Instantaneous Carboxylation Efficiency Research Articles

The responses of pepper plants to nitrogen form and dissolved oxygen concentration of nutrient solution in hydroponics

BackgroundThe presence of oxygen in the growth medium is absolutely essential for root development and the overall metabolic processes of plants. When plants do not have an adequate oxygen supply for respiration, they can experience a condition known as hypoxia. In order to investigate the impact of different nitrogen forms and varying oxygen levels in nutrient solutions on the growth, photosynthesis, and chlorophyll fluorescence parameters of bell pepper plants, a comprehensive study was conducted. The experiment was designed as a factorial experiment, considering two main factors: nitrogen forms (calcium nitrate and ammonium sulfate) with a fixed nitrogen concentration of 5 mM, and the oxygen levels of the nutrient solutions (ranging from 1.8 ± 0.2 to 5.3 ± 0.2 mg. L-1).ResultsThe study examined the effects of nitrogen (NH4+ and NO3−) application on various parameters of vegetative growth. The results demonstrated that the use of ammonium (NH4+) led to a reduction in the most measured parameters, including the fresh and dry mass of both the root and shoot, at low O2 concentrations of 1.8 ± 0.2; 2.6 ± 0.2 and 3.8 ± 0.2 mg. L-1. However, an interesting observation was made regarding the impact of oxygen levels on root growth in plants grown with nitrate (NO3−). Specifically, the highest levels of oxygen significantly increased root growth in NO3−-fed plants. Additionally, the application of NH4+ resulted in an increase in chlorophyll concentration in the leaves, particularly when combined with high oxygen levels in the nutrient solution. On the other hand, leaves of plants fed with NO3− exhibited higher photosynthetic rate (A), intrinsic water use efficiency (iWUE), and instantaneous carboxylation efficiency (A/Ci) compared to those fed with NH4+. Furthermore, it was found that NO3−-fed plants displayed the highest instantaneous carboxylation efficiency at oxygen levels of 3.8 and 5.3 mg. L-1, while the lowest efficiency was observed at oxygen levels of 1.8 and 2.6 mg. L-1. In contrast, NH4+-grown plants exhibited a higher maximal quantum yield of PSII photochemistry (Fv/Fm), as well as increased variable fluorescence (Fv) and maximum fluorescence (Fm), compared to NO3−-grown plants. Interestingly, the NO3−-fed plants showed an increase in Fv/Fm, Fv, and Fm with the elevation of oxygen concentration in the nutrient solution up to 5.3 mg. L-1.ConclusionThis study showed that, the growth and photosynthesis parameters in bell pepper plants are sensitive to oxygen stress in floating hydroponic culture. Therefore, the oxygen level in the nutrient solution must not be lower than 3.8 and 5.3 mg. L-1 in NH4+ and NO3− –supplied culture media or nutrient solutions, respectively.

Morfofisiologia de feijão-caupi sob estresse salino e aplicação de nanobioestimulante de carbono na fase vegetativa

ABSTRACT Several technologies have been implemented to improve plant performance in irrigated crops, and one of them is the use of nanobiostimulants. Therefore, the aim of the present study was to explore the effects of applying different concentrations of a carbon-based biostimulant on the morphophysiology of cowpea plants subjected to varying electrical conductivities of irrigation water. The experiment was performed in a completely randomized design, in a 2 × 6 factorial scheme, with two electrical conductivities of irrigation water (ECw: 0.35 and 4.0 dS m-1) and six concentrations of nanobiostimulant applied through the leaves (0, 80, 160, 240, 320, and 400 mg L-1), with four replications. Growth and gas exchange variables were evaluated 31 days after sowing (V9 stage). Concentrations between 240 and 320 mg L-1 of carbon-based nanobiostimulant promoted greater increases in growth and physiological variables, but they caused decreases in non-photochemical quenching. Water electrical conductivity of 4.0 dS m-1 reduced the number of leaves (17.1%), stem diameter (10.0%), SPAD index (10.3%), net photosynthesis (10.9%), stomatal conductance (46.4%), transpiration (34.5%), instantaneous carboxylation efficiency (22.4%), and photochemical quenching (4.5%); in contrast, it increased the ratio between internal and ambient CO2 concentration (18.0%), leaf temperature (2.9%), water use efficiency (32.5%), and non-photochemical quenching (12.4%). Concentrations of 240 to 320 mg L-1 of the nanobiostimulant enhance the development and gas exchange of cowpea plants under non-stress conditions, whereas the concentration of 240 mg L-1 promotes the maximum increase in plant height under salinity.

Esterco bovino e substâncias húmicas estimulam a morfofisiologia e a nutrição em pimentão

ABSTRACT Species of the genus Capsicum, especially peppers, are economically important and widely consumed worldwide. The application of animal waste as organic fertilizer is a simple and cost-effective technique for applying nutrients to the soil. Combining cattle manure with humic substances can stimulate plant metabolism, resulting in increased nutrient absorption and assimilation. Therefore, the objective in this study was to evaluate doses of cattle manure combined with humic substances for stimulating plant metabolism and morphophysiological and nutritional processes in pepper plants. A randomized block design with four replicates was used, in a 4×3 factorial arrangement consisting of four cattle manure doses (8, 18, 28, and 38 Mg ha-1) and three humic substance doses (0, 8, and 12 kg ha-1). Humic substances (12 kg ha-1) enhanced gas exchange, increasing net photosynthesis (34.2%), stomatal conductance (12.7%), instantaneous water use efficiency (15.87%), instantaneous carboxylation efficiency (37.37%), and absorbed energy conversion efficiency (23.53%). Cattle manure adequately met the crop’s nutritional requirements, while humic substances increased the number and thickness of plant root hairs. The most effective combination to increase photosynthetic activity in pepper plants was 38 Mg ha-1 of cattle manure combined with 8 kg ha-1 of humic substances. Humic substances stimulated positive morphophysiological responses in organic pepper crops, which resulted in increased production.

Photosynthetic Costs and Impact on Epidemiological Parameters Associated with Ht Resistance Genes in Maize Lines Infected with Exserohilum turcicum.

Northern corn leaf blight, caused by Exserohilum turcicum, is mainly controlled by the use of resistant cultivars. Maize lines carrying individual resistance genes B37Ht1, B37Ht2, B37Ht3, and B37Htn1 express different defense symptoms having an impact on the photosynthetic activity, the accumulation of reactive oxygen species, and epidemiological parameters. Plants were inoculated with a race 0 isolate of E.turcicum conferring a compatible interaction with B37 and incompatible interactions with plants carrying resistance genes. Five days postinoculation (dpi), the resistant lines displayed a reduction in leaf CO2 assimilation of 30 to 80% compared with healthy plants. At 14 dpi, inoculated plants of B37Ht1 showed a significant decrease in leaf CO2 assimilation, similar to B37 (up to 94%). The instantaneous carboxylation efficiency was significantly reduced on inoculated plants of the lines B37Ht2, B37Ht3, and B37Htn1 (54 to 81%) at 5 dpi. Curiously, the reduction in carboxylation efficiency for B37 and B37Ht1 (up to 95%) was higher at 14 dpi than at 5 dpi (up to 81%). At 6 dpi, low levels of H2O2 were detected in B37Ht1, in contrast to B37Htn1, where a high H2O2 level and peroxidase activity were observed. The sporulation rate on B37Ht1, B37Ht3, and B37Htn1 decreased by 92% compared with the susceptible control, whereas strong sporulation occurred in lesions on line B37Ht2. The resistance in maize to E. turcicum conferred by Ht resistance genes is associated with photosynthetic costs and may have quite contrasting effects on host physiology and major epidemiological parameters, such as sporulation, which contributes inoculum for secondary infections.

Multi-trait selection for nutritional and physiological quality of cacao genotypes in irrigated and non-irrigated environments

Water is a scarce, strategic resource and the most important input for economic development, especially in agricultural countries such as Brazil. Cocoa production is directly related to water availability, and, as climate changes, selecting drought-tolerant genotypes is vital to keep cacao crops sustainable. Here, we evaluated cacao genotypes under irrigated and water-stressed conditions and selected drought-tolerant ones based on nutritional and physiological traits. Thirty-nine genotypes were monitored for three years for agronomic traits and higher fruit yield. After this evaluation, the 18 most promising genotypes were evaluated in a randomized block design, under a 2 (with and without irrigation) ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 18 (genotypes) factorial arrangement, with three replicates and five plants per plot. We evaluated seven physiological and 11 nutritional traits, selecting genotypes based on the Genotype-by-Trait Biplot approach. Significant effects (p < 0.05) were observed for the nutritional traits N, P, Mg, S, Zn, Cu, Mn and for the physiological traits CO2 assimilation rate (A), stomatal conductance (gs), transpiration (E), intercellular and atmospheric CO2 concentrations (Ci/Ca), intrinsic water use efficiency (A/gs), instantaneous water use efficiency (A/E), and instantaneous carboxylation efficiency (A/Ci), as determined by analysis of variance. The genotype ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} irrigation treatment interaction was significant (p < 0.05) for the traits A, gs, and E. Genotypes CP 41, CP 43, and CCN 51 exhibited superior performance for both nutritional and physiological traits (A, gs, and E). In the irrigated environment, CP 41 showed superiority in traits such as P, A/E, A/gs, Mn, S, and Zn. Conversely, under non-irrigated conditions, CP 43 exhibited better performance in nutritional properties, specifically Mn, Mg, and Zn. Notably, in both irrigated and non-irrigated environments, CCN 51 excelled in key physiological traits, including A/Ci, A/E, and A/gs. This robust performance across diverse conditions suggests that these three genotypes possess physiological mechanisms to endure water-stressed conditions. Our research can generate valuable insights into these genotypes informing suitable choices for cocoa cultivation, especially in the context of global climate change.

Seed Priming with Nanoencapsulated Gibberellic Acid Triggers Beneficial Morphophysiological and Biochemical Responses of Tomato Plants under Different Water Conditions

Water deficit (WD) promotes great losses in agriculture, and the development of new sustainable technologies to mitigate the effects of this stress on plants is essential. This study aimed to evaluate the morphophysiological and biochemical alterations induced by the priming of tomato seeds with different formulations in plants under field capacity and WD conditions. In the first experiment, the treatments consisted of nanoparticles of alginate/chitosan and chitosan/tripolyphosphate containing gibberellic acid (GA3) in different concentrations (0.5, 5, and 50 µg mL−1 GA3), in addition to control with deionized water. The alginate/chitosan (5 µg mL−1 GA3) provided the greatest gains in plant growth under field capacity. In addition, under WD this treatment reduced damage to photosystem II (−14%), stomatal conductance (−13%), and water loss (−38%) and increased the instantaneous carboxylation efficiency (+24%) and intrinsic water use efficiency (+12%). In the second experiment, the treatments were alginate/chitosan nanoparticles containing GA3 (NPGA3 5 µg mL−1), free GA3 (GA3 5 µg mL−1), nanoparticles without GA3 (NP), deionized water (WATER), and non-primed seeds (CONT). Under WD, GA3 and CONT maintained plant growth and lost water rapidly, reducing stomatal conductance (−87%) and net photosynthesis (−69%). In contrast, NPGA3 decreased leaf area (−44%) and increased root-to-shoot ratio (+39%) when compared to GA3, reducing water loss (−28%). Activation of protective mechanisms (e.g., superoxide dismutase and catalase activities) by WATER, NPGA3, and NP treatments also resulted in lower susceptibility to WD compared to CONT and GA3. The results highlight the positive effect of seed priming on plant response to WD, which was enhanced by the use of nanoencapsulated GA3.

Impact of boron fertilisation on soybean grain yield as affected by associated physiological factors

ABSTRACT High soybean yields generally requires fields to have an adequate supply of boron (B). However, there remains uncertainty around how different cultivars might respond to differing levels of available B. The objective of this study was to evaluate the effect of B fertilisation on physiological efficiencies, yield, and export of B in various soybean cultivars. A randomised block experiment was carried out under field conditions in Region, Brazil consisting of 10 soybean cultivars and two levels of B fertilisation (without application and with application of 3 kg ha−1 of B). Water-use efficiency, instantaneous carboxylation efficiency, B content in the seed, export of B, and grain yield were evaluated. There was a significant interaction between B fertilisation x genotypes for all variables evaluated. In general, B fertilisation improved physiological and nutritional characteristics, increasing grain yield and B seed content on average by 21% and 35%, respectively. The soybean cultivars 7110 and Soyoro showed increases in all physiological and agronomic variables evaluated with B fertilisation. The results of this research confirm that B fertilisation improves the physiological and agronomic performance of the majority of soybean genotypes evaluated.

Morfofisiologia e trocas gasosas da romãzeira sob estresse salino e aplicação foliar de nitrogênio

ABSTRACT Salinity is one of the abiotic stresses that affect gas exchange and growth of pomegranate. In this context, the application of nitrogen fertilizer through the leaves can minimize these effects. Thus, the objective of present study was to evaluate the effect of foliar nitrogen fertilization on pomegranate seedlings irrigated with brackish water. The design used was randomized blocks, in an incomplete factorial scheme (Central Composite Design) with five electrical conductivities of irrigation water - ECw (0.50, 1.15, 2.75, 4.35, and 5.00 dS m-1) and five doses of foliar nitrogen fertilization - FNF (0, 0.33, 1.15, 1.97, and 2.30 g L-1), with four replicates and two plants per experimental plot. Plant height, number of leaves, stem diameter, and gas exchange (stomatal conductance, net photosynthesis, intercellular CO2 concentration, transpiration rate, instantaneous carboxylation efficiency, instantaneous water use efficiency, and intrinsic water use efficiency) were evaluated at 60 days after the beginning of irrigation with saline water. Salinity of irrigation water negatively affects the gas exchange of pomegranate seedlings. Foliar nitrogen fertilization up to 1.31 g L-1 improves plant height and number of leaves in pomegranate seedlings under salt stress. Foliar nitrogen fertilization up to 1.59 g L-1 increases the net photosynthesis of pomegranate seedlings.

Morfofisiologia de gravioleira sob estresse salino e aplicação de H2O2 na fase de pré-floração

ABSTRACT In the semi-arid region of the Brazilian Northeast, water sources generally have high levels of salts, standing out as one of the abiotic stresses that restrict the growth and development of plants. In this context, the objective of the present study was to evaluate the effects of foliar applications of hydrogen peroxide on the morphophysiology of soursop under salt stress in the pre-flowering phase. The experiment was carried out in a greenhouse, using a randomized block design and a 4 × 4 factorial arrangement, with four values of electrical conductivity of the irrigation water - ECw (0.8, 1.6, 2.4, and 3.2 dS m-1) and four concentrations of hydrogen peroxide - H2O2 (0, 10, 20, and 30 μM), with three replicates. An increase in water electrical conductivity from 0.8 dS m-1 reduced stomatal conductance, CO2 assimilation rate, instantaneous carboxylation efficiency, and leaf water saturation deficit. It inhibited the growth of soursop plants at 370 days after transplanting. Hydrogen peroxide at concentrations of up to 10 μM increased leaf transpiration and water use efficiency of soursop plants irrigated with 1.8 dS m-1 water in the pre-flowering phase.

Fertilizantes líquidos na eficiência fotoquímica e trocas gasosas em maracujazeiro-amarelo sob estresse salino

ABSTRACT The Northeast region of Brazil is the primary producer of yellow passion fruit. In recent years, water scarcity has led passion fruit growers to use highly saline water for cultivation. Therefore, implementing technologies that alleviate the negative effects of salt stress on plants is a promising approach, particularly in semi-arid conditions. This study aimed to assess the efficacy of organomineral fertilizers in mitigating salt stress effects on chlorophyll-a fluorescence and gas exchange in ‘Guinezinho’ yellow passion fruit seedlings. The treatments were arranged in randomized blocks with four replicates and four seedlings per plot, following a 2 × 3 factorial design. The factors considered were irrigation using water with low (0.18 dS m-1) and high (4.0 dS m-1) electrical conductivity and three liquid organomineral attenuators (Codasal™, Aminoagro Raiz™, and a mixture of Codasal™ + Aminoagro Raiz™ at a 1:1 v/v ratio), applied through fertigation. Irrigation with water containing 4.0 dS m-1 electrical conductivity, combined with liquid fertilizers, resulted in increased substrate salinity, and reduced stomatal conductance in yellow passion fruit seedlings, particularly when Codasal™ was applied. Application of Codasal™ alone or in combination with Aminoagro Raiz™ significantly enhanced variable fluorescence, quantum efficiency of PSII, CO2 assimilation rate, and instantaneous carboxylation efficiency in ‘Guinezinho’ yellow passion fruit seedlings.

Effects of Cadmium, Thallium, and Vanadium on Photosynthetic Parameters of Three Chili Pepper (Capsicum annuum L.) Varieties.

Photosynthesis is a crucial process supporting life on Earth. However, unfavorable environmental conditions including toxic metals may limit the photosynthetic efficiency of plants, and the responses to those challenges may vary among genotypes. In this study, we evaluated photosynthetic parameters of the chili pepper varieties Jalapeño, Poblano, and Serrano exposed to Cd (0, 5, 10 µM), Tl (0, 6, 12 nM), and V (0, 0.75, 1.5 µM). Metals were added to the nutrient solution for 60 days. Stomatal conductance (Gs), transpiration rate (Tr), net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), instantaneous carboxylation efficiency (Pn/Ci), instantaneous water use efficiency (instWUE), and intrinsic water use efficiency (iWUE) were recorded. Mean Pn increased with 12 nM Tl in Serrano and with 0.75 µM V in Poblano. Tl and V increased mean Tr in all three cultivars, while Cd reduced it in Jalapeño and Serrano. Gs was reduced in Jalapeño and Poblano with 5 µM Cd, and 0.75 µM V increased it in Serrano. Ci increased in Poblano with 6 nM Tl, while 12 nM Tl reduced it in Serrano. Mean instWUE increased in Poblano with 10 µM Cd and 0.75 µM V, and in Serrano with 12 nM Tl, while 6 nM Tl reduced it in Poblano and Serrano. Mean iWUE increased in Jalapeño and Poblano with 5 µM Cd, in Serrano with 12 nM Tl, and in Jalapeño with 1.5 µM V; it was reduced with 6 nM Tl in Poblano and Serrano. Pn/Ci increased in Serrano with 5 µM Cd, in Jalapeño with 6 nM Tl, and in Poblano with 0.75 µM V. Interestingly, Tl stimulated six and inhibited five of the seven photosynthetic variables measured, while Cd enhanced three and decreased two variables, and V stimulated five variables, with none inhibited, all as compared to the respective controls. We conclude that Cd, Tl, and V may inhibit or stimulate photosynthetic parameters depending on the genotype and the doses applied.

Gas exchange in umbu tree accessions

The objective of this work was to evaluate gas exchanges in umbu tree accessions. A 5 × 7 × 2 split-split plot experiment was carried out in a completely randomized design (five accessions – BRS-68, EPAMIG-05, BGU-61, BGU-75, and BGU-50 × seven evaluation dates × two reading times – 8 a.m. and 2 p.m.) with three repetitions. The lower leaf temperatures recorded in BRS-68 and EPAMIG 05 accessions favor higher net photosynthetic rates, water use efficiency and instantaneous carboxylation efficiency compared to BGU 61 accession. Umbu tree regulates transpiration by reducing stomatal conductance under high vapor pressure deficit, although the tree increases transpiration as a defense strategy against heat stress, even with a reduction in stomatal conductance. High temperatures limit instantaneous carboxylation efficiency, photosynthetic rate, and the ratio of photosynthesis to radiation incident on the leaf. Transpiration varies directly with stomatal conductance, while intrinsic water use efficiency varies inversely with internal CO2 concentration.

Índices fisiológicos e clorofila em mangueira “Palmer” submetida a fontes de potássio

Grown in different regions of Brazil, mango is of great importance at the national level. However, mango cultivation is directly related to physiological factors such as photosynthesis, stomatal conductance and chlorophyll. Physiological factors are related to the nutritional balance of the plant. Among the nutrients, potassium (K) can be highlighted, which, despite not being a structural element for the plant, stimulates, or is part of several physiological plant processes. Therefore, an experiment was carried out with the purpose of evaluating, in the vegetative period of 'Palmer' mango, the effect of different sources of K to accelerate the maturation stage of mango branches and verify their influence on physiological indexes and chlorophyll. Treatments consisted of three ripeners and a control, which were applied directly to the branches and leaves of “Palmer” mango trees. The variables analyzed were chlorophyll A, B and Total indexes; Internal concentration of CO2; Stomatal conductance; transpiration rate; Net photosynthesis; Instantaneous Carboxylation Efficiency and Water Use Efficiency. After collecting, and analyzing the data, it was concluded that the vegetative period of the “Palmer” mango tree, in relation to the different evaluation dates, was not influenced by potassium sources. The use of T4 treatment (SpeedFol® induction mango) can provide a greater increment of chlorophyll A, B and Total than KCl and K2SO4.

Drought-triggered leaf transcriptional responses disclose key molecular pathways underlying leaf water use efficiency in sugarcane (Saccharum spp.).

Drought is a major constraint to sugarcane (Saccharum spp.) production and improving the water use efficiency (WUE) is a critical trait for the sustainability of this bioenergy crop. The molecular mechanism underlying WUE remains underexplored in sugarcane. Here, we investigated the drought-triggered physiological and transcriptional responses of two sugarcane cultivars contrasting for drought tolerance, 'IACSP97-7065' (sensitive) and 'IACSP94-2094' (tolerant). After 21 days without irrigation (DWI), only 'IACSP94-2094' exhibited superior WUE and instantaneous carboxylation efficiency, with the net CO2 assimilation being less impacted when compared with 'IACSP97-7065'. RNA-seq of sugarcane leaves at 21 DWI revealed a total of 1,585 differentially expressed genes (DEGs) for both genotypes, among which 'IACSP94-2094' showed 617 (38.9%) exclusive transcripts (212 up- and 405 down-regulated). Functional enrichment analyses of these unique DEGs revealed several relevant biological processes, such as photosynthesis, transcription factors, signal transduction, solute transport, and redox homeostasis. The better drought-responsiveness of 'IACSP94-2094' suggested signaling cascades that foster transcriptional regulation of genes implicated in the Calvin cycle and transport of water and carbon dioxide, which are expected to support the high WUE and carboxylation efficiency observed for this genotype under water deficit. Moreover, the robust antioxidant system of the drought-tolerant genotype might serve as a molecular shield against the drought-associated overproduction of reactive oxygen species. This study provides relevant data that may be used to develop novel strategies for sugarcane breeding programs and to understand the genetic basis of drought tolerance and WUE improvement of sugarcane.

Trocas gasosas e eficiência fotoquímica de goiabeira irrigada com águas salinas e adubação nitrogenada-potássica

ABSTRACT The objective of this study was to evaluate the effects of different combinations of nitrogen and potassium fertilization on gas exchange and chlorophyll a fluorescence in seedlings of guava cv. Paluma irrigated with water of different salinity levels. The experiment was set up in a randomized block design and analyzed in 5 × 4 factorial scheme, with four replicates. The treatments were composed of the combination of the factor electrical conductivity of irrigation water - ECw (0.3, 1.1, 1.9, 2.7, and 3.5 dS m-1), with the factor combinations (C) formed from recommended doses of nitrogen (N) and potassium (K2O), 70% N + 50% K2O, 100% N + 75% K2O, 130% N + 100% K2O, and 160% N + 125% K2O. The fertilization combination 130% N + 100% K2O mitigated the effects of salt stress up to mean ECw of 1.3 dS m-1, resulting in increments in CO2 assimilation rate, transpiration, instantaneous carboxylation efficiency, and electron transport rate. For maximum quantum efficiency of photosystem II, only treatment irrigated with ECw 3.5 dS m-1 under the combination 160% N + 125% K2O showed damage to the photosynthetic apparatus.

Bio-inputs promoting marandu grass growth: productivity, physiological response and nitrogen accumulation

Nutrient replenishment is one of the significant factors limiting the full development of extensive pasturelands. As a result, bio-inputs have been increasingly used under field conditions to improve plant growth in low-fertility soils. This study aimed to evaluate their effects on the productivity, physiological responses to and nitrogen (N) accumulation in marandu grass (Urochloa brizantha cv. marandu). The experiment was carried out using a randomized block design with four treatments and three replicates in a greenhouse under controlled conditions. In low-fertility soils, lower synthetic fertilizer inputs were simulated (40% N-P-K) (Control), and three bio-inputs were additionally applied (bio-inputs + 40% N-P-K): Azo (Azospirillum brasilense seed inoculation); HS+Herb (leaf application of humic substances combined with a cocktail consisting of Herbaspirillum species), and Coinoc (a combination of Azo and HS+Herb). We evaluated the plant biometrics (shoot and root dry matter, stem diameter and height) and physiological parameters (CO2 assimilation rate, internal CO2 concentration, transpiration, instantaneous carboxylation efficiency, and the maximum quantum yield of photosystem II), as well as the N accumulation 45 days after seedling emergence. Azo-treatment did not differ from the control in most of the variables studied. HS+Herb and Coinoc significantly (p ≤ 0.05) increased the dry matter of shoots (+237% and +255%, respectively) and roots (+106% and 83%, respectively) compared to the control. These treatments (HS+Herb and Coinoc) significantly (p ≤ 0.05) increased (almost double) the size and stem diameter, improved physiological parameters, and accumulated more N (up to 89%) compared to the control. Applying humic substance-based bio-inputs combined with the Herbaspirillum species cocktail was more efficient in stimulating the growth of marandu grass grown in soil of reduced fertility.

Índices fisiológicos do maracujazeiro-azedo sob estratégias de irrigação com água salobra e adubação potássica

ABSTRACT The objective of this study was to evaluate the physiological indices of sour passion fruit under brackish water irrigation strategies and potassium fertilization. The study was carried out under field conditions in São Domingos, PB, Brazil, using a randomized block design in a 6 × 2 factorial scheme, with treatments consisting of six brackish water irrigation strategies (irrigation with moderately saline (1.3 dS m-1) water throughout the crop cycle - WS; irrigation with high-salinity (4.0 dS m-1) water in the vegetative stage - VE; flowering stage - FL; fruiting stage - FR; successively in the vegetative/flowering stages - VE/FL; and vegetative/fruiting stages - VE/FR) and two doses of potassium (207 and 345 g K2O per plant per year, corresponding, respectively, to 60 and 100% of recommendation), with four replicates and three plants per plot. Irrigation with water of 4.0 dS m-1 reduced the osmotic and water potentials in the leaf blade, synthesis of chlorophylls a and b, transpiration, and instantaneous carboxylation efficiency of sour passion fruit, regardless of the development stage. Salt stress in the vegetative, flowering, fruiting, and successively in the vegetative/flowering and vegetative/fruiting stages increases intercellular electrolyte leakage in sour passion fruit. Fertilization with 100% of the K recommendation increased stomatal conductance, CO2 assimilation rate, and instantaneous water use efficiency of sour passion fruit cv. BRS GA1 under irrigation with water of 1.3 dS m-1 throughout the crop cycle.

Photosynthesis of plants of shade-tolerant ecotype of Paubrasilia echinata are more tolerance to drought than the sun-tolerant ecotype

Frequent and prolonged droughts are predicted for the Northeast region of Brazil until the end of this century. How the sun-tolerant and shade-tolerant tree species of the tropical forests in this region of the planet will respond to this climate scenario is a matter of global interest. To clarify this issue, we used plants of the shade-tolerant ecotype and the sun-tolerant ecotype of Paubrasilia echinata as a biological model. One batch of each ecotype was subjected to water suspension (drought simulation) for 17 days followed by water restitution (rainfall simulation) for 36 days. In the initial, intermediate, and final time of drought (7, 12, and 17 days, respectively) and rain (5, 12, and 36 days, respectively), we analyzed the water potential (Ψwp), electrolyte leakage (EL), net assimilation of CO2 (A), stomatal conductance (gs), transpiration (E), water use efficiency (A/E), the internal concentration of CO2 (Ci), instantaneous carboxylation efficiency (A/Ci), and fluorescence parameters of the chlorophyll a, among which are the photochemical performance indices (PIABS and PITOTAL). The photosynthetic activity and Ψwp of the shade-tolerant ecotype were more tolerance to the short dry period than the sun-tolerant one. Even so, the two ecotypes withstood water scarcity with 100% survival. The restitution of water, after a period of drought, allowed some of the gas exchange variables (E, A/E, and Ci), the Ψwp, and membrane damage (EL), from both ecotypes, to completely recover their values ​​to those at time zero, reaching the values of their respective controls. On the other hand, the variables most closely associated with CO2 assimilation (A, gs, and A/Ci) and ATP and NADPH production (PITotal and PIABS) did not fully recover from drought damage. We conclude that, if the droughts intensify in the northeast region of Brazil by the end of this century, the CO2 assimilation, and the photochemical efficiency of photosynthesis of the shade-tolerant species will possibly suffer greater impacts than the sun-tolerant ones. Predictably, this can affect the plant production of shade-tolerant species.

Trocas gasosas e produção em couve folha sob concentrações de Ca(NO3)2 em solução nutritiva salinizada

ABSTRACT Adequate mineral supplementation can be a strategy to enable the use of brackish water in the production of vegetables. This study intended to evaluate the effect of calcium nitrate concentrations on leaf gas exchanges and yield of kale (Brassica oleracea L) fertigated with salinized nutrient solutions. The experiment was conducted in a randomized block experimental design (4 + 1), with four replicates. Four nutrient solutions prepared in brackish water (6.0 dS m-1) containing four concentrations of Ca(NO3)2 [(750, 1,125, 1,500, and 1,875 mg L-1)] and a control treatment (standard nutrient solution using low-salinity water, 0.5 dS m-1 (750 mg L-1 of Ca(NO3)2) were used in the study. The following analyses were performed: leaf gas exchanges, leaf area, and fresh matter yield. The standard nutrient solution promoted higher values for photosynthetic rate (13.06 µmol CO2 m-2 s-1), stomatal conductance (0.19 mol H2O m-2 s-1), transpiration (2.76 mmol H2O m-2 s-1), instantaneous water use efficiency (4.73 mmol CO2 mol-1 H2O), instantaneous carboxylation efficiency (0.053 mmol CO2 mol-1 CO2), leaf area (2.78 cm2 per plant), and leaf fresh matter yield (2.64 kg per plant). The Ca(NO3)2 not nullified but mitigated the deleterious effect of salt stress on leaf gas exchanges, except for kale yield (leaf fresh matter).

The influence of ABA on the photosynthesis of the rare and endangered Emmenopterys henryi under salt stress

Emmenopterys henryi Oliv., a monotypic genus in family Rubiaceae with high scientific and application value, is currently endangered. Adaptability of E. henryi to environment is important for its cultivation, management, and application. In this paper, the effect of abscisic acid (ABA) on the photosynthesis of E. henryi under salt stress was discussed. Results showed that 0.3 % (m/v) NaCl led to reduction of net photosynthetic rate (PN), instantaneous carboxylation efficiency (ICE), and Rubisco activity but the increase of intercellular CO2 concentration (ci), which were remarkable relieved by ABA pretreatment. NaCl also induced reduction of the maximal efficiency of PS II photochemistry (Fv/Fm), the photochemical quenching (qP), the non-photochemical quenching (NPQ), the actual PS II efficiency [Y(II)], the regulated-energy dissipation [Y(NPQ)], whereas the increase of the unregulated energy dissipation [Y(NO)]. ABA application remarkably mitigated the depression of Fv/Fm, qP, Y(II) and the increase of Y(NO), but further promoted NPQ and Y(NPQ) in E. henryi due to high salinity. In addition, decrease of chlorophyll content, accumulation of MDA, and ion leakage in E. henryi due to high salinity were significantly alleviated by ABA pretreatment. Fluridone, an inhibitor of endogenous ABA synthesis, partially or completely reversed ABA mediated effects. These results suggested that ABA might improve the photosynthesis of E. henryi under salt stress via allocating more energy to photochemical reactions, or/and mitigating the decrease of Rubisco activity, or/and protecting photosynthetic apparatus by reinforcement of heat dissipation and alleviating oxidative damage.