Abstract
Seagrasses live in highly variable light environments and adjust to these variations by expressing acclimatory responses at different plant organizational levels (meadow, shoot, leaf and chloroplast level). Yet, comparative studies, to identify species’ strategies, and integration of the relative importance of photoacclimatory adjustments at different levels are still missing. The variation in photoacclimatory responses at the chloroplast and leaf level were studied along individual leaves of Cymodocea nodosa, Zostera marina and Z. noltei, including measurements of variable chlorophyll fluorescence, photosynthesis, photoprotective capacities, non-photochemical quenching and D1-protein repair, and assessments of variation in leaf anatomy and chloroplast distribution. Our results show that the slower-growing C. nodosa expressed rather limited physiological and biochemical adjustments in response to light availability, while both species of faster-growing Zostera showed high variability along the leaves. In contrast, the inverse pattern was found for leaf anatomical adjustments in response to light availability, which were more pronounced in C. nodosa. This integrative plant organizational level approach shows that seagrasses differ in their photoacclimatory strategies and that these are linked to the species’ life history strategies, information that will be critical for predicting the responses of seagrasses to disturbances and to accordingly develop adequate management strategies.
Highlights
Seagrasses live in highly variable light environments and adjust to these variations by expressing acclimatory responses at different plant organizational levels
This resulted in differences in Leaf Area Index (LAI), which was lowest in Z. noltei (LAI = 0.50 m2 m−2), followed by C. nodosa (LAI = 0.7 m2 m−2) with the highest value found for Z. marina (LAI = 1.04 m2 m−2)
While C. nodosa expressed rather limited physiological and biochemical adjustments in response to light availability compared to Zostera spp., the opposite was found with respect to leaf anatomical adjustments
Summary
Seagrasses live in highly variable light environments and adjust to these variations by expressing acclimatory responses at different plant organizational levels (meadow, shoot, leaf and chloroplast level). Comparative studies on acclimatory responses of different seagrass species, as well as studies integrating the relative importance of adjustments at different organizational levels, are needed The latter represents a concept widely applied in terrestrial plant science to define the ‘acclimation potential’ and strategy of species[1,2]. Many observations of photoacclimatory responses of northeastern Atlantic seagrasses have been reported, ranging from changes in leaf biomass and/or shoot density, variations in leaf morphology, to physiological and biochemical adjustments (Table 1). Both Cymodocea nodosa and Zostera marina generally increased their leaf biomass, while decreasing shoot height, resulting in shorter, narrower and thinner leaves, even though a few studies reported the opposite response in Z. marina. Similar to its sister species, this species responds with increasing shoot density in response to higher light conditions, while there are contrasting reports on the changes in leaf morphology and photosynthetic capacity (Table 1)
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