Contrasting phosphate acquisition of mycorrhizal fungi with that of root hairs using the root hairless barley mutant

Comparisons between plant species or cultivars differing in root hair length have indicated a major impact of root hairs on the mycorrhizal dependency of plants with respect to phosphate (P) uptake. The current study aimed to investigate this relationship by comparing directly the mycorrhizal dependency of a spontaneous root hairless mutant, brb, in Hordeum vulgare cv Pallas and its wild type. Both brb and wild type were grown at different soil P levels in association with different mycorrhizal fungi. P uptake of brb and wild type was similar at high P levels, but P uptake by non-mycorrhizal brb plants at low P levels was substantially lower than that of the non-mycorrhizal wild-type plants. However, P uptake of the mutant was much increased by mycorrhizas and with one fungus, the additional P uptake was effectively translated into increased plant growth. Roots of the mutant contained typical colonization structures and a radioactive tracer confirmed P transport by the extraradical mycelium. This is the first direct evaluation of the relative effectiveness of root hairs and mycorrhizas. Mycorrhizas effectively substituted root hairs in P uptake, whereas the additional P was most often used less effectively in promoting plant growth than P provided by root hairs

Dependência e resposta de mudas de cedro a fungos micorrízicos arbusculares Cedar seedlings dependency and responsiveness to arbuscular mycorrhizal fungi

Os objetivos deste trabalho foram avaliar a resposta de mudas de cedro (Cedrela fissilis Vell.) a espécies de fungos micorrízicos arbusculares (FMA) e determinar o grau de dependência micorrízica dessas mudas. O ensaio foi conduzido em casa de vegetação, em delineamento de blocos inteiramente casualizados, em esquema fatorial 5 (doses de P) x 5 (4 espécies de FMA e testemunha sem inoculação), com seis repetições. Glomus clarum foi a espécie de FMA mais eficiente em promover o crescimento e a nutrição fosfatada de mudas de cedro, principalmente quando a inoculação foi realizada em substrato com P disponível em torno de 12 mg dm-3. A economia de P aplicado equivale a aproximadamente 63%, em relação à testemunha sem inoculação, quando foram buscados 80% do crescimento máximo. Verificou-se elevado grau de dependência micorrízica das mudas de cedro e, portanto, a inoculação de FMA é um procedimento que deve ser considerado na fase de viveiro, para garantir o sucesso do estabelecimento e crescimento em campo dessas mudas.<br>The objectives of this work were to evaluate cedar (Cedrela fissilis Vell.) seedlings responsiveness to arbuscular mycorrhizal fungi (AMF) species and to determine mycorrhizal dependency degree of this seedling. The experiment was carried out at greenhouse, in a complete randomized block design as a factorial set 5 (P doses) x 5 (4 AMF species + noninoculated treatment) with six replications. Glomus clarum was the most efficient AMF species in promoting the growth and P nutrition of cedar seedlings, especially when the inoculation was done in substratum containing P available levels close to 12 mg dm-3. The saving of applied P was approximately 63%, regarding noninoculated treatment when 80% of the maximum growth was estimated. The elevated degree of mycorrhizal dependency of cedar seedlings was verified, so AMF inoculation is a procedure that should be considered in nursery stage, in order to guarantee cedar seedlings successful establishment and growth on field conditions