Digging deeper to study the distribution of mycorrhizal arbuscular fungi along the soil profile in pure and mixed Eucalyptus grandis and Acacia mangium plantations

Abstract

The presence of Arbuscular mycorrhizal fungi (AMF) in pure and mixed Eucalyptus grandis and Acacia mangium plantations has not been clearly characterised, especially regarding their vertical distribution along a deep soil profile. Our aim was to study the AMF community in layers from 0 to 800 cm deep, comparing pure and mixed E. grandis and A. mangium plantations. We investigated whether AMF are able to colonize roots and produce spores down to 800 cm of depth, and whether intercropping of A. mangium increases AMF abundance and diversity in E. grandis plantations at the surface and subsurface layers of soil. AMF spore abundance and identification were evaluated morphologically, while the quantification of root colonization following the methodology of root clarification, dyeing and determination of the percentage of root length colonized by AMF. Total root DNA was extracted, and specific PCR was applied, which resulted in clones of the 18S rRNA small-subunit (SSU) gene region of AMF. Results show that AMF spores and some root colonization were present even in the deepest soil layers. Spore evaluation identified 16 species across six AMF genera (Acaulospora, Gigaspora, Glomus, Intraornatospora, Scutellospora and Racocetra). The genus Glomus was the most abundant and found in all treatments and depths. E. grandis in the mixed plantation with A. mangium presented a significant increase in root colonization in the 0–20 and 20–50 cm layers, indicating a possible stimulation at superficial soil layers of the symbiosis in E. grandis roots when in consortium. Amplification of the 18S region of AMF revealed specific predominant groups at each soil depth. We found that the deep layers, although presenting comparatively low root colonization, still harbour a considerable range of AMF.