Gas exchange and photosynthetic pigments in bell pepper irrigated with saline water

Abstract

A B S T R A C TThe tools that evaluate the salinity effects on plants have great relevance as they contribute to understanding of the mechanisms of tolerance. This study aimed to evaluate gas exchanges and the contents of photosynthetic pigments in bell peppers cultivated with saline solutions (0, 1, 3, 5, 7 and 9 dS m -1 ) prepared using two sources: NaCl and a mixture of Ca, Mg, K, Na and Cl salts, in randomized blocks with a 6 x 2 factorial scheme and 4 replicates, totaling 48 experimental plots. The net photosynthesis (A), stomatal conductance (gs), transpiration (E), internal CO 2 concentration (Ci), instantaneous carboxylation efficiency (A/Ci) and water use efficiency (WUE), besides chlorophyll a, b and carotenoids were evaluated. The gas exchange parameters were efficient to indicate the effects of salinity. All photosynthetic pigments decreased with increased electrical conductivity, and the chlorophyll a is the most sensitive to salinity, while the water use efficiency increased with the increment of electrical conductivity.Trocas gasosas e pigmentos fotossintéticos em pimentão irrigado com água salina R E S U M O As ferramentas que avaliam os efeitos da salinidade nos vegetais apresentam grande relevância uma vez que contribuem para compreender os mecanismos de tolerância. Objetivou-se avaliar as trocas gasosas e os teores dos pigmentos fotossintéticos em pimentão cultivado com água salina (0, 1, 3, 5, 7 e 9 dS m -1 ) elaboradas de duas formas: NaCl e uma mistura de sais de Ca, Mg, K, Na e Cl. O delineamento experimental foi em blocos ao acaso com arranjo fatorial 6 x 2, com 4 repetições totalizando 48 parcelas experimentais. Foram avaliadas a fotossíntese líquida (A), a condutância estomática (gs), a transpiração (E), a concentração interna de CO 2 (Ci), a eficiência instantânea de carboxilação (A/Ci) e a eficiência do uso da água (EUA) além da clorofila a, clorofila b e carotenoides. Os parâmetros de trocas gasosas foram eficientes para indicar os efeitos da salinidade. Todos os pigmentos fotossintéticos reduziram com o aumento da condutividade elétrica sendo a clorofila a de maior sensibilidade à salinidade enquanto a eficiência do uso da água aumentou com a elevação da condutividade elétrica. Key words:salt stress photosynthesis chlorophyll brazilian semi-arid region Palavras-chave: estresse salino fotossíntese clorofila semiárido brasileiro

Gas exchange, leaf and root dry mass in Bell Pepper under fertigation with nitrogen and potassium

“…However, even at decreasing Ci values, the values of A/Ci found in the present study followed the same behavior as data on A, because of the nitrogen application. Melo et al (2017) obtained similar results for A/Ci and Ci. According to these authors, the instantaneous carboxylation efficiency has a close relation with CO 2 assimilation rate and the intracellular concentration of CO 2 .…”

“…2001), who observed a lower photosynthetic rate in lettuce plants at low N. The reduction of A may be associated with the closure of the stomata, which respond directly to the lack of nitrogen or to the increase of CO 2 partial pressure inside the chloroplasts (BROADLEY et al, 2001). The maximum value of A, 14.72 µmol of CO 2 m -2 s -1 , was estimated at level K2 (53.3 kg ha -1 ) with 168.5 kg ha -1 of N, a value within the range found by Melo et al (2017), which was 7 to 18 µmol of CO 2 m -2 s -1 , with the application of water with different electrical conductivities in the bell pepper crop.…”

“…This behavior demonstrates that the reduction of the photosynthetic process depends not only on the reduction of the stomata opening, but also on the structure of the cells responsible for the assimilation of CO 2 , possibly caused by the reduction in the osmotic-hydraulic potential and the accumulation of ions outside the range tolerated by the crop (ANDRADE JÚNIOR et al 2011). If the values of Ci are very low, CO 2 entry into the mesophyll cells is limited, so there is a limitation of the photosynthetic rate because the plant uses CO 2 from the respiration to maintain a minimum level of assimilation (TAIZ;ZEIGER, 2013;MELO et al, 2017).…”

Gas exchanges in sugar apple (Annona squamosa L.) subjected to salinity stress and nitrogen fertilization

“…According to these authors, the Fv/Fm parameter was not influenced up to the salinity level of 3 dS m -1 , however, its values started to decrease as the water salinity level increased. The Fv/Fm values reduction may be due to chlorophyll degradation, especially chlorophyll a (Melo et al, 2017). The photosynthetic decline caused by salinity stress generates an excess of energy excitation, which may cause additional damage to the photosystems if not dissipated properly (Mancarella et al, 2016).…”

“…Subsequently to the data collection, water-use efficiency (WUE -A/E), intrinsic wateruse efficiency (iWUE -A/gs) and instantaneous carboxylation efficiency (iCE -A/Ci) were calculated. Chlorophyll fluorescence emission was determined according to the method described by Melo et al (2017), using a modulated fluorometer (Plant Efficiency Analyser PEA II ® -Hansatech Instruments Co., UK). The following fluorescence parameters were determined: initial fluorescence (F0), maximum fluorescence (Fm), variable fluorescence (Fv = Fm -F0) and quantum yield of photosystem II (Fv/Fm).…”