Instantaneous Carboxylation Efficiency Research Articles

Photosynthetic pigments and gas exchange in red and green cabbage under no-tillage and conventional systems

The aim of the present study was to verify changes in the levels of photosynthetic pigments as well as gas exchange in the Fuyutoyo and Red Cabbage cultivars, grown under no-tillage (NT) and conventional (CT) systems. A randomised block design with four replications was used, in a 2 x 2 factorial scheme, where the Fuyutoyo and Red Cabbage cultivars were evaluated under two tillage systems. The levels of chlorophyll a, chlorophyll b, total chlorophyll and anthocyanins in the leaves were evaluated in triplicate. Localised gas exchange was measured at different times of the day, together with different photosynthetic photon flux density curves (PPFD). The Fuyutoyo cultivar showed a higher mean value for chlorophyll a (34.58%), chlorophyll b (35.09%) and total chlorophyll (34.76%), however, no difference was seen between cultivars for the levels of anthocyanin. Greater mean values for chlorophyll a (76.07%), chlorophyll b (77.87%), total chlorophyll (76.74%) and anthocyanin (72.24%) were found under CT compared to the cultivars grown under NT. The relative chlorophyll content of the Red Cabbage plants was influenced by adoption of the no-till system, showing a higher value for the SPAD index. The Fuyutoyo cabbage cultivar showed greater photosynthetic capacity during the day, promoting greater instantaneous carboxylation efficiency. All the cultivars and tillage systems gave a linear reduction in water use efficiency during this period. Under the conventional system, despite presenting higher rates of stomatal conductance, the Red Cabbage cultivar achieved lower values for net photosynthesis when submitted to light-curve analysis.

Silicon Supplementation Improves Tolerance to Water Deficiency in Sorghum Plants by Increasing Root System Growth and Improving Photosynthesis

This study was conducted to assess the effects of silicon treatments on architecture and morphometry of root systems of sorghum plants grown at two different soil water levels and to elucidate whether physiological improvements caused by silicon were related to morphometric modifications of the root system. Plants of the sorghum genotype BRS332 which is sensitive to drought at pre-flowering stage were used in this study. These plants were grown in a greenhouse, either at field capacity or under water deficiency, and were treated with silicon or were untreated. Leaf water potential was evaluated at noon, and gas exchange, photosynthetic pigment levels, relative aquaporin expression, root system morphometry, and grain yield were assessed. Silicon treatments mitigated the effects of water deficiency on leaf potential, photosynthesis, instantaneous carboxylation efficiency, and morphometry of the root system. These positive effects contributed to a higher grain yield, and thus indicated higher tolerance to drought. The beneficial effects of silicon also occurred in plants grown at field capacity. Silicon treatments did not increase the relative expression of aquaporin genes. However, we observed that expression of aquaporin TIP4 responded more strongly to drought than that of aquaporins PIP1;6 and PIP1;3/1;4. We conclude that silicon supplementation increases the tolerance of sorghum plants to drought by increasing growth of the root system and mitigating adverse effects of drought on photosynthesis.

Gas exchanges and growth of passion fruit under saline water irrigation and H2O2 application

ABSTRACT The study was carried out to evaluate the photosynthetic efficiency and growth of yellow passion fruit, cultivated under different levels of irrigation water salinity and exogenous application of hydrogen peroxide. The experiment was carried out in greenhouse of the Universidade Federal de Campina Grande, PB, Brazil, using drainage lysimeters with capacity for 100 dm3, filled with Entisol of sandy texture. The experimental design was randomized blocks using a 4 x 4 factorial scheme, with three repetitions, corresponding to four water salinity (0.7; 1.4; 2.1 and 2.8 dS m-1) and four concentrations of hydrogen peroxide (0, 20, 40 and 60 µM). The different concentrations of hydrogen peroxide were applied by soaking the seed for a period of 24 h and spraying the leaves on the adaxial and abaxial sides. At 35 days after transplanting, the interaction between water salinity and hydrogen peroxide concentrations did not significantly interfere with plant physiology and growth, except for the number of leaves. The hydrogen peroxide did not cause significant effects on any of the evaluated plant variables. Increasing salinity of irrigation water led to reduction in gas exchanges at 61 and 96 days after transplanting. Water salinity inhibited the CO2 assimilation, transpiration, stomatal conductance, instantaneous carboxylation efficiency and stem diameter of passion fruit plants.

Ecofisiologia e rendimento forrageiro do capim elefante roxo em função de adubação nitrogenada

A maximização da produtividade vegetal é almejada em qualquer cultivo, inclusive de Pennisetum purpureum, entretanto, isto depende do estado nutricional das plantas, nesse aspecto o nitrogênio exerce função essencial. O objetivo da pesquisa foi avaliar os aspectos ecofisiológicos e o rendimento forrageiro do capim elefante roxo em função de adubação nitrogenada. O experimento foi realizado na Estação Experimental de Alagoinha, pertencente à Empresa Estadual de Pesquisa Agropecuária da Paraíba, localizada no município de Alagoinha, estado da Paraíba, Brasil. Utilizou-se o delineamento de blocos ao acaso, com cinco tratamentos e quatro repetições. Os tratamentos consistiram na aplicação de 0, 20, 40, 60 e 80 kg de N ha-¹. As variáveis avaliadas foram: índice de clorofila a, b e total, fotossíntese líquida, concentração interna de carbono, eficiência instantânea de carboxilação, eficiência do uso da chuva, pegada hídrica cultural, eficiência de uso do nitrogênio, produtividade de matéria verde e seca e capacidade de suporte para vacas leiteiras. O aumento das doses de N estimula positivamente os índices de clorofila, trocas gasosas, eficiência de uso da chuva, pegada hídrica cultural, produtividade e capacidade de suporte animal do capim elefante roxo, entretanto, reduz a eficiência de uso do N.

Anatomical and physiological characteristics of Raphanus sativus L. submitted to different selenium sources and forms application

Increasing food production along with the nutritional value of diets with micronutrients and vitamins (e.g., selenium) is a worldwide concern that can be overcome by many strategies, including agronomic biofortification. This study tested different application forms and sources of selenium (Se) on Raphanus sativus L, assessing for their effects on characteristics such as biomass accumulation and Se content, as well as parameters related to gas exchange and anatomical modifications. The treatments consisted of two sources of Se (sodium selenate and sodium selenite) and two forms of application (soil and foliar application). A control treatment without addition of Se was also included. The experiment was conducted in a completely randomized design with 5 replicates, arranged in a 2 × 2 + 1 factorial scheme. The sources and forms of application did not affect plant biomass accumulation. The application of Se as selenate, via soil, resulted in greater selenium content in the plant, as well as in higher values of photosynthetic rate and instantaneous carboxylation efficiency, when compared with the other treatments. All treatments with Se resulted in increasing stomatal conductance, transpiratory rate, instantaneous efficiency of water use and intrinsic efficiency of water use when compared with the control treatment. Regarding the anatomy of the plant, the values of total area of the vascular bundle, xylem area, and number of xylem cells per cross-scectional area in leaves were higher when selenate was applied in the leaves, whereas the opposite was observed following the foliar application of selenite. The number of xylem cells per cross sectional area in the root was higher in the absence of Se. Our findings showed that roots of radish can be biofortified with Se without causing harmful effects, with the application of sodium selenate, and with a greater accumulation of Se when this source is applied via soil.

Photosynthesis and biomass accumulation in young sugarcane plants grown under increasing ammonium supply in nutrient solution

The aim of this study was to evaluate the sugarcane responses to varying ammonium:nitrate (NH4+:NO3−) ratio and to reveal how much NH4+ plants can tolerate before showing impairment of photosynthesis and growth. Sugarcane plants were grown in nutrient solution with the following NH4+:NO3− ratios (%): 20:80; 30:70; 40:60; 60:40; 70:30; and 80:20. The lowest photosynthetic rates, stomatal conductance, instantaneous carboxylation efficiency and leaf chlorophyll a content were found in plants supplied with higher than 60% NH4+. The leaf content of chlorophyll b proved to be more sensitive than chlorophyll a and decreases were found from 40% NH4+. We did not observe significant differences in leaf NO3− concentration under varying NH4+:NO3− ratio. However, plants that received 80% NH4+ showed the highest leaf NH4+ concentration and lowest leaf [NO3−]:[NH4+] ratio. The estimated leaf nitrogen content was higher in plants supplied with 20% and 30% NH4+. Taken together, our data revealed that sugarcane plants are sensitive to NH4+, with photosynthesis and plant growth being impaired when NH4+ supply was higher than 30% in nutrient solution. Root biomass was significantly reduced under high NH4+ supply, which explains decreases in stomatal conductance. Besides stomatal limitation, photosynthesis was also limited by low carboxylation efficiency under high NH4+ supply. Apparently, leaf NH4+ concentrations higher than 1.0 µmol g−1 were enough to impair photosynthesis. The balance between [NO3−] and [NH4+] in leaves was more correlated to photosynthesis than either [NO3−] or [NH4+] alone.

Fertilization with Silicon in Sweet Pepper Improved Plants Grown under Salt Stress

Aims: The objective of this research was to investigate the effect of calcium silicate on gaseous exchanges and production factors in the sweet pepper, cultivated under conditions of soil salinity induced by potassium fertilization, in protected cultivation.
 Study Design: The experiment was arranged in a randomized complete block design in a 2 × 5 factorial scheme with five replications.
 Place and Duration of Study: The experiment was conducted in the sector of Olericultura and Experimentation of the course of Agronomy from October 12, 2018 to February 2019.
 Methodology: The experiment was arranged in a randomized complete block design in a 2 × 5 factorial scheme (two sources of correction: calcareous and silicon and five increasing rates of KCl equivalent to 150, 300, 450, 600 and 700 kg ha-1 of K2O). Ten treatments with five replicates where each experimental unit consisted of a polyethylene pot, with a volume of 19 dm3. The electrical conductivity, the determination and quantification of silicon in soil and plant, liquid photosynthesis, stomatal conductance, intercellular CO2 concentration, transpiration, water use efficiency and instantaneous carboxylation efficiency were analyzed.
 Results: With the increase of K2O in the soil there was a tendency of reduction in liquid photosynthesis, transpiration, stomatal conductance, intercellular CO2 concentration, water use efficiency and instantaneous carboxylation efficiency in the presence and absence of calcium silicate. Higher rates of K2O (300, 450 and 600 kg ha-1) reduced the length and yield of sweet pepper fruits in the presence and absence of calcium silicate. The rate of 150 Kg K2O favored the growth of sweet pepper plants in the presence of calcium silicate.
 Conclusion: It is concluded from the research that the dose of 300 kg ha-1 of K2O, in the presence of calcium silicate, provided the best results for the electrical conductivity of 2.76 dS m-1, silicon content in the soil of 5.70 mg kg-1, 14% silicon leaf content, improving photosynthetic rates, transpiration, water use efficiency and fruit production. The increase in salinity reduced fruit yield, in the presence and absence of Si.

Biochar increases plant water use efficiency and biomass production while reducing Cu concentration in Brassica juncea L. in a Cu-contaminated soil

Biochar has been recently used as an alternative strategy to improve soil quality and plant growth in metal contaminated soils. However, the effects of biochar on gas exchange parameters such photosynthetic rate (A), water use efficiency (WUE) and instantaneous carboxylation efficiency (ICE) in metal tolerant plant species in contaminated soils is still unknown. Such information is important to understand how different biochar types can influence plant biomass production and metal uptake. Hence, a greenhouse experiment was set up as a completely randomized design combining two types of crop residue biochar (coconut husk (CB) and orange shell (OB) and two rates of application (30 t ha−1 and 60 t ha−1)). A control treatment (no biochar) was also included. The aim of the study was to investigate the influence of biochar on the physiological performance, growth and concentration of copper (Cu) in the shoot of B. juncea plants in a Cu-contaminated soil. Besides reduced growth on the control soil, all other treatments increased plant growth. No toxicity symptom was observed in the plant, confirming its Cu tolerance. Biochar increased plant biomass by approximately 170% and reduced Cu concentration up to 51%. Application of 30 t ha−1 biochar significantly increased net photosynthesis in 59% (CB) and in 34% (OB) while reducing stomatal conductance in 40% and transpiration rate in 14% (CB) and 19% (OB). Application of 60 t ha−1 of biochar reduced stomatal conductance and transpiration rate in 51% and 60% (CB) and 26% and 7% (OB), respectively. All biochars improved the water use efficiency (WUE) in the plants (52–182%) for the instantaneous WUE and 80–162% for the intrinsic (IWUE). Therefore, biochar, especially CB, caused an improved regulation of the stomata aperture so that plant could maintain a high photosynthetic rate while efficiently controlling the use of water. This could be an important mechanism to reduce the excessive uptake of Cu by the plant.

Photosynthetic damage caused by grapevine rust (Phakopsora euvitis) in Vitis vinifera and Vitis labrusca

Grapevine rust Phakopsora euvitis is an important disease in tropical and subtropical grapevine-producing areas, and both American (Vitis labrusca) and European (Vitis vinifera) grapevine species are sensitive to rust. Grapevine rust can cause early plant defoliation, reducing photosynthesis and photoassimilate supply and storage. This study evaluated the photosynthetic damage induced by varying grapevine rust intensities in leaves of V. vinifera cv. Moscato Giallo and V. labrusca cv. Niagara Rosada. The disease effect in tissues adjacent to the lesion, called virtual lesion (β), was estimated for photosynthetic variables, considering measurements taken in both healthy and diseased tissues. The average lesion size was higher in V. vinifera (0.66 mm2) than in V. labrusca (0.24 mm2). A water-soaked halo around the lesion was observed only in V. vinifera. The β-values estimated for the photosynthetic rate were 4.99 for V. labrusca and 5.93 for V. vinifera, taking into account the water-soaked and sporulating areas. When considering only the sporulating area, the β-value increased to 11.49 in V. vinifera. Grapevine rust had similar negative effects on photosynthesis in both species with increasing disease severity. While stomatal conductance was slightly affected, the pathogen caused significant reductions in the effective quantum efficiency of photosystem II and the instantaneous carboxylation efficiency of V. vinifera and V. labrusca with increasing disease severity. The β-value of instantaneous carboxylation efficiency was higher in V. vinifera (9.26) than in V. labrusca (4.76). In conclusion, Phakopsora euvitis dramatically affects photosynthesis in both V. vinifera cv. Moscato Giallo and V. labrusca cv. Niagara Rosada, causing large virtual lesions and substantial damage to the photochemical and biochemical reactions associated with CO2 assimilation.

Photosynthesis and Survival of Young Carpotroche brasiliensis Endl. (Achariaceae) Plants Subjected to Flooding

Abstract Carpotroche brasiliensis is a native tree of the Brazilian Atlantic Forest with potential economic value for cultivation in agroforestry systems. We conducted an experiment to determine the photosynthetic and survival responses of young C. brasiliensis plants to electrochemical changes in flooded soils as an indication of their flood tolerance and potential for cultivation in flood-prone areas. Soil flooding decreases the reduction–oxidation potential (redox) potential (Eh), pH, and electrical conductivity (Ec) of the soil, with subsequent recovery of the pH and Ec. Decreases in Eh negatively affect net photosynthesis (A). In flooded soil, decreased A was associated with decreased stomatal conductance (gs) and after 21 days was also associated with decreases in the instantaneous carboxylation efficiency (A/Ci) and potential quantum yield of photosystem II (Fv/Fm). Although flooded C. brasiliensis seedlings developed morphological structures known to increase flood tolerance, this was not enough to prevent severe signs of flooding stress. After 21 days of flooding, flooded plants were unflooded, and 17 days after plants were removed from flood, 90 percent of the unflooded plants died. Our results demonstrate that young plants of C. brasiliensis are suitable for planting in agroforestry systems only in areas with well-drained soils.

Gas exchanges and growth of cotton cultivars under water salinity

ABSTRACT Indication of salt-tolerant cotton cultivars can make the agricultural exploitation with saline water irrigation feasible in the Brazilian semi-arid region. Thus, this study aimed to evaluate the gas exchanges and growth of cotton cultivars irrigated with saline water. The study was conducted in pots adapted as drainage lysimeters under greenhouse conditions, using a sandy loam Entisols as substrate. Treatments were distributed in completely randomized design, in 5 x 2 factorial arrangement, relative to five levels of irrigation water electrical conductivity - ECw (1.5, 3.0, 4.5, 6.0 and 7.5 dS m-1) and two cotton cultivars (BRS 368 RF and BRS Safira). Increase in irrigation water salinity inhibits the vegetative growth and gas exchanges of the cotton cultivars BRS Safira and BRS 368 RF. Leaf area and instantaneous carboxylation efficiency are the most affected variables. Physiological and growth performance of the cultivar BRS Safira in response to water salinity was higher than that of BRS 368 RF.

Physiological responses to drought of Cnidoscolus quercifolius Pohl in semi-arid conditions

This study aimed to evaluate the physiological behavior of faveleira (Cnidoscolus quercifolius Pohl) plants grown in the field, in Caatinga, during wet and dry seasons. Adult plants were selected for evaluation in March and April (wet season) and May and June (dry season), during 2016. We evaluated the soil water content, water potential (Ψw), osmotic potential (Ψπ), relative water content (RWC), stomatal conductance (gs), transpiration rate (E), photosynthetic rate (A), intercellular CO2 concentration (Ci), instantaneous water use efficiency (A/E) and carboxylation efficiency (A/Ci). The reduction in water availability in the soil promoted a marked decrease in soil water potential, which was more affected than the relative water content. The opening of the stomata was affected by the decrease in soil moisture content, reducing the stomatal conductance, transpiration rate, photosynthesis rate, instantaneous water use efficiency and carboxylation efficiency. The photosynthesis was more affected than transpiration by the reduction in soil moisture content.

Salt stress and exogenous application of hydrogen peroxide on photosynthetic parameters of soursop

ABSTRACT This study aimed to evaluate the gas exchanges and photosynthetic pigments of soursop seedlings cv. ‘Morada Nova’ irrigated with saline waters and subjected to exogenous application of hydrogen peroxide by seed soaking and foliar spraying. The study was carried out using plastic bags under greenhouse conditions at the Center of Technology and Natural Resources of the Federal University of Campina Grande, PB, Brazil, using a eutrophic Regolithic Neosol of sandy loam texture. Treatments were arranged in a randomized block design, in 5 x 5 factorial scheme, which consisted of five levels of electrical conductivity – ECw (0.7; 1.4; 2.1; 2.8 and 3.5 dS m-1) of irrigation water and five concentrations of hydrogen peroxide - H2O2 (0, 25, 50, 75 and 100 µM), with four replicates and three plants per plot. As the salt stress increased, there were reductions in internal CO2 concentration, instantaneous carboxylation efficiency and water use efficiency, and instantaneous carboxylation efficiency was the most sensitive variable. Hydrogen peroxide at concentrations of 25 and 50 µM attenuated the deleterious effects of water salinity on stomatal conductance, CO2 assimilation rate and chlorophyll a content, and the concentration of 25 µM was the most efficient. The content of chlorophyll b and carotenoids of soursop cv. ‘Morada Nova’ had the deleterious effects caused by the salinity of irrigation water mitigated by the exogenous application of hydrogen peroxide in the concentration of 25 μM.

Changes in growth and photosynthesis linked with intensity and duration of salinity in Phragmites karka

Phragmites karka is gaining increasing attention as a biofuel crop due to high ligno-cellulosic biomass. In this study we investigated plant growth, gas exchange, chlorophyll fluorescence, photosynthetic pigments, and soluble sugar after 7, 15, and 30 days exposure to saline conditions [0 (control), 100 mM (moderate) and 300 mM (high) NaCl treatments]. Growth rate and net photosynthesis (ANET) were unchanged during short term (0–7 days) exposure to moderate salinity but decreased at 300 mM NaCl due to reduction in net assimilation rate, stomatal conductance (gs), and intercellular carbon dioxide concentration (Ci). However, growth rate decreased under long term (15–30 days) exposure to moderate salinity, while an increase in water use efficiency (WUE) and instantaneous carboxylation efficiency (COE) helped to maintain ANET. Higher photosynthetic pigments, respiration, sugar content and efficiency of photosystem II (YII) appear to work together to reduce the risk of oxidative stress at 100 mM NaCl. Long term exposure at 300 mM NaCl decreased the ANET, gs, COE, and YII. Stomatal closure improved WUE but resulted in increased ROS production (ETR/Agross). Photosynthesis was reduced by stomatal limitation under short-term exposure to high salinity and by both stomatal and biochemical limitation during long term exposure. These results indicate that P. karka can survive in moderate salinity for long durations by photosynthetic adaptations (photochemistry and gas exchange) that are vital for growth and biomass production in natural ecosystems.

Transpiratory Rate, Biomass Production and Leaf Macronutrient Content of Different Plant Species Cultivated on a Regosol in the Brazilian Semiarid

The transpiratory rate, growth rate and biomass production of plant species from Fabaceae and Poaceae group were investigated in a long-term field study. We compared photosynthetic rate, stomatal conductance, leaf transpiration, internal CO2 concentration, water use efficiency, intrinsic instantaneous water use efficiency, instantaneous carboxylation efficiency, growth rate, biomass production, and leaf macronutrient content of eight different plant species in a long-term field experiment. We found the highest values for all studied variables with C. juncea, C. ochroleuca, C. ensiformis, D. lablab and M. pruriens. We also found significant differences among Fabaceae and Poaceae group for all studied variables. Our findings suggest that the plant species from Family Fabaceae present high transpiratory rate, fast-growth and better nutritional status than plant species from Family Poaceae, and these results highlight the importance of considering the long-term use of legume plants as green manure in order to create positive plant-soil feedback.

Agronomic performance and gaseous exchanges of the radish under saline stress and ascorbic acid application

The radish is a short-cycle vegetable that has excellent nutritional and medicinal properties. It is considered rustic, meaning it tolerates adverse conditions with the possibility of being irrigated with saline water, which creates stress. In this context, this study aimed to evaluate the effect of electrical conductivities in irrigation water and doses of ascorbic acid on the agronomic performance and gaseous exchanges of radishes. This experiment was carried out in a protected environment at the Agricultural Sciences Center of the Federal University of Paraíba, Areia, Paraíba (Brazil). The experiment design used randomized blocks with five doses of ascorbic acid (0.0, 0.29, 1.0, 1.71 and 2.0 mM) and five electrical conductivities in the irrigation water (0.5, 1.3, 3.25, 5.2 and 6.0 dS m-1), with four replicates. The growth, gas exchange and production were evaluated. The doses of ascorbic acid were not significant. The increase in the electrical conductivities of the irrigation water provided a reduction in the agronomic performance and gas exchanges, except for the net photosynthesis, water use efficiency and instantaneous carboxylation efficiency, which were not significant. There was a relationship between the net photosynthesis, transpiration, internal concentration of CO2 and water use efficiency and the stomatal conductance. The agronomic performance and gaseous exchanges of the radish culture were influenced by the salinity. The foliar application of ascorbic acid did not influence the agronomic yield and gaseous exchanges of the radishes at the tested doses.

Drought tolerance of sugarcane propagules is improved when origin material faces water deficit.

Drought stress can imprint marks in plants after a previous exposure, leading to plant acclimation and a permissive state that facilitates a more effective response to subsequent stress events. Such stress imprints would benefit plants obtained through vegetative propagation (propagules). Herein, our hypothesis was that the propagules obtained from plants previously exposed to water deficit would perform better under water deficit as compared to those obtained from plants that did not face stressful conditions. Sugarcane plants were grown under well-hydrated conditions or subjected to three cycles of water deficit by water withholding. Then, the propagules were subjected to water deficit. Leaf gas exchange was reduced under water deficit and the propagules from plants that experienced water deficit presented a faster recovery of CO2 assimilation and higher instantaneous carboxylation efficiency after rehydration as compared to the propagules from plants that never faced water deficit. The propagules from plants that faced water deficit also showed the highest leaf proline concentration under water deficit as well as higher leaf H2O2 concentration and leaf ascorbate peroxidase activity regardless of water regime. Under well-watered conditions, the propagules from plants that faced stressful conditions presented higher root H2O2 concentration and higher activity of catalase in roots as compared to the ones from plants that did not experience water shortage. Such physiological changes were associated with improvements in leaf area and shoot and root dry matter accumulation in propagules obtained from stressed plants. Our results suggest that root H2O2 concentration is a chemical signal associated with improved sugarcane performance under water deficit. Taken together, our findings bring a new perspective to the sugarcane production systems, in which plant acclimation can be explored for improving drought tolerance in rainfed areas.

Phosphorus-zinc interactions in cotton: consequences for biomass production and nutrient-use efficiency in photosynthesis.

The fragmentary information on phosphorus (P) × zinc (Zn) interactions in plants warrants further study, particularly in plants known for their high P and Zn requirements, such as cotton (Gossypium hirsutum L.). The objective of this study was to investigate the effect of P × Zn interactions in a modern cultivar of cotton grown hydroponically. Biomass, mineral nutrition and photosynthetic parameters were monitored in plants receiving contrasting combinations of P and Zn supply. Root biomass, length and surface area were similar in plants with low P and/or low Zn supply to those in plants grown with high P and high Zn supply, reflecting an increased root/shoot biomass quotient when plants lack sufficient P or Zn for growth. Increasing P supply and reducing Zn supply increased shoot P concentrations, whilst shoot Zn concentrations were influenced largely by Zn supply. A balanced P × Zn supply (4 mM P × 4 μM Zn) enabled greatest biomass accumulation, while an imbalanced supply of these nutrients led to Zn deficiency, P toxicity or Zn toxicity. Net photosynthetic rate, stomatal conductance, transpiration rate and instantaneous carboxylation efficiency increased as P or Zn supply increased. Although increasing P supply reduced the P-use efficiency in photosynthesis (PUEP) and increasing Zn supply reduced the Zn-use efficiency in photosynthesis (ZnUEP), increasing Zn supply at a given P supply increased PUEP and increasing P supply at a given Zn supply increased ZnUEP. These results suggest that agricultural management strategies should seek for balanced mineral nutrition to optimize yields and resource-use efficiencies.

Photosynthetic Efficiency in Aroeira and Cedro After the Application of Salicylic Acid

The objective of this research was to quantify the photosynthetic efficiency of Cedrela fissilis and Schinus terebinthifolius seedlings after application of salicylic acid for eight weeks. The experimental design was completely randomized, composed of four treatments, with five replicates of 20 seedlings each. The treatments consisted of increasing doses of the salicylic acid solution: 0, 100, 200, 300 mg L-1. The solution was composed of salicylic acid, deionized water and adjuvant and applied with hand sprayer, weekly for 2 months. The parameters evaluated after the application of the acid consisted of the rate of CO2 assimilation, leaf transpiration, stomatal conductance and internal CO2 concentration, as well as water use efficiency, intrinsic water use efficiency and instantaneous carboxylation efficiency. In seedlings of Schinus terebinthifolius there was a reduction of the photosynthetic parameters and consequently a better use of water as the doses of the plant growth regulator were increased. In the seedlings of Cedrela fissilis the dose of 200 mg L-1 resulted in greater CO2 fixation per molecule of water lost and in this sense, it can be inferred that the increase in the doses of salicylic acid improved the photosynthetic efficiency, but the use of water was lower. Thus, for both species, lower doses are more recommended because there must be a balance between the fixed amount of CO2, the plant generated from photoassimilates and the amount of water lost, in order not to generate a negative potential in the plant metabolism.

Growth and gas exchanges of red pitaya under different shading conditions

Plants with yellow cladodes are commonly present in commercial red pitaya orchards, in Ceara, mainly during the warmer seasons of the year. Therefore, this study aimed to evaluate the effect of shading on the growth and gas exchanges of red pitaya. We tested five shading levels on stock plants (full sunlight, 35, 50; 65 and 80% shading) via randomized block design (RBD), with five replications and two plants per plot. After 180 days, the following characteristics were evaluated: sum of the length of the axillary shoots, number of axillary shoots, diameter, thickness of secondary shoots, photosynthetic rate, stomatal conductance of water vapor, transpiration, internal carbon dioxide concentration, ratio of internal to external CO2 concentration, instantaneous and intrinsic water use efficiency, and instantaneous carboxylation efficiency. The plants presents large and thin cladodes, apparently blanching under 80% shading; therefore, we concluded that cultivation in full sunlight caused a negative effect on gas exchanges and growth of red pitaya.. The use of 35% shading at 180 days increased the photosynthetic rate, water use efficiency and carboxylation, with increase vegetative growth.