The natural history of vesicular-arbuscular mycorrhizae in a California tidal salt marsh

Vesicular arbuscular mycorrhizae (VAM) are a ubiquitious component of terrestrial rhizospheres where they function primarily in the acquisition of phosphorus thus enhancing plant growth. VAM are thought to be rare or absent in flooded salt marsh soils due to low oxygen tension and high phosphorus availability. This study documents the relationships between the growth and mycorrhizal development of Jaumea carnosa (Less) Gray and edaphic properties unique to a California tidal salt marsh. In particular, it tests whether VAM are limited to the drier, more oxygenated regions of this environment.;VAM fungi and spores were present in each location at depths of up to 40 cm, but were particularly abundant in the tidal channel site--an apparent function of the "streamside effect." Upland plants, exposed to seasonal extremes in redox potential, soil moisture, and salinity, exhibited the lowest levels of fungal colonization--except when soils were flooded and reduced. Arbuscular colonization was greatest throughout the marsh during the winter months of December and March when soils were supersaturated with wintertime precipitation and sea water, and plants were relatively dormant. VAM appeared to be more sensitive to extremes in soil moisture and salinity, than to redox potential.;VAM fungi colonized the radial files of host plant aerenchyma. This, coupled with periodic pulses of oxygen produced by draw down and tidal action, suggests a rationale for fungal survival in reduced salt marsh soils. Greenhouse trials under flooded, reduced and saline conditions indicate that VAM enhance phosphorus uptake in inoculated plants. Four species of Glomus were recovered from trap cultures including G. intraradices, G. occultum and two new, unidentified species.;Soil redox potential and other variables were measured at three environmentally distinct locations along an elevational gradient in the Walker Creek marsh, Tomales Bay. Changes in redox potential as a function of tidal flux were highly significant for five of the six 24 hour sampling periods. Plant growth appeared to be nitrogen-limited rather than phosphorus-limited.