Ana María de Miguel

Post-fire, seasonal and annual dynamics of the ectomycorrhizal community in a Quercus ilex L. forest over a 3-year period

Two study plots, burned and control, were established in autumn 1998 in a Quercus ilex forest located in northern Spain, part of which had been affected by a low intensity fire in 1994. Soil samples for ectomycorrhizae (ECM) were taken over a 3-year period in each study plot in spring, summer, autumn and winter. ECM morphotypes were identified and the relative abundance of each morphotype in each soil sample calculated, along with species richness, Shannon diversity index and percentage of mycorrhization in each soil sample. The relative abundance of certain ECM morphotypes differed between burned and control plots, and the percentage of mycorrhizal tips was significantly lower in the burned than in the control plot. Nevertheless, there were no significant differences in the diversity, species richness or species composition of the ECM community in the burned and control plots. The dominant ECM morphotypes in both stands were Cenococcum geophilum and several thelephoroid fungi. Sphaerosporella brunnea and Pisolithus tinctorius thrived especially in the burned plot, whereas three ectomycorrhizal morphotypes assigned to the genus Hebeloma were especially abundant in the control plot. There was no significant variation in the relative abundance of the ECM morphotypes between seasons, but ECM community species richness was highest in autumn and lowest in summer. The percentage of mycorrhizal tips reached a maximum in winter, with its minimum in autumn. Collection of samples over the 3-year period also enabled us to detect a significant increase in percentage of ECM colonisation in the burned stand over time.

A revision of the descriptions of ectomycorrhizas published since 1961

All available publications providing descriptions of ectomycorrhizas (ECM) were reviewed in order to build a database containing details on fungus forming the ECM, host tree, country where the material for description was collected, and habitat of the ECM. Other secondary data were also recorded. In all 1244 descriptions of ECM published since 1961 in 479 papers were reviewed. The number of different ECM morphotypes described was 814. Most ECM described were collected in Europe and North America. Gymnosperms were the most common tree associates, and boreal and temperate forests the most studied ecosystems. Fungal symbionts were mostly Basidiomycota, epigeous, and with mushroom-like morphology. The paper also addresses the gaps in ECM knowledge that mycorrhizologists should address in future studies.

Ectomycorrhizal communities within beech (Fagus sylvatica L.) forests that naturally regenerate from clear-cutting in northern Spain

The objectives of the work described here were to evaluate the diversity of ectomycorrhizal (ECM) fungi within Spanish beech (Fagus sylvatica L.) forests subjected to clear-cutting and natural regeneration and to elucidate the extent to which the carbohydrate concentration in roots of trees of different ages and sizes is related to ECM colonization. The study concerned an unmanaged forest, a stand clear-cut in 1996 and another clear-cut in 2001. ECM colonization of beech roots showed seasonal dynamics in the disturbed areas, but the percentage of roots colonized by ECM was not always related to the accumulation of non-structural carbohydrates. The composition of ECM communities differed between different stands and 40% of ECM morphotypes only occurred in disturbed ecosystems. However, comparable numbers of different ECM morphotypes (24, 25) were found in the three beech stands. This finding indicates that ECM diversity was quite high and similar within disturbed and unmanaged areas. This finding suggests that (1) ECM diversity was not affected by the size and age of trees and (2) the potential of ECM inocula remained high within clear-cut areas. Consequently, the introduction of ECM inocula by silvicultural practices would not be needed to improve the regeneration of clear-cut areas described in our study.

Ectomycorrhizae and vascular plants growing in brûlés as indicators of below and above ground microecology of black truffle production areas in Navarra (Northern Spain)

The diversity below (ectomycorrhizae) and above (vascular flora) ground in brûlés of black truffle production areas have been studied together for the first time, both in plantations and in natural areas, as possible indicators of the microecology of these zones. Studies on the ectomycorrhizal community of mature plantations are scarce. However, monitoring the dynamics of such systems is important to understand the conditions that promote truffle fructification. In the study described here the most frequent ectomycorrhizae are Tuber melanosporum and Quercirrhiza quadratum. In the plantations, Q. quadratum is the most abundant morphotype and in the natural area it is Cenococcum geophilum. The development of truffle ecosystems involves the appearance of competitor species with wide networks of hyphae and rhizomorphs. On the other hand, there are few studies concerning the special composition of the vascular flora growing in brûlés. We identified 199 taxa, most of them Mediterranean or Eurosiberian xerophiles and therophytes. This is consistent with the ecology of truffle production areas (dry, sunny and stony). These plants are heavily influenced by the inhibiting substances produced by the truffle and, as a result, they suffer from inhibited growth and in some cases cannot complete their life cycle.

How Ectomycorrhizae Structures Boost the Root System

Mycorrhizae are classic examples to explain the mutualistic interaction between two different organisms in nature: the roots of a vascular plant and a fungus. Both species establish a permanent relationship, they live together in symbiosis, and that differentiates the nature of mycorrhizae from other plant–fungus interactions. Ectomycorrhizal associations increase the root exploration area in soil, boosting the potential for mineral nutrition, water availability, and mutual survival of plant and fungus. The diversity of ectomycorrhizal fungal communities in the roots of spermatophyte plants is impressively high and means a complex diversity of structures in the root system, including emanating hyphae and rhizomorphs, which enlarge its area of influence. The distribution of the ectomycorrhizae living in the root system in an ever-changing balance is conditioned by many factors. Some of them are related with the root morphology of the host tree and also with ectomycorrhizal morphology, but abiotic factors (such as soil properties) also play a role.