Abstract
Berardia subacaulis Vill. is a monospecific genus that is endemic to the South-western Alps, where it grows on alpine screes, which are extreme habitats characterized by soil disturbance and limiting growth conditions. Root colonization by arbuscular mycorrhizal fungi (AMF) is presumably of great importance in these environments, because of its positive effect on plant nutrition and stress tolerance, as well as on structuring the soil. However, there is currently a lack of information on this topic. In this paper, we tested which soil characteristics and biotic factors could contribute to determining the abundance and community composition of AMF in the roots of B. subacaulis, which had previously been found to be mycorrhizal. For such a reason, the influence of soil properties and environmental factors on AMF abundance and community composition in the roots of B. subacaulis, sampled on three different scree slopes, were analysed through microscopic and molecular analysis. The results have shown that the AMF community of Berardia roots was dominated by Glomeraceae, and included a core of AMF taxa, common to all three scree slopes. The vegetation coverage and dark septate endophytes were not related to the AMF colonization percentage and plant community did not influence the root AMF composition. The abundance of AMF in the roots was related to some chemical (available extractable calcium and potassium) and physical (cation exchange capacity, electrical conductivity and field capacity) properties of the soil, thus suggesting an effect of AMF on improving the soil quality. The non-metric multidimensional scaling (NMDS) ordination of the AMF community composition showed that the diversity of AMF in the various sites was influenced not only by the soil quality, but also by the slope. Therefore, the slope-induced physical disturbance of alpine screes may contribute to the selection of disturbance-tolerant AMF taxa, which in turn may lead to different plant-fungus assemblages.
Highlights
A great deal of literature exists on the global species richness and distribution of mycorrhizal and non-mycorrhizal endophytic fungi ([1,2,3])
The root colonization percentages largely exceeded those found by Binet et al [20] in Artemisia umbelliformis, a plant that grows on alpine calcareous bedrocks in Switzerland, which are very poor in phosphorous nutrients, and confirmed that Arbuscular mycorrhizal fungi (AMF) root colonization is not depressed at altitudes of between approximately 2000 and 3000 m asl ([19]-[23]) in the Alps
Arbuscular mycorrhizal fungi of Berardia subacaulis species in this harsh environment are subjected to extreme climatic and edaphic variable ranges, and they have to adapt to debris falls and substrate movements
Summary
A great deal of literature exists on the global species richness and distribution of mycorrhizal and non-mycorrhizal endophytic fungi ([1,2,3]). Arbuscular mycorrhizal fungi (AMF), or Glomeromycota [4], are obligate symbiotic fungi that penetrate plant roots and form the arbuscule, that is, a specialized hyphal structure that develops inside cortex cells, and represents the main site of nutrient exchange between partners [5]. These fungi have played an important role in the evolution of land plants for more than four hundred million years [6], and they today colonize the roots of most plants [5]. DSEs have been shown to influence plant growth and physiology [11], even though the role of these endophytes in plant fitness is less clear than for mycorrhizal fungi [10]
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