| Arbuscular mycorrhizal (AM) fungi are known to exist in wetlands, but little is known about their function in these environments. Our objectives were to determine how flooding, phosphorus, and vegetation affected the dynamics of arbuscular mycorrhizal (AM) fungi, total fungi, and bacteria in Blue Cypress Marsh (BCM), a central Florida wetland, with the goal of identifying early indicators of change. In addition, we conducted greenhouse experiments to study the effects of AM fungal communities collected from different vegetation types in BCM, under flooded and free-drained conditions, and at three P levels on growth and nutrition of Typha latifolia L. and Panicum hemitomon Crantz. We also studied the effects of flooding on extraradical hyphae of BCM AM fungal communities. Dominant BCM plant communities (Panicum, Cladium, Typha, Salix, mixed herbaceous, and slough area plants) were sampled seasonally from nutrient-impacted and nonimpacted areas. We measured ergosterol concentration and total bacterial counts in detrital and soil samples, and percentage of root colonization by AM fungi.; We found that nutrient loading increased soil and detrital ergosterol and detrital bacterial counts, and decreased AM fungal colonization; however, the nutrient effects were confounded by vegetation type, and varied seasonally. We also found that AM fungi in BCM were not influenced by water level, and soil bacterial counts were not sensitive to nutrient impact. In the greenhouse for both T. latifolia and P. hemitomon no arbuscular mycorrhizal (AM) fungal community had a consistent impact on plant growth and nutrition. For T. latifolia, flooding eliminated AM fungal colonization and extraradical hyphae; however, in the free-drained treatments, P amendment suppressed colonization. Furthermore, some mycorrhizal communities affected shoot and root P concentrations, but there were no significant plant growth responses. For P. hemitomon , the mycorrhizal association was suppressed (but not eliminated) by flooding and P amendment. Flooding was also detrimental for extraradical hyphae. Mycorrhizal colonization improved plant growth and P nutrition at lower P levels, but conferred no benefit or was detrimental at higher P levels. We conclude that the impact of the mycorrhizal association on these wetland plants was a function of the complex interactions among AM fungal communities, plant species, water condition, and P level. |
