The effects of arbuscular mycorrhizal fungal species and taxonomic groups on stressed and unstressed plants: a global meta-analysis

The great majority of plants gain access to soil nutrients and enhance their performance under stressful conditions through symbiosis with arbuscular mycorrhizal fungi (AMF). The benefits that AMF confer vary among species and taxonomic groups. However, a comparative analysis of the different benefits among AMF has not yet been performed. We conducted a global meta-analysis of recent studies testing the benefits of individual AMF species and main taxonomic groups in terms of plant performance (growth and nutrition). Separately, we examined AMF benefits to plants facing biotic (pathogens, parasites, and herbivores) and abiotic (drought, salinity, and heavy metals) stress. AMF had stronger positive effects on phosphorus nutrition than on plant growth and nitrogen nutrition and the effects on the growth of plants facing biotic and abiotic stresses were similarly positive. While the AMF taxonomic groups showed positive effects on plant performance either with or without stress, Diversisporales were the most beneficial to plants without stress and Gigasporales to plants facing biotic stress. Our results provide a comprehensive analysis of the benefits of different AMF species and taxonomic groups on plant performance and useful insights for their management and use as bio-inoculants for agriculture and restoration.

Genetic diversity patterns of arbuscular mycorrhizal fungi associated with the mycoheterotroph Arachnitis uniflora Phil. (Corsiaceae)

Background and Aims

Arachnitis uniflora is a mycoheterotrophic plant that exploits arbuscular mycorrhizal fungi of neighbouring plants. We tested A. uniflora 's specificity towards fungi across its large latitudinal range, as well as the role of historical events and current environmental, geographical and altitudinal variables on fungal genetic diversity.

Methods

Arachnitis uniflora mycorrhizas were sampled at 25 sites. Fungal phylogenetic relationships were reconstructed, genetic diversity was calculated and the main divergent lineages were dated. Phylogeographical analysis was performed with the main fungal clade. Fungal diversity correlations with environmental factors were investigated.

Key Results

Glomeraceae fungi dominated, with a main clade that likely originated in the Upper Cretaceous and diversified in the Miocene. Two other arbuscular mycorrhizal fungal families not previously known to be targeted by A. uniflora were detected rarely and appear to be facultative associations. High genetic diversity, found in Bolivia and both northern and southern Patagonia, was correlated with temperature, rainfall and soil features.

Conclusions

Fungal genetic diversity and its distribution can be explained by the ancient evolutionary history of the target fungi and by micro-scale environmental conditions with a geographical mosaic pattern.

Hongos micorrícico-arbusculares asociados a Chenopodiaceae en dos ambientes salinos de Córdoba

Los hongos micorrícico-arbusculares (HMA) colonizan proximadamente el 82% de las plantas terrestres en cualquier ecosistema, aún en condiciones extremas tales como los suelos salinos. En el presente trabajo se reporta la colonización micorrícica arbuscular (CMA) y su concentración radical encuatro especies de Chenopodiaceae (Allenrolfea patagonica, Atriplex argentina, Heterostachys ritteriana y Suaeda divaricata) en cinco profundidades del suelo en dos salinas del Centro de Argentina. Todas las plantas mostraron colonización micorrícica que varió significativamente entre especies y sitios para todas las profundidades. Atriplex argentina presentó el mayor porcentaje de CMA en casi todas las profundidades(0-50 cm). En todas las especies, la concentración radical disminuyó a medida que se incrementó la profundidad en ambos sitios. La presencia de raíces micorrizadas en las capas más profundas del suelo para las cuatro especies de Chenopodiaceae, muestran que estos hongos son tolerantes a vivir en los suelos salinos del centro de Argentina.

Arbuscular mycorrhizal fungi in saline soils: vertical distribution at different soil depth

Arbuscular mycorrhizal fungi (AMF) colonize land plants in every ecosystem, even extreme conditions such as saline soils. In the present work we report for the first time the mycorrhizal status and the vertical fungal distribution of AMF spores present in the rhizospheric soil samples of four species of Chenopodiaceae (Allenrolfea patagonica, Atriplex argentina, Heterostachys ritteriana and Suaeda divaricata) at five different depths in two saline of central Argentina. Roots showed medium, low or no colonization (0-50%). Nineteen morphologically distinctive AMF species were recovered. The number of AMF spores ranged between 3 and 1162 per 100 g dry soil, and AMF spore number decreased as depth increased at both sites. The highest spore number was recorded in the upper soil depth (0-10 cm) and in S. divaricata. Depending of the host plant, some AMF species sporulated mainly in the deep soil layers (Glomus magnicaule in Allenrolfea patagonica, Septoglomus aff. constrictum in Atriplex argentina), others mainly in the top layers (G. brohultti in Atriplex argentina and Septoglomus aff. constrictum in Allenrolfea patagonica). Although the low percentages of colonization or lack of it, our results show a moderate diversity of AMF associated to the species of Chenopodiaceae investigated in this study. The taxonomical diversity reveals that AMF are adapted to extreme environmental conditions from saline soils of central Argentina.

Hongos arbusculares (Glomeromycota) en la rizosfera de Atriplex lampa en dos ambientes salinos de Córdoba: influencia de la profundidad en la colonización radical y presencia de morfoespecies Arbuscular fungi (Glomeromycota) in the rhizosphere of

Summary: Arbuscular fungi (Glomeromycota) in the rhizosphere of Atriplex lampa at two saline environments of Córdoba (Argentina): depth influence on root colonization and the presence of morphospecies. Atriplex lampa is a valuable fodder shrub available for browsing by livestock even during drought periods in the Chaco Phytogeographical Province. Halophytes may benefit from the association with arbuscular mycorrhizal fungi (AMF) through improved tolerance to drought and salt. Ecological studies of AMF are generally restricted to the main rooting zone. However, AMF vertical distribution and seasonal dynamics in natural saline soils of Argentina have been poorly studied. The aim of this work was to explore AMF root colonization, root concentration and to identify AMF morphoespecies in A. lampa rhizosphere in two saline environments (Salinas de Ambargasta and Salinas Grandes) of central Argentina, in five soil depth levels, during the wet and dry seasons. Despite we did not find arbuscules, AMF were found colonizing A. lampa roots in all depth levels. Salinas Grandes showed the highest root colonization value, and showed the highest root concentration, during wet season. The 20 AMF morphospecies identified in this work belonged to the genera: Acaulospora, Ambispora, Claroideoglomus, Diversispora, Funneliformis, Glomus, Septoglomus and Scutellospora. This is the second record in Argentina of AMF structures in A. lampa roots. Future studies that evaluate mycorrhizal dependency of the plant are necessary to confirm the function of the symbiosis.Key words: Arbuscular mycorrhizal fungi; saline soils; Atriplex lampa; depth soil; seasonality.Resumen: Atriplex lampa es un arbusto halófito de la provincia fitogeográfica Chaqueña que constituye un recurso forrajero a lo largo de todo el año. Las plantas halófitas se pueden beneficiar al asociarse con los hongos micorrícico arbusculares (HMA), ya que le proveen resistencia contra la salinidad y la sequía. En general, los estudios acerca de los HMA están restringidos a los primeros centímetros del suelo y existe poca información sobre su presencia a mayores profundidades. El objetivo de este trabajo fue estudiar la colonización, la concentración radical e identificar las morfoespecies de HMA en la rizosfera de A. lampa en dos ambientes salinos del norte de la provincia de Córdoba, durante dos estaciones del año, y en cinco profundidades del suelo. Aunque no se encontraron arbúsculos, A. lampa presentó colonización radical por HMA en todas las profundidades. El mayor valor de colonización micorrícica y de concentración radical se observó en las Salinas Grandes. Se identificaron 20 morfoespecies de HMA pertenecientes a los géneros: Acaulospora, Ambispora, Claroideoglomus, Diversispora, Funneliformis, Glomus, Septoglomus y Scutellospora.Este es el segundo registro en Argentina de la presencia de HMA en raíces de A. lampa. Es necesario realizar estudios que evalúen la respuesta de A. lampa frente a la inoculación con HMA para confirmar la funcionalidad de la simbiosis.Palabras clave: Hongos micorrícico arbusculares; suelos salinos; Atriplex lampa; profundidad del suelo, estacionalidad.