Velocidade De Carboxilação Da Rubisco E Transporte De Elétrons Em Espécies Arbóreas Em Resposta a Fatores Do Ambiente Na Amazônia Central

Abstract

RESUMOA disponibilidade de luz é um dos fatores que mais limita a fotossíntese de árvores juvenis no sub-bosque da floresta. Os objetivos deste estudo foram determinar como os parâmetros fotossintéticos (velocidade máxima de carboxilação da Rubisco -Vc-max e as taxas máximas de transporte de elétrons -Jmax) respondem à irradiância, temperatura e horário do dia no interior da floresta. Os dados foram coletados nos meses de setembro a novembro de 2010, entre 08h00 e 16h00, em condições ambientais de temperatura (27 ± 2ºC) e umidade relativa do ar (70 ± 3% Ausência de efeito do horário do dia é importante para a folha poder utilizar com alta eficiência os feixes de luz direta que ocasionalmente atingem o sub-bosque da floresta. Palavras-chave: limitação não estomática; colimitação da fotossíntese; variação diurna. ABSTRACTLight availability is one of the main factors that limits photosynthetic rates in saplings in the forest understory. The aims of this study were to determine how photosynthetic parameters (maximum carboxylation velocity of Rubisco -V c-max and maximum rate of electron transport -J max ) respond to irradiance, temperature and diurnal variations in the physical environment. Gas exchange data were collected between 08h00 and 16h00, and from September to November (2010) under ambient conditions, temperature of 27± 2 ºC and relative humidity of 70 ± 3%. CO 2 saturated photosynthesis (A pot ) was measured under light saturation and [CO 2 ] of 2000 μmol mol -1 . Data were subjected to analysis of variance and then the Tukey test was used for mean separations. V c-max and J max correlated with photosynthetic rates at [CO 2 ] of 380 μmol mol -1 (A 380 ) and A pot . The increase in intercellular CO 2 concentration (C i ) led to increase in photosynthetic rates, up to the point of photosynthesis limitation by the electron transport rate. Below the collimation point (300-569 μmol mol -1) photosynthetic rates were limited by V c-max . Increases in irradiance and temperature in the forest understory led to increasing the values of A 380 , A pot , V c-max and J max . However, the effect of time of day on

Stevia rebaudiana under a CO2 Enrichment Atmosphere: Can CO2 Enrichment Overcome Stomatic, Mesophilic and Biochemical Barriers That Limit Photosynthesis?

“…V cMAX essentially depends on the A N at low CO 2 concentrations, while J MAX is based on A N at high [CO 2 ] levels, well above those to which the leaf is normally exposed [73]. A lower V cMAX as a lower investment in rubisco protein was also reported in many species [73][74][75]. Theoretically, a lower V cMAX would represent a lower carboxylation activity and, therefore, lower A N .…”

“…Decreased photosynthesis under higher temperatures can be lowered by both protein content and decreased enzyme activation, playing a role in the downregulation of rubisco mediated by elevated [CO 2 ] [67,72]. V cMAX essentially depends on the A N at low CO 2 concentrations, while J MAX is based on A N at high [CO 2 ] levels, well above those to which the leaf is normally exposed [73]. A lower V cMAX as a lower investment in rubisco protein was also reported in many species [73][74][75].…”

Changes in leaf functional traits with leaf age: when do leaves decrease their photosynthetic capacity in Amazonian trees?

“…The biochemical parameters of the maximum carboxylation rate of Rubisco and the maximum electron transport rate (V cmax and J max , respectively; µmol m -2 s -1 ) were calculated with an R script that applies a curve-fitting routine based on minimum least-squares (Domingues et al 2010). The photosynthetic capacity was defined by the V cmax modeled and adjusted to the standard temperature of 25 °C (Bernacchi et al 2001) since net assimilation rates (A) are more susceptible to environmental changes and are therefore more liable to daily and seasonal stomatal conductance oscillations (Niinemets et al 2004, Mendes and Marenco 2014, Mendes et al 2017.…”

Potassium silicate and light availability affect photochemical efficiency and morphology of Alibertia edulis

“…Light availability is a determinant environmental factor in the capacity of plants in silvicultural activities since the plants can be inserted in open areas, clearings, understories, or dense forests in different vegetation and/or agroforestry systems. Thus, high or low light intensity can be a stressful condition affecting the production of photoassimilates since it correlates with the thylakoid structure (Petrova et al, 2020), mesophilic conductance, and carboxylation efficiency of RuBisCO (Mendes et al, 2017), and overall photosynthesis. On the other hand, some species can acclimatize to these conditions, adjusting their metabolism through receptors that control the expression of cell division genes and the formation of meristematic tissues (Anpo et al, 2019).…”