Survey of ectomycorrhizal fungi associated with oak trees in the forests of Lorestan province, Iran

Background and Objectives: Ectomycorrhizal symbiosis is established between groups of Basidiomycete and Ascomycete fungi and several forest tree species in temperate, Mediterranean, and semi-warm regions, playing an important role in the establishment, performance, and development of trees in these areas. This type of symbiosis is fundamental in improving plant health by protecting against biotic and abiotic stresses and by improving soil structure. Ectomycorrhizal fungi play a key role in the growth and nutrient uptake of oak trees. Studies have shown that oak seedlings benefit from ectomycorrhizal symbionts, and their nutrient absorption, especially in nutrient-poor soils, increases. These fungi form a network with plants and help oak seedlings overcome nutrient limitations in unfavorable environments. The presence of a diverse and abundant ectomycorrhizal community is essential for the restoration and sustainability of oak forests and highlights the complex relationship between these fungi and oak trees. The aim of this study was to identify the existing morphotypes in the oak forests of Lorestan province and to statistically evaluate the populations of these ectomycorrhizal fungi.
Methodology: To investigate the ectomycorrhizal fungi associated with oak trees in the forests of Lorestan province, six natural oak habitats (Shorab, Pol Keshkan, Grit, Kashraf, Chenar Bagali, and Nozhian) were selected. After recording the geographic information of each site, 15 trees were randomly selected in each habitat. Soil samples along with root fragments were collected from the rhizosphere (0–30 cm depth) of each oak tree and transferred to the laboratory. The percentage of dead roots, non-mycorrhizal roots, mycorrhizal roots, as well as the number of morphotypes and fungal taxa were determined, and the data were statistically analyzed using SPSS software.
Results: In the studied sites, the percentage of ectomycorrhizal roots ranged from 10% to 56%, and the identified morphotypes mainly belonged to the two genera Cenococcum and Hygrophorus. Statistical analysis showed that the differences in the percentage of dead roots, non-mycorrhizal roots, mycorrhizal roots, and the type and number of symbiotic fungal taxa among the studied sites were highly significant (P< 0.01), but the differences in the number of morphotypes were not significant (P> 0.05). A significant negative correlation was found between the number of taxa and the percentage of dead roots (r= −0.33), and between the percentage of mycorrhizal roots and dead roots (r= −0.37) (P< 0.05). There was also a strong negative correlation between the percentage of non-mycorrhizal roots and the number of taxa (r= −0.64, P< 0.01), and a significant negative correlation between the percentage of non-mycorrhizal roots and the number of morphotypes (r= −0.44, P< 0.05). Among the studied sites, the average number of isolates per tree in the Kashraf area was in the superior group (Group A), while the Chenar Bagali area was ranked in the lower group (Group C) (P< 0.05). Similarly, the average number of morphotypes per tree in the Kashraf area was in the superior group (Group A), while the Chenar Bagali and Nozhian areas were classified in the lower group (Group C) (P< 0.05).
Conclusion: The morphotypes identified across different sites were partly similar, but the percentage of mycorrhizal roots varied among the studied areas. Overall, the average number of isolates ranged from 1.47 to 18.20 per ten 10-cm root segments, and the average number of morphotypes per site ranged from 0.94 to 1.60. The differences in the number of isolates per root in different areas may be due to environmental conditions such as temperature, humidity, soil type, and light, which have a great influence on the growth and establishment of these microorganisms. In addition, the type and diversity of oak trees may be associated with different levels of fungal abundance, which can affect ectomycorrhizal populations. Soil nutrients, especially nitrogen and phosphorus, can also influence ectomycorrhizal fungal populations. Moreover, human activities and changes in oak habitats affect their ecosystems and modify ectomycorrhizal populations. Competition among soil microorganisms, including the presence of different fungal and bacterial species, may also contribute to these variations and affect ectomycorrhizal populations. Since no prior study has been conducted on the identification and diversity of ectomycorrhizal populations in the Zagros oak forests, this study can provide part of the basic information in this field.