Respostas da curva de luz em Atriplex nummularia L irrigada com água salina - Geografia (2024)

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105Revista de Ciências Agrárias, 2022, 45(3): 105-115Light-curve responses in Atriplex nummularia L. irrigated with saline waterRespostas da curva de luz em Atriplex nummularia L. irrigada com água salinaCíntia Maria Teixeira Lins1, Edivan Rodrigues de Souza1,*, Danilo Rodrigues Monteiro1, Martha Katharinne Silva Souza Paulino1, Hidelblandi Farias de Melo2, Pablo Rugero Magalhães Dourado1, Jailson Cavalcante Cunha1, Monaliza Alves dos Santos1 and Bruce Schaffer31 Universidade Federal Rural de Pernambuco – UFRPE, Departamento de Agronomia, Rua Dom Manuel de Medeiros, s/n, CEP: 52171-900, Recife, Pernambuco, Brazil2 Universidade Federal de Viçosa – UFV. Viçosa- MG, Brazil3 Tropical Research and Education Center, University of Florida, 18905 S.W. 280 Street, Homestead, FL 33031, USA(*E-mail: edivan.rodrigues@ufrpe.br)https://doi.org/10.19084/rca.27265Received/recebido: 2022.05.28Accepted/aceite: 2022.07.26A B S T R A C TAtriplex nummularia L. is one of the most studied halophytes in research on phytoremediation of salt-affected soils. However, the optimization of biomass requires studies that indicate the appropriate way to evaluate the photosynthesis. The objective of this study was to investigate the photosynthetic efficiency of A. nummularia irrigated with saline water in order to indicate the best range of photosynthetically active radiation (PAR) that should be used. Plants were subjected to daily irrigations (0, 50, 100, 200, 250 and 300 mmol L-1 of NaCl). The light curves were determined at 15 and 84 days applying twenty light intensities (2000, 1750, 1500, 1250, 1000, 750, 500, 250, 200,175, 150, 125, 100, 75, 50, 25, 15, 10, 5, 0 μmol m-2 s-1 PAR). The highest values of photosynthesis rate were observed at PAR of 2000 μmol m-2 s-1 and of 800 μmol m-2 s-1 to 15 and 84 days of evaluation, independent of the NaCl concentration. The present study provides data that support the choice of the ideal PAR in evaluations of gas exchange in A. nummularia.Keywords: phytoremediation, gas exchanges, salt-affected soils, net photosynthesis106 Revista de Ciências Agrárias, 2022, 45(3): 105-115INTRODUCTIONPlants of the genus Atriplex are popular because they are used in phytoremediation programs in several regions of the globe (Calone et al., 2021, Ahmadi et al., 2022). Their cultivation ranges from arid envi-ronments with salinity problems to coastal regions. Many of these sites have in common the presence of salts at high concentrations in soil and different wa-ter regimes. However, they differ with respect to the incidence of light radiation (Falasca et al., 2014; Melo et al., 2017; Alharby et al., 2018; Tawfik et al., 2019).Among the abiotic factors that interfere in plant development, solar radiation is one of the most im-portant with regard to photosynthesis performan-ce, as it affects plant growth and yield. Different climatic zones have different light intensities or show variations according to the seasons (Khalifa et al., 2018). Therefore, photosynthesis performan-ce can vary greatly depending on the amount and duration of light interception (Zhang et al., 2022).The photosynthetic performance of A. nummular-ia has been extensively investigated in warm-cli-mate countries of South America (De Tafur et al., 1997; El-Sharkawy and Tafur, 2010; El-Sharkawy et al., 2012). However, a detailed description of pho-tosynthesis x irradiance curves of this species in response to the increase of NaCl in irrigation wa-ter remains unexplored, leading to lack of infor-mation on its tolerance to high light intensities or acclimation to irradiance.Variations observed in photosynthesis curves in re-sponse to different light intensities can be reliably used to indicate the photosynthetic performance of plants under different conditions of abiotic and biotic stress, including stresses by light (Park et al., 2020), nutrients (Lachapelle and Shipley, 2012), competition (Gao et al., 2015), disease (Habermann et al., 2003), pollution (Lin et al., 2015) and salinity (Geissler et al., 2015).Soil salinity, in turn, is one of the main abiotic stresses that affect crop yield as it reduces growth and affects different physiological functions of plants, especially those of agronomic interest (Ka-laji et al., 2016). However, thanks to the develop-ment of various mechanisms at the cellular and molecular level responsible for protecting the photosynthetic apparatus from salinity through-out the evolution, halophytes are able to develop even in environments with high concentrations of salts (Rozentsvet et al., 2017).Atriplex nummularia, for example, is a xerohalo-phyte species widely used in studies aimed at the recovery of salt-degraded areas due to its phytore-mediation potential (Souza et al., 2014; Cunha et al., 2017; Lam et al., 2017; Miranda et al., 2018). For some years, research groups have been striving to understand the physiological mechanisms that en-able the high performance of this species in envi-ronments degraded by salinity (Silveira et al., 2009; Souza et al., 2012, 2014; Melo et al., 2016, 2017; Lins et al., 2018). Nevertheless, data on the physiological responses of this species to different light intensi-ties are scarce, especially those related to the dam-age caused by the osmotic and ionic effects on the photosynthetic apparatus.In general, the effect of salts on the plant occurs in two main distinct phases: a rapid response to the increase in osmotic pressure of the soil solu-tion that is independent of the nature of the ions involved and can occur from minutes to days; and a second phase, which in turn occurs over a period of days to weeks and is related to a slower response associated with the effects of accumulation of so-dium and chloride ions at toxic concentrations in the shoots (De Souza et al., 2013; Coelho et al., 2014).In halophyte plants the protection of the photosyn-thetic apparatus can also occur through heat by means of the xanthophyll cycle, which is consid-ered the first line of defense against damage caused by excessive excitation energy or by the consump-tion of excess electrons in the photosystem I (PSI) by the water cycle. Another way to prevent exces-sive reduction of the electron transport chain and protect other components of photochemistry is through the inactivation of photosystem II (PSII) (Jaleel et al., 2007; Taiz and Zeiger, 2015). In studies aimed at investigating the physiological responses of plants to the effects of salt stress, it is common to evaluate photosynthesis, given the known dele-terious effect of salts on the photosynthetic appa-ratus of plants. In general, these evaluations are performed using equipment that quantifies gas ex-change, such as IRGA, at a fixed photosynthetical-ly active radiation (PAR) around 1500 μmol m-2s-1.107Lins et al., Light-curve responses in Atriplex nummulariaConsidering that most halophytes evolved in en-vironments characterized by high luminosity, a large number of studies may be generating under-estimated values of photosynthetic rates and mis-takenly attributing them to salinity. For these rea-sons, the objective of this study was to investigate the photosynthetic efficiency of A. nummularia un-der a wide range of salt concentration in irrigation water by constructing light curves in vivo in order to identify and indicate the best range of photosyn-thetically active radiation that should be used in research studies involving the performance of this species under salinity.MATERIAL AND METHODSPlant material and stress conditionsAtriplex nummularia plants were propagated by cuttings, using a single plant as parent, in order to minimize genetic variability. Cuttings of approx-imately 12 cm were placed to root in a protected environment in polyethylene tubes containing washed sand. Plantlets aged two months completely rooted and acclimated were transplanted to pots with 5 Lca-pacity containing soil. During the entire exper-imental period, the plants were cultivated in soil with moisture content corresponding to 80% of the pot capacity. The saline treatment began to be ap-plied 15 days after transplantation. Irrigation was always carried out in the late afternoon, replacing the water lost by evapotranspiration, using irri-gation waters with six different concentrations of NaCl (0, 50,100, 200, 250 and 300 mmol L-1), in four replicationsIrrigation with the saline waters was performed gradually to prevent the plants from suffering osmotic shock, so the saline treatments were es-tablished through the addition of a 50 mmol L1 NaCl solution until the concentration of the re-spective treatment was reached. Experimental ConfigurationThe present study was conducted in a protected en-vironment located in the Department of Agronomy (DEPA), at the main campus of the Federal Rural University of Pernambuco (UFRPE), whose coor-dinates are 8º01’00” South latitude, 34º59’40” West longitude. During the experiment, the average temperature and relative humidity in the green-house were 28.59 º C and 70%, respectively.The experiment was conducted using polyethylene pots with 5 L capacity filled with soil classified as Fluvisol (IUSS Working Group WRB, 2015), col-lected in the municipality of Pesqueira - PE. The soil collection site is located on Nossa Senhora do Rosário farm, whose coordinates are 8° 34’11” South latitude, 37°48’54” West longitude and is lo-cated at 630 m above sea level. According to Köp-pen’s classification, the climate of the soil collec-tion region is BSh (extremely hot and semi-arid), with total annual average precipitation of 730 mm and average annual reference evapotranspiration of 1.683 mm.Table 1 - Mean values (n=10) of the chemical characteristics of the saturation extract, sorption complex and physical characteristics of the soil used for the cultivation of Atriplex nummularia under different salinity levelsCharacteristics ValueSaturation extractapH 7.77Electrical Condutivity (dS/m) 2.17Na+ (mmol/L) 13.26K+ (mmol/L) 1.83Ca+2 (mmol/L) 3.15Mg+2 (mmol/L) 1.36Cl- (mmol/L) 14.37Sodium adsorption ratio 8.5Exchangeable complex apH (1:2.5) 6.85Na+ (cmolc /kg) 1.64K+(cmolc /kg) 3.7Ca+2(cmolc /kg) 7.78Mg2+(cmolc /kg) 1.73Sum of bases (cmolc /kg) 14.85Exchangeable sodium percentage (%) 11.07Physical characteristics bFine sand (g/kg) 435.00Coarse sand (g/kg) 17.00Silt (g/kg) 386.00Clay (g/kg) 162.00Soil bulk density (g/cm3) 1.36Soil particle density (g/cm3) 2.66Total porosity (%) 49.57a USSLS (1954); b (EMBRAPA, 1997).108 Revista de Ciências Agrárias, 2022, 45(3): 105-115The soil was collected in the 0-30 cm layer, air-dried, pounded to break up clods and sieved through a 4-mm mesh to preserve microaggre-gates and subsequently fill the pots. For chemical characterization (Table 1), ten individual samples of the total soil volume were collected and sieved through a 2 mm to obtain air-dried fine earth (ADFE). The value of the initial characterization refers to an average of ten samples.Light curvesCarbon assimilation responses were evaluated when plants were subjected to different levels of Photosynthetically Active Radiation (PAR) incident on the leaf surface, using PAR variation between 0 and 2000 μmol photons m-2 s-1 (0, 5, 10, 15, 25, 50, 75, 100, 125, 150, 175, 200, 250, 500, 750, 1000, 1250, 1500, 1750, 2000). This evaluation was performed at 15 and 84 (DAT) using a portable Infrared Gas Analyzer (IRGA), LICOR Li-6400 model, from 9 am to 11 am.Prior to the incidence of the highest PAR, the leaf was subjected to light acclimation at 500 μmol pho-tons m-2 s-1 for 5 minutes. CO2 concentration, block temperature and relative humidity were 400 μmol m2 s-1, 27 ºC and 50-60%, respectively.To construct the light saturation curves, plants representative of each treatment were selected and readings were performed on healthy, fully expand-ed leaves from the middle third. The values of pho-tosynthesis (A) were recorded after the coefficient of variation was lower than or equal to 0.3%, for each PAR variation.Analysis of the light curve allowed the determina-tion of the maximum photosynthesis rate (Amax), light saturation constant (K), respiration in the dark (Rd), light compensation point (LCP) and pho-tosynthesis efficiency (φ). The values of the respira-tion rate in the dark (Rd) used to fit the curve were obtained when PAR was 0.0 μmol m-2 s-1.Curve data were analyzed using Statistix software with the data fitted using the Michaelis-Menten model (Michaelis & Mentel, 1913) (Equation 1). Equation (1)Where: A= Net photosynthesis; Asat = a = Photo-synthetic rate at maximum light saturation (Amax); K= b = Light saturation constant (Defined as ½ of saturating PAR); Rd= c = Respiration rate; Light compensation point (LCP) was calculated using Equation 2: Equation (2)Data Analysis Gas exchange data were subjected to regression analysis. The parameters derived from the light curves were estimated through quadratic equa-tions generated from the fit of the Michaelis-Ment-en model to the data using Statistix software (https://www.statistix.com/faq/).RESULTSEvaluations of the photosynthetic apparatus re-sponses obtained by means of light curves per-formed in the plants at 15 DAT demonstrated that, despite the short time of exposure to stress, the increase in NaCl concentration in irrigation water led to significant reductions (p≤0.05) in net photo-synthesis, light saturation constant, respiration in the dark and light compensation point (Table 2).At 15 days of evaluation, plants irrigated using water with 50, 100, 200, 250 and 300 mmol of Na-Cl showed reductions of 24.47%, 41.43%, 58.07%, and 45.97% in photosynthesis compared to those in the control treatment, respectively. The light saturation constant showed a significant reduction (p≤0.05) in response to increasing salinity. Reduc-tions of 64.94% and 57.63% could be observed at NaCl levels 250 and 300 mmol L-1, respectively. The respiration variable showed small reductions in re-sponse to the increase of NaCl in irrigation water, with the highest ones observed at the NaCl lev-els of 250 and 300 mmol L-1 (23.70% and 34.22%), respectively. In regard to the light compensation 109Lins et al., Light-curve responses in Atriplex nummulariapoint, the reductions were around 25%, but plants showed a reduction of ~50% at the NaCl level of 300 mmol L-1.The responses of plants to the variation of differ-ent PAR levels, evaluated at 15 days after the be-ginning of irrigation with saline waters, made it possible to observe that, regardless of the light in-tensity applied, there was a significant reduction in all parameters derived from the light curve with the increase in NaCl concentration in the irriga-tion water, and this response was observed from the treatment with 200 mmol L-1 of NaCl (Table 2). However, even plants irrigated using solutions with the highest concentration of NaCl (300 mmol L-1) showed values of photosynthesis considered high (20.95 μmol CO2 m-2 s-1), which demonstrates the ability of this species to develop under saline conditions (Figure 1).Plants irrigated using solutions with lower NaCl concentrations in irrigation water (up to 100 mmol L-1) at the beginning of the evaluations had a pro-gressive increase in photosynthesis as the light radiation pulse increased, with the highest values observed at PAR of 2000 μmol m-2 s-1 (Figure 1).In plants irrigated with solutions more concen-trated in NaCl (250 and 300 mmol L-1), significant gains were observed in photosynthesis up to the PAR of approximately 1400 μmol m-2 s-1; however, from this point on, the photosynthetic rates re-mained virtually unchanged (Figure 1). For each of these curves, the equations corresponding to each level of saline treatmentwere fitted separately and showed good performance in the modeling, with R2 values ranging from 0.72 to 0.99. These equa-tions are described in Table 3.Plants subjected to prolonged stress (84 DAT) showed a pronounced reduction in net photosyn-thesis when compared to plants evaluated at 15 days (Table 3).The increase of salinity in irrigation water caused more accentuated significant reductions (p≤0.05) in photosynthesis at 84 DAT than at 15 days. At the level of 50 mmol L-1, there was a reduction of 42.94%. However, much higher reductions (93.93%) were observed at the NaCl level of 250 mmol L-1.Table 2 - Parameters obtained through the equations generated from the light curves at 15 and 84 days after the beginning of the saline treatmentNaCl(mmol L-1)Amax(µmol CO2 m-2s-1)K(µmol m-2s-1)Rd(µmol CO2 m-2s-1)LCP(µmol m-2s-1)15 DAT 84 DAT 15 DAT 84 DAT 15 DAT 84 DAT 15 DAT 84 DAT0 38.78 a 9.57 a 691.98 a 292.9 a 5.99 a 1.21 a 126.39 a 42.31 a50 29.29b 5.46b 512.33c 129.47c 4.86d 1.19 a 102.00c 36.12b100 29.07b 2.30c 562.12b 131.76b 5.18c 0.08d 121.90b 4.66d200 22.71c 2.30c 283.57e 128.50c 5.51b 0.16c 91.00e 9.53c250 16.26e 0.58d 242.57f 22.03e 4.57e 0.04e 94.77d 1.72e300 20.95d 0.94e 293.15d 70.76d 3.94f 0.31b 67.80f 35.06bAmax= Maximum photosynthesis; K= Light saturation constant; Rd= Respiration rate; LCP= Light compensation point; 84 days after the beginning of saline treatment. Means followed by equal letters in columns do not differ from each other by Tukey test, at 0.05% probability level.Figure 1 - CO2 assimilation curves as a function of photosyn-thetically active radiation (PAR) intensity in Atri-plex nummularia plants subjected to irrigation using water with different NaCl concentrations at 15 days after the beginning of saline treatment.110 Revista de Ciências Agrárias, 2022, 45(3): 105-115Plants irrigated with water containing high con-centrations of salts showed lower light saturation constant and the values ranged from 292.9 μmol m-2 s-1 in plants of the control treatment to 22.03 μmol m-2 s-1 in plants irrigated with water contain-ing 250 mmol L-1 of NaCl (Table 2).For this parameter, it was possible to observe re-ductions equivalent to 92.47 and 75.84% at Na-Cl levels of 250 and 300 mmol L-1, respectively. Re-garding respiration in the dark, plants evaluated at 15 DAT experienced little or no reduction in this parameter. However, when plants were evaluated at 84 DAT, this parameter showed a large reduc-tion already from the concentration of 50 mmol L-1 and, in general, the reductions were around 80%, demonstrating how debilitated the plants were (Tables 2).With regard to the light compensation point, the decreases ranged from 14.63% at NaCl level 50 mmol L-1 to 95.93% at NaCl level of 300 mmol L-1.At 84 DAT, plants were very stressed and virtually did not respond to the increase in light intensity. Except for plants in the control treatment, which exhibited an increase in net photosynthesis up to PAR of 1000 μmol m-2 s-1, all the others kept their photosynthesis rates practically unchanged from PAR of 800 μmol m-2 s-1, evidencing the presence of damage to the photosynthetic apparatus (Figure 2).Stomatal conductance (Figure 3) was reduced as NaCl increased. The average values varied be-tween 0.052 mol m-2s-1 and 0.01 mol m-2 s-1, corre-sponding to the control and exposed plants with concentrations of 0 and 300 mmol L-1 of NaCl, respectively.Figure 2 - CO2 assimilation curves as a function of Photosyn-thetically Active Radiation (PAR) intensity in Atri-plex nummularia plants subjected to irrigation using water with different concentrations of NaCl at 84 days after the beginning of saline treatment.Figure 3 - Stomatal conductance (gs) in Atriplex nummularia plants irrigated with saline water at 84 days after saline treatment.Table 3 - Equations generated from the fit of the Michaelis-Menten model corresponding to the NaCl levels at 15 and 84 days of salt stress impositionTreatament Equations (15 DAT) R2 Equations (84 DAT) R20 0.99 0.9950 0.99 0.95100 0.99 0.94200 0.98 0.98250 0.97 0.72300 0.99 0.96111Lins et al., Light-curve responses in Atriplex nummulariaDISCUSSIONAlthough A. nummularia is a halophyte species with C4 metabolic pathway, this study demonstrat-ed that when these plants are subjected to irriga-tions with concentrated saline solutions, they may exhibit a sharp reduction in photosynthetic rate.This type of response to increasing salinity is probably the result of the activation of stomatal closure, which leads to reduction of CO2 diffusion to carboxylation sites (Dourado et al., 2022). Stoma-tal limitations, with subsequent reduction in pho-tosynthesis and transpiration rates, can be consid-ered as plant adaptation mechanisms to cope with the imposed salt stress (Benzarti et al., 2012).The physiological logic that explains reductions in stomatal conductance in plants exposed to high salt concentrations in the saturation extract sug-gests that this mechanism may be the effect of the attempt to reduce water loss under “physiological drought” conditions imposed by salinity (Shaba-la, 2013). In general, these responses are mediated by the increase in the production of abscisic acid (ABA) (Ashraf and Harris, 2013) or by the reduc-tion in the availability of K+ to maintain the turgor pressure of guard cells (Anschütz et al., 2014).Under conditions of high salinity or prolonged salt stress, the photosynthetic rate may also be compro-mised due to the inhibition (synthesis or activity) of various photosynthesis-related enzymes, such as rubisco (Rivelli et al., 2002). In addition, ionic imbalances caused by excess Na+ and Cl- ions in cells can also lead to deficiency of ions such as po-tassium and to phytotoxicity, resulting in a lower photosynthetic efficiency (Abogadallah, 2010).Under salinity, at 15 DAT, the maximum photosyn-thesis decreased to almost half of that in plants of the control treatment compared to those irrigated with solutions containing 300 mmol L-1 of NaCl. This could be visualized by observing the slope point of the curve of response to photosynthesis. Similar results, but with much lower values of pho-tosynthesis, were observed at 84 DAT. Findings similar to those found in our study were observed by Geissler et al. (2015), who evaluated the effect of salinity on photosynthesis of A. nummularia plants by means of light curves.Photosynthesis is considered an activity related to the Calvin cycle and indicates the regeneration capacity of rubisco under stress conditions. These results suggest that, although photosynthesis was inhibited by the reduction in CO2 supply due to stomatal closure, under both stress conditions, the potential of the reaction system in the dark was drastically reduced only when plants were exposed to long period of salt stress (Ueda et al., 2018).In addition to stomatal closure, the reduction of photosynthesis in response to the saline treatment and prolonged exposure to salts can also be attrib-uted to the reduction in chlorophyll concentration. On the other hand, the latter can reduce the capaci-ty of light absorption by the leaf (Lu et al., 2003; Sil-va et al., 2013), which is evidenced by a lower light compensation point. This is also correlated with the decrease in photosynthetic efficiency (Φc) and is considered an important mechanism in relation to the defense of the plant against oxidative stress (Eisa et al., 2012).In the present study, the effect of prolonged stress under salinity was evident, since the greatest re-ductions in photosynthesis were observed at the end of the experiment, compared to the increase in salt concentration in irrigation water, demonstrat-ing that both photosynthetic efficiency and water use were more preserved at the beginning of the experiment. These results are in agreement with reports fromother studies (Eisa et al., 2012, Huss-in et al., 2013), and this is considered an important characteristic that allows halophytes to survive in saline environments during long periods of expo-sure to salts (Koyro, 2000).The results demonstrate that excess sodium in ir-rigation water may have been responsible for the degradation of the thylakoid membrane reflect-ed in the decrease in chlorophyll according with Geissler et al. (2015). Eisa et al. (2012), evaluating the effect of different NaCl concentrations (0, 100, 200, 300, 400 and 500 mmol L-1) in quinoa plants observed that the reduction in chlorophyll b con-centration was accompanied by the increase in chlorophyll a and led to a reduction in photosyn-thesis efficiency in stressed plants.112 Revista de Ciências Agrárias, 2022, 45(3): 105-115In the evaluations at 15 DAT, plants did not show a reduction in photosynthesis efficiency; howev-er, the prolonged exposure to irrigation observed at 84 DAT led to a decrease in photosynthesis ef-ficiency even in plants of the control treatment, demonstrating that the decrease in this parameter may have been caused by other factors, such as the high temperatures of the protected environment or the size of the pot, which may have acted as a stress factor.Eisa et al. (2012) also observed a decrease in pho-tosynthetic efficiency (φ) as a function of the in-crease in NaCl concentration in irrigation water. The authors attribute this reduction to the produc-tion of reactive oxygen species (ROS), which conse-quently leads to a reduction in the flow of electrons through the photosystem. As observed by Hussin et al. (2013), it was also noticed in the present study, at both evaluation times, that the light compen-sation point (LCP) decreased with the increase of NaCl in irrigation water. For these authors, this may be due to the greater stimulation of respira-tion, biosynthesis of compatible solutes and may be an adaptation mechanism of the plant to cope with stress.In both evaluations, the highest values of net pho-tosynthetic rate were observed at PAR correspond-ing to 2000 μmol m-2 s-1, and this result was inde-pendent of the NaCl concentration in the irrigation water. However, it was possible to observe that, at a given time, the plants no longer responded to the increase in light intensity. In plants evaluated at 15 days, the light intensity at which there was no significant increments in net photosynthesis corre-sponded to 1500, and this result could be observed in the most stressed plants (250 and 300 mmol NaCl L-1).On the other hand, in the evaluations performed at 84 days, the light intensity at which the plants did not show gains in photosynthesis was much lower and corresponded to PAR of 800 μmol m-2 s-1, which demonstrates that in the case of salinity for the species evaluated, the time of exposure to salts, and consequently the ionic stress, is the main responsible for limiting the electron transport re-action, rubisco activity or the metabolism of triose phosphates.CONCLUSIONSEven in halophyte plants, such as A. nummularia, prolonged stress under high salt concentrations can cause damage to the photosystem both due to the occurrence of stomatal damage and due to the degradation of thylakoid membranes. The data obtained from the construction of photosynthesis x PAR curves demonstrated that the time of expo-sure to stress reduced the tolerance of this species to light stress.In addition, the study provides data that support the choice of ideal PAR in evaluations of gas ex-change in Atriplex nummularia, since our results clearly demonstrate under which condition of PAR the photosynthesis is maximum.The knowledge of the photosynthetic perfor-mance of A. nummularia is relevant for application in programs of phytoremediation in salt-affected soils. Also, this research contributes effectively for providing data to help in the management of this species.ACKNOWLEDGMENTSThe authors thank the Agronomic Institute of Per-nambuco (IPA) for donating the parent plants used for propagation, the Pernambuco State Science and Technology Support Foundation (FACEPE), the Coordination for the Improvement of Higher Edu-cation Personnel (CAPES) and the National Coun-cil for Scientific and Technological Development (CNPq) for granting scholarships and funding the research project.113Lins et al., Light-curve responses in Atriplex nummulariaREFERENCESAbogadallah, G.M. (2010) - Antioxidative defense under salt stress. Plant Signaling and Behavior, vol. 5, n. 4, p. 369-374. http://dx.doi.org/10.4161/psb.5.4.10873Ahmadi, F., Mohammadkhani, N. & Servati, M. (2022) - Halophytes play important role in phytoremediation of salt-affected soils in the bed of Urmia Lake, Iran. 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