Biotic interactions in salt marsh zonation with particular reference to abuscular mycorrhizas
Salt marshes occupy a narrow intertidal zone where conditions change from marine to
terrestrial. As a consequence they exhibit severe clines in salinity and soil saturation.
The characteristic zonation of the vascular plant communities occupying these habitats
is believed to develop as a result of differential tolerance and competitive abilities of the
plants that comprise them. There are however few data on the structure of salt marsh
communities relative to either elevation or tidal inundation.
The consequences of soil saturation and salinity may also affect the distributions of soil
microflora, including the occurrence and development of arbuscular mycorrhizal fungi.
As AM development can result in enhanced plant performance, and may alter
competitive interactions, any edaphic limitation in their development could influence
plant community development.
Detailed surveying, and the use of two objective methods of defining zonation, has
allowed a full description of the plant community structure, relative to elevation, to be
made. This identifies three distinct species groupings within the zonation, and has
enabled the identification of competitive dominants within the zonational sequence.
The occurrence of AM development within the salt marsh community has also been
accurately determined for the first time. This represents the first survey of AM fungi in
UK salt marshes since 1928, and identifies a distinct cline in the occurrence of these
fungi relative to inundation.
The effects of mycorrhizal development by AMF isolated from salt marsh sediments on
the growth of 5 halophytes is ascertained. The results suggest salt marshes are
environments where the usual benefits of AM development do not apply. This may
explain the low levels of mycotrophy observed amongst halophytes.