Recovery of Cymodocea nodosa (Ucria) Ascherson photosynthesis after a four-month dark period

Resumen

Cymodocea nodosa plants were dark incubated for four months. The potential of reactivating photosynthesis was tested in an experiment in which half of the plants were reilluminated (HL) while the other half were grown under very low irradiance levels (LL). Photosynthesis was measured using PAM fluorescence and tissue nutrient and carbohydrate contents were analysed. Photosynthetic efficiency (Fv/Fm) in HL plants increased from 0 to 0.58, whereas LL plants remained inactive. Photosynthetic parameters also increased, resulting in a final Ik of 97.5 µmol m-2 s-1. Leaf shedding led to a negative mean RGR in HL plants. Tissue C and N dropped considerably during dark incubation in both rhizomes and shoots. Starch content was nearly equal for rhizomes and shoots (4.3 mg /g DW) and was not affected by dark incubation. In contrast, sucrose content dropped from 40.0 mg /g DW to zero in shoots and from 240 to 40.0 mg /g DW in rhizomes in HL plants. We conclude that C. nodosa is capable of recovering photosynthetic activity after four months darkness, which is considerably longer than the 80 d recorded so far for a seagrass. Stored carbohydrates, more specifically sucrose, play an important role in both survival and reactivation.