Study of seasonal variations in the growth of leaves and roots of Posidonia oceanica
The growth of leaves and roots of Posidonia oceanica (L.) Delile was studied in order to explain seasonal variations observed in the mean length of the leaves. From July 1977 to November 1978 a colony of P. oceanica off the coast of Cape Croisette, in Cannes, France, was sampled and tagged at regular intervals. The collection area was about 1 ha. The results reveal that fluctuations (20 to 70 cm) in the lengths of mature leaves arise from variations in the speed of growth and in the length of the growth period during the course of a year. New leaves in autumn attain a maximum length of 70 cm in July, with a total life-span of 9 too; however, new leaves at the end of spring reach a maximum length of only 20 cm in October with a shorter life-span of 3 to 4 mo. The roots also display seasonal differences in growth and development. The causes of the seasonal variations are discussed. The slower growth of the leaves during the warm season could be connected with a drop in photosynthesis and absorption induced by physical environmental conditions and in particular the abundance of epiphytes on the leaves during summer.
Mattriel et mtthodes
Prdlbvements d'hchantillons ,,in situ,, Ces etudes, sur la croissance des feuilles de Posidonia oceanica (L.) Delile ont 6t6 rdalisdes ~ partir de 11 prdldve-