Seasonal Changes in Nitrogen, Free Amino Acids, and C/N Ratio in Mediterranean Seagrasses

Seasonal changes in nitrogen, free amino acids, and carbon were investigated in the three Mediterranean seagrasses Posidonia oceanica, Cymodocea nodosa, and Zostera noltii. Leaves, rhizomes, roots, as well as dead plant material were analysed separately. Highest N‐concentrations were obtained in the winter months, regardless of species or plant part. In contrast to the other two species, the N‐content in Posidonia was higher in the rhizomes than in the leaves. In the investigated species, marked differences in the free amino acid (FAA) composition were detected between species: Proline, lacking in Posidonia, was the main component in Cymodocea. In Posidonia, FAA decreased from 320umol g‐1 (dry wt) in leaf sheaths to 1.5 umol g‐1 (dry wt) in the leaf tips. The function of proline as a possible storage and/or stress metabolite is discussed. High C/N values in dead P. oceanica and C. nodosa rhizomes as well as in P. oceanica wrack seem to be related to considerable resistance to decomposition. Low C/N ratios did not increase in detached C. nodosa and Z. noltii leaves, which began to decompose shortly after detachment from the plants.