High diversity of ectomycorrhizal fungi associated with Arctostaphylos uva-ursi in subalpine and alpine zones: Potential inoculum for afforestation

Abstract

Arctostaphylos uva-ursi plant associations have long been suggested to be a suitable location for afforestations, but systematic studies on the observed beneficial effect are still missing in Alpine areas. In this study we address the question which ectomycorrhizal (ECM) fungal communities exist in Austrian alpine and subalpine Arctostaphylos habitats, and if they persist in A. uva-ursi stands even hundred of years after disappearance of trees in these areas. The diversity of fungal communities associated with A. uva-ursi was assessed in four study sites (1800–2450 m a.s.l.) in the Central European Alps of Tyrol (Austria). Three approaches were applied: (i) collecting and identifying fungal fruit bodies; (ii) studying the arbutoid mycorrhiza morphotypes of A. uva-ursi; (iii) molecular identification of the most common arbutoid morphotypes. The detected diversity of ECM fungal species was very high (99 taxa), and the occurrence of e.g. Boletus, Cantharellus, Suillus, Tricholoma, Russula spp. in sites that have been treeless for centuries is especially remarkable. Fruit bodies of 82 fungal species were found in association with A. uva-ursi, 63 of them were ECM. Seventy arbutoid morphotypes were detected on 2072 mycorrhized root tips, and 39 taxa of basidiomycete mycobionts were identified with molecular methods. Twelve Cortinarius spp. clearly dominated the mycobiont species richness, followed by nine spp. of Thelephoraceae and four spp. of Boletaceae. Most mycobionts of A. uva-ursi were generalists, but fungal taxa (e.g. Lactarius deterrimus and Suillus spp.) known to be specifically associated with other host plants were also detected. We therefore consider A. uva-ursi as a “non-selective” host, providing mycorrhizal inoculum of highly specialized and effective mycorrhizal fungi for afforestation. This explains why A. uva-ursi plant associations represent suitable locations for forest regeneration and afforestation, especially in the harsh environmental conditions of subalpine and alpine sites.

Introduction

Arctostaphylos uva-ursi (L.) Spreng. (Bearberry) is a widespread, circumpolar shrub species common on dry, nutrient-poor soils in the subalpine and alpine zone. Adapted to the harsh climatic conditions of arctic and alpine environments, it often dominates communities forming an evergreen groundcover. This plant is typical for windy, snow-poor, sun-exposed habitats with high danger of frost damage. With its extensively trailing twigs, it can (re)invade successional sites from adjacent, undisturbed areas. Thus, A. uva-ursi stabilizes the soil and is therefore of capital importance for the rehabilitation of disturbed sites, e.g. after avalanches or wildfire (Visser, 1995). In forest practice, A. uva-ursi plant associations have long been suggested to be a suitable location for afforestations, especially with Pinus cembra (Aulitzky, 1962, Mayer and Pitterle, 1988). However, systematic studies on Alpine A. uva-ursi plant associations and the related mycobiota are still missing.

The roots of A. uva-ursi and their symbiotic fungi develop so-called arbutoid mycorrhizae: the main feature characterising arbutoid mycorrhizae, and delimiting them from ectomycorrhizae, is that fungal hyphae penetrate the cortical cells of A. uva-ursi forming branched hyphal complexes. Zak (1976) assumed that most fungal partners of arbutoid mycorrhizae are basidiomycetes, being very likely the same species that form ECM of forest trees. This hypothesis was corroborated by Molina and Trappe (1982) who found that in vitro 25 out of 28 cultures of ectomycorrhizal fungi isolated from diverse host- and habitat associations formed arbutoid mycorrhizae with Arbutus menziesii Pursh and A. uva-ursi. Hagerman et al. (2001) identified mycobionts of A. uva-ursi with PCR-RFLP techniques: they found that they belong to genera commonly known as ectomycorrhizal partner of forest trees, e.g. Inocybe, Cortinarius or Russula. Thus, Hagerman et al. (2001) concluded that A. uva-ursi has a high potential to provide ectomycorrhizal inoculum in 2 years old clear cuts following logging.

The beneficial effect of ectomycorrhizal associations for growth and survival of many tree species at both early and late stages of development is well documented (e.g. Smith and Read, 1997, Horton et al., 1999, Landeweert et al., 2001, Högberg and Högberg, 2002, Read and Perez-Moreno, 2003). Just as Inocybe, Cortinarius or Russula spp., most ectomycorrhizal fungal species form ectomycorrhizae with a wide range of different tree species (Horton and Bruns, 1998, Massicotte et al., 1999). A mycorrhizal community shared among plant species has important implications for the maintenance of ectomycorrhizal fungal inoculum on a site, and the establishment of mycorrhizae with planted or naturally regenerating seedlings. Moreover, ectomycorrhizal fungal mycelia often connect seedlings to mature plants (Nara, 2006). However, the quantity and diversity of ectomycorrhizal fungal inoculum is often reduced at successional sites, e.g. after clear-cut, landslides, avalanches or erosion.

Deforestation is well documented in Austria and adjacent areas: it was often due to century-long altitude farming, grazing management, or due to natural disasters. Reforestation of such areas can be essential for landslide and avalanche protection.

The main aim of this project was to assess the biodiversity of A. uva-ursi mycobionts in the subalpine dwarf shrub zone, with special emphasis on sites lacking a tree covering for long periods. Are ectomycorrhizal fungal communities also present in European alpine and subalpine Arctostaphylos habitats, and if yes, are they still persisting as mycobionts of A. uva-ursi, even hundred of years after disappearance of trees in these areas? The biodiversity of A. uva-ursi mycobionts and fungal communities was assessed with three approaches: (i) by collecting and identifying fungal fruit bodies; (ii) by the study of the arbutoid fungal mycorrhiza morphotypes; and (iii) by molecular identification of the belowground basidiomycete community forming arbutoid mycorrhizas with A. uva-ursi.