Variação da temperatura do substrato e fotossíntese em mudas de laranjeira 'Valência'

Abstract

Resumo -O objetivo deste trabalho foi avaliar a influência da temperatura do substrato nas trocas gasosas, atividade fotoquímica e relações hídricas, em plantas jovens de laranjeira 'Valência' enxertadas sobre limoeiro 'Cravo'. Foram utilizadas mudas com seis meses de idade. O experimento foi conduzido em câmara de crescimento, em que o substrato foi mantido a 10, 20 (controle) ou 30 o C, e a temperatura do ar variou de 25 a 20 o C entre o dia e a noite, com fotoperíodo de 12 horas e densidade de fluxo de fótons fotossinteticamente ativos de 800 µmol m -2 s -1 . Mediu-se, em cada tratamento, a assimilação de CO 2 em resposta à concentração de CO 2 no mesofilo, a fluorescência da clorofila a e o potencial da água na folha às 6 e às 13h. A temperatura de 30 o C promoveu aumento na assimilação de CO 2 , em razão de fatores difusivos e metabólicos, tendo-se observado aumento na eficiência máxima de carboxilação (V c, máx ), na regeneração da ribulose-1,5-bisfosfato, (J máx ) e nas condutâncias estomática (gs) e do mesofilo (gi), em relação à temperatura controle. A menor temperatura causou aumento do dreno alternativo de elétrons e queda da assimilação de CO 2 , em consequência de limitações difusivas e metabólicas, evidenciadas por decréscimos em gs, gi, V c, máx e J máx .Termos para indexação: Citrus limonia, Citrus sinensis, fluorescência, relações hídricas, troca gasosa. Root temperature variation and photosynthesis of 'Valencia' sweet orange nursery treesAbstract -The aim of this work was to evaluate the influence of the substrate temperature on gas exchange, photochemical activity and water relations in 'Valencia' sweet orange grafted onto 'Rangpur' lime. Six-month-old nursery trees were used. The experiment was carried out in a growth chamber, where the root system was maintained at 10, 20 (control) or 30ºC, the air temperature varied between 25 and 20ºC from day to night, the photoperiod and photosynthetic photon flux density were set to 12 hours and 800 µmol m -2 s -1 , respectively. The CO 2 assimilation rates in response to the intercellular CO 2 , chlorophyll a fluorescence and leaf water potential at 6 h and 13 h were measured for each treatment. The higher root temperature increased the CO 2 assimilation in relation to the control temperature, due to diffusive and metabolic factors: plants showed enhanced maximum carboxylation efficiency (V c, max ), ribulose-1,5-bisphosphate regeneration (J max ), and both stomatal (gs) and mesophyll (gi) conductances. The lowest root temperature led to increased alternative electron sink and decreased CO 2 assimilation, due to diffusive and metabolic limitations, indicated by decreases in gs, gi, V c, max , and J max .

NCED expression is related to increased ABA biosynthesis and stomatal closure under aluminum stress

“…Although the plants were grown directly on nutrient solution, the pd = soil principle is still accepted because pd is measured before sunrise in non-transpiring plants and, therefore, pd represents the plant's capacity to rehydrate overnight (Turner, 1981). This method was previously used for measuring KL in Citrus sinensis (Magalhães Filho et al, 2009) and C. limonia (Cavalheiro et al, 2020) grown on nutrient solution.…”

Towards a New Ecophysiological Approach to Understand Citrus Crop Yield Under Abiotic Stresses Mirroring in the Brazilian Savanna Genetic Resources

“…Although efficient scion/rootstock combinations may increase the water use efficiency in citrus plants (Ribeiro & Machado, 2007), low stomatal conductance affects the CO 2 assimilation rates by decreasing carbon availability at the carboxylation sites. Such effects may be caused by the low values of soil temperatures (Magalhães Filho et al, 2009), soil water availability (Ribeiro & Machado, 2007) and also by high vapor pressure deficits (Habermann et al, 2003) observed during the dry season in subtropical areas (Ribeiro & Machado, 2007;Habermann & Rodrigues, 2009). Significant reductions in the water use efficiency have been reported for irrigated field-grown citrus plants during the dry season (Ribeiro, 2006), which confirm that other factors, other than soil water availability, may affect the photosynthesis of citrus plants (Ribeiro & Machado, 2007).…”

Estudio de viabilidad del uso de agua regenerada y riego deficitario controlado en cítricos

“…Sobre estos patrones se injerta la variedad, que es la planta o árbol que realmente se quiere cultivar (Alcobendas, 2014). Las relaciones hídricas en cítricos han sido bien estudiadas y muchos trabajos muestran que los portainjertos alteran el desempeño fisiológico bajo déficit hídrico (Romero et al, 2006, Magalhães Filho et al, 2009Forner-Giner et al, 2011) -Citrus volkameriana: Es un híbrido de limonero, el cual induce un gran vigor, y a su vez, la producción de las variedades injertadas sobre este patrón dan las mayores cosechas con diferencia, aunque la calidad parece ser inferior a la de otros patrones. Tiene buena resistencia a la caliza y moderada a la salinidad y, como Citrange, adelanta la cosecha.…”