Arbuscular Mycorrhizal Status Research Articles

The mycorrhizal status of plants colonizing a calamine spoil mound in southern Poland

The arbuscular mycorrhizal (AM) status of two plant communities on a calamine spoil mound (rich in cadmium, lead and zinc) in southern Poland was surveyed: an undisturbed grassland community and an early succession community that developed after complete removal of the surface layer of the calamine substrate about 10 years earlier. The undisturbed site harbored 40 herbaceous species making up 87% of the absolute cover. AM colonization was recorded in 25 species accounting for 77% of the relative cover. Species with 51–75% AM root colonization such as Festuca ovina and Leontodon hispidus dominated the undisturbed turf, contributing 45% to the relative cover. Carex ssp. were the most abundant nonmycorrhizal plants and accounted for 9% of the relative cover. Spores of Glomus aggregatum, G. constrictum, G. fasciculatum, G. pansihalos, Glomus sp. and Entrophospora sp. averaged 25 per 100 g dry substrate at the undisturbed site. The disturbed site was colonized by 25 species accounting for 17% of the absolute cover. Among the AM plants, most abundant were the species with up to 20% AM root colonization, such as Agrostis stolonifera and Thymus pulegioides, wich accounted for 24% of the relative cover. Nonmycorrhizal species, such as Biscutella laevigata,Cardaminopsis arenosa, Gypsophila fastigiata and Silene vulgaris, dominated the early succession community and contributed 64% to the relative cover. Spores of G. fasciculatum and Entrophospora sp. averaged 20 per 100 g dry substrate at the disturbed site.

A nodulation ( [formula omitted]) mutant of Phaseolus vulgaris L. has nodule-like structures lacking peripheral vascular bundles (Pvb −) and is resistant to mycorrhizal infection (Myc −)

Phenotypic characterization of two nodulation mutants (R69 and R99) of Phaseolus vulgaris L. was undertaken. The nodule anatomy of R69 ( Nod + Fix − ), was examined and compared to its wild-type parent, OAC Rico. The arbuscular mycorrhizal (AM) status of R69 and R99 (Nod −) was also compared to OAC Rico. Small whitish growths resembling nodules were produced on the roots of R69 in response to inoculation with Rhizobium leguminosarum biovar phaseoli. These nodule-like structures were variable in shape and occasionally had lateral roots growing from them. A layer of crystalline inclusions (possibly calcium oxalate) occurred between the periderm and parenchyma cells in the mutant nodules. A central infected zone was not present and the vascular system occupied the centre of the nodule instead of the periphery, as seen in wild-type nodules. Given the distinctive phenotype of the nodules of R69, they were designated Pvb − (peripheral vascular bundles, minus). The Nod − mutant, R99, could establish a symbiosis with AM (Myc +), however, R69 was resistant to infection by AM (Myc −). Appressoria would form on the roots and internal hyphae would start to develop, but these would fail to develop into a normal AM symbiosis. We suggest that specific anatomical characteristics of the Nod + Fix − and Myc − phenotypes in R69 supports the hypothesis of a common regulation of the development of the two symbioses.

Companion plants affect colonization of Myrica cerifera by vesicular–arbuscular mycorrhizal fungi

The vesicular–arbuscular mycorrhizal (VAM) status of Myrica cerifera L. (wax myrtle) was investigated under greenhouse and field conditions. Myrica cerifera and Paspalum notatum Flügge (bahiagrass) were grown in inter- and intra-specific plant combinations with and without VAM fungi. Roots of field-collected M. cerifera were also examined for colonization by VAM fungi. Myrica cerifera became colonized by VAM fungi only in the presence of a VAM colonized grass plant; however, arbuscules were consistently lacking. VAM fungi had no effect on root or shoot growth of M. cerifera. When grown in the presence of P. notatum, shoot growth of M. cerifera was reduced, regardless of inoculation treatment. Colonization of field-collected M. cerifera roots ranged from 0 to 75%; however, nearly all samples lacked arbuscules. Unexpectedly, samples from wet sites had the highest colonization levels. Failure of M. cerifera to become colonized when grown without a VAM companion plant and the absence of arbuscules when M. cerifera became colonized in the presence of a VAM companion plant suggest that the VAM association of M. cerifera is nonfunctional. Key words: arbuscule, Glomus, interspecific, intraspecific, nonhost.

Arbuscular mycorrhiza, rhizospheric microbe populations and soil enzyme activities in citrus orchards under two types of no-tillage soil management

The arbuscular mycorrhizal (AM) status [total AM colonization (RLT), percentage of root length with arbuscules (RLA) and vesicles (RLV), spore density and hyphal length density], microbial populations and soil enzyme activities were investigated in citrus (Satsuma Mandarin grafted on Poncirus trifoliata L. Raf) orchards. Two types of no-tillage soil management, natural grass cover and use of herbicides, were employed in these orchards. The citrus AM colonization (37.26-70.09%) was high in all the experimental orchards sampled. The highest RLA (43.83%), spore density (384.63 spores/100 g soil), hyphal length density (4.09 m g–1 soil), rhizospheric microbial populations and enzyme activities were observed in the orchards with a natural grass cover, and the lowest values, except urease activity, were found in the orchards treated with herbicides. Spore density, hyphal length density, catalase activity and phosphatase activity varied notably between no-tillage/natural grass and no-tillage/herbicides treated orchards in the soil layers above 40 cm. A correlation analysis showed that the hyphal length density and organic matter were significantly positively correlated. Soil enzyme activities, except phosphatase, were strongly correlated with the bacteria populations. The data presented here demonstrates that the RLA, spore density, hyphal length density, rhizospheric microbe populations and enzyme activities were significantly better in the soil layers above 40 cm of orchards with a natural grass cover than herbicidetreated soils. So, the establishment of a natural grass cover benefits soil quality in citrus orchards in Southern China.