Molecular description of ascomycete fungal communities on Spartina spp. in the U.S.
Lyons, Justine Isabelle
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Ascomycetous fungi play a crucial role in the decomposition of salt marsh vegetation. The first part of this research used molecular methods to examine whether physical associations exist between individual bacterial and common ascomycetous fungal species that co-occur on decaying smooth cordgrass, Spartina alterniflora, in a southeastern U.S. salt marsh. We found that bacterial communities were unaffected by the identity of initial fungal decomposers, suggesting that few species-specific associations exist between those members of the Spartina decomposer community. The next part of the study involved a characterization of ascomycetes involved in the decomposition of different species of Spartina in different environments. In California, the fungi associated with S. alterniflora, S. foliosa, the hybrid between them, and S. densiflora were all characterized using terminal restriction fragment length polymorphism (T-RFLP) analysis of their internal transcribed spacer (ITS) region of rRNA genes as well as clone libraries. Although we found no effect from the hybridization of two host species, we did see significant differences in the fungal decomposer communities both within and among species. S. densiflora hosted several unique ascomycetes. Two previously described ascomycetes, Phaeosphaeria spartinicola and Mycosphaerella, were ubiquitous on all samples analyzed. On the east coast, ascomycete communities on samples of S. alterniflora and S. patens collected in four states (Georgia, North Carolina, New York, and Massachusetts) were compared, again using T-RFLP analysis of the interspacer region. Results show that diversity of the ascomycete taxa on S. patens hosts a higher number of unique ascomycete species than S. alterniflora, and that it has significantly higher diversity, but there were no consistent differences among states. P. spartinicola and Mycosphaerella again dominated most T-RFLP profiles. The data suggest that two fragments (147 and 149 bp), although not confirmed to represent separate taxa, were specific to host plant species. Preliminary data from samples of the same species of grass collected in states along the Gulf coast (FL, LA, MS, AL) confirm all conclusions drawn for samples collected along the east coast, including the higher diversity on S. patens, omnipresence of P. spartinicola and P. halima, and species-specificity of fragments at 147 and 149 bp.