Survival of Ranunculus repens L. (Creeping Buttercup) in an Amphibious Habitat

Underwater breathing apparatus

The remarkable variation between populations of Ranunculus repens leads us again to western Ireland. It is here that Lynn and Waldren (Trinity College, Dublin, pp. 75-84) have been investigating the ability of a form of R. repens to survive several months� submergence, often at depths of several metres, in temporary alkaline lakes (turloughs in Gaelic). They first compared the responses of a ruderal form and the turlough form to �normal� flooding. Both exhibit some pre-adaptation to flooding in that they develop aerenchyma even in drained soil, and the amount of aerenchyma does not increase when plants are flooded to the soil surface. Thus, both forms survive this type of flooding. However, the difference between the turlough and ruderal populations becomes apparent when the plants are submerged. The ruderal form initially exhibits elongation growth of the petioles (the depth accommodation response), which, provided the water is not too deep, restores the leaves to contact with air. However, this is not enough to protect the plants from the effects of total submergence: there is extensive cell and tissue death. By contrast, the turlough population fails to show the depth accommodation response (which surely points to an interesting deviation from normal ethylene physiology), and yet this population survives submergence. The authors suggest that the difference between death and survival lies in a very subtle difference in photosynthetic biochemistry. In earlier work they had shown that neither form could use bicarbonate to any great extent, which means that photosynthesis in the alkaline waters of the turloughs is very limited. However, data in the current paper indicate that the turlough form of R. repens is able to utilize bicarbonate just about well enough to prevent depletion of carbohydrate stores and, more importantly, to generate oxygen within the submerged plants, thus preventing anoxia. So, research on wild plants gives us a breath of fresh air.