Banca de DEFESA: RAFAELLA DE PAULA AVELAR

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE: RAFAELLA DE PAULA AVELAR
DATA: 24/09/2025
HORA: 08:00
LOCAL: On line
TÍTULO:

NITROGEN DYNAMICS IN SUGARCANE: NUTRITIONAL STRATEGIES UNDER ELEVATED CO₂ AND THE SPATIAL DISTRIBUTION ALONG THE LEAF BLADE

PALAVRAS-CHAVES:

Nitrogen metabolism, Chloroplast, photosynthesis, climate change

PÁGINAS: 54
GRANDE ÁREA: Ciências Agrárias
ÁREA: Agronomia
SUBÁREA: Fitotecnia
ESPECIALIDADE: Fisiologia de Plantas Cultivadas
RESUMO:

Nitrogen (N) is an essential macronutrient involved in critical plant metabolic processes, including the synthesis of amino acids, proteins, nucleic acids, and pigments. Elevated atmospheric CO₂ (eCO₂) generally enhances photosynthesis but often reduces leaf N content, a phenomenon known as CO₂ acclimation. Adjusting the NO₃⁻:NH₄⁺ ratio in nutrient solutions may help mitigate this decline, particularly in sugarcane (Saccharum spp.), which exhibits genotypic variation in NH₄⁺ uptake and tolerance. Besides this Understanding N assimilation, redistribution, and utilization along the leaf can reveal adaptive strategies to optimize N use and photosynthetic capacity, supporting sustainable agronomic practices. This study tested two hypotheses: (i) eCO₂ enhances NH₄⁺ assimilation in sugarcane, and increasing NH₄⁺ supply alleviates N decline, potentially mediated by chloroplast positioning due to its role in photosynthetic efficiency; and (ii) total N, NH₄⁺, and NO₃⁻ follow a gradient along the sugarcane leaf blade, which is modified under increased NH₄⁺ supply. Sugarcane stem nodes (var. RB 855536) were sprouted and grown in 10 L pots with washed sand under greenhouse conditions (28.8°C, 79% RH) for 45 days. Plants were fertigated every two days with a complete nutrient solution at two NO₃⁻:NH₄⁺ ratios (87.5:12.5 and 50:50), gradually increasing ionic strength during acclimation. Afterward, plants were transferred to open-top chambers (OTCs) for nine days for acclimatation, before exposure to either ambient CO₂ (400 µmol mol⁻¹) or elevated CO₂ (800 µmol mol⁻¹) for 35 days. CO₂ concentrations inside the OTCs were monitored every three hours using an infrared gas analyzer. A 2 × 2 factorial design with nine replicates per treatment was employed. Results show that eCO₂ enhanced NH₄⁺ assimilation, with higher NH₄⁺ supply increasing total leaf N. Both eCO₂ and elevated NH₄⁺ shifted chloroplasts toward a centripetal arrangement, suggesting enhanced PEPCK activity and photosynthetic efficiency. Biochemical analyses revealed gradients of total N, NH₄⁺, and NO₃⁻ along the leaf blade, and increased NH₄⁺ promoted redistribution of inorganic N, potentially optimizing N use and reducing toxicity. These findings provide mechanistic insights into N metabolism under eCO₂ and inform strategies to improve N use efficiency in sugarcane under future climate scenarios

MEMBROS DA BANCA:
Externo à Instituição - ANTONIA ALMEIDA DA SILVA - UFLA (Suplente)
Externo à Instituição - CRISTINA RODRIGUES GABRIEL SALES - UC (Membro)
Externo à Instituição - DANIEL AMORIM VIEIRA - UFLA (Suplente)
Externo à Instituição - FERNANDO CESAR BACHIEGA ZAMBROSI - IAC (Membro)
Presidente - PAULO EDUARDO RIBEIRO MARCHIORI (Membro)
Interno - VITOR DE LAIA NASCIMENTO (Membro)
Externo à Instituição - Zulma Catherine Cardenal Rubio - UPTC (Membro)