Molecular Diversity of Arbuscular Mycorrhizae in Roots of Juniperus virginiana Invasive to Grasslands

Abstract

Core Ideas Glomus spp. dominate the arbuscular mycorrhizal fungal (AMF) community in eastern red cedar (ERC) roots. Young seedlings harbor the most diverse AMF, similar to grassland soils from the same site. AMF diversity within ERC roots tended to decrease with plant age suggesting narrower plant and edaphic selection pressures with increasing ERC stand density. A change in biotic and abiotic factors resulting from displacement of grassland with ERC is likely responsible for successional changes in the AMF community. Eastern red cedar (ERC; Juniperus virginiana) is an invasive species of juniper native to eastern North America that causes significant economic loss to grasslands. Recent findings of high molecular diversity of arbuscular mycorrhizal fungi (AMF) in soils under ERC stands led us to consider that the invasiveness of ERC into grasslands may arise in part from its ability to form associations with extant grassland AMF communities. The diversity of AMF in roots of ERC was determined for five age groups ranging from 1 to 65 yr old and varying in stand density from individual seedlings in grassland (<5 yr) to closed ERC canopies devoid of grass species (65 yr). Roots were analyzed by nested polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE) fingerprinting, cloning, and insert screening by DGGE, and sequencing of ribosomal DNA small‐subunit regions. Phylogenetically analyzed AMF sequences were used to define phylotypes. The majority of the sequences obtained were classified into Glomus Group A, with only a few belonging to Gigasporaceae and Acaulosporaceae, the latter two largely restricted to roots from ERC < 5 yr old. The richness of phylotypes tended to decrease with time, ranging from 11 in the youngest age group (1–5 yr) to 4 in the oldest age group (46–65 yr). Abundance of phylotypes varied greatly among the age groups. Overall, AMF diversity within ERC roots tended to decrease with plant age suggesting narrower plant and edaphic selection pressures with increasing ERC stand density.