the previous crops on AM formation was pronounced on drier soils, in which AM colonization of maize following mycorrhizal crops occurred more frequently than that after non-mycorrhizal crops. Arbuscular mycorrhizal colonization of maize, however, improved with increasing soil moisture status even after non-mycorrhizal crops, despite the differences in the AM spore population. The influence of previous crops on maize growth was also distinct, but it declined markedly with the increase in the soil moisture status. Phosphorus uptake and maize growth were positively correlated with AM colonization. The increase in AM colonization with the increase in the soil moisture status despite the low AM spore population suggests that a higher soil moisture status improved the efficiency of AM colonization, thus promoting AM formation. Such effects may have, in turn, stimulated P uptake and enhanced plant growth, thereby reducing the influence of the cropping history.

Nitrogen fixation in legume and non-legume trees

Nitrogen-fixing root nodules are found in 10 plant families containing trees and shrubs associated with rhizobia or Frankia. The nodulation status and nodule characteristics have been extensively studied for herbaceous legumes, while for many legume trees species these characters are unknown. Hardwood timber production represents the major economic use of both leguminous and actinorhizal trees, although other roles in providing shelter, land conservation, land reclamation and as medicinal plants are important. Their success relies not only on their ability to fix N 2 symbiotically, but also on a range of other adaptations including flooding and drought tolerance, mycorrhizal formation, cluster root production and herbivore defences. Future research to detail nodulation status, nitrogen fixation rates, physiological adaptations and genetic diversity in both legumes and actinorhizal trees will provide fundamental knowledge to further conservation and utilisation of these plants.

Effect of previous crops on arbuscular mycorrhizal formation and growth of succeeding maize

The effects of fallow and cultivation of sunflower, maize, soybean, potato, wheat, sugar beet, rape on arbuscular mycorrhizal (AM) colonization and growth of succeeding maize were examined under field conditions from 1990 to 1992. All the crops except for sugar beet and rape were mycorrhizal. Shoot weight and grain yield of maize were much higher in the plots following sunflower, maize, soybean, potato than in those succeeding rape, fallow, and sugar beet. It was thus concluded that maize growth after cultivation of mycorrhizal crops was more enhanced than after the cultivation of non-mycorrhizal crops. Phosphorus uptake and AM colonization in succeeding maize were closely correlated with shoot weight and grain yield. The results showed that the cultivation of mycorrhizal crops in the previous season promoted AM formation on roots of succeeding maize, which in turn enhanced the P uptake and growth, finally increased the grain yield.