Vesicular-arbuscular mycorrhizas in submerged aquatic plants of New Zealand

Abstract

Vesicular-arbuscular mycorrhizas were found in 22 submerged water-plant species. The existence of mycorrhizal infections in permanently submerged plants was established with records down to 6.0 m depth of water in one lake, and at 2–3 m depth in two other lakes. These depths were lower than the minimum water levels ever recorded for these lakes. Mycorrhizal plants were also found in 17 other lakes around New Zealand. Infection levels showed a general decline with increasing water depth. No relationship was established between the incidence of mycorrhizal infection and the trophic status of the lakes sampled. An association was observed between mycorrhizal infection, the degree of root hair development and the growth form of aquatic plants. High levels of infection were often found in shallow water plants, particularly those without root hairs or with noticeably sparse root hair growth. Most of these plants were also low-growing, shallow rooted plants. Plants with abundant root hairs were either not infected or tended to have low levels of infection. Most of these plants were tall-growing, deeper rooted plants and normally grow in deeper water. Possible explanations for the observed associations are suggested including high absorptive shoot surfaces for tall plants making them less dependent on roots for nutrients, and the probable existence of aerobic substrates in shallow water sandy substrates of the wave wash zone in lakes which could cause soluble phosphorus levels to be low in the rhizosphere of plants growing in this zone.