Morphological and physiological differences between two morphotypes of Zostera noltii Hornem. from the south-western Iberian Peninsula

The morphological and physiological differences between two morphotypes of Z. noltii Hornem. were studied in the intertidal meadows on the southwester n Iberian Peninsula (Palmones river estuary and Ria Formosa). A small-leave d morphotype (SM) grows mainly at high intertidal sites, meadow edges or in recently deposited sandbanks, whereas a large-leaved morphotype (LM) gener ally thrives in well-structured beds or in deeper places. This study deals with the mol phological, biochemical and physiological differences between these morphotypes as well as the ecological implications of the occurrence of different morphotypes in the same meadow. Shoot length, leaf width, rhiz ome internode length, roots per node, root length, leaf nutrient and pigmen t contents, and photosynthetic rates of both morphotypes were compared. The below-ground architecture (root and rhizome complex of both morphotypes wa s more developed in sites characterized by higher hydrodynamics and/or a lo wer nitrogen content in sediments. Both morphotypes showed similar values f or photosynthetic efficiency, dark respiration rate and compensation irradi ance. On the other hand, the net photosynthetic capacity was much greater ( 5-fold) for the SM. This difference could explain the greater growth rate a nd faster leaf turnover rate of the Sh? compared with the LM. The occurrenc e of the SM in newly settled areas land in the meadow edges) could be expla ined on the basis of its higher growth rate, which would allow a faster spr eading of the meadow and/or better recovery after burial resulting from sto rmy weathers.