Banca de DEFESA: LEÔNIDAS CANUTO DOS SANTOS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE: LEÔNIDAS CANUTO DOS SANTOS
DATA: 04/08/2026
HORA: 08:00
LOCAL: DCS02
TÍTULO:

Selenium Distribution in Brazilian Soils and Agronomic Biofortification Strategies for Rice under Water Deficit

PALAVRAS-CHAVES:

Selenium geochemistry; Geochemical baseline; Tropical soils; Rice physiology; Food security; In vitro bioaccessibility; Plant protection; Food quality.

PÁGINAS: 170
GRANDE ÁREA: Ciências Agrárias
ÁREA: Agronomia
SUBÁREA: Ciência do Solo
ESPECIALIDADE: Fertilidade do Solo e Adubação
RESUMO:

Selenium (Se) is an essential element for humans, who require only trace amounts
(approximately 70 μg day⁻¹) for adequate nutrition. However, malnutrition,
including Se deficiency, has caused public health issues in vulnerable regions
worldwide. The low intake of this element by humans is directly linked to low
concentrations in soils, especially highly weathered tropical soils in Brazil. Parent
material, soil moisture, pH, organic matter, clay content, and iron and aluminum
oxides strongly influence the concentration and mobility of Se in soils. As an
alternative, agronomic biofortification has attracted interest because it increases

element availability to plants, allowing its incorporation into organic compounds
that subsequently enter the human diet, thereby promoting food security.
Furthermore, Se enhances the activity of antioxidant enzymes in plants,
mitigating the deleterious effects of environmental stresses, particularly water
deficit, which limits agricultural production. Therefore, the objective of this
thesis was to evaluate the distribution of Se in Brazilian soils and its correlation
with chemical and physical attributes, as well as to develop agronomic
biofortification strategies with Se and evaluate its potential to mitigate water
deficit in upland rice (Oryza sativa L.). Therefore, four experiments were
conducted: 1. Selenium in tropical soils: what is the role of biogeoclimatic variables?; 2.
Agronomic selenium biofortification in rice: impact of water deficit on plant physiology and
post-cooking mineral bioaccessibility; 3. Physiological and nutritional responses and mineral
bioaccessibility in selenium-biofortified rice grains under water deficit; and 4. Combined
application of selenium, zinc, and urea mitigates water deficit and enhances biofortification
and bioaccessibility in upland rice. The mean Se concentration in Brazilian tropical
soils varied widely according to parent material and soil management. Reference
soils derived from sedimentary rocks exhibited a higher mean Se concentration
(0.404 mg kg⁻¹) than soils from other origins. Reference soils showed a mean Se
concentration ranging from 0.150 to 0.404 mg kg⁻¹, whereas cultivated soils
showed a mean variation from 0.239 to 0.746 mg kg⁻¹. In cultivated soils of the
Atlantic Forest biome, Se concentration was significantly higher than in soils of
the Cerrado biome, demonstrating that biomes with distinct biogeoclimatic
characteristics strongly influence element distribution. Soil organic carbon, clay,
and oxyhydroxides were the main determining factors of Se concentration in
Brazilian soils. Regarding the rice crop, Se protected the plants against water
deficit by stimulating antioxidant system enzymes and reducing stress markers
(MDA). Moreover, it improved physiological and biochemical resilience by
increasing water-use efficiency, stomatal conductance, and gas exchange, as well
as proline, protein, and amino acid contents. Furthermore, the combined foliar
application of Se and Zn, along with the addition of urea to the spray solution,
increased rice yield. However, the production environment strongly influenced
plant responses to the imposition of water deficit. In conclusion, the distribution
of Se in Brazilian tropical soils results from the interaction among lithology, soil
management, chemical and physical attributes, and biogeoclimatic conditions.
Agronomic biofortification strategies proved highly beneficial for the rice crop,
increasing the concentration of essential elements and protecting plants against
water deficit. The efficacy of Se application (especially in combination with Zn)

enhanced agricultural systems, constituting a promising tool to combat "hidden
hunger," contributing to bioaccessibility in the human gastrointestinal system,
and reinforcing food security.

MEMBROS DA BANCA:
Interno - CYNTHIA DE OLIVEIRA - UFLA (Suplente)
Externo à Instituição - FLAVIO HENRIQUE SILVEIRA RABELO - USP (Membro)
Externo à Instituição - FÁBIO AURÉLIO DIAS MARTINS - EPAMIG (Suplente)
Presidente - GUILHERME LOPES (Membro)
Externo à Instituição - JOSINALDO LOPES ARAÚJO ROCHA - UFCG (Membro)
Interno - LEONIDAS CARRIJO AZEVEDO MELO (Suplente)
Interno - LUIZ ROBERTO GUIMARAES GUILHERME (Membro)
Externo à Instituição - MARIA MANUELA ABREU DA SILVA - UNL (Membro)