Effect of Soil pH On Growth, Nutrient Uptake, and Mycorrhizal Colonization in Exotic Invasive Lygodium Microphyllum .

Lygodium microphyllum (Old World climbing fern) is an invasive exotic plant species taking over many sites in freshwater and moist habitats in Florida. Managing L. microphyllum has been a significant challenge for land resource managers and researchers due to its extensive rapid invasion in natural areas of south Florida. To assess the effects of soil pH on growth, nutrient uptake, and mycorrhizal colonization in the roots of L. microphyllum, we conducted a 60-day greenhouse experiment, growing L. microphyllum plants in pots filled with pH adjusted soils spanning a range from pH 4.5 to 8.0. L. microphyllum was able to survive and grow at all soil pH levels; however, final biomass, relative growth rate, photosynthesis, and specific leaf area were all significantly greater in soil pH 5.5 - 6.5 compared to the other treatments. Correspondingly, nitrogen concentration was also significantly related to these four plant parameters. Root colonization by mycorrhizal fungi was significantly higher in soil pH 5.5-7.5 than in lower or higher pH soil, and was significantly correlated with plant growth parameters as well as elemental concentration in the leaves. In its native Australia, L. microphyllum responds robustly following fire. Fire is also known to commonly raise soil pH, and given the treatment response to soil pH in our study this may help partially explain L. microphyllum’s response to burning. Recently, fire has been used as a potential management control option in its introduced range in Florida; given the results of this study, and the plant’s known fire tolerance in its home range, this management option should likely be reconsidered.