EFFECT OF LIGHT DARK TRANSITION ON CARBON TRANSLOCATION IN EELGRASS ZOSTERA-MARINA SEEDLINGS/

Carbon translocation in the marine macrophyte Zostera marina L. (eelgr ass) was investigated to elucidate the impact of light/dark transition s on sucrose partitioning between roots and shoots. After exposure of leaves to C-14-bicarbonate, the level of C-14-labelled photoassimilate s increased monotonically in both leaves and fully aerobic roots of pl ants maintained in the light. Accumulation of C-14 in roots and leaves ceased abruptly when plants were transferred to darkness that induced root anaerobiosis even though C-14 levels remained high in the dark-e xposed leaves. Thus, translocation of C-14 photoassimilates from shoot s to roots was inhibited when roots became anoxic. Anoxia induced by l ight limitation of photosynthesis, whether due to day/night transition s or periods of extreme light attenuation in the water column, can hav e an impact on carbon availability in subterranean tissues of eelgrass . As a consequence, light availability is likely to control the produc tivity and distribution of eelgrass in highly variable and light-limit ed coastal environments through its effects on carbon partitioning bet ween shoots and roots, in addition to whole-plant carbon balance.