Soil and microbe interactions in two populations of Appalachian black cohosh (Actaea racemosa L.)

Abstract

Soil and whole plant samples were collected from two natural populations of Appalachian black cohosh (Actaea racemose L.) to assess soil-plant-microbe interactions and determine seasonal mineral acquisition by the species. A. racemosa is one among medicinal forest plants subject to excessive harvesting, and there is increasing concern over the sustainability of natural populations. Following standard procedures, mineral content and chemistry of soils sampled from the two sites were determined, and monthly (May to August) A. racemosa root, stem, and leaf mineral content were analyzed. Fresh tissue samples were processed for isolation and genotyping of associated endophytic organisms, and classical root staining was used to assess presence and extent of the arbuscular mycorrhizal (AM) symbiosis. Results showed that forest soils in the natural habitat of A. racemosa are slightly acidic (pH 4.5-6.0; 40-70% base saturation) with high organic matter (6-25%) and microelement content. Significant (P ≤ 0.05) variation was observed in seasonal concentration of key elements in leaf, stem, and root samples, with high levels of iron (Fe), aluminum (Al), manganese (Mn), and zinc (Zn) sequestered in root tissues. Root colonization by AM fungi was found to be high (85-100%) at both locations throughout the sampling period. A total of 22 fungal and 24 bacterial endophytes were isolated from A. racemosa root, shoot, and flower organs. Molecular characterization revealed bacterial isolates to be primarily Bacillus, Pseudomonas, and Serratia spp., whereas fungal isolates included Alternaria, Cadophora, Diaporthe, Penicillium, and Volutella spp. We conclude that potential exists for managed cultivation of black cohosh in arable land. Further, our findings confirm endophytic (mycorrhizal and nonmycorrhizal) associations in A. racemosa. We believe associated organisms could play a role in the adaptation of A. racemosa to the Appalachian ecosystem and recommend further examination of these relationships.