It’s that time of year again when a lucky group of 1st year undergraduates from the University of Manchester head to the Mediterranean to learn about plant evolution and adaptations. This year in Mallorca we stopped at a slightly wetter part of the Albufereta, a small salt marsh near to the town of Alcudia (north-west of the lager famous wetland and Ramsar site, the Albufera). With more water in evidence, this part looked like a better place for the students to learn about mechanisms plants can use to tolerate salt stress.
The area is dominated by three plant species Arthocnemum macrostachyum (Glaucus glasswort), Halimione portulacoides (Sea purslane) and Juncus maritmus (Sea rush). Each of these has has specialised mechanisms for living in high salt, waterlogged soils such as succulent stems, the ability to exudes salt onto the leaves or air-filled spaces within the leaves and stems.
Patches of slightly higher ground, however, allowed other plants to grow, including this Grey birdsfoot trefoil (Lotus cytisoides). The weather had been a little cold over the preceding weeks and as this was one of the few plants in flower it was getting a lot of attention from the bees.
We see a lot of this plant on the strand-line and sand dune systems around Alucudia. It is clearly also salt-tolerant, but likes freer-draining soils and cannot cope with waterlogging. In flooded soils, air spaces fill up with water and bacteria rapidly use up available oxygen. Without special adaptations, plants in waterlogged soils can die as their roots are effectively suffocated as the flow of oxygen and carbon dioxide in and out of the roots is limited. Roots can then be invaded by fungi and other pathogens and the above ground parts of the plant suffer as water and nutrient transport from the roots is affected.