Seed photosynthesis enhances Posidonia oceanica seedling growth

Posidonia oceanica seeds demonstrate photosynthetic activity during germination as well as throughout seedling development, a fact which suggests that seed photosynthesis can influence seedling growth. This study examines the contribution of seed photosynthesis to changes in leaf and root biomass, the concentration of seed carbohydrate reserves (free sugars and starch) and elemental C, N and P content in seedlings exposed to different light/dark treatments. Green seeds attached to seedlings remained photosynthetically active for three months and photosynthetic activity in the seeds enhanced seedling growth in leaves and roots. It was estimated that ca. 29.26% of leaf biomass and ca. 42.31% of root biomass production was due to seed photosynthetic activity. Photosynthesis occurred at a higher rate in seeds than in leaves during early seedling growth, and extreme light limitation reduced the mobilization of carbon reserves stored in the seeds. These adaptations control leaf self‐shading and plant competition in well‐established P. oceanica beds while also promoting increased seedling survival rates in open, uncolonised areas where clonal growth is limited.