Banca de DEFESA: HENRIQUE DOUGLAS DOS SANTOS BORBUREMA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : HENRIQUE DOUGLAS DOS SANTOS BORBUREMA
DATE: 12/07/2022
TIME: 09:00
LOCAL: Google meet (meet.google.com/imw-qkvr-bie)
TITLE:

EFFECTS OF GLOBAL CHANGE ON THE PHYSIOLOGY OF Bostrychia spp. (RHODOPHYTA) FROM GENETICALLY DIVERGENT TROPICAL AND SUBTROPICAL POPULATIONS

KEY WORDS:

COI-5P; dulcitol; ecophysiology; estuarine salinization; genetic divergence; light stress; macroalgae; mangroves; ocean acidification; ocean warming

PAGES: 183
BIG AREA: Ciências Biológicas
AREA: Ecologia
SUMMARY:

Increased greenhouse gas concentrations in the Earth’s atmosphere have resulted in an atmospheric and oceanic warming. Global warming has caused climate change and sea level rise worldwide. Estuarine salinization is expected due to the sea level rise, longer droughts, and estuary warming. In addition to these global changes, a decrease in oceanic pH has been recorded because of increased dissolved carbon dioxide (CO 2 ) in seawater, an environmental disturbance termed ocean acidification. Fluorinated gases emitted into the atmosphere, in addition to being greenhouse gases, lead to a stratospheric ozone depletion, resulting in a higher harmful solar radiation on the Earth. Primary producers in coastal ecosystems such as mangrove swamps can be negatively affected by these global changes. Thus, in this thesis, we investigated the physiology of the mangrove macroalgae Bostrychia montagnei and Bostrychia calliptera from tropical and subtropical populations after being subjected to global change experimental conditions. The genetic divergence between tropical and subtropical macroalgal populations was also investigated using mitochondrial (COI-5P) and plastidial (rbcL- 3P) DNA markers. The results from our investigation are shown in five scientifi articles, whose main results are briefly described hereafter. In the first article (doi.org/10.1016/j.jembe.2022.151740), we reported that tropical macroalgal populations are genetically divergent from subtropical macroalgal populations, based on the COI-5P marker. We also demonstrated that macroalgae from both climatic niches are tolerant of decreased pH (7.6 and 7.2) by CO 2 enrichment of the seawater (ocean acidification), increasing their growth under decreased pH treatments due to increased CO 2 availability for photosynthesis. Tropical B. montagnei increased its polysaccharide and allophycocyanin content at pH 7.2, and subtropical B. montagnei increased its low molecular weight carbohydrate content at pH 7.2 as well. In the second article (doi.org/10.1016/j.marenvres.2022.105662), we reported that tropical and subtropical B. montagnei and B. calliptera decreased their growth and photosynthetic performance under simultaneous increase in temperature and salinity. We evidenced that macroalgae synthesized proteins, carbohydrates and antioxidants to tolerate detrimental temperatures and salinities, as well as they adjusted their pigment contents (phycobiliproteins, carotenoids, and chlorophyll a) for efficient light-harvesting under thermal and saline stress. In the third article, we observed that tropical B. calliptera and B. montagnei decreased their photosynthetic performance under rising salinity  (salinization in tropical estuaries influenced by semi-arid climate). Bostrychia montagnei showed osmotic acclimation by synthesizing and accumulating organic osmolytes dulcitol and sorbitol under rising  alinity, whereas B. calliptera mainly synthesized and accumulated dulcitol. Sorbitol was only synthesized by B. calliptera at salinities of 37.1, 47.1, and 57.3 S A , as a trace compound. Between species, B. montagnei showed a greater photophysiological tolerance to the salt stress by synthesizing and accumulating both dulcitol and sorbitol, since sorbitol is a physicochemically better osmolyte than dulcitol. In the fourth article, we registered that under increase in photon flux density (increased solar radiation on the Earth due to stratospheric ozone depletion), tropical B. calliptera and B. montagnei exhibited a lower photosynthetic performance. We also recorded a photodamage on the pigment content of B. montagnei under light stress, whereas in B. calliptera a photodamage was only observed on its chlorophyll a content. In both species a photodamage was also registered on their mycosporine–like amino acid (photoprotective compounds) contents under increasing light stress. More pronounced photodamage was observed on B. montagnei. This lower tolerance of B. montagnei to the light stress may explain its preferential occurrence at more shaded microhabitats, as documented in the scientific literature. In the fifth article, we evidenced that tropical and subtropical B. montagnei and B. calliptera increased their dulcitol and sorbitol concentrations under decreased pH by CO 2 enrichment of the seawater. Thus, these polyols also have an energetic function. The carbon content in the macroalgae also increased under ocean acidification. Tropical and subtropical B. montagnei and B. calliptera increased their dulcitol and sorbitol contents under rising temperature and salinity. This demonstrates that these polyols also have a thermal protection function in Bostrychia species. In conclusion, our data support that tropical and subtropical  opulations of B. montagnei and B. calliptera are genetically divergent and benefit from increased CO 2 in seawater, since they increased their productivity and were tolerant of decreased pH. Thereby, these macroalgae can be relevant for CO 2 sequestration in mangrove ecosystems. However, the ocean warming and increased salinity in estuaries will be detrimental to the physiological performance of macroalgae from both climatic niches, even as they adjust their metabolism to synthesize compounds related to thermal and saline tolerance. Our data suggest that tropical macroalgal populations are more vulnerable to warming than subtropical populations, since tropical populations already live closer to their upper thermal tolerance limits. Our data also demonstrate that both species are euryhaline and can be characterized as typical “shade plants”. Thus, increased solar radiation on estuarine ecosystems due to global change will be harmful to both Bostrychia species. In our investigation, we documented for the first time the effects of ocean acidification on Bostrychia species, the first COI-5P sequences generated for both species, physiological strategies of Bostrychia spp. for thermal acclimation, a lethal temperature condition for Bostrychia species (34 ºC for the tropical specimens), a new organic osmolyte distribution pattern in Bostrychia species (only dulcitol in B. calliptera), and the deleterious effects of increased light stress on Bostrychia spp.

COMMITTEE MEMBERS:
Interna - 1279472 - ELIANE MARINHO SORIANO
Interna - 2412921 - JULIANA DEO DIAS
Externo à Instituição - EDSON APARECIDO VIEIRA FILHO
Externo à Instituição - ESTELA MARIA PLASTINO
Externo à Instituição - VINICIUS PERUZZI DE OLIVEIRA