Dark septate and arbuscular mycorrhizal fungal endophytes in roots of prairie grasses

Root symbioses with dark septate endophytic fungi (DSE) and arbuscular mycorrhizal fungi (AMF) provide plant tolerance to environmental stresses. This research answers several fundamental questions about the occurrence of these fungi in roots of prairie grasses. Traditional methods and current molecular techniques were combined in order to: (1) define the role and specificity of DSE in plant tolerance to drought; (2) assess the level of host specificity in DSE; (3) document AMF biodiversity and pattern of root colonization at different soil depths; (4) define the influence of soil depth and plant species on the distribution of DSE and AMF in roots and; (5) reveal how DSE and AMF interact in plant roots.;In the field, soil depth influenced root colonization in A. cristatum, Panicum virgatum L., Nassella viridula Trin and Pascopyrum smithii (Rydb.) A. Love., while AMF diversity was influenced by the interaction between soil depth and host plant species. Molecular analysis of roots serially sampled during one growing season from the A and B soil horizons, in stands of these grasses, revealed spatial and temporal changes in DSE and AMF community composition, and a significant correlation in DSE and AMF community structure.;These results suggest that DSE and AMF are adapted to specific environmental conditions and that root occupation by these fungi is a dynamic phenomenon. It is proposed that temporal variation in root occupation by DSE and AMF impacts plant and ecosystem processes at different times during the growing season.;Under controlled conditions, DSE isolates showed host preference in colonizing roots and promoting plant growth. They colonized with more intensity the plant species from which they were isolated [Agropyron cristatum L. or Psathyrostachys juncea (Fisch) Nevski subsp. Juncea (Syn: Elymus junceus Fisch)]. Inoculation with five DSE isolates resulted in growth stimulation of the C3 grasses A. cristatum and P. juncea, and growth depression of the C4 grass Bouteloua gracillis (Willd. ex Kunth) Lag. ex Griffiths, under water stress. Plant C concentration suggested that DSE inoculation may have resulted in net C drain from B. gracillis.