Specialized compounds across ontogeny in the seagrass Posidonia oceanica

Patch age alters seagrass response mechanisms to herbivory damage

Natural disturbances can produce a mosaic of seagrass patches of different ages, which may affect the response to herbivory. These pressures can have consequences for plant performance. To assess how seagrass patch age affects the response to herbivory, we simulated the effect of herbivory by clipping leaves of Halodule wrightii in patches of 2, 4 and 6 years. All clipped plants showed ability to compensate herbivory by increasing leaf growth rate (on average 4.5-fold). The oldest patches showed resistance response by increasing phenolic compounds (1.2-fold). Contrastingly, the concentration of phenolics decreased in the youngest patches (0.26-fold), although they had a similar leaf carbon content to controls. These results suggest that younger plants facing herbivory pressure reallocate their phenolic compounds towards primary metabolism. Results confirm the H. wrightii tolerance to herbivory damage and provides evidence of age-dependent compensatory responses, which may have consequences for seagrass colonization and growth in perturbed habitats.

Sources of variability in seagrass fatty acid profiles and the need of identifying reliable warming descriptors

Global warming is expected to have inexorable and profound effects on marine ecosystems, particularly in foundation species such as seagrasses. Identifying responses to warming and comparing populations across natural temperature gradients can inform how future warming will impact the structure and function of ecosystems. Here, we investigated how thermal environment, intra-shoot and spatial variability modulate biochemical responses of the Mediterranean seagrass Posidonia oceanica. Through a space-for-time substitution study, Fatty acid (FA) profiles on the second and fifth leaf of the shoots were quantified at eight sites in Sardinia along a natural sea surface temperature (SST) summer gradient (about 4 °C). Higher mean SST were related to a decrease in the leaf total fatty acid content (LTFA), a reduction in polyunsaturated fatty acids (PUFA), omega-3/omega-6 PUFA and PUFA/saturated fatty acids (SFA) ratios and an increase in SFA, monounsaturated fatty acids and carbon elongation index (CEI, C18:2 n-6/C16:2 n-6) ratio. Results also revealed that FA profiles were strongly influenced by leaf age, independently of SST and spatial variability within sites. Overall, this study evidenced that the sensitive response of P. oceanica FA profiles to intra-shoot and spatial variability must not be overlooked when considering their response to temperature changes.