Seasonal Photoacclimation and Vulnerability Patterns in the Brown Macroalga Lessonia spicata (Ochrophyta)

Abstract

Fluctuations in solar radiation are one of the key factors affecting productivity and survival in habitat forming coastal macroalgae, in this regard, photoacclimation has a direct impact on the vulnerability and the capacity of seaweed to withstand, for instance, radiation excess. Here, we study ecophysiological responses through photosynthetic activity measurements under time-dependent (one year) fluctuations in solar radiation in the brown macroalga L. spicata. The responses presented seasonal patterns, with an increase in photosynthetic capacity during summer, expressed in greater maximal electron transport rate (ETRmax) and diminished thermal dissipation (NPQmax). Moreover, we studied photoprotective compounds (phenolic compounds) and total antioxidant capacity, which demonstrated an increase during periods of high solar radiation. In addition, content of photosynthetic pigment (Chla, Chlc and Carotenoids) increased under greater solar irradiance. The L. spicata can accumulate as reservoir photoprotective and antioxidant substances to withstand periods of high solar irradiance. All ecophysiological and biochemical responses in L. spicata indicate high photoacclimation and low vulnerability in the species, especially during with greater levels of solar irradiance.

Solar Radiation as an Isolated Environmental Factor in an Experimental Mesocosm Approach for Studying Photosynthetic Acclimation of Macrocystis pyrifera (Ochrophyta)

“…Rather, antioxidant capacity remained at 50% in both high-and low-exposure fronds in the first daily cycle, whereas, in the second cycle, this was somewhat lower, at about 30%, but not significantly different from the first daily cycle. This finding contrasts with positive correlations between phenolic compounds and antioxidant activity found in many other studies (Abdala-Díaz et al, 2014;Figueroa et al, 2014;Celis-Plá et al, 2016;Gómez et al, 2016;Beratto-Ramos et al, 2019, Zúñiga et al, 2021. The low antioxidant activity in the second daily cycle was also related to a decreased ETR in situ .…”

“…The low antioxidant activity in the second daily cycle was also related to a decreased ETR in situ . Thus, antioxidant activity seems to be linked somehow to photosynthetic activity, and this has been reported in a few other habitat forming species of macroalgae (e.g., Celis-Plá et al, 2014Zúñiga et al, 2021). Palacios et al (2021) showed that the M. pyrifera grows in channels and fjords of the Chilean FIGURE 6 | Chlorophyll a (Chla) content in Macrocystis pyrifera fronds during the first daily cycle experiment (A) and the second daily cycle experiment (B) at three time points (8:00, 13:00, and 17:00 h) in the total, attenuated, and low radiation treatments.…”

“…Marambio et al (2017) show the increase of the rETR max in the apical fronds in spring, autumn, and winter. Similarly, ETR max values in Ulva rigida were also higher when determining Y II under solar radiation than under artificial actinic light (Longstaff et al, 2002;Figueroa et al, 2021). A possible explanation is that, under solar radiation, not only chlorophyll but also accessory pigments can be excited, which transfers photons to chlorophyll to a greater extent than under blue actinic artificial light.…”

“…But because large-sized macroalgae with complex morphology, such as M. pyrifera, can modify currents (Gaylord et al, 2003) that, in turn, alter diffusion of nutrients and gases (Hurd, 2017); several authors have called for avoiding unrealistic laboratory experimental designs using tissue portions normally extracted from blades (Figueroa and Korbee, 2010;Drobnitch et al, 2017). For these reasons, other researchers have studied growth responses, photosynthesis, in outdoor tanks conditions (Cabello-Pasini et al, 2000;Figueroa et al, 2021), in laboratory conditions (Colombo-Pallotta et al, 2006), and/or nutrient uptake under field conditions (Edwards and Kim, 2010;Celis-Plá et al, 2015;Palacios et al, 2021).…”

“…Short-term (days) mesocosm studies give information on rapid acclimation to environmental conditions as climate change factors (Stengel et al, 2014;Figueroa et al, 2019Figueroa et al, , 2021, whereas long-term (months, years) mesocosm studies give information on adaptation to the variations in the environmental condition in a scale that allows reaching relevant conclusion of the vulnerability and adaptation to a climate change factor under different scenarios (Liborissen et al, 2005;Harley et al, 2012;Sordo et al, 2016). Also, transplant experiments from coldnutrient rich to warmer-nutrient poor concentrations performed during the 1980's expanded our understanding of how large, morphologically complex kelps (M. pyrifera) can respond to light under those environmental factors (e.g., Gerard, 1982Gerard, , 1984 but cannot decouple the environmental factors that change between the transplant sites.…”