Effects of arbuscular mycorrhizal fungi on seedling growth and development of two wetland plants, Bidens frondosa L., and Eclipta prostrata (L.) L., grown under three levels of water availability

To identify the importance of arbuscular mycorrhizal fungi (AMF) colonizing wetland seedlings following flooding, we assessed the effects of AMF on seedling establishment of two pioneer species, Bidens frondosa and Eclipta prostrata grown under three levels of water availability and ask: (1) Do inoculated seedlings differ in growth and development from non-inoculated plants? (2) Are the effects of inoculation and degree of colonization dependent on water availability? (3) Do plant responses to inoculation differ between two closely related species? Inoculation had no detectable effects on shoot height, or plant biomass but did affect biomass partitioning and root morphology in a species-specific manner. Shoot/root ratios were significantly lower in non-inoculated E. prostrata plants compared with inoculated plants (0.381 +/- 0.066 vs. 0.683 +/- 0.132). Root length and surface area were greater in non-inoculated E. prostrata (259.55 +/- 33.78 cm vs. 194.64 +/- 27.45 cm and 54.91 +/- 7.628 cm(2) vs. 46.26 +/- 6.8 cm(2), respectively). Inoculation had no detectable effect on B. frondosa root length, volume, or surface area. AMF associations formed at all levels of water availability. Hyphal, arbuscular, and vesicular colonization levels were greater in dry compared with intermediate and flooded treatments. Measures of mycorrhizal responsiveness were significantly depressed in E. prostrata compared with B. frondosa for total fresh weight (-0.3 +/- 0.18 g vs. 0.06 +/- 0.06 g), root length (-0.78 +/- 0.28 cm vs.-0.11 +/- 0.07 cm), root volume (-0.49 +/- 0.22 cm(3) vs. 0.06 +/- 0.07 cm(3)), and surface area (-0.59 +/- 0.23 cm(2) vs.-0.03 +/- 0.08 cm(2)). Given the disparity in species response to AMF inoculation, events that alter AMF prevalence in wetlands could significantly alter plant community structure by directly affecting seedling growth and development.