Occurrence and ecological significance of vesicular arbuscular mycorrhiza in the salt marsh environment

The infection by vesicular arbuscular mycorrhizal fungi (VAM) of various salt marsh plant species has been estimated and compared. This kind of infection appeared to be high or intermediate and frequent in Aster tripolium, Plantago maritima, Glaux maritima and Festuca rubra ssp. litoralis. rare or absent in Spartina anglica, Triglochin maritima, Juncus gerardii, J. maritimus, Atriplex hastata and Suaeda maritima and variable or intermediate in Salicornia dolichostachya and S. brachystachya. The sodium content of shoots of mycorrhizal Aster tripolium plants was lower than of nonmycorrhizal plants when grown at 300 mM NaCl. The potassium and phosphorus content of the shoot was not significantly affected by the presence of mycorrhiza. Improved growth of mycorrhizal plants of Aster tripolium under salinity stress could be related to increased leaf elongation and to smaller diurnal changes in the leaf thickness. Both parameters indicate increased water uptake by mycorrhizal roots. The causes of increased water uptake in mycorrhizal plants are discussed in terms of reduced root resistance to water transport and its consequences for prolonged stomatal opening and increased photosynthesis.