Endomycorrhizae of isoetids along a biogeochemical gradient

Wigand, C., F. Ø. Andersen, K. K. Christensen, M. Holmer, H. S. Jensen

Limnol. Oceanogr., 43(3), 1998, 508-515 | DOI: 10.4319/lo.1998.43.3.0508

ABSTRACT: Endomycorrhizae of aquatic plants may be important in phosphorus uptake and carbon exchange in lakes, but the environmental controls on mycorrhizal distribution are not known. We examined biogeochemical variables that were correlated with aquatic endomycorrhizae of isoetid-type macrophytes in an oligotrophic, softwater lake. Endomycorrhizal infection was greatest in the shallow stations with high sediment redox potential and lowest in the deeper stations where there was low redox potential and high sediment organic content and porewater P levels. There was a significant 0. = +0.93, P < 0.05) positive correlation between percentage of hyphal infection of the roots and a root ergosterol (a specific fungal sterol) index determined per root mass. Fungal vesicle infection was also positively correlated with the root ergosterol index, although not significantly (r = +0.76, P = 0.14). Furthermore, the root ergosterol index was significantly correlated with plant rosette density (r = +0.97, P < 0.03. An increase in rosette density of isoetids increases the number of lacunae transporting oxygen to the roots, perhaps increasing fungal infection. The root ergosterol index was also significantly (P < 0.05) correlated with sediment redox status, porewater phosphate, solid phase iron-bound P, exchangeable inorganic P, and inorganic adsorbed P There were no significant correlations between above- or belowground biomass or porewater NH4+ with the root ergosterol index, and porewater DOC was weakly correlated (P = 0.08) with the ergosterol index. Isoctid-type plants are common in oligotrophic softwater lakes, and knowledge of environmental variables that are associated with endomycorrhizae will facilitate in management and restoration of these types of submersed vegetation.

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