Photoacclimation strategies in northeastern Atlantic seagrasses: Integrating responses across plant organizational levels

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.

Heatwave Effects on the Photosynthesis and Antioxidant Activity of the Seagrass Cymodocea nodosa under Contrasting Light Regimes

“…Thalassia hemprichii is less responsive to high light than Halophila ovalis [22], in which the photoprotective mechanisms involve increased dissipation of excess energy and the activity of antioxidant enzymes. Schubert et al [23] found anatomic modifications in seagrass leaves in response to light availability, more pronounced in C. nodosa than in Zostera marina and Zostera noltii. Co-occurring stressors, such as high-temperatures, condition the plants' light use capacity by affecting several metabolic processes, such as electron transport rate [20], carbon acquisition, and fixation [21].…”

Photoacclimation and Light Thresholds for Cold Temperate Seagrasses

“…The subtle change in carotenoid contents with light intensity can be related to the preservation of heat dissipation mechanisms, as mentioned above, and/or to an optimization of light harvesting in low-light environments ( Silva et al, 2013 ; Davey et al, 2018 ). Changes in pigment contents are often considered as photoacclimatory mechanisms enabling better light absorption ( Ralph et al, 2007 ; Schubert et al, 2018 ). However, the adaptation of seagrasses to the aquatic life, consisting of concentrating the chloroplasts in the leaf epidermis to optimize inorganic carbon acquisition ( Hemminga and Duarte, 2000 ; Enríquez, 2005 ), leads to a strong package effect ( Cummings and Zimmerman, 2003 ; Enríquez, 2005 ; Durako, 2007 ).…”

“…For example, rapid adjustments to a new constant irradiance take place in a matter of days through subcellular photosynthetic changes ( Lambers et al, 2008 ). On the other hand, photoacclimation, i.e., photosynthetic, physiological, and morphological adjustments to light conditions may take weeks to months, and occur from subcellular to plant scale ( McMahon et al, 2013 ; Schubert et al, 2018 ). At shoot scale, an increase in leaf surface or photosynthetic biomass, often approximated by an increase of the above or below-ground biomass ratio, helps maintain carbon balance by decreasing the proportion of non-photosynthetic tissues relative to photosynthetic ones ( Olesen and Sand-Jensen, 1993 ).…”

Comparative study on anatomical traits and gas exchange responses due to belowground hypoxic stress and thermal stress in three tropical seagrasses

“…Our investigation solely focused on the youngest mature ramets as they represent a significant site with a fully developed structure and function. These youngest mature ramets are metabolically active, and they have been widely used in physiological investigations ( Short & Duarte, 2001 ; Collier et al, 2008 ; Park et al, 2016 ; Schubert et al, 2018 ; Rasmusson et al, 2019 ; Nguyen et al, 2020 ). Following the literature mentioned above, we used the third ramet from the growing apex of C. rotundata and T. hemprichii and the second ramet from the growing apex of H. ovalis .…”