Decomposition of Posidonia oceanica (L.) Delile Leaf Blade and Rhizome in Terrestrial Conditions: Effect of Temperature and Substrate Fertility

Purpose Posidonia oceanica litter debris accumulate in large quantities in coastal areas and pose a serious problem of negative economic impact on tourism activities. Here, we investigated the possibility of managing such residues by in situ decomposition using green leaves, brown litter, and rhizomes for 720 days at two temperatures (10 and 20 °C) alone or in the presence of nitrogen-rich soil or compost. Methods P. oceanica debris were characterized for remaining mass, carbon, nitrogen, sodium, cellulose, lignin content, and by 13 C CPMAS NMR. Temperature sensitivity of litter decomposition was assessed by Q 10 index. Results Nitrogen was highest in green leaves compared to brown litter and rhizomes, with C/N and lignin/N ratios highest in rhizomes. Lignin was higher in brown litter and rhizomes compared to green leaves. Sodium was highest in green leaves compared to brown litter and rhizomes. Data from 13 C CPMAS NMR showed that O-alkyl-C predominated in all litter. Aromatic C regions were highest in rhizomes compared to green leaves and brown litter. Decomposition was slow in all debris, with mass loss never exceeding 46.59% after 720 days of incubation. Based on Q 10 values, P. oceanica debris showed a limited temperature sensitivity to decomposition, and was highest for brown litter compared to green leaves and rhizomes. Conclusion Our two-year experiment showed that P. oceanica is highly resistant to microbial decomposition, and the presence of nitrogen-rich substrate does little to promote the process. Overall, in situ decomposition does not seem to be a suitable way to manage human-induced P. oceanica deposition under terrestrial conditions. Graphical Abstract