Mycorrhizal dependency of some endemic and endangered Hawaiian plant species

Four endemic species of Hawaiian plants were tested for their response to inoculation with a Hawaiian isolate of Glomus aggregatum (all arbuscular mycorrhizal fungus [AMF]) when grown in a native soil with or without P added to achieve different soil-solution P levels The endangered species (Sesbania tomentosa [Fabaceae] and Colubrina oppositifolia [Rhammaceae]) and two nonendangered species (Bidens sandvicensis and B. asymmtrica X sandvicensis [Asteraceae]) were tested. When soil-solution P levels in greenhouse trials were similar to unfertilized field soils (e.g., 0.005-0020 m P/L), shoots of moculated plants were 2.1 to 7.0 times larger than noninnoculated plants. Leaf tissue P levels and root biomass in these species showed similar responses to inoculation. Mycorrhizal dependencies ranging from 44 to 88% were measured when plants were grown in low-P soils and were -4-42% ill soil with P levels typical of highly productive agricultural soils. A survey of P levels in a variety of native (nonagriculatural) Hawaiian soils indicated the widespread occurrence of P-limited sites (mean = 0 010 mg P/L, range = <0001-0.030 mg P/L. N = 41) The terms "ecological mycorrhizal dependency" (EMD) and "agricultural mycorrhizal dependency" (AMD) are introduced to refine the concept of mycorrhizal dependency.