Baixa temperatura noturna e deficiência hídrica na fotossíntese de cana‑de‑açúcar

Abstract

Resumo -O objetivo deste trabalho foi avaliar as respostas fotossintéticas da cana-de-açúcar aos efeitos simultâneos e isolados de baixa temperatura noturna (TN) e deficiência hídrica (DH). Após 128 dias do plantio, as plantas da cultivar IACSP94-2094 foram submetidas aos tratamentos: controle, sem DH e com TN de 20°C (TN20); com DH e TN de 20°C (DH/TN20); sem DH e com TN de 12°C (TN12); e com DH e TN de 12°C (DH/TN12) por cinco dias. Após o período de tratamento, as plantas foram irrigadas e submetidas à TN de 20°C por mais quatro dias, para recuperação. Houve decréscimos na assimilação de CO 2 em todos os tratamentos. A recuperação total da assimilação de CO 2 foi observada apenas nas plantas do tratamento TN12. A ocorrência simultânea da baixa temperatura noturna e da deficiência hídrica causou dano acentuado e persistente na condutância estomática, na capacidade máxima da ribulose-1,5-bisfosfato carboxilase, no transporte aparente de elétrons, no fator de eficiência e na eficiência operacional do fotossistema II, o que resultou em limitações difusivas, bioquímicas e fotoquímicas da fotossíntese das plantas de cana-de-açúcar.Termos para indexação: Saccharum, assimilação de CO 2 , PEPcase, resfriamento, Rubisco. Low night temperature and water deficit on photosynthesis of sugarcaneAbstract -The objective of this work was to evaluate the photosynthetic responses of sugarcane to the simultaneous and isolated effects of low night temperature (TN) and water deficit (DH). After 128 days of planting, plants of the cultivar IACSP94-2094 were subjected to the following treatments: control, without DH and with TN of 20°C (TN20); with DH and TN of 20°C (DH/TN20); without DH and with TN of 12°C (TN12); and with DH and TN of 12°C (DH/TN12). After the period of treatment, plants were irrigated and subjected to TN of 20°C for four more days, for recovery. There were decreases in CO 2 assimilation in all treatments. Total recovery of CO 2 assimilation was observed only in plants from the treatment TN12. The simultaneous occurrence of low night temperature and water deficit caused a accentuated and persistent effect on stomatal conductance, on the maximum capacity of ribulose-1,5-bisphosphate carboxylase, on the electron transport rate, on the efficiency factor, and on the operational efficiency of photosystem II, which resulted in diffusive, biochemical, and photochemical limitations of photosynthesis of sugarcane plants.

PHYSIOLOGICAL RELATIONSHIPS IN Aleurites fordii Hemsl. SEEDLINGS

“…This result is in agreement with Machado et al (2013) that, when working with Saccharum officinarum L. (sugarcane), verified that the assimilation of CO 2 decreased in the nocturnal period, when the temperatures were low. Rezende et al (2011) found that stomatal opening is considered the main control mechanism in gas exchange by plants.…”

Physiological Plasticity Is Important for Maintaining Sugarcane Growth under Water Deficit

“…Taking into account plant responses ( Figures 2 – 5 ) and also soil water availability ( Figure 1 ), we may consider that IW represents a slight water deficit whereas LW represents a severe water deficit. In general, the physiological responses to IW and LW treatments reported herein are already known and described in recent papers (Machado et al, 2009, 2013; Ribeiro et al, 2013; Sales et al, 2013). For instance, reductions in stomatal conductance, carboxylation and photochemistry were associated with the inhibition of sugarcane photosynthesis ( Figures 2 , 3 ) and such responses were genotype-dependent.…”

“…Then, we may argue that increases in root growth improved soil volume exploration, indicating an important morphological response under marginally reduced water availability. In general, sugarcane performance under water deficit has been evaluated considering only shoot responses (Inman-Bamber and Smith, 2005; Basnayake et al, 2012; Machado et al, 2013; Ribeiro et al, 2013; Santos et al, 2015), even knowing that plants should maximize the uptake of water and nutrient use to tolerate water deficit (Blum, 2005). Our data revealed that IACSP95-5000 presents higher ability than IACSP94-2094 in acquiring soil water at the initial growth stage when plants face reductions in water availability.…”

“…When studying sugarcane responses to water deficit, several morphological and physiological traits have been evaluated and reported (Machado et al, 2009, 2013; Ribeiro et al, 2013; Sales et al, 2013). Such large dataset of numbers and variables turns difficult an overall idea of how water deficit affects plants and how plants respond to such limiting condition.…”

Stalk yield of sugarcane cultivars under different water regimes by subsurface drip irrigation

“…The cultivars with best performances were RB867515 (210.9 Mg ha -1 ) and RB931011 (200.0 Mg ha -1 ), which produced 24.7 and 18.2% more stalks in comparison to the mean yield of the experiment in 2011-2012 (169.2 Mg ha -1 ). However, in 2012However, in -2013, the most critical cropping season with respect to the water availability in the soil, the cultivar RB962962 (155.6 Mg ha -1 ) produced 33.7 and 10.5% more stalks than the mean TCH of 2012-2013 ) and the overall mean of the experiment (140.8 Mg ha -1 ) ( Figure 2B).…”