RESUMO

Despite the strong ecological importance of ectomycorrhizal (ECM) fungi, their vertical distribution remains poorly understood. To our knowledge, ECM structures associated with trees have never been reported in depths below 2 meters. In this study, fine roots and ECM root tips were sampled down to 4-m depth during the digging of two independent pits differing by their water availability. A meta-barcoding approach based on Illumina sequencing of internal transcribed spacers (ITS1 and ITS2) was carried out on DNA extracted from root samples (fine roots and ECM root tips separately). ECM fungi dominated the root-associated fungal community, with more than 90% of sequences assigned to the genus Pisolithus. The morphological and barcoding results demonstrated, for the first time, the presence of ECM symbiosis down to 4-m. The molecular diversity of Pisolithus spp. was strongly dependent on depth, with soil pH and soil water content as primary drivers of the Pisolithus spp. structure. Altogether, our results highlight the importance to consider the ECM symbiosis in deep soil layers to improve our understanding of fine roots functioning in tropical soils.

Assuntos

RESUMO

• A differential effect of ectomycorrhizal symbiosis on soil P mobilization and host P nutrition is shown after culture of Pinus pinaster associated with Hebeloma cylindrosporum and Rhizopogon roseolus, poor and good oxalate/proton producers, respectively. • Plants were grown in minirhizoboxes with a thin layer of a Mediterranean soil with a low level of easily available P. This soil was supplemented, or not, with inorganic P and/or CaCO3 . The fungal efficiency on P mobilization and host mineral nutrition was quantified after a 3-month culture period. • R. roseolus had a strong effect on the mobilization of poorly available P, whereas H. cylindrosporum had no effect. However, CaCO3 suppressed the positive effect of R. roseolus. Hydroxyapatite had the greatest effect on growth and P nutrition of nonmycorrhizal plants. With soluble P addition, both ectomycorrhizal species improved shoot P concentrations. • The relationship between soil available P and shoot P concentrations enabled us to separate the fungal effects into two categories, the chemical actions and the soil exploration, explaining the positive effect of ectomycorrhizal symbiosis on P. pinaster P nutrition.