Sisal bole rot disease is the major phytosanitary problem of Agave plantations in Brazil. The disease is caused by a cryptic species of Aspergillus: A. welwitschiae. To date, the only way to diagnose the disease was to observe external symptoms, visible only when the plant is already compromised, or through the isolation and sequencing of the pathogen, which requires cutting the entire plant for bole tissue sampling. We developed a new primer set based on a unique gene region of A. welwitschiae, which can detect the phytopathogenic strains through PCR directly from sisal leaves. Using the new marker to study the main sisal-producing areas in Brazil, we discovered a troublesome situation. The main producing areas of this crop had a pathogen incidence of 78%–88%. The dispersion index indicates a regular spatial pattern for disease distribution, suggesting that the use of contaminated suckers to establish new fields may be the main disease-spreading mechanism. Altogether, the high incidence of the pathogen, the unavailability of clean plants, the unpredictability of disease progression, and the low investment capacity of farmers reveal the vulnerability of this sector to a potential phytosanitary crisis. By correlating the disease symptomatology with soil nutritional traits, we suggest that higher potassium availability might decrease visual symptoms, while phosphorus may have the opposite effect. Also, we observe a potential cultivar effect, suggesting that common sisal may be more susceptible than hybrid cultivars (especially H400). This new molecular tool is a significant advance for understanding the disease, enabling the implementation of a monitoring program and studies that may lead to pathogen control strategies and changes in the Brazilian production model.

Fábio T. Raya, Gabriel Quintanilha-Peixoto, Adriele B. de Oliveira, Marina P. Marone, Wagner J. V. dos Reis, João Gabriel O. Marques, Rafael L. Almeida, Cezar Augusto T. F. Filho, Oldair D. V. Costa, Rafael V. Ribeiro, Ana Cristina F. Soares, Aristóteles Goés-Neto & Gonçalo A. G. Pereira

Global air temperature is rising and resulting in higher frequency and intensity of extreme climatic events. This scenario threatens food security, requiring measures to mitigate the harmful effects of heat stress on agricultural production. Therefore, our study focused on understanding how phosphorus (P) availability during the reproductive period affects seed weight responses of soybean to terminal heat stress. The experiment was carried out in a complete 3 × 2 factorial design, with varying post-flowering P supply (severe deficiency: 20 μmol P L−1; mild deficiency: 100 μmol P L−1; sufficiency: 500 μmol P L−1) and thermal regimes imposed during the seed filling phase (control: 28.0/18.0 °C; heat stress: 42.0/28.5 °C). Our results revealed that seed weight and yield were unaffected by heat stress in the plants grown under P sufficiency, whereas a detrimental effect of warming on these traits was found in the plants facing post-flowering P deficiency. Sufficient post-flowering P supply alleviated also the harmful effects of heat stress on the integrity of the photosynthetic apparatus, which contributed to improve biomass partitioning to the harvestable organs by extending seed filling duration. Moreover, heat stress disturbed sink metabolism and caused reduction in the concentration of oil and starch solely in the seeds of the plants exposed to P limitation. In conclusion, maintaining adequate post-flowering P supply proves critical in enhancing soybean’s tolerance to terminal heat stress by supporting essential processes involved in effective seed filling. Consequently, implementing precise P nutritional management during the reproductive period of soybean might be a promising approach to improve crop yield stability in challenging environmental conditions.

Matheus D. Laira, Sara A.L. Andrade, Neidiquele M. Silveira, Eduardo C. Machado, Rafael V. Ribeiro & Fernando C.B. Zambrosi

Our aim was to test the hypothesis that root growth of ‘Mandarin’ lime—a drought tolerant citrus rootstock—under water deficit is associated with higher nitric oxide (NO) content in roots. As a reference, ‘Swingle’ citrumelo was compared with ‘Mandarin’ lime, two well-known citrus rootstocks. ‘Valencia’ sweet orange plants grafted on ‘Mandarin’ lime or ‘Swingle’ citrumelo were kept well-hydrated or grown under water withholding. After 14 days of water deficit, root morphology was evaluated, and leaf and root samples were collected for NO analysis. Under low water availability, ‘Mandarin’ lime exhibited higher root NO content and root growth than ‘Swingle’ citrumelo. Indeed, NO seems to modulate not only root biomass accumulation but also root morphology as higher NO was associated with large increase in root length and area. Such findings suggest that root NO content is a relevant marker for early screening of drought-tolerant citrus genotypes. As a novelty, we show that ‘Mandarin’ lime drought tolerance is significantly associated with root NO content.

Neidiquele M. Silveira, Maria Isabel M. de Oliveira, Simone F. da Silva, Marcela T. Miranda, Matheus P. Passos, Eduardo C. Machado & Rafael V. Ribeiro

Secondary sexual dimorphism (SSD) in flowering plants is expressed by sexual differences of characters that are not directly related to gamete production. The leaf C/N ratio, photosynthetic traits or clonal responses have never been studied in relation to SSD in yerba-mate. It was hypothesized that leaf and plant photosynthesis are higher in female than in male individuals because females must supply photoassimilates to compensate for the additional reproductive investments of SSD in biomass. Here, we investigated how two contrasting light environments (monoculture—MO and agroforestry—AFS) and plant genders change leaf and plant photosynthesis, plant architecture, leaf and branch biomass production and C and N investments of two male and two female clones. To model the 3D yerba-mate structure, virtual trees were constructed using measurements of plant morphology using VPlant modelling software. The light-response curves of leaf CO2 assimilation were used to model instantaneous leaf and daily plant photosynthesis. Photosynthetic traits derived from light-response curves did not differ between MO and AFS. Some architectural traits were segregated sexually only in MO, while some physiological ones only in AFS. Leaf photosynthesis was higher in females than in males in AFS over a large part of the diurnal cycle, but SSD was not expressed in carbon gains at plant or daily scales. Leaf C/N ratio was higher in MO than in AFS, indicating MO as an ecosystem with higher degree of environmental degradation. Female clones had leaves with lower C/N ratio than males in both systems, relating to higher leaf photosynthesis on an area basis in females. SSD expressed in leaf photosynthesis over a large part of the diurnal cycle in AFS was not observed in carbon gains at plant or daily scales, indicating that the integration of physiology and architecture equalized the gender specificities. The insensitivity of photosynthetic traits derived from light-response curves indicated acclimation of yerba-mate leaves to a wide range of incoming light.

Miroslava Rakocevic, Eunice R. Batista, Fabio T. Matsunaga, Ivar Wendling, Gustavo G. Marcheafave, Roy E. Bruns, Ieda S. Scarminio & Rafael V. Ribeiro

Agaves have been a valuable resource in dryland areas for centuries, providing fibers (sisal), food, and beverages. However, the advent of synthetic fibers has led to a decrease in research on Agave, resulting in the cessation of breeding programs in Brazil. With the rise of climate change, there is renewed interest in Agave for its potential as a biofuel feedstock in semiarid regions. Since 2016, we have been collecting Agave accessions throughout the country and retrieving what is left of Brazil’s original breeding program to establish a new germplasm bank. Here, we evaluated 21 of those accessions growing in the field. We used molecular markers and morphophysiological traits to characterize the plants. Based on the Mayahuelin molecular marker, we were able to reconstruct a phylogeny for the Brazilian accessions. The morphophysiological traits explained 34.6% of the phenotypic variation in the dataset, with physiological traits such as leaf water content, effective quantum efficiency of photosystem II (ΦPSII), and specific leaf mass (SLM) as the most significant traits. Specifically, we evaluated nine Agave species and found that the physiological traits, rather than the morphological ones, were the most significant. Leaf water content was negatively correlated with specific leaf mass, which could be used as a marker for selecting cultivars with higher biomass accumulation. Interestingly, ΦPSII and chlorophyll content were negatively correlated, suggesting photochemical adaptations throughout the rosette. Molecular and phenotypic data suggest that A. amaniensis, which is frequently considered a synonym of A. sisalana, is effectively another species. Overall, this study provides valuable information on the physiological traits of Brazilian Agave accessions and is a starting point for selecting more productive and climate-resilient cultivars for biorenewables production.

Fabio T. Raya, Lucas M. de Carvalho, Juliana José, Larissa P. da Cruz, Rafael L. Almeida, Heliur Alves de A. Delevatti, Neidiquele M. Silveira, Simone F. da Silva, Maria D. Pissolato, Adriele B. de Oliveira, Wagner J. V. dos Reis, Luís Guilherme F. de Abreu, Jesús Gutiérrez, Marcelo F. Carazzolle, Ana Cristina F. Soares, Jorge N. Sotelo, Rafael V. Ribeiro & Gonçalo A. G. Pereira

Intervessel pits are considered to function as valves that avoid embolism spreading and optimize efficient transport of xylem sap across neighbouring vessels. Hydraulic transport between vessels would therefore follow a safety-efficiency trade-off, which is directly related to the total intervessel pit area (Ap), inversely related to the pit membrane thickness (TPM) and driven by a pressure difference. To test this hypothesis, we modelled the relative transport rate of gas (ka) and water (Q) at the intervessel pit level for 23 angiosperm species and correlated these parameters with the water potential at which 50% of embolism occurs (Ψ50). We also measured ka for 10 species using pneumatic measurements. The pressure difference across adjacent vessels and estimated values of ka and Q were related to Ψ50, following a convex safety-efficiency trade-off based on modelled and experimental data. Minor changes in TPM and Ap exponentially affected the pressure difference and flow, respectively. Our results provide clear evidence that a xylem safety-efficiency trade-off is not linear, but convex due to flow across intervessel pit membranes, which represent mesoporous media within microporous conduits. Moreover, the convex nature of long-distance xylem transport may contribute to an adjustable fluid balance of plants, depending on environmental conditions.

Luciano Pereira, Lucian Kaack, Xinyi Guan, Luciano de Melo Silva, Marcela T. Miranda, Gabriel S. Pires, Rafael V. Ribeiro, H. Jochen Schenk & Steven Jansen

Plants with C4 metabolism normally have higher photosynthetic rates than C3 ones. As a result, several of the most productive species known are NADP-ME C4 grasses, such as sugarcane and maize. However, the advantages of the C4 cycle are most evident under high light as the CO2 concentrating mechanism comes at the expense of additional ATP. Recent works have suggested a negative impact of shading across NADP-ME C4 grasses, causing a downregulation of maximal quantum efficiency of CO2 assimilation (ϕCO2,max). The mechanisms behind the loss in photosynthetic efficiency and whether these results apply for other C4 crops species and within germplasm of a species remain unclear. We analysed the photosynthetic acclimation to shade in four sugarcane genotypes with contrasting yield. To find out whether the effects of leaf history, i.e., shading a leaf developed under full sunlight and exposed later on to shade differ from a leaf fully developed under shading, these two types of leaves were evaluated. Shaded sugarcane plants showed decreased CO2 assimilation efficiency compared to plants grown under full sunlight. Based on the fluorescence measurements, it seems that this reduction coincided with a more reduced QA redox state, which could point to a metabolic limitation downstream of the light-dependent reactions. The results were similar for all genotypes and were observed regardless of whether leaves developed under shade or under full sunlight conditions and exposed subsequently to shade, suggesting that light is the main factor affecting photosynthetic efficiency. This study reinforces the notion that this negative impact of shade could reflect a common bottleneck across NADP-ME C4 grasses.

Cristina R.G. Sales, Rafael V. Ribeiro, Paulo E.R. Marchiori, Johannes Kromdijk & Eduardo C. Machado

Chen et al. (2021) reported discrepancies between pneumatic and other methods for measuring embolism vulnerability in plant xylem tissue, leading them to caution against using the pneumatic method. We show that this discrepancy arises from faulty implementation: failing to measure air discharge to sufficiently negative water potentials, they under-estimated maximum air discharge (ADmax), and hence embolism resistance. Embolism vulnerability methods identify how dehydrated a stem must become (in water potential, P50) to cause a 50% loss in xylem conductivity. Pneumatic methods require measurements to water potentials roughly twice as dehydrated as P50. Yet Chen et al. often stopped at magnitudes even less than what other methods showed P50 to be, making it mathematically impossible for their pneumatic implementation to measure true P50. Our simulations confirmed that premature stopping causes large errors in derived P50, accounting for reported discrepancies. Further, literature studies show consistent agreement between pneumatic and other methods. Thus, Chen et al.’s pneumatic results are invalid, and should not be taken to undermine confidence in pneumatic measurements. We recommend best practices, including the ‘Pneumatron’ for automated measurements, that prevent the errors of Chen et al. and make pneumatic measurements of embolism vulnerability that are fast, replicable, and accurate.

Mauro Brum, Luciano Pereira, Rafael V. Ribeiro, Steven Jansen, Paulo R. L. Bittencourt, Rafael S. Oliveira & Scott R. Saleska

Increasing the efficiency of photosynthesis in sugarcane canopies is the key for improving crop yield. Herein, we evaluated the photosynthetic performance along the canopy of ten sugarcane cultivars and three Saccharum species. Canopy morphological traits were evaluated, and leaf gas exchange was measured in the first (sun-exposed, +1) and the fourth (shaded, +4) fully expanded leaves and under low- and high-light conditions. Similar photosynthetic capacity was found in leaves +1 and +4 under high light in genotypes with a high leaf area index and a high fraction of the sky blocked by the foliage (> 85%). Interestingly, such canopy characteristics cause low light availability to leaves +4, suggesting the photosynthetic acclimation of these leaves to self-shading in some genotypes. We highlight IACCTC06-8126 and CTC4 as those genotypes with higher canopy photosynthetic capacity, presenting high leaf area, high photosynthetic rates in sun-exposed leaves, and high responsiveness of shaded leaves to increasing light availability.

Rafael L. Almeida, Neidiquele M. Silveira, Marcela T. Miranda, Vinícius S. Pacheco, Larissa P. Cruz, Mauro A. Xavier, Eduardo C. Machado & Rafael V. Ribeiro

Drought is considered as the major environmental stress affecting coffee production, and high phosphorus (P) supply may alleviate the drought effects on crop metabolism. Here, we hypothesized that high P supply would mitigate the impacts of drought on Arabica coffee physiology, morphology, and biomass accumulation. Potted Arabica coffee plants were grown under two P levels: the recommended P fertilization (P), and twice the recommended fertilization (+P), and two water regimes: well-watered and water withholding for 32 days. Leaf, stem, and root P concentrations were increased under +P, with plants showing higher photosynthesis and growth than the ones receiving the recommended P dose. Higher plant growth under high P supply seems to upregulate leaf photosynthesis through the source–sink relationship. Under the water deficit, the reduction of leaf photosynthesis, stomatal conductance, transpiration, water use efficiency, carboxylation efficiency, chlorophyll content, number of plagiotropic branches, plant leaf area, and vegetative biomass production was similar comparing plants fertilized with the recommended P to those supplied with +P. However, Arabica coffee trees under high P supply and water deficit presented morphological and physiological traits similar to plants under well-watered and recommended P fertilization.

Miroslava Rakocevic, Paulo Eduardo R. Marchiori, Fernando C. B. Zambrosi, Eduardo C. Machado, Aline de Holanda N. Maia & Rafael V. Ribeiro

Water stress is a major environmental factor affecting Citrus spp. and Rangpur lime is a drought-tolerant rootstock used to enhance orange yield in rainfed orchards. Here, we combined morpho-physiological analyses with metabolic profiling of roots and leaves of Valencia orange scions grafted onto Rangpur lime, Swingle citrumelo or Sunki mandarin rootstocks under water deficit. Our aim was to present a comprehensive spatio-temporal evaluation of citrus responses to drought and highlight the metabolic adjustments associated with drought tolerance induced by Rangpur lime. Plant responses were evaluated during the initial phase of reduction in water availability, when water deficit was maximum and also after rehydration. Fifty-eight primary metabolites were modulated by water deficit, mainly amino acids, organic acids and sugars. Metabolic changes indicated adjustments related to osmotic, energetic and redox processes under low water availability, which were dependent on rootstock and varied between roots and leaves and along the experimental period. Rangpur lime prioritized root growth in the initial phase of water deficit, which was linked to less sugar accumulation, changes in nucleotide metabolism and downregulation in Shikimic acid pathway. After rehydration, the resume of shoot growth was associated with high accumulation of arginine and asparagine. The better performance of Rangpur lime seems to be associated with its high sensitivity of roots to changes in water availability and possible signaling compounds, such as auxin and nitric oxide, have been suggested.

Simone F. Silva, Marcela T. Miranda, Camila P. Cunha, Adilson P. Domingues-Jr, Juliana A. Aricetti, Camila Caldana, Eduardo C. Machado & Rafael V. Ribeiro

Morpho-physiological strategies to deal with water deficit vary among citrus species and the chemical signaling through ABA and anatomical, hydraulic, and physiological traits were evaluated in saplings of Rangpur lime, Swingle citrumelo and Valencia sweet orange. Trunk and roots of Swingle citrumelo presented lower vessel diameter and higher vessel frequency as compared to the other species. However, relative water content at the turgor loss point (RWCTLP), the osmotic potential at full turgor (Ψ0), the osmotic potential at the turgor loss point (ΨTLP), bulk modulus of elasticity (ε) and the xylem water potential when hydraulic conductivity is reduced by 50% (Ψ50) and 88% (Ψ88) indicated similar hydraulic traits among citrus species, with Rangpur lime showing the highest hydraulic safety margin. Roots of Rangpur lime and Swingle citrumelo were more water conductive than ones of Valencia sweet orange, which was linked to higher stomatal conductance. Chemical signaling through ABA prevented shoot dehydration in Rangpur lime under water deficit, with this species showing a more conservative stomatal behavior, sensing, and responding rapidly to low soil moisture. Taken together, our results suggest that Rangpur lime – the drought tolerant species – has an improved control of leaf water status due to chemical signaling and effective stomatal regulation for reducing water loss as well as decreased root hydraulic conductivity for saving water resources under limiting conditions.

Marcela T. Miranda, Erick Espinoza-Núnez, Simone F. Silva, Luciano Pereira, Adriana H. Hayashi, Raquel L. Boscariol-Camargo, Sergio A. Carvalho, Eduardo C. Machado e Rafael V. Ribeiro

Some studies have shown that long photoperiods result in high biomass accumulation, others have reported damage caused by the lack of darkness. Since indoor production depends on a favorable cost-benefit ratio, it is essential to evaluate the biomass produced per energy consumed by LEDs. We expected that photosynthesis and energetic efficiency of biomass production would decrease under long photoperiods due to the circadian cycle. Lettuce (Lactuca sativa L.) plants were grown in nutrient solution under different photoperiod regimes. In each photoperiod (12, 14, 16, 18, 20, 22, and 24 h), plants were germinated and harvested after 21 days. Leaf gas exchange was monitored over 24 h, whereas plant growth and energy consumed by LEDs were evaluated after 20 days of growth in each regime. Although the maximum photosynthetic rates have not changed when varying photoperiod, the daily-integrated CO2 assimilation on leaf area basis was higher at 20, 22, and 24 h. Biomass accumulation, leaf number, and leaf area increased linearly between 12 and 18 h of photoperiod. In regimes longer than 18 h, extending the photoperiod did not increase the number of leaves and dry mass accumulation and decreased leaf area and fresh mass. The highest energetic efficiency of biomass production was noticed between 12 and 18 h, while the lowest one was found at 22 and 24 h of photoperiod. The best photoperiod for growing lettuce was 18 h, as it was the shortest photoperiod that led to the highest plant growth while maintaining high energetic efficiency of biomass production.

Luciano M. Silva, Larissa P. Cruz, Vinícius S. Pacheco, Eduardo C. Machado, Luis Felipe V. Purquerio & Rafael V. Ribeiro

Aquaporins are water channel proteins that facilitate water transport through the transcellular pathway, a route with high resistance due to lipid bilayer membranes. Aquaporins occur as multiple isoforms and plasma membrane aquaporins (PIPs) are known to modulate plant responses to abiotic stress such as drought. Previous studies have reported changes in PIPs expression in roots of Citrus plants under abiotic stresses; however, such changes are limited to grafted citrus trees with plant responses to environmental stresses being driven by two species. Therefore, the ability of a given Citrus species—i.e., non-grafted Citrus saplings—in modulating aquaporin expression under water deficit remains unknown. This study aimed to evaluate how water deficit changes aquaporin expression (PIP1; PIP2.1; and PIP2.5) and leaf gas exchange of saplings of three Citrus species: ‘Mandarin’ lime, ‘Swingle’ citrumelo and ‘Valencia’ sweet orange. Root aquaporin expression did not vary under water deficit or among species, but the predawn leaf water potential of ‘Valencia’ sweet orange was reduced due to water deficit. Decreases in stomatal conductance were found in all species under water deficit, which were associated with reduced PIP2.1 expression in leaves. However, ‘Mandarin’ lime exhibited the largest reduction in stomatal conductance and significant gene repression of not only PIP2.1 but also PIP2.5 in leaves under water deficit. ‘Mandarin’ lime is known as a drought tolerant rootstock widely used in citriculture and our data suggest that this rootstock presents a fast-response mechanism against drought based on stomatal closure associated with downregulation of PIP2.1 and PIP2.5 in leaves.

Marcela T. Miranda, Erick Espinoza-Núñez, Simone F. Silva, Raquel L. Boscariol-Camargo, Eduardo C. Machado e Rafael V. Ribeiro

The classical method to estimate the light conversion efficiency (εc) gives a single value for the whole crop cycle (εco) but does not reveal any variation along the growing season. We proposed the segmented approach to uncover such variations along sugarcane (Saccharum sp. hybrid) growth cycle. Our analyses revealed that longer sampling intervals could overestimate εco and that the segmented light conversion efficiency (εcs) varied between 0.09 and 5.39 g MJ-1 during the crop cycle. The εcs would provide insights on how the environment affects εc and how to increase biomass production through crop management practices.

Larissa P. Cruz, Eduardo C. Machado & Rafael V. Ribeiro

Despite a long research history, we do not fully understand why plants are able to transport xylem sap under negative pressure without constant failure. Microbubble formation via direct gas entry is assumed to cause hydraulic failure, while the concentration of gas dissolved in xylem sap is traditionally supposed to be constant, following Henry’s law. Here, the concentration of soluble gas in xylem sap was estimated in vivo using well-watered Citrus plants under varying levels of air temperature and photoperiodic exposure, and compared to modelled data. The gas concentration in xylem sap showed non-equilibrium curves, with a minimum over- or undersaturation of 5% compared to gas solubility based on Henry’s law. A similar diurnal pattern was obtained from the gas concentration in the cut-open conduits and discharge tube, and oversolubility was strongly associated with decreasing xylem water potentials during transpiration. Although our model did not explain the daily changes in gas solubility for an anisobaric situation, oversolubility characterises nanoconfined liquids, such as sap inside cell walls. Thus, plants are able to transport sap under negative pressure with relatively high amounts of dissolved gas, providing them with a buffering capacity to prevent hydraulic failure, despite diurnal changes in pressure and temperature. Despite a long research history, we do not fully understand why plants are able to transport xylem sap under negative pressure without constant failure. Microbubble formation via direct gas entry is assumed to cause hydraulic failure, while the concentration of gas dissolved in xylem sap is traditionally supposed to be constant, following Henry’s law. Here, the concentration of soluble gas in xylem sap was estimated in vivo using well-watered Citrus plants under varying levels of air temperature and photoperiodic exposure, and compared to modelled data. The gas concentration in xylem sap showed non-equilibrium curves, with a minimum over- or undersaturation of 5% compared to gas solubility based on Henry’s law. A similar diurnal pattern was obtained from the gas concentration in the cut-open conduits and discharge tube, and oversolubility was strongly associated with decreasing xylem water potentials during transpiration. Although our model did not explain the daily changes in gas solubility for an anisobaric situation, oversolubility characterises nanoconfined liquids, such as sap inside cell walls. Thus, plants are able to transport sap under negative pressure with relatively high amounts of dissolved gas, providing them with a buffering capacity to prevent hydraulic failure, despite diurnal changes in pressure and temperature. Despite a long research history, we do not fully understand why plants are able to transport xylem sap under negative pressure without constant failure. Microbubble formation via direct gas entry is assumed to cause hydraulic failure, while the concentration of gas dissolved in xylem sap is traditionally supposed to be constant, following Henry’s law. Here, the concentration of soluble gas in xylem sap was estimated in vivo using well-watered Citrus plants under varying levels of air temperature and photoperiodic exposure, and compared to modelled data. The gas concentration in xylem sap showed non-equilibrium curves, with a minimum over- or undersaturation of 5% compared to gas solubility based on Henry’s law. A similar diurnal pattern was obtained from the gas concentration in the cut-open conduits and discharge tube, and oversolubility was strongly associated with decreasing xylem water potentials during transpiration. Although our model did not explain the daily changes in gas solubility for an anisobaric situation, oversolubility characterises nanoconfined liquids, such as sap inside cell walls. Thus, plants are able to transport sap under negative pressure with relatively high amounts of dissolved gas, providing them with a buffering capacity to prevent hydraulic failure, despite diurnal changes in pressure and temperature. Despite a long research history, we do not fully understand why plants are able to transport xylem sap under negative pressure without constant failure. Microbubble formation via direct gas entry is assumed to cause hydraulic failure, while the concentration of gas dissolved in xylem sap is traditionally supposed to be constant, following Henry’s law. Here, the concentration of soluble gas in xylem sap was estimated in vivo using well-watered Citrus plants under varying levels of air temperature and photoperiodic exposure, and compared to modelled data. The gas concentration in xylem sap showed non-equilibrium curves, with a minimum over- or undersaturation of 5% compared to gas solubility based on Henry’s law. A similar diurnal pattern was obtained from the gas concentration in the cut-open conduits and discharge tube, and oversolubility was strongly associated with decreasing xylem water potentials during transpiration. Although our model did not explain the daily changes in gas solubility for an anisobaric situation, oversolubility characterises nanoconfined liquids, such as sap inside cell walls. Thus, plants are able to transport sap under negative pressure with relatively high amounts of dissolved gas, providing them with a buffering capacity to prevent hydraulic failure, despite diurnal changes in pressure and temperature. Despite a long research history, we do not fully understand why plants are able to transport xylem sap under negative pressure without constant failure. Microbubble formation via direct gas entry is assumed to cause hydraulic failure, while the concentration of gas dissolved in xylem sap is traditionally supposed to be constant, following Henry’s law. Here, the concentration of soluble gas in xylem sap was estimated in vivo using well-watered Citrus plants under varying levels of air temperature and photoperiodic exposure, and compared to modelled data. The gas concentration in xylem sap showed non-equilibrium curves, with a minimum over- or undersaturation of 5% compared to gas solubility based on Henry’s law. A similar diurnal pattern was obtained from the gas concentration in the cut-open conduits and discharge tube, and oversolubility was strongly associated with decreasing xylem water potentials during transpiration. Although our model did not explain the daily changes in gas solubility for an anisobaric situation, oversolubility characterises nanoconfined liquids, such as sap inside cell walls. Thus, plants are able to transport sap under negative pressure with relatively high amounts of dissolved gas, providing them with a buffering capacity to prevent hydraulic failure, despite diurnal changes in pressure and temperature.

Luciano Pereira, Steven Jansen, Marcela T. Miranda, Vinícius S. Pacheco, Lucian Kaack, Gabriel S. Pires, Xinyi Guan, Juliana L.S. Mayer, Eduardo C. Machado, H. Jochen Schenk & Rafael V. Ribeiro

Using the same production system as sugarcane, energy cane (Saccharum spp. hybrid, as sugarcane) can produce more biomass, which can be associated with its high tillering and a vigorous root system with rhizomes. These traits enable energy cane to capture natural resources efficiently and convert more energy into biomass than sugarcane. Our aim is to understand the morpho-physiological bases of biomass production by energy cane. We evaluated the efficiencies of light interception and light conversion into biomass in a field experiment, measuring morphological and physiological traits of energy canes (Vertix 2 and Vertix 3) and sugarcane (IACSP95-5000). When plants have a low leaf area index (< 4 m2 m−2), the high tillering of energy cane increases the efficiency of light interception. High leaf insertion angles also favored light interception by canopies with high tiller density, as one found in Vertix 3. However, high tiller density likely caused excessive self-shading in energy cane canopy and then energy canes exhibited similar or lower photosynthetic activity than sugarcane, depending on environmental conditions. All three genotypes faced severe water stress during the ratoon cycle, but energy cane was less sensitive when considering light conversion efficiency and biomass yield.

Larissa P. Cruz, Vinícius S. Pacheco, Luciano M. Silva, Rafael L. Almeida, Marcela T. Miranda, Maria D. Pissolato, Eduardo C. Machado & Rafael V. Ribeiro

Sugarcane (Saccharum spp.) is one of the main alternatives for the bioenergy sector due to its great potential for phytomass production, being the photosynthesis a key process related to conversion of the intercepted sunlight energy into phytomass. The aim of this study was to investigate the photosynthesis of nine sugarcane varieties originated from crosses between 1948 and 2006, as well as the species Saccharum officinarum, S. spontaneum and S. robustum. In plants grown inside a growth chamber, photosynthetic response curves to increasing air CO2 concentration were performed and key photosynthetic traits and their heritabilities were estimated. Fourteen physiological traits explained ~ 95% of the variation observed. Significant differences were found in leaf CO2 assimilation at air CO2 concentration of 1500 (A1500) and 400 (A400) μmol mol−1 among sugarcane genotypes, with S. spontaneum, IAC87-3396 and RB83-5486 presenting the highest photosynthetic rates. Sugarcane photosynthesis was strongly correlated with effective quantum yield of photosystem II (r = 0.93), non-photochemical quenching (r = − 0.74), stomatal conductance (r = 0.87), in vivo maximum carboxylation rates of PEPC (Vpmax, r = 0.83) and Rubisco (Vcmax, r = 0.91) and leaf nitrogen content (r = 0.83). The heritability varied from 0.97 (leaf CO2 assimilation) to 0.84 (leaf area). The A1500:A400 ratio higher than one for all genotypes indicates that Rubisco carboxylation sites are not saturated by CO2 and a non-efficient CO2 concentration mechanism. This study revealed a significant natural genotypic variation in sugarcane photosynthesis with high heritability of important traits, suggesting the possibility of breeding for increased photosynthetic activity.

Rafael L. Almeida, Neidiquele M. Silveira, Vinícius S. Pacheco, Mauro A. Xavier, Rafael V. Ribeiro & Eduardo C. Machado.

The combination of nitric oxide (NO) donors with nanomaterials for agricultural purposes is a promising approach. The encapsulation of NO donors emerged as a strategy for protecting these molecules from rapid degradation, besides allowing more controlled release. This study aimed to test the hypothesis that encapsulated NO donors attenuate oxidative stress and then enhance physiological recovery of sugarcane plants after water deficit. Well-hydrated sugarcane plants (control) were compared to plants subjected to water deficit and previously sprayed with water (WD) or encapsulated NO donors (100 μM): S-nitroso-mercaptosuccinic acid (SN-MSA); S-nitrosoglutathione (GSNO); S-nitroso-N-acetylcysteine (SNAC); or sodium nitroprusside (SNP). Our data indicated that SNAC spraying partially attenuated the negative impact of WD on the photosynthetic rate, maintained water use efficiency similar to control plants, and promoted growth under stressful conditions. In addition, spraying of encapsulated SNAC and GSNO improved sugarcane photosynthesis during the recovery period. Contrarily, SNP spraying was not effective in mitigating water deficit effects on sugarcane plants, which presented oxidative damage after rehydration. Overall, leaf spraying with SNAC or GSNO is an alternative to improve the physiological performance of sugarcane plants after water deficit, which would favor plant growth and crop yield due to a rapid recovery of photosynthesis.

Neidiquele M. Silveira, Paula J. C. Prataviera, Joana C. Pieretti, Amedea B. Seabra, Rafael L. Almeida, Eduardo C. Machado & Rafael V. Ribeiro

The root system is essential for sugarcane regrowth and the vigor of ratoon cycles as it represents the unique source of carbon skeletons and energy for the initial plant development. However, root system dynamics after shoot harvesting and its role in sugarcane regrowth remains poorly known. Here, it was hypothesized that sugarcane plants with small volume of root system will accumulate less biomass after shoot harvesting than plants with larger volume and that such regrowth is dependent on root reserves. In sugarcane plants grown in nutrient solution, shoots were cut, and two root treatments were established: reference plants with the entire root system (100%); and plants with half of the root system (50%), randomly removing half of root system. After 37 days of shoot harvesting, plants with the entire root system showed higher shoot, root and total dry mass, root length, root diameter, root area and root volume, when compared with those with 50% of the root system. Sugarcane plants with the entire root system had higher root content of starch, soluble sugar and nonstructural carbohydrates as compared to plants with 50% of the root system. A significant positive correlation was found between the variation of shoot dry mass and the variation of root nonstructural carbohydrates. Interestingly, this data revealed a disproportionate effect of root system size on sugarcane regrowth, with plants with the entire root system accumulating almost three times more biomass than plants with half of the root system during regrowth.

Maria D. Pissolato, Larissa P. Cruz, Neidiquele M. Silveira, Eduardo C. Machado & Rafael V. Ribeiro

The role of bundle sheath conductance (gbs) in sustaining sugarcane photosynthesis under nitrogen deficiency was investigated. Sugarcane was grown under different levels of nitrogen supply and gbs was estimated using simultaneous measurements of leaf gas exchange and chlorophyll fluorescence at 21% or 2% [O2] and varying air [CO2] and light intensity. Maximum rates of PEPC carboxylation, Rubisco carboxylation, and ATP production increased with an increase in leaf nitrogen concentration (LNC) from 1 to 3 g m−2. Low nitrogen supply reduced Rubisco and PEPC abundancies, the quantum efficiency of CO2 assimilation and gbs. Because of reduced gbs, low photosynthetic rates were not associated with increased leakiness under nitrogen deficiency. In fact, low nitrogen supply increased bundle sheath cell wall thickness, probably accounting for low gbs and increased estimates of [CO2] at Rubisco sites. Effects of nitrogen on expression of ShPIP2;1 and ShPIP1;2 aquaporins did not explain changes in gbs. Our data revealed that reduced Rubisco carboxylation was the main factor causing low sugarcane photosynthesis at low nitrogen supply, in contrast to the previous report on the importance of an impaired CO2 concentration mechanism under N deficiency. Our findings suggest higher investment of nitrogen into Rubisco protein would favour photosynthesis and plant performance under low nitrogen availability.

Vanessa R. Tofanello, Larissa M. Andrade, Denisele N. A. Flores-Borges, Eduardo Kiyota, Juliana L. S. Mayer, Silvana Creste, Eduardo C. Machado, Xinyou Yin, Paul C. Struik & Rafael V. Ribeiro

The Pneumatron device measures gas diffusion kinetics in the xylem of plants. The device provides an easy, low-cost, and powerful tool for research on plant water relations and gas exchange. Here, we describe in detail how to construct and operate this device to estimate embolism resistance of angiosperm xylem, and how to analyse pneumatic data. Simple and more elaborated ways of constructing a Pneumatron are shown, either using wires, a breadboard, or a printed circuit board. The instrument is based on an open-source hardware and software system, which allows users to operate it in an automated or semi-automated way. A step-by-step manual and a troubleshooting section are provided. An excel spreadsheet and an R-script are also presented for fast and easy data analysis. This manual aims at helping users to avoid common mistakes, such as unstable measurements of the minimum and maximum amount of gas discharged from xylem tissue, which has major consequences for estimating embolism resistance. Major advantages of the Pneumatron device include its automated and accurate measurements of gas diffusion rates, including highly precise measurements of the gas volume in intact, embolised conduits. It is currently unclear if the method can also be applied to woody monocots, gymnosperm species that possess torus-margo pit membranes, or to herbaceous species.

Christophe L. Trabi, Luciano Pereira, Xinyi Guan, Marcela T. Miranda, Paulo R. L. Bittencourt, Rafael S. Oliveira, Rafael V. Ribeiro & Steven Jansen

Arginine (Arg) metabolism is associated with many cellular and developmental processes in plants and proline, nitric oxide (NO) and polyamines (PAs) have a wide range of physiological functions in plants, including increased tolerance to environmental stresses. This study aimed to test the hypothesis that Arg spraying would stimulate the synthesis of proline, NO and PAs, reducing the oxidative damage caused by water deficit (WD) and increasing drought tolerance of sugarcane plants. Sugarcane plants were sprayed with water or Arg 1 mM, and subjected to WD by gradual addition of polyethylene glycol (PEG-8000) to the nutrient solution. As references, sugarcane plants were grown in nutrient solution without PEG-8000 and sprayed or not with Arg. Our data indicate that exogenous Arg supply improved leaf gas exchange during water deficit and enhanced the root antioxidative protection of sugarcane plants during the recovery period. Arg supply prevented the proline accumulation induced by water deficit and then the main pathway for proline synthesis is likely through glutamate instead of arginine. Although Arg is a substrate for NO and PAs production, supplying Arg had only slight effects in both NO and PAs levels. The spraying of amino acids capable of reducing the harmful effects of drought, such as Arg, can be an alternative to improve crop growth under field conditions.

Neidiquele M. Silveira, Rafael V. Ribeiro, Sabrina F. N. de Morais, Sarah C. R. de Souza, Simone F. da Silva, Amedea B. Seabra, John T. Hancock & Eduardo C. Machado

Stability is a key trait for plant growth and development in a changing environment, involving homeostasis and resilience. While homeostasis refers to the maintenance of the internal structural and functional plant integrity, resilience is associated with the plant ability in returning to the initial conditions after a given disturbance. Such concepts are especially relevant for perennial and semi-perennial plants facing seasonal and frequent stress conditions. Although plant memory is closely associated with plant performance under recurrent stresses, to date, there is no study evaluating how stress memory is linked to stability under varying water conditions. Herein, we evaluated the association between drought stability and memory in sugarcane plants and proposed a new stability index to evaluate plant memory. Two datasets were analyzed, the first deals with leaf gas exchange and photochemistry of sugarcane plants grown in nutrient solution and exposed to one, two or three water deficit cycles. The second takes into account the physiological performance of sugarcane propagules obtained by vegetative propagation from plants that faced drought. To quantify sugarcane stability, we estimated the drought impact, the disturbance rate (DR), drought perturbation, and recovery rate (RR) for plants from both datasets. Drought memory – given by improved performance after previous stress events or when origin material faced drought – was detected in both datasets, changing either DR or RR. Based on these indices, we proposed the overall stability (OSt), defined as the ratio between RR and DR. While DR is associated to plant homeostasis, RR is a measure of plant resilience. Sugarcane plants exposed to three cycles of water deficit or those propagules originated from stressed plants presented the highest OSt values, showing higher RR and/or lower DR when compared to well-watered plants or to propagules from well-watered plants. Regarding the physiological traits evaluated, leaf CO2 assimilation and stomatal conductance were the most consistent variables in revealing drought stability and memory. Concluding, OSt revealed consistently patterns of response associated with plant memory, besides quantifying plant stability under stressful conditions.

Rafael Vasconcelos Ribeiro, Karine A. Vitti, Fernanda Castro Correia Marcos, Gustavo M. Souza, Maria Dolores Pissolato, Luiz Fernando R. Almeida & Eduardo C. Machado

Carbon allocation between source and sink organs determines plant growth and is influenced by environmental conditions. Under water deficit, plant growth is inhibited before photosynthesis and shoot growth tends to be more sensitive than root growth. However, the modulation of source-sink relationship by rootstocks remain unsolved in citrus trees under water deficit. Citrus plants grafted on Rangpur lime are drought tolerant, which may be related to a fine coordination of the source-sink relationship for maintaining root growth. Here, we followed 13C allocation and evaluated physiological responses and growth of Valencia orange trees grafted on three citrus rootstocks (Rangpur lime, Swingle citrumelo and Sunki mandarin) under water deficit. As compared to plants on Swingle and Sunki rootstocks, ones grafted on Rangpur lime showed higher stomatal sensitivity to the initial variation of water availability and less accumulation of non-structural carbohydrates in roots under water deficit. High 13C allocation found in Rangpur lime roots indicates this rootstock has high sink demand associated with high root growth under water deficit. Our data suggest that Rangpur lime rootstock used photoassimilates as sources of energy and carbon skeletons for growing under drought, which is likely related to increases in root respiration. Taken together, our data revealed that carbon supply by leaves and delivery to roots are critical for maintaining root growth and improving drought tolerance, with citrus rootstocks showing differential sink strength under water deficit.

Simone F. da Silva, Marcela T. Miranda, Vladimir E. Costa, Eduardo C. Machado & Rafael V. Ribeiro

Comparisons among methods are essential to validate plant traits measured across studies. However, a rigorous analysis is a complex task that needs to take into account not only the principle of the method and its correct use, but also inherent intraspecific trait variability, something we feel is not fully considered by Sergent et al. (2020). They compared the Bench dehydration, MicroCT, and Pneumatic methods using three long-vesseled species and found divergence among these methods. As a key finding, Sergent and colleagues reported unreliable estimates of Ψ50 for Olea europaea when using the Pneumatic method in a such long-vesseled species. Here, we tested this finding by measuring independently vulnerability curves for O. europaea. Our results reinforce the viability of the Pneumatic method to estimate embolism vulnerability in long-vesseled species, as already found by others. Briefly, we also discuss important procedures when using the Pneumatic method and encourage further experiments, as the only way to know better the limitations of available methods and improve our understanding about plant water relations.

Luciano Pereira, Paulo R. L. Bittencourt, Lucy Rowland, Mauro Brum, Marcela T. Miranda, Vinicius S. Pachecom, Rafael S. Oliveira, Eduardo C. Machado, Steven Jansen & Rafael V. Ribeiro