Recent advances in exploring physiology and biodiversity of ectomycorrhizas highlight the functioning of these symbioses in ecosystems

Abstract

Ectomycorrhizas, the dominating mycorrhizal symbiosis in boreal, temperate and some tropical forests, are formed by 5000-6000 species of the asco- and basidiomycetes. This high diversity of fungal partners allows optimal foraging and mobilisation of various nitrogen and phosphorus forms from organic soil layers. In this review, two approaches to study the functioning of this multitude of symbiotic associations are presented. On selected culture models, physiological and molecular investigations have shown that the supply of hexoses has a key function in controlling the plant-fungus interaction via partner-specific regulation of gene expression. Environmental factors which affect fungal carbon supply, such as increased nitrogen availability, also affect mycorrhiza formation. Based on such laboratory results, the adaptative capability of ectomycorrhizas to changing field conditions is discussed. The second approach consists of analysing the distribution of mycorrhizas in ecosystem compartments and to relate distribution patterns to variations of ecological factors. Recent advances in identification of fungal partners in ectomycorrhizas by analysing the internal transcribed spacer of ribosomal DNA are presented, which can help to resolve sampling problems in field studies. The limits of the laboratory and the field approaches are discussed. Despite some problems, this combined approach is the most promising. Direct investigation of gene expression, which has been introduced for soil bacteria, will be difficult in the case of mycorrhizal fungi which constitute organisms with functionally varying structures.

Effects of temperature, pH and carbon and nitrogen sources on growth of in vitro cultures of ectomycorrhizal isolates from Pinus heldreichii forest

“…Based on this, it was assumed there are differences among their physiological functions as a prerequisite for selective exploitation of different nutrients from the soil. The observations suggest that the differences in nitrogen utilization and also their dependency on carbohydrates could be important ecophysiological markers of ectomycorrhizal fungi (Buscot et al, 2000). Capabilities of using different nitrogen and carbon sources, at different pH levels may allow species to adapt to specific soil conditions, but it is still unknown to what extent the function of different ectomycorrhizal species can be considered to be the same.…”

“…The isolates were incubated at 22˚C for 15-20 days in the dark, and maintained onto MMN medium by transfer every three months (Rincon et al, 1999). It is possible that certain physiological characteristics of ectomycorrhizal fungi, especially those relating to their enzymatic activity, are altered as a result of in vitro cultivation (Cairney, 1999;Buscot et al, 2000). Therefore, almost all cultures used were of the same age and were examined immediately after isolation.…”

Microbial abundance, composition and enzymatic activity during decomposition of copepod carcasses

“…Amplification of 16S rRNA gene fragments of bacteria using the universal primers 341f-GC and 907r and subsequent DGGE analysis of bacterial community structure were performed according to Brinkhoff & Muyzer (1997). Amplification of 18S rRNA gene fragments of fungi using the primers ITS3f-GC and ITS4r (White et al 1990) was done according to Buscot et al (2000). For subsequent DGGE analysis of fungal community structure the same protocol was used as for bacteria.…”

Caracterización de las ectomicorrizas formadas por Laccaria trichodermophora y Suillus tomentosus en Pinus montezumae

“…a ectomicorriza es una forma de relación simbiótica entre las raíces de árboles o arbustos autotrófi cos y un hongo cuyas hifas forman un manto alrededor de éstas (Buscot et al, 2000;Brundrett, 2004). En esta asociación el hongo también desarrolla una estructura laberíntica a través del apoplasto del córtex de la raíz, llamada red de Hartig, donde se lleva a cabo la transferencia de nutrientes entre las células fúngicas y vegetales (Brundrett, 2004).…”

“…En esta asociación el hongo también desarrolla una estructura laberíntica a través del apoplasto del córtex de la raíz, llamada red de Hartig, donde se lleva a cabo la transferencia de nutrientes entre las células fúngicas y vegetales (Brundrett, 2004). Este tipo de micorriza se puede establecer entre hongos de las clases Basidiomycetes y Ascomycetes y diversos grupos angiospermas o gimnospermas (Buscot et al, 2000). Las ectomicorrizas son comunes en suelos moderadamente ácidos y ricos en materia orgánica, tanto en regiones boreales y templadas como tropicales (Sylvia, 1999; Nava-Gutiérrez y Hernández-Cuevas, 2003;Pérez-Moreno y Read, 2004).…”