Photochemical Apparatus Research Articles

Marine Plant Growth Promoting Bacteria (PGPB) inoculation technology: Testing the effectiveness of different application methods to improve tomato plants tolerance against acute heat wave stress

Regenerative agriculture aims to boost native biodiversity and ensure sustainable production. Plant Growth Promoting Bacteria (PGPB) enhance crop yield through improved nutrient use efficiency or stress tolerance. Utilizing synthetic bacterial communities (SynCom) tailored to specific challenges holds promise for enhancing plant resilience. However, challenges include designing microbial consortia and selecting SynCom application techniques. This study tested four PGPB SynCom application methods on tomato plants to evaluate their effectiveness in promoting plant resistance and recovery from short extreme heat waves. Non-invasive phenotyping techniques were used to assess plant responses to three delivery methods (watering, foliar spray, and alginate spheres immobilization) under heat stress. Plants treated with the marine PGPB SynCom through methods like leaf spraying or encapsulation in alginate spheres exhibited improved resilience in terms of Kautsky curve intensity and shape, indicating better photochemical apparatus function. These techniques also facilitated post-stress recovery. Deep photochemical analysis revealed SynCom-induced improvements in the plant's photochemical apparatus, particularly the PS II donor side. Moreover, it was also possible to observe that upon stress relief these two techniques, alongside the plants inoculated throughout watering were able to recover their photochemical profiles. Analysing the Fv/Fm values, plants inoculated through watering, alginate beads and leaf spray can be considered heat-tolerant, a characteristic conserved throughout the three sampling moments. Heat-wave exposure led to an increase in the energy absorbed by the non-inoculated plants as a counteractive measure to overcome the low energy use efficiency observed (low trapping and transported energy fluxes). The reduction in stress impact was attributed to SynCom's ACC-deaminase production, which lowered ethylene accumulation, promoting growth and photosynthetic efficiency. The study also noted reduced energy dissipation under stress relief, indicating efficient heat dissipation mechanisms due to SynCom application. Statistical models generated with the attained photochemical data allowed depicting specific fluorescence signatures of each thermal and inoculation treatment with a very high degree of accuracy, reinforcing that these different inoculation treatments have in fact different impacts on plant photochemistry but also provide a tool for future phenotyping assessments using the proposed inoculation techniques. Alginate bead based PGPB release emerged as an efficient, scalable technique with continuous benefits for plant growth and stress response.

Influence of Anthocyanin Expression on the Performance of Photosynthesis in Sweet Orange, Citrus sinensis (L.) Osbeck

Anthocyanins are a class of natural pigments that accumulate transiently or permanently in plant tissues, often in response to abiotic and biotic stresses. They play a photoprotective role by attenuating the irradiance incident on the photochemical apparatus and quenching oxyradicals through their powerful anti-oxidative function. The objective of the current study is to understand the impact of introducing Vitis vinifera mybA1 (VvmybA1) in ‘Hamlin’ sweet orange trees on various aspects, including photosynthetic performance, pigment composition, and gene expression related to photosynthesis and light harvesting. We describe the relationship between anthocyanin accumulation and photosynthetic measurements in genetically modified ‘Hamlin’ sweet orange trees expressing the grapevine-derived Vitis vinifera mybA1 (VvmybA1). The juvenile leaves of transgenic plants displayed an intense purple color compared to the mature leaves, and microscopic visualization showed anthocyanin accumulation primarily in the leaf epidermal cells. Under optimal growth conditions, there were no significant differences in leaf gas exchange variables, suggesting normal photosynthetic performance. The chlorophyll fluorescence maximum quantum yield of PSII was slightly reduced in VvmybA1 transgenic leaves compared to the performance of the control leaves, while the total performance index per absorbance remained unaffected. Comparison of the chlorophyll and carotenoid pigment contents revealed that chlorophyllide a and carotenoid pigments, including trans-neoxanthin, trans-violaxanthin, cis-violaxanthin, zeaxanthin, antheraxanthin, and total xanthophylls were enhanced in VvmybA1 transgenic leaves. Although there were no significant changes in the rates of the gas exchange parameters, we recorded a high relative expression of the ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (RuBP) and rubisco activase (RCA) in the mature leaves of transgenic plants, indicating activation of Rubisco. Our findings confirm an efficient photoacclimation of the photosynthetic apparatus, allowing the transgenic line to maintain a photosynthetic performance similar to that of the wild type.

Plasticity of Plantago lanceolata L. in Adaptation to Extreme Environmental Conditions.

This study aimed at characterizing some adaptive changes in Plantago lanceolata L. exposed to harsh conditions of a desert-like environment generating physiological stress of limited water availability and exposure to strong light. It was clearly shown that the plants were capable of adapting their root system and vascular tissues to enable efficient vegetative performance. Soil analyses, as well as nitrogen isotope discrimination data show that P. lanceolata leaves in a desert-like environment had better access to nitrogen (nitrite/nitrate) and were able to fix it efficiently, as compared to the plants growing in the surrounding forest. The arbuscular mycorrhiza was also shown to be well-developed, and this was accompanied by higher bacterial frequency in the root zone, which might further stimulate plant growth. A closer look at the nitrogen content and leaf veins with a higher number of vessels and a greater vessel diameter made it possible to define the changes developed by the plants populating sandy habitats as compared with the vegetation sites located in the nearby forest. A determination of the photosynthesis parameters indicates that the photochemical apparatus in P. lanceolata inhabiting the desert areas adapted slightly to the desert-like environment and the time of day, with some changes of the reaction center (RC) size (photosystem II, PSII), while the plants' photochemical activity was at a similar level. No differences between the two groups of plants were observed in the dissipation of light energy. The exposure of plants to harsh conditions of a desert-like environment increased the water use efficiency (WUE) value in parallel with possible stimulation of the β-carboxylation pathway.

Basking in the sun: how mosses photosynthesise and survive in Antarctica.

The Antarctic environment is extremely cold, windy and dry. Ozone depletion has resulted in increasing ultraviolet-B radiation, and increasing greenhouse gases and decreasing stratospheric ozone have altered Antarctica's climate. How do mosses thrive photosynthetically in this harsh environment? Antarctic mosses take advantage of microclimates where the combination of protection from wind, sufficient melt water, nutrients from seabirds and optimal sunlight provides both photosynthetic energy and sufficient warmth for efficient metabolism. The amount of sunlight presents a challenge: more light creates warmer canopies which are optimal for photosynthetic enzymes but can contain excess light energy that could damage the photochemical apparatus. Antarctic mosses thus exhibit strong photoprotective potential in the form of xanthophyll cycle pigments. Conversion to zeaxanthin is high when conditions are most extreme, especially when water content is low. Antarctic mosses also produce UV screening compounds which are maintained in cell walls in some species and appear to protect from DNA damage under elevated UV-B radiation. These plants thus survive in one of the harshest places on Earth by taking advantage of the best real estate to optimise their metabolism. But survival is precarious and it remains to be seen if these strategies will still work as the Antarctic climate changes.

Biofertilization with PGP Bacteria Improve Strawberry Plant Performance under Sub-Optimum Phosphorus Fertilization

Biofertilization with plant growth-promoting bacteria (PGPB) could optimize chemical fertilization for strawberry crop cultivation. A greenhouse study was arranged to assess the impact of an isolated PGPB consortium from halophytes on strawberry development, physiological traits, and nutritional balance subjected to two phosphorus fertilization limitation treatments (with and without insoluble phosphorus form application). Biofertilization had a positive effect on strawberry development. Thus, shoot and root biomass was c. 20 and 32% higher in inoculated plants grown with insoluble phosphorus. This effect was mediated by a positive bacterial impact on plant carbon absorption capacity and water use efficiency, through a reduction in CO2 diffusional and biochemical photosynthesis limitation. Thus, net photosynthetic rate and intrinsic water use efficiency showed increments of 21–56% and 14–37%, respectively. In addition, inoculation led to a better efficiency of the plant photochemical apparatus, as indicated by the invariable higher PSII photochemistry parameters. Furthermore, these effects correlated with improved nutritional balance of phosphorus and nitrogen, which was directly related to the beneficial impact on carbon metabolism and, consequently, on strawberries’ growth. In conclusion, we can recommend the biofertilization based on PGPB for achieving more efficient strawberry P fertilization management practices, providing high efficiency in yields.

Kaolin particle film mitigates supra-optimal temperature stress effects at leaf scale and increases bean size and productivity of Coffea canephora

Summary In young plants of Coffea canephora, fine particle film based on calcined kaolin (KF) causes a decrease in leaf temperature (Tleaf), minimizing the damages to the photochemical apparatus, especially in summer season, but no report about the ecophysiological responses to KF over phenology is available on this species. We hypothesized that greater ecophysiological effects of KF would occur during the summer phenophase of leaf area and berry expansion (BE) compared with autumn berry maturation phase (BR), and that those benefits will have impact on bean productivity and physical quality. In this sense, the present study aimed to analyze the effects of KF on some ecophysiological parameters in the last phenophases of C. canephora biennial cycle, bean productivity, and bean size classification. During the complete phenological cycle, eight applications of KF were performed, totaling 80 kg of KF ha−1 in two years. KF applications and ecophysiological measurements occurred during the BE and BR phenophases. Firstly, we documented temporal dynamics in responses of field-grown C. canephora adult plants to KF application. KF reduced Tleaf and crop water stress index and increased the thermal index of relative stomatal conductance and relative chlorophyll content (SPAD index) observed in the autumn BR (opposite to young plants). The positive impact of KF on chlorophyll a fluorescence was proportionally similar among the observed phenophases. Secondly, KF increased bean size 16 by 50% and increased total productivity. The plants treated with KF increased productivity by 1.7 t ha− commercially useful bean mass compared to the control. The kaolin dose of 40 kg ha−1 distributed four times per year was highly effective as a protection strategy against high-light and elevated Tair.

Soybean resilience to drought is supported by partial recovery of photosynthetic traits.

Climate change affects precipitation dynamics and the variability of drought frequency, intensity, timing, and duration. This represents a high risk in spring-sown grain legumes such as soybean. Yet, under European conditions, no evidence supports the potential recovery and resilience of drought-tolerant soybean cultivars after episodic drought, at different growth stages. A field experiment was conducted using a representative drought-tolerant cultivar of soybean (cv. Acardia), in 2020 and 2021, on sandy soils in Germany, applying four water regimes (irrigated, rainfed, early-drought, and late-drought stress). Drought stress was simulated by covering the plots during the event of rain with 6 × 6m rainout shelters, at the vegetative (V-stage) and flowering (Fl-stage) stages. Drought response was quantified on plant height, chlorophyll fluorescence ratio (ChlF ratio), chlorophyll content (Chlc), and leaf surface temperature (LST), at different intervals after simulating drought until pod filling. Grain yield and yield components were quantified at the end of the growing season. Compared to rainfed conditions, a drought at V-stage and Fl-stage reduced significantly plant height, ChlF ratio, and Chlc by 20%, 11%, and 7%, respectively, but increased LST by 21% during the recovery phase. There was no recovery from drought except for Chlc after V-stage in 2021, that significantly recovered by 40% at the end of the growing season, signifying a partial recovery of the photochemical apparatus. Especially, there was no recovery observed in LST, implying the inability of soybean to restore LST within the physiological functional range (Graphical abstract). Under rainfed conditions, the grain yield reached 2.9t ha-1 in 2020 and 5.2t ha-1 in 2021. However, the episodic drought reduced the yield at V-stage and Fl-stage, by 63% and 25% in 2020, and 21% and 36% in 2021, respectively. To conclude, the timing of drought was less relevant for soybean resilience; however, pre- and post-drought soil moisture, drought intensity, and drought duration were likely more important. A drought-tolerant soybean cultivar may partially be drought-resilient due to the recovery of photosynthetic traits, but not the leaf thermal traits. Overall, these findings will accelerate future efforts by plant breeders, aimed at improving soybean drought resilience.

Short waterlogging events differently affect morphology and photosynthesis of two cucumber (Cucumis sativus L.) cultivars.

Waterlogging induces growth and developmental changes in sensitive crops such as cucumber (Cucumis sativus L.) during early plant development. However, information on the physiological mechanisms underpinning the response of cucumber plants to waterlogging conditions is limited. Here, we investigated the effects of 10-day waterlogging stress on the morphology, photosynthesis, and chlorophyll fluorescence parameters in two cultivars of cucumber seedlings. Waterlogging stress hampered cultivars’ growth, biomass accumulation, and photosynthetic capacity. Both cultivars also developed adventitious roots (ARs) after 10 days of waterlogging (DOW). We observed differential responses in the light- and carbon-dependent reactions of photosynthesis, with an increase in light-dependent reactions. At the same time, carbon assimilation was considerably inhibited by waterlogging. Specifically, the CO2 assimilation rate (A) in leaves was significantly reduced and was caused by a corresponding decrease in stomatal conductance (gs). The downregulation of the maximum rate of Rubisco efficiency (Vcmax) and the maximum rate of photosynthetic electron transport (Jmax) were non-stomatal limiting factors contributing to A reduction. Exposure of cucumber to 10 DOW affected the PSII photochemistry by downregulating the PSII quantum yield (ΦPSII). The redox state of the primary quinone acceptor in the lake model (1-qL), a measure of the regulatory balance of the light reactions, became more oxidized after 10 DOW, indicating enhanced electron sink capacity despite a reduced A. Overall, the results suggest that waterlogging induces alterations in the photochemical apparatus efficiency of cucumber. Thus, developing cultivars that resist inhibition of PSII photochemistry while maintaining carbon metabolism is a potential approach for increasing crops’ tolerance to waterlogged environments.

Respostas morfofisiológicas de Setaria viridis ao estresse por frio

Abstract The objective of this work was to determine the suitability of Setaria viridis as a model plant in studies to validate candidate genes for cold tolerance by evaluating the response of two of its accessions to different durations of abrupt or gradual cold stress in the vegetative and reproductive stages. Plants of accessions A10.1 and Ast-1, cultivated at 25°C, were subjected to the following cold stress treatments: gradual reduction in temperature from 25 to 0°C, 5°C at a time, every 24 hours in a same chamber; or abrupt reduction in temperature, by transferring plants from a chamber at 25°C to another at 0°C. Plants were kept at 0°C for 3, 5, or 10 days, after which temperature was increased back again to 25°C; a control group remained at 25ºC. Low temperatures – reduced abruptly or gradually – caused a decrease in the gas exchange rates and shoot and root biomass of the plants, besides damage to their photochemical apparatus; the longer the cold lasted, the more pronounced the effect was. Regardless of stress duration, plants recovered and completed their life cycle. The studied accessions are tolerant to cold and, therefore, are not suitable as a model plant in studies to validate candidate genes for cold tolerance.

Tannery Sludge Applied in High Doses in Elephant Grass as an Alternative Fertilization

ABSTRACT Tannery sludge has great potential for use in agriculture, however it is a potentially toxic waste, and it is necessary to establish the ideal dose for each crop. The objective of this study was to evaluate the influence of fertilization with liquid tannery sludge on growth, chlorophyll a fluorescence and gas exchange of Pennisetum purpureum in two production cycles. A 2 × 6 + 1 split plot scheme was used, where the first factor was composed of two productive cycles, the second factor different fertilizations doses: 0, 30, 70, 110, 150, 190 t ha−1 of liquid tannery sludge and an additional treatment with nitrogen, phosphorus and potassium control. Plant height, number of leaves and tillers, canopy and stem diameter, leaf area, dry matter, chlorophyll index (SPAD), chlorophyll a fluorescence and gas exchange were evaluated. The highest production of total dry matter was observed in the second production cycle. The range between 72–100 t ha−1 of liquid tannery sludge showed the greatest gains in growth and production of elephant grass. At doses above 150 t ha−1 of liquid tannery sludge, the photochemical apparatus begins to show possible damage to the photosystem II (PSII) and reductions in gas exchange.

Discrimination of responses of corn genotypes to drought through physiological, growth, and yield traits

Abstract: The objective of this work was to evaluate different traits of four corn (Zea mays) genotypes with contrasting responses to drought and to determine the main traits associated to such responses. The experiment was carried out in a greenhouse. The plants were grown in pots subjected to full irrigation. Drought was imposed to plants at 54 days after sowing and kept constant for 12 consecutive days; however, a group of plants remained under full irrigation. Traits related to leaf gas exchange, photochemical apparatus, growth, and yield were assessed, and data were subjected to hierarchical agglomerative clustering and principal component analysis. DKB 390 distinguishes from the other genotypes for growth and yield traits, while 2B-707 and DKB 390 discriminate from 'BRS 1030' and 'BRS 1010' for physiological traits. Ear length, kernel number per ear, above-ground dry matter, shoot dry matter, and plant height are the most important growth and yield traits to discriminate genotype-dependent drought tolerance. Among the physiological traits, the most important are: chlorophyll content, absorptivity, leaf temperature, maximum fluorescence in the dark-adapted state, minimum fluorescence in the dark-adapted state, water-use efficiency, and intercellular CO2 concentration.

Understanding the impact of a complex environmental matrix associated with climate change on the European marshes engineer species Spartina martima

A challenge exists in the need to understand plant responses in complex environmental matrixes, such as those predicted by climate change models, being this information essential for species that support important ecosystem functions. A factorial climatic chamber experiment was designed to evaluate the impact of atmospheric CO2 concentration (400 ppm and 700 ppm CO2) in combination with two maximum and minimum temperature ranges (28/13 °C and 32/17 °C) and salinity concentrations (0 and 171 mM NaCl) on the growth and photosynthetic responses of the ecosystem engineer species Spartina maritima. Plants grown at 32/17 °C showed a reduction ∼39 % on relative growth rate (RGR) and this was more drastic (i.e. 64 %) in those exposed to 700 ppm CO2, which also showed an increment in the percentage of dead tillers regardless of salinity. These reductions were explained by the negative impact on net photosynthetic rate (AN), which decreased with temperature increment, being this reduction more acute at 700 ppm CO2. This response was associated with an augmentation in CO2 diffusion limitations, as indicated the lower stomatal conductance (gs), together with a down-regulation photochemical apparatus efficiency, as indicated the lower electron transport rate (ETR) and energy fluxes derived from Kautsky curves. In addition, the greatest gs drop at 700 ppm CO2, would limit plant ability to cope with temperature excess through evapotranspiration, a fact that could have boosted temperature-triggered damage and, consequently, leaf senescence. Therefore, we can conclude that temperature and atmospheric CO2 increments would compromise the development of S. maritima and consequently the maintaining of its ecosystem functions.

Foliar-applied glycine betaine minimizes drought stress-related impact to gas exchange and the photochemical efficiency of PSII in sugarcane

Sugarcane is one of the most important crops in the world, but subject to yield losses caused by sporadic droughts during the growing season. To mitigate the effects of drought stress, different strategies have already been used, including the foliar application of glycine betaine (GB). Thus, the present study aimed to evaluate the effect of GB spraying via leaf on gas exchange, chlorophyll fluorescence and on the sugarcane water status subjected to drought stress and rewatering. The experiment was carried out in a greenhouse, using the RB92579 sugarcane variety. A randomized block design was used, in a 3 × 2 factorial scheme, composed of three GB applications (G0—without GB, G1—one application and G2—two applications) and two water treatments: irrigated (Control) and non-irrigated (Drought Stress), with subsequent rewatering. The foliar application of GB minimized the impact of drought stress on gas exchange, on the photochemical efficiency of photosystem II (PSII) and leaf tissue water status in stressed plants. In addition, it favored the energy use in the PSII and reduced photoinhibition, a fact not observed in the G0 stressed plants. Thus, it can be inferred that the GB foliar application mitigates the negative effects of drought stress on gas exchange and photochemical apparatus of PSII in young sugarcane plants.

Impact of Plant Growth Promoting Bacteria on Salicornia ramosissima Ecophysiology and Heavy Metal Phytoremediation Capacity in Estuarine Soils.

Salicornia ramosissima is a C3 halophyte that grows naturally in South Western Spain salt marshes, under soil salinity and heavy metal pollution (mostly Cu, Zn, As, and Pb) caused by both natural and anthropogenic pressure. However, very few works have reported the phytoremediation potential of S. ramosissima. In this work, we studied a microbe-assisted phytoremediation strategy under greenhouse conditions. We inoculated plant growth promoting (PGP) and heavy metal resistant bacteria in pots with S. ramosissima and natural non-polluted and polluted sediments collected from Spanish estuaries. Then, we analyzed plant ecophysiological and metal phytoaccumulation response. Our data suggested that inoculation in polluted sediments improved S. ramosissima plant growth in terms of relative growth rate (RGR) (32%) and number of new branches (61%). S. ramosissima photosynthetic fitness was affected by heavy metal presence in soil, but bacteria inoculation improved the photochemical apparatus integrity and functionality, as reflected by increments in net photosynthetic rate (21%), functionality of PSII (Fm and Fv/Fm) and electron transport rate, according to OJIP derived parameters. Beneficial effect of bacteria in polluted sediments was also observed by augmentation of intrinsic water use efficiency (28%) and slightly water content (2%) in inoculated S. ramosissima. Finally, our results demonstrated that S. ramosissima was able to accumulate great concentrations of heavy metals, mostly at root level, up to 200 mg Kg–1 arsenic, 0.50 mg Kg–1 cadmium, 400 mg Kg–1 copper, 25 mg Kg–1 nickel, 300 mg Kg–1 lead, and 300 mg Kg–1 zinc. Bioaugmentation incremented S. ramosissima heavy metal phytoremediation potential due to plant biomass increment, which enabled a greater accumulation capacity. Thus, our results suggest the potential use of heavy metal resistant PGPB to ameliorate the capacity of S. ramosissima as candidate for phytoremediation of salty polluted ecosystems.

Similarities and Differences in the Effects of Toxic Concentrations of Cadmium and Chromium on the Structure and Functions of Thylakoid Membranes in Chlorella variabilis.

Trace metal contaminations in natural waters, wetlands, and wastewaters pose serious threats to aquatic ecosystems—mainly via targeting microalgae. In this work, we investigated the effects of toxic amounts of chromium and cadmium ions on the structure and function of the photosynthetic machinery of Chlorella variabilis cells. To halt the propagation of cells, we used high concentrations of Cd and Cr, 50–50 mg L−1, in the forms of CdCl2 x 2.5 H2O and K2Cr2O7, respectively. Both treatments led to similar, about 50% gradual diminishment of the chlorophyll contents of the cells in 48 h, which was, however, accompanied by a small (~10%) but statistically significant enrichment (Cd) and loss (Cr) of ß-carotene. Both Cd and Cr inhibited the activity of photosystem II (PSII)—but with more severe inhibitions with Cr. On the contrary, the PsbA (D1) protein of PSII and the PsbO protein of the oxygen-evolving complex were retained more in Cr-treated cells than in the presence of Cd. These data and the higher susceptibility of P700 redox transients in Cr-treated cells suggest that, unlike with Cd, PSII is not the main target in the photochemical apparatus. These differences at the level of photochemistry also brought about dissimilarities at higher levels of the structural complexity of the photosynthetic apparatus. Circular dichroism (CD) spectroscopy measurements revealed moderate perturbations in the macro-organization of the protein complexes—with more pronounced decline in Cd-treated cells than in the cells with Cr. Also, as reflected by transmission electron microscopy and small-angle neutron scattering, the thylakoid membranes suffered shrinking and were largely fragmented in Cd-treated cells, whereas no changes could be discerned with Cr. The preservation of integrity of membranes in Cr-treated cells was most probably aided by high proportion of the de-epoxidized xanthophylls, which were absent with Cd. It can thus be concluded that beside strong similarities of the toxic effects of Cr and Cd, the response of the photosynthetic machinery of C. variabilis to these two trace metal ions substantially differ from each other—strongly suggesting different inhibitory and protective mechanisms following the primary toxic events.

Uncovering PGPB Vibrio spartinae inoculation-triggered physiological mechanisms involved in the tolerance of Halimione portulacoides to NaCl excess

Plant growth promoting bacteria’ (PGPB) beneficial role on plant tolerance to salinity stress has previously been well recognized. However, bacteria-triggered plant physiological mechanisms involved in this response require investigation, especially in plants with innate salt tolerance. A glasshouse experiment was designed to investigate the effect of the PGPB Vibrio spartinae on Halimione portulacoides growth, physiological performance and ion homeostasis in plants exposed to 0, 171, 510 and 1020 mM NaCl for 100 days. Bacterial inoculation alleviated ~28% of the deleterious impact of salinity excess on the relative growth rate (RGR) in plants grown at 510 mM and led to 30% and 44% enhancements in those exposed to 0 and 171 mM NaCl, respectively. This effect was linked to a reduction in Na tissue concentrations which improved plant ion homeostasis at elevated NaCl concentration, and to the overall protective effects on various steps in the photosynthetic pathway between 0 and 510 mM NaCl. Thus, inoculated plants were able to maintain higher net photosynthesis (AN) than their non-inoculated counterparts. Hence, AN differences under saline conditions were ascribed to inoculation amelioration NaCl-induced CO2 diffusion limitations, as reflected in the greater gs and Ci values recorded at 171 and 510 mM NaCl, together with an enhancement of photochemical apparatus functionality (in terms of energy absorption, transformation and transport), as indicated by a higher electron transport rate (ETR) and energy fluxes derived from Kautsky curves, compared with their non-inoculated counterparts.

Efeito de subdoses de 2,4-D sal colina na eficiência quântica do fotossistema II do algodoeiro

Deleterious effects of herbicides on the photochemical apparatus of plants can be quantified by studying the quantum yield potential of photosystem II (Fv/Fm). Therefore, the objective of this work was to evaluate the effect of subdoses of the herbicide 2,4-D choline salt formulation on the quantum efficiency of the photosystem II of cotton plantsat different phenological stages. The study adopted a completely randomized experimental design with seven replications, and the treatments consisted of nine fractions of the average rate indicated on the 2,4-D choline salt herbicide label: 0 (control); 0.4275; 0.855; 1.71; 3.42; 8.55; 17.1; 34.2 and 68.4 g ae ha-1applied at phenological stages V4 or B4 of cotton plants. The plants were evaluated for the visual symptoms of injury and the emission kinetics of maximum chlorophyll a (Fv/Fm) fluorescence at 3, 7 and 14 days after application (DAA) of the herbicide. The values obtained were analyzed by the F test and the effects of the treatments were compared by the Scott-Knott test at 5% probability. The data obtained from visual injury and Fv/Fmwere also submitted to Pearson's correlation. The correlation between visual injury and Fv/Fmin the V4 and B4 stages is negative and significant for both years of conducting the experiment. The Fv/Fmvariable was not affected by the application of subdoses lower than 3.42 g aeha-1of 2,4-D saline choline in the V4 stage and below 1.71 g aeha-1in the B4 stage of the cotton plant.

Chlorophyll a fluorescence as an indicator of water stress in Calophyllum brasiliense

The objective of this study was to evaluate chlorophyll a fluorescence as a stress indicator in Calophyllum brasiliense Cambess seedlings grown with different concentrations of abscisic acid (ABA) under intermittent water deficit condition: daily irrigation without ABA (I); daily irrigation + 10 μM ABA (I 10); daily irrigation + 100 μM ABA (I 100); suspension of daily irrigation without ABA (SI); suspension of daily irrigation + 10 μM ABA (SI 10) and suspension of daily irrigation + 100 μM ABA (SI 100). The intermittent water deficit reduces water status and impairs the photochemical apparatus functioning and seedling quality. The fluorescence measurements helped identify the stress condition of water deficit in the cultivation of C. brasiliense and the beneficial effect of the application of 10 μM of ABA in minimizing stress and facilitating the recovery of seedlings after re-irrigation, while maintaining the integrity and function of the photosynthetic apparatus.

Effect of eucalyptus proximity and weed presence on soybean grown in a CFI system

The growing demand for food, bioenergy, and forest products requires solutions that encourage socioeconomic development without compromising the sustainability of natural resources. It is in this scenario that the integration strategy has been pointed as an alternative to reconcile conflicts of interest. This study evaluates possible changes in nodulation, photosynthetic efficiency, and yield of soybean grown in a Crop-Forest Integration system with eucalyptus as a tree component. The experiment was conducted in a randomized complete block design with four replications. Treatments were arranged in a 3x5 factorial scheme, corresponding to three sowing conditions (near eucalyptus stands; 3.0 meters away from the stands, in a clean seedbed; and 3.0 m away from the stands, among the vegetation) and five points of distance between soybean and the stands, represented by planting rows, namely: 1 st , 2 nd , 3 rd , 11 th , and 21 st row. We evaluated morphophysiological and productive variables of soy­bean plants. Soybean cultivation near eucalyptus stands does not affect the number and dry matter of soybean nodules, but reduces yield in the first two rows. The presence of weeds in the range between eucalyptus stands and soybean plants impaired the photochemical apparatus and the chlorophyll α fluorescence of soybean crop, decreasing the shoot dry matter accumulation, number and dry matter of nodules, and yield of plants present in the first planting rows.

Using Rapid Chlorophyll Fluorescence Transients to Classify Vitis Genotypes

When a dark-adapted leaf is illuminated with saturating light, a fast polyphasic rise of fluorescence emission (Kautsky effect) is observed. The shape of the curve is dependent on the molecular organization of the photochemical apparatus, which in turn is a function of the interaction between genotype and environment. In this paper, we evaluate the potential of rapid fluorescence transients, aided by machine learning techniques, to classify plant genotypes. We present results of the application of several machine learning algorithms (k-nearest neighbors, decision trees, artificial neural networks, genetic programming) to rapid induction curves recorded in different species and cultivars of vine grown in the same environmental conditions. The phylogenetic relations between the selected Vitis species and Vitis vinifera cultivars were established with molecular markers. Both neural networks (71.8%) and genetic programming (75.3%) presented much higher global classification success rates than k-nearest neighbors (58.5%) or decision trees (51.6%), genetic programming performing slightly better than neural networks. However, compared with a random classifier (success rate = 14%), even the less successful algorithms were good at the task of classifying. The use of rapid fluorescence transients, handled by genetic programming, for rapid preliminary classification of Vitis genotypes is foreseen as feasible.