Arbuscular Mycorrhizal Inoculation Affects Root Development of Acer and Magnolia Species

Abstract

Abstract The effects of arbuscular mycorrhizal fungi (AMF) inoculation on fine root development of four woody landscape plants were studied during the first year after transplant. Test species included two members of obligately mycorrhizal Magnoliaceae (Magnolia virginiana and Magnolia stellata) and two members of facultatively mycorrhizal Aceraceae (Acer × freemanii and Acer buergerianum). Field-grown, balled and burlapped plants were treated with a commercial inoculant containing Glomus spp. and Gigaspora spp. mycorrhizal fungi and transplanted to a piedmont field site. Root architecture and demographics were evaluated in situ using minirhizotrons. One year after transplant, AMF colonization levels had increased in three of the four species regardless of whether they had been intentionally inoculated. AMF-treated M. virginiana and A. buergerianum had significantly lower standing root crops (total root length visible on minirhizotrons) than control plants, and a similar trend was observed in Acer × freemanii. Inoculated M. virginiana roots exhibited reduced branching and shorter life spans, but were less likely to develop brown pigmentation. Species-specific effects of inoculation on root longevity and browning were also observed in the maples. AMF inoculation had no effect on above ground growth or foliar nutrient concentrations. Investment of photosynthate in the growth and maintenance of AMF may represent a more efficient nutrient acquisition strategy than root proliferation, leading to lower fine root production in heavily mycorrhizal plants.