Triclosan inhibits arbuscular mycorrhizal colonization in three wetland plants.

In terrestrial ecosystems, plant growth, plant community structure, and ultimately the ecosystem services provided by plants are dependent on the presence and composition of below ground arbuscular mycorrhizal (AM) fungal communities. AM fungi form obligate symbioses with plants providing nutrients to their host plants in exchange for photosynthates. While AM have been found in most wetland ecosystems, the effects of urban contaminants on AM associations are largely unknown. Triclosan (5-chloro-2-[2,4-dichlorophenoxy]phenol; TCS) is a widespread contaminant found in surface waters throughout North America and in addition to antimicrobial properties is purported to have antifungal properties. To determine the effects of TCS on arbuscular mycorrhizal associations, we exposed AM inoculated wetland plant species (Eclipta prostrata, Hibiscus laevis, and Sesbania herbacea) to TCS at concentrations of 0.0, 0.4 and 4.0 μg/L in a continuous flow-through exposure system. TCS exposure caused significant reductions in hyphal and arbuscular colonization while no significant effect was detected for vesicular colonization. Across all species, hyphal colonization was significantly higher in controls (18.58 ± 1.84%) compared to 0.4 and 4.0 μg/L (10.20 ± 1.34% and 9.86 ± 1.32% respectively) TCS treatments. Similarly, arbuscular colonization was significantly higher in the controls (4.58 ± 0.75%) compared to 0.4 μg/L (2.20 ± 0.38%) and 4.0 μg/L (1.22 ± 0.24%) TCS exposures. Since our lowest effect concentration, 0.4 μg/L, lies within the range of concentrations found in North American streams it is plausible that AM colonization has been impacted in streams receiving WWTP effluent. Further studies are required to understand the mechanism of TCS inhibition of mycorrhizal colonization in wetland plant species as well as the potential ecological consequences that a decline in the AM colonization levels may represent.