The water availability at early phenological stages is critical for crop establishment and sugarcane varieties show differential performance under drought. Herein, we evaluated the relative importance of morphological and physiological plasticity of young sugarcane plants grown under water deficit, testing the hypothesis that high phenotypic plasticity is associated with drought tolerance. IACSP95-5000 is a high yielding genotype and IACSP94-2094 has good performance under water limiting environments. Plants were grown in rhizotrons for 35 days under three water availabilities: high (soil water matric potential [Ψm] higher than -20 kPa); intermediate (Ψm reached -65 and -90 kPa at the end of experimental period) and low (Ψm reached values lower than -150 kPa). Our data revealed that morphological and physiological responses of sugarcane to drought are dependent on genotype and intensity of water deficit. In general, IACSP95-5000 showed higher physiological plasticity given by leaf gas exchange and photochemical traits, whereas IACSP94-2094 showed higher morphological plasticity determined by changes in leaf area (LA) and specific LA. As IACSP94-2094 accumulated less biomass than IACSP95-5000 under varying water availability, it is suggested that high morphological plasticity does not always represent an effective advantage to maintain plant growth under water deficit. In addition, our results revealed that sugarcane varieties face water deficit using distinct strategies based on physiological or morphological changes. When the effectiveness of those changes in maintaining plant growth under low water availability is taken into account, our results indicate that the physiological plasticity is more important than the morphological one in young sugarcane plants.

Paulo Eduardo Ribeiro Marchiori, Eduardo C. Machado, Cristina Rodrigues Gabriel Sales, Erick Espinoza-Núñez, José R. Magalhães Filho, Gustavo M. Souza, Regina Célia de Matos Pires& Rafael Vasconcelos Ribeiro

Abscisic acid (ABA) attenuates stomatal conductance (gs) and transpiration (E) in response to drought. Broadly known as ‘Brazilian savanna’, the Cerrado sensu lato is a mosaic of landscapes, including savanna-type vegetation, such as the cerrado sensu stricto (s. str.), and riparian forests occurring along rivers. These habitats share floristic elements, and congeneric species are adapted to grow in these drought- and flood-prone environments. We assessed leaf concentration of ABA and its metabolites, as well as gs, E and leaf water potential (Ψw) in shrubs of Styrax ferrugineus in a cerrado s. str. (savanna species) and in trees of S. pohlii in a riparian forest (forest species), in both the wet and dry seasons. We also quantified 9-cis epoxycarotenoid dioxygenase (NCED) gene expression in leaves, and wood anatomical features in stems. We expected that the forest species would not increase their leaf ABA content during the dry season because of the moist soil from the riparian forest. Regardless of the environment, both species expressed NCED, synthesized ABA, and exhibited reductions in both Ψw and gs in the dry season, confirming these as universal responses to the dry season. The savanna species had more xylem vessels per mm2 and these vessels were narrower than those observed in stems of the forest species, resulting in a low vulnerability to cavitation (lvul) estimated for both species. Our results demonstrate that, despite inhabiting contrasting habitats, these species display similar ecophysiological responses to the dry season and their wood anatomical features may explain their geographical distribution.

Carolina M. S. Silva, Ricardo Harakava, Julia Sonsin-Oliveira, Carmen R. Marcati, Silvia R. Machado, Rafael Vasconcelos Ribeiro& Gustavo Habermann

Asian grapevine rust (Phakopsora euvitis) is a serious disease, which causes severe leaf necrosis and early plant defoliation. These symptoms are unusual for a strict biotrophic pathogen. This work was performed to quantify the effects of P. euvitis on photosynthesis, carbohydrates, and biomass accumulation of grapevine. The reduction in photosynthetic efficiency of the green leaf tissue surrounding the lesions was quantified using the virtual lesion concept (β parameter). Gas exchange and responses of CO2 assimilation to increasing intercellular CO2 concentration were analyzed. Histopathological analyses and quantification of starch were also performed on diseased leaves. Biomass and carbohydrate accumulation were quantified in different organs of diseased and healthy plants. Rust reduced the photosynthetic rate, and β was estimated at 5.78, indicating a large virtual lesion. Mesophyll conductance, maximum rubisco carboxylation rate, and regeneration of ribulose-1,5-bisphosphate dependent on electron transport rate were reduced, causing diffusive and biochemical limitations to photosynthesis. Hypertrophy, chloroplast degeneration of mesophyll cells, and starch accumulation in cells close to lesions were observed. Root carbohydrate concentration was reduced, even at low rust severity. Asian grapevine rust dramatically reduced photosynthesis and altered the dynamics of production and accumulation of carbohydrates, unlike strict biotrophic pathogens. The reduction in carbohydrate reserves in roots would support polyetic damage on grapevine, caused by a polycyclic disease.

Antonio F. Nogueira Júnior, Rafael Vasconcelos Ribeiro, Beatriz Appezzato-da-Glória, Marli K. M. Soares, Júlia B. Rasera & Lilian Amorim

Nitrogen (N) and phosphorus (P) are nutrients that frequently limit plant performance and crop yield. Currently, awareness of the importance of plant-microbe interactions in plant nutrient acquisition and growth promotion persist, particularly under stressful conditions, such as those resulting from P scarcity. The aim of the present study was to evaluate the effects of P starvation on the influence of arbuscular mycorrhiza (AM) symbiosis on N2-fixing capacities, plant growth, nutrient uptake and photosynthetic performance of soybean plants at flowering and grain filling stages. To this end, soybean (Glycine max) plants were nodulated with Bradyrhizobium elkanii and inoculated or not with the AM fungus Glomus macrocarpum. The +AM and −AM plants were grown under low P conditions (50 μM), and a control treatment with −AM plants under sufficient P concentration (500 μM) was also performed (−AM + P). Plants were grown until the beginning of the flowering and another set till the grain filling stage. The results showed that mycorrhization improved soybean plant performance under P scarcity compared with non-AM associated plants under the same conditions. AM positively influenced growth and plant nodulation at both flowering and grain-filling stages, without significant changes in plant P content. AM symbiosis increased nitrogenase activity, P content in nodules and leaf N content, the maximum carboxylation rate of Rubisco and reduced the metabolic limitation of photosynthesis under P starvation, which indicated the AM stimulus to symbiotic N2 fixation (SNF) and photosynthesis. Under these conditions, mycorrhizal symbiosis could not completely meet soybean P demand compared with well-nourished soybean plants, which produced higher plant and nodules biomass. In conclusion, AM association in nodulated soybean plants is likely an important strategy for maintaining SNF functioning, conferring increased plant growth and better N status under P scarcity conditions and significantly attenuating the negative effects of low Pi in nodulated-soybean plants.

Rafaela Gageti Bulgarelli, Fernanda Castro Correia Marcos, Rafael Vasconcelos Ribeiro& Sara Adrián López de Andrade

Exogenous supply of nitric oxide (NO) increases drought tolerance in sugarcane plants. However, little is known about the role of NO produced by plants under water deficit. The aim of this study was to test the hypothesis that drought-tolerance in sugarcane is associated with NO production and metabolism, with the more drought-tolerant genotype presenting higher NO accumulation in plant tissues. The sugarcane genotypes IACSP95-5000 (drought-tolerant) and IACSP97-7065 (drought-sensitive) were submitted to water deficit by adding polyethylene glycol (PEG-8000) in nutrient solution to reduce the osmotic potential to −0.4 MPa. To evaluate short-time responses to water deficit, leaf and root samples were taken after 24 h under water deficit. The drought-tolerant genotype presented higher root extracellular NO content, which was accompanied by higher root nitrate reductase (NR) activity as compared to the drought-sensitive genotype under water deficit. In addition, the drought-tolerant genotype had higher leaf intracellular NO content than the drought-sensitive one. IACSP95-5000 exhibited decreases in root S-nitrosoglutathione reductase (GSNOR) activity under water deficit, suggesting that S-nitrosoglutathione (GSNO) is less degraded and that the drought-tolerant genotype has a higher natural reservoir of NO than the drought-sensitive one. Those differences in intracellular and extracellular NO contents and enzymatic activities were associated with higher leaf hydration in the drought-tolerant genotype as compared to the sensitive one under water deficit.

Neidiquele Maria Silveira, John T. Hancock, Lucas Frungillo, Eleni Siasou, Fernanda Castro Correia Marcos, Ione Salgado, Eduardo Caruso Machado& Rafael Vasconcelos Ribeiro

Sugarcane (Saccharum spp.) is the main raw material for sugar and ethanol production. Among the abiotic stress, drought is the main one that negatively impact sugarcane yield. Although gene expression analysis through quantitative PCR (qPCR) has increased our knowledge about biological processes related to drought, gene network that mediates sugarcane responses to water deficit remains elusive. In such scenario, validation of reference gene is a major requirement for successful analyzes involving qPCR.

Larissa Mara de Andrade, Michael dos Santos Brito, Rafael Fávero Peixoto Junior, Paulo Eduardo Ribeiro Marchiori, Paula Macedo Nóbile, Alexandre Palma Boer Martins, Rafael Vasconcelos Ribeiro& Silvana Creste

Water deficit is a major environmental constraint on crop productivity and performance and nitric oxide (NO) is an important signaling molecule associated with many biochemical and physiological processes in plants under stressful conditions. This study aims to test the hypothesis that leaf spraying of S‐nitrosoglutathione (GSNO), an NO donor, improves the antioxidant defense in both roots and leaves of sugarcane plants under water deficit, with positive consequences for photosynthesis. In addition, the roles of key photosynthetic enzymes ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) in maintaining CO2 assimilation of GSNO‐sprayed plants under water deficit were evaluated. Sugarcane plants were sprayed with water or GSNO 100 μM and subjected to water deficit, by adding polyethylene glycol (PEG‐8000) to the nutrient solution. Sugarcane plants supplied with GSNO presented increases in the activity of antioxidant enzymes such as superoxide dismutase in leaves and catalase in roots, indicating higher antioxidant capacity under water deficit. Such adjustments induced by GSNO were sufficient to prevent oxidative damage in both organs and were associated with better leaf water status. As a consequence, GSNO spraying alleviated the negative impact of water deficit on stomatal conductance and photosynthetic rates, with plants also showing increases in Rubisco activity under water deficit.

Neidiquele Maria Silveira, Fernanda Castro Correia Marcos, Lucas Frungillo, Bárbara Baêsso Moura, Amedea Barozzi Seabra, Ione Salgado, Eduardo C. Machado, John T. Hancock& Rafael Vasconcelos Ribeiro

Although plant physiological responses to drought have been widely studied, the interaction between photoprotection, photorespiration and antioxidant metabolism in water‐stressed plants is scarcely addressed. This study aimed to evaluate the physiological adjustments preserving photosynthesis and growth in two plant species with different tolerance to drought: Jatropha curcas and Ricinus communis. We measured stress indicators, gas exchange, photochemistry of PSII and PSI, antioxidant enzymes, cyclic electron flow and photorespiration. Physiological stress indicators associated with reduction in growth confirmed R. communis as sensitive and J. curcas as tolerant to drought. Drought induced loss of photosynthesis in R. communis, whereas J. curcas maintained higher leaf gas exchange and photochemistry under drought. In addition, J. curcas showed higher dissipation of excess energy and presented higher cyclic electron flow when exposed to drought. Although none of these mechanisms have been triggered in R. communis, this species showed increases in photorespiration. R. communis displayed loss of Rubisco content while the Rubisco relative abundance did not change in J. curcas under drought. Accordingly, the in vivo maximum Rubisco carboxylation rate (Vcmax) and the maximum photosynthetic electron transport rate driving RuBP regeneration (Jmax) were less affected in J. curcas. Both species displayed an efficient antioxidant mechanism by increasing activities of ascorbate peroxidase (APX) and superoxide dismutase (SOD). Overall, we suggest that the modulation of different photoprotective mechanisms is crucial to mitigate the effects caused by excess energy, maintaining photosynthetic apparatus efficiency and promoting the establishment of young plants of these two species under drought.

Milton Costa Lima Neto, J. V. A. Cerqueira, J. R. da Cunha, Rafael Vasconcelos Ribeiro& Joaquim Albenisio Gomes Silveira

The effects of ethephon as a sugarcane ripener are attributed to ethylene. However, the role of this phytohormone at the molecular level is unknown. We performed a transcriptome analysis combined with the evaluation of sucrose metabolism and hormone profiling of sugarcane plants sprayed with ethephon or aminoethoxyvinylglycine (AVG), an ethylene inhibitor, at the onset of ripening. The differential response between ethephon and AVG on sucrose level and sucrose synthase activity in internodes indicates ethylene as a potential regulator of sink strength. The correlation between hormone levels and transcriptional changes suggests ethylene as a trigger of multiple hormone signal cascades, with approximately 18% of differentially expressed genes involved in hormone biosynthesis, metabolism, signalling, and response. A defence response elicited in leaves favoured salicylic acid over the ethylene/jasmonic acid pathway, while the upper internode was prone to respond to ethylene with strong stimuli on ethylene biosynthesis and signalling genes. Besides, ethylene acted synergistically with abscisic acid, another ripening factor, and antagonistically with gibberellin and auxin. We identified potential ethylene target genes and characterized the hormonal status during ripening, providing insights into the action of ethylene at the site of sucrose accumulation. A molecular model of ethylene interplay with other hormones is proposed.

Camila P. Cunha, Guilherme Garcia Roberto, Renato Vicentini, Carolina G. Lembke, Glaucia M. Souza, Rafael Vasconcelos Ribeiro, Eduardo C. Machado, Ana Maria Magalhães de Andrade Lagôa& Marcelo Menossi

Climate forecasts suggest that [CO 2 ] in the atmosphere will continue to increase, stimulated by anthropogenic actions. Artificial facilities are available to study the physiological responses of plants to high air [CO 2 ], such as Free-Air-CO 2 -Enrichment (FACE) systems. The structural and ecophysiological responses to elevated air [CO 2 ] in tree species are contradictory, due to species-dependent responses and relatively short-term experiments. After long-term cultivation (four years) under elevated air [CO 2 ], we studied structural and photosynthetic acclimation of Arabica coffee trees (Coffea Arabica L.), with significant changes in leaf area along the vertical profile, number of metamers, leaf and whole-plant photosynthesis. We evaluated the responses of plant leaf area, total number of metamers, leaf and whole-plant photosynthesis along the plant vertical profile to elevated air [CO 2 ], trying to reveal the acclimation of both plant structure and photosynthesis and its relevance for overall photoassimilate production during the reduced growth period. Coffee plants were grown under two [CO 2 ] conditions since transplantation of coffee seedlings to the field: actual (~390 μL CO 2 L -1 ) and elevated (actual + ~200 μL CO 2 L -1 ). Plants were codified following the VPlants methodology and computational modules of CoffePlant3D software, to obtain coffee mock-ups. The plants were separated in three 50 cm-thick layers in vertical profile. Leaf photosynthetic light response curves were determined under actual and elevated air [CO 2 ]. Under elevated air [CO 2 ]: 1) the tree leaf area was strongly reduced and this was associated with the occurrence of coffee leaf rust disease, significantly diminishing the area of the lowest and the upper plant layers; 2) leaf photosynthesis presented decreases in light compensation point and increases in the light-saturated photosynthetic rate; 3) the leaf scale photosynthesis was increased about three to four folds in the middle and upper plant layers and slightly in the lowest plant layer; and 4) the negative impact of leaf area reduction was mitigated by high whole-plant photosynthesis during the dry tropical winter conditions. The possible response pattern of Arabica coffee plants growth under the complex scenarios of long term elevated air [CO 2 ] integrated structural and functional modifications and mitigated the negative impacts of leaf loss and winter water deficit through the leaf and whole-plant photosynthesis. So, after four years under FACE conditions, Arabica coffee trees are still responsive to elevated air [CO 2 ] at leaf or plant scales.View less

Miroslava Rakocevic, Rémy Ferrandes, Paulo Eduardo Ribeiro Marchiori& Rafael Vasconcelos Ribeiro

Spraying sucrose inhibits photosynthesis by impairing Rubisco activity and stomatal conductance (gs), whereas increasing sink demand by partially darkening the plant stimulates sugarcane photosynthesis. We hypothesized that the stimulatory effect of darkness can offset the inhibitory effect of exogenous sucrose on photosynthesis. Source-sink relationship was perturbed in two sugarcane cultivars by imposing partial darkness, spraying a sucrose solution (50 mM) and their combination. Five days after the onset of the treatments, the maximum Rubisco carboxylation rate (Vcmax) and the initial slope of A-Ci curve (k) were estimated by measuring leaf gas exchange and chlorophyll fluorescence. Photosynthesis was inhibited by sucrose spraying in both genotypes, through decreases in Vcmax, k, gs and ATP production driven by electron transport (Jatp). Photosynthesis of plants subjected to the combination of partial darkness and sucrose spraying was similar to photosynthesis of reference plants for both genotypes. Significant increases in Vcmax, gs and Jatp and marginal increases in k were noticed when combining partial darkness and sucrose spraying compared with sucrose spraying alone. Our data also revealed that increases in sink strength due to partial darkness offset the inhibition of sugarcane photosynthesis caused by sucrose spraying, enhancing the knowledge on endogenous regulation of sugarcane photosynthesis through the source-sink relationship.

Rafael Vasconcelos Ribeiro, Eduardo C. Machado, José R. Magalhães Filho, Ana Karla Moreira Lobo, Márcio O. Martins, Joaquim Albenisio Gomes Silveira, Xinyou Yin & Paul C. Struik

Sugarcane is generally cultivated in low fertility acid soils that are prone to the occurrence of manganese (Mn) toxicity. However, the use of genotypes more tolerant to such limiting condition could enhance plant performance in poor soils. Therefore, the aims of this study were to add insights into the mechanisms driving sugarcane adaptation to Mn stress by testing the hypothesis that genotypes with higher tolerance maintain improved ultrastructure of leaf cell organelles (i.e., chloroplast and nucleus) and photosynthetic capacity under high Mn concentrations. Accordingly, six sugarcane varieties were grown in sand and fertigated with two Mn concentrations (control = 10 μM; and toxicity = 500 μM). After growing for 110 days under both conditions, the plants were harvested to estimate dry mass production and tissue Mn concentrations. Leaf gas exchange and chlorophyll fluorescence were assessed in mature leaves that were further evaluated for antioxidant metabolism and cell organelle ultrastructure. Sugarcane varieties exhibited differential tolerance to Mn stress, and based on the relative total dry mass production of plants growing under Mn toxicity versus the control, tolerant (mean relative growth of 98%) and sensitive (mean relative growth of 71%) genotypes could be identified. Our results suggested that the different capabilities of these varieties in sustaining photoassimilate supply for biomass production under Mn stress were explained by leaf area formation rather than photosynthetic rate per unit of leaf area as tolerant varieties presented reduction in photosynthesis. Moreover, as revealed by the transmission electronic microscopy analysis, tolerant varieties were able to sustain greater integrity in the nucleus of the mesophyll cells under Mn stress than sensitive varieties, improving leaf growth and canopy development. Taken together, our results revealed the mechanisms underlying sugarcane tolerance to Mn toxicity, contributing to the identification of strategies aimed at developing genotypes better adapted to low fertility acid soils, with subsequent positive effects on crop yield stability.

Fernando C. Bachiega Zambrosi, Geisa Lima Mesquita, Paulo Eduardo Ribeiro Marchiori, Francisco A. Ossamu Tanaka, Eduardo Caruso Machado& Rafael Vasconcelos Ribeiro

This manuscript brings a critical reflection on the epistemological foundations of the science of plant physiology. We discuss the limits of the reductionist view of the science, indicating new epistemological possibilities to plant physiology, specially based on General System Theory and Complex System paradigm, and the further implications of this major science to the human future.

Gustavo M. Souza, Carlos H. B. A. Prado, Rafael Vasconcelos Ribeiro, João Paulo R. A. D. Barbosa, Antonio Natal Gonçalves & Gustavo Habermann

The present study aimed to evaluate the development, yield and quality of four sugarcane cultivars fertigated by subsurface drip system. The experiment was carried out in Campinas-SP, Brazil, from January 2012 to November 2013, with the cultivars SP79-1011, IACSP94-2101, IACSP94-2094 and IACSP95-5000 subjected to daily irrigations. The irrigations depths were applied to bring soil moisture to field capacity. Soil moisture was monitored using soil moisture probes. Samples were collected along the crop cycle in order to evaluate crop development and yield, at the end of the first and second ratoons. Stalk height showed good correlation for the estimation of crop yield, with R2 equal to or higher than 0.96. The cultivar IACSP95-5000 showed the highest yield in the first ratoon. In the second ratoon the highest yield was observed in IACSP94-2101, followed by IACSP95-5000 and SP79-1011. Considering the yield results associated with the technological analysis, such as soluble solids content and apparent sucrose, the cultivar IACSP95-5000 excelled the others in the cultivation under subsurface drip irrigation.

André Luiz Barros de Oliveira Silva, Regina Célia de Matos Pires, Rafael Vasconcelos Ribeiro, Eduardo C. Machado, Gabriel C. Blain & Augusto Yukitaka Pessinatti Ohashi

Firstly, I would like to say that it is a great honour to take over the position of Editor-in-chief of Experimental Agriculture, one of the most important journals devoted to publishing original and high quality papers addressing the many facets of agricultural sciences in subtropical and tropical areas. Tradition! I would say that this single word has an enormous meaning for me. I am proud in serving Experimental Agriculture, a journal published by the Cambridge University Press since 1933. Originally titled The Empire Journal of Experimental Agriculture (1933-1964), the publication's mission was ambitious “every new fruit of discovery and invention in the agricultural field”, publishing critical information for improving agricultural systems. So pertinent was the Journal's remit that it was recognised in an article published in Nature in May 27th, 1933. Currently, Experimental Agriculture has an Impact Factor of 1.079 (ISI Thomson Reuters) and stands as a Q1 journal in ‘Agronomy and Crop Science’ (SCImago Journal and Country Rank). In 2015, we received submissions from the five continents, with the majority coming from Asia and Africa. Thank you for considering Experimental Agriculture as a potential journal to publish your paper!

Rafael Vasconcelos Ribeiro

Drought is an environmental limitation affecting sugarcane growth and yield. The redox-active molecule nitric oxide (NO) is known to modulate plant responses to stressful conditions. NO may react with glutathione (GSH) to form S-nitrosoglutathione (GSNO), which is considered the main reservoir of NO in cells. Here, we investigate the role of NO in alleviating the effects of water deficit on growth and photosynthesis of sugarcane plants. Well-hydrated plants were compared to plants under drought and sprayed with mock (water) or GSNO at concentrations ranging from 10 to 1000 μM. Leaf GSNO sprayed plants showed significant improvement of relative water content and leaf and root dry matter under drought compared to mock-sprayed plants. Additionally, plants sprayed with GSNO (≥ 100 μM) showed higher leaf gas exchange and photochemical activity as compared to mock-sprayed plants under water deficit and after rehydration. Surprisingly, a raise in the total S-nitrosothiols content was observed in leaves sprayed with GSH or GSNO, suggesting a long-term role of NO-mediated responses to water deficit. Experiments with leaf discs fumigated with NO gas also suggested a role of NO in drought tolerance of sugarcane plants. Overall, our data indicate that the NO-mediated redox signaling plays a role in alleviating the negative effects of water stress in sugarcane plants by protecting the photosynthetic apparatus and improving shoot and root growth.

Neidiquele Maria Silveira, Lucas Frungillo, Fernanda Castro Correia Marcos, Milena Trevisan Pelegrino, Marcela Trevenzoli Miranda, Amedea Barozzi Seabra, Ione Salgado, Eduardo Caruso Machado& Rafael Vasconcelos Ribeiro

In Citrus, water, nutrient transport and thereby fruit production, are influenced among other factors, by the interaction between rootstock and boron (B) nutrition. This study aimed to investigate how B affects the anatomical structure of roots and leaves as well as leaf gas exchange in sweet orange trees grafted on two contrasting rootstocks in response to B supply. Plants grafted on Swingle citrumelo or Sunki mandarin were grown in a nutrient solution of varying B concentration (deficient, adequate, and excessive). Those grafted on Swingle were more tolerant to both B deficiency and toxicity than those on Sunki, as revealed by higher shoot and root growth. In addition, plants grafted on Sunki exhibited more severe anatomical and physiological damages under B deficiency, showing thickening of xylem cell walls and impairments in whole-plant leaf-specific hydraulic conductance and leaf CO2 assimilation. Our data revealed that trees grafted on Swingle sustain better growth under low B availablitlity in the root medium and still respond positively to increased B levels by combining higher B absorption and root growth as well as better organization of xylem vessels. Taken together, those traits improved water and B transport to the plant canopy. Under B toxicity, Swingle rootstock would also favor plant growth by reducing anatomical and ultrastructural damage to leaf tissue and improving water transport compared with plants grafted on Sunki. From a practical point of view, our results highlight that B management in citrus orchards shall take into account rootstock varieties, of which the Swingle rootstock was characterized by its performance on regulating anatomical and ultrastructural damages, improving water transport and limiting negative impacts of B stress conditions on plant growth.

Geisa Lima Mesquita, Fernando C. Bachiega Zambrosi, Francisco A. Ossamu Tanaka, Rodrigo M. Boaretto, José A. Quaggio, Rafael Vasconcelos Ribeiro& Dirceu Mattos-Jr

Cowpea grains are the main protein source for many people in semi-arid regions. The goal of this study was to study the in vivo photosynthetic behavior of two cowpea cultivars under well-watered, drought stress, and recovery conditions. The cultivars differ in their sensitivity to drought stress, being classified as tolerant and sensitive based on grain production. After 10 days of water deficit, the leaf water potential of the tolerant cultivar was higher than in the sensitive cultivar, suggesting a mechanism of drought tolerance related to the maintenance of shoot water status. During drought stress, the leaf gas exchange and chlorophyll fluorescence parameters decreased faster in the sensitive cultivar as compared to the tolerant one. After 48 h of rehydration, the stressed plants of both cultivars did not recover the maximum rates of carboxylation, the maximum rate of electron transport driving the RuBP regeneration and photosynthetic capacity. However, tolerant cultivar recovered all photosynthetic parameters faster than the sensitive cultivar after 60 h of rehydration. Our results suggest that the tolerant cultivar was able to maintain higher photochemical activity and leaf gas exchange during water deficit for a longer period than the sensitive cultivar does, which could alleviate the stress effects to the photosynthetic machinery and improve its recovery ability. The consequences of this behavior are discussed.

Rebeca Rivas, H. M. Falcão, Rafael Vasconcelos Ribeiro, Eduardo Caruso Machado, Carlos Pimentel& Mauro Guida dos Santos

The shoot regrowth vigour of sugarcane varieties having contrasting phosphorus (P) efficiency was evaluated under varying soil P availability. The P-inefficient (IAC91–1099 and IACSP94–2101) and -efficient (IACSP94–2094 and IACSP95–5000) sugarcane varieties were grown under low (25 mg P kg−1 soil) or high (400 mg P kg−1 soil) P supply at planting. After 90 days (first cycle of growth), the shoots were harvested and regrowth was studied 70–75 days later by evaluating photosynthesis, leaf area formation, biomass production and P uptake. The shoot dry matter (DM) of sugarcane regrowth subjected to a low P supply was genotype-dependent, with the P-efficient varieties exhibiting greater values than the inefficient ones. This result was explained by the greater efficiency of IACSP94–2094 and IACSP95–5000 in acquiring P rather than P utilization efficiency for shoot biomass production. The root P stored during the first cycle of growth would represent only a minor fraction (< 20%) of the total P content in the shoots at the end of the regrowth period. Thus, we argue that the improved shoot P uptake of the P-efficient varieties was related to their ability to sustain P acquisition after harvesting rather than to the remobilization of root P reserves. Moreover, our data revealed that net CO2 assimilation per leaf area was not associated with differential performance among varieties under P deficiency, suggesting a more critical role of total leaf area in photosynthate supply for sugarcane regrowth. In conclusion, sugarcane regrowth is improved in P-efficient varieties under P deficiency conditions, a finding of practical relevance as such ability might benefit the productivity and the longevity of sugarcane ratoons in low P tropical soils.

Fernando C. Bachiega Zambrosi, Rafael Vasconcelos Ribeiro, Eduardo Caruso Machado& Júlio César Garcia

Sugarcane is one of the major crops worldwide. It is cultivated in over 100 countries on 22 million ha. The complex genetic architecture and the lack of a complete genomic sequence in sugarcane hamper the adoption of molecular approaches to study its physiology and to develop new varieties. Investments on the development of new sugarcane varieties have been made to maximize sucrose yield, a trait dependent on photosynthetic capacity. However, detailed studies on sugarcane leaves are scarce. In this work, we report the first molecular and physiological characterization of events taking place along a leaf developmental gradient in sugarcane. Photosynthetic response to CO2 indicated divergence in photosynthetic capacity based on PEPcase activity, corroborated by activity quantification (both in vivo and in vitro) and distinct levels of carbon discrimination on different segments along leaf length. Additionally, leaf segments had contrasting amount of chlorophyll, nitrogen and sugars. RNA-Seq data indicated a plethora of biochemical pathways differentially expressed along the leaf. Some transcription factors families were enriched on each segment and their putative functions corroborate with the distinct developmental stages. Several genes with higher expression in the middle segment, the one with the highest photosynthetic rates, were identified and their role in sugarcane productivity is discussed. Interestingly, sugarcane leaf segments had a different transcriptional behavior compared to previously published data from maize. This is the first report of leaf developmental analysis in sugarcane. Our data on sugarcane is another source of information for further studies aiming to understand and/or improve C4 photosynthesis. The segments used in this work were distinct in their physiological status allowing deeper molecular analysis. Although limited in some aspects, the comparison to maize indicates that all data acquired on one C4 species cannot always be easily extrapolated to other species. However, our data indicates that some transcriptional factors were segment-specific and the sugarcane leaf undergoes through the process of suberizarion, photosynthesis establishment and senescence.

Lucia Mattiello, Diego Mauricio Riaño-Pachón, Marina Camara Mattos Martins, Larissa Prado da Cruz, Denis Bassi, Paulo Eduardo Ribeiro Marchiori, Rafael Vasconcelos Ribeiro, Mônica T. Veneziano Labate, Carlos Alberto Labate & Marcelo Menossi

Um importante índice para a indústria sucroalcooleira é a produtividade de sacarose em cana-de-açúcar, que pode ser relacionada à capacidade da planta em acumular sacarose durante a maturação. Apesar de se conhecer a eficiência de tratamentos como a restrição hídrica e a aplicação de reguladores para estimular o acúmulo de sacarose nos colmos, pouco se conhece sobre as respostas fisiológicas da planta que levam à maturação. Nesse contexto, o objetivo deste estudo foi avaliar as respostas fisiológicas da cana-de-açúcar a diferentes tratamentos indutores de maturação e, assim, compreender melhor a fisiologia desse processo. Duas variedades, a IACSP95-5000, de alta produtividade, e a IACSP94-2094, de produtividade moderada, foram submetidas ao déficit hídrico, à aplicação de regulador químico (etefom 480 g ha–1) e aos dois tratamentos associados. Foram medidos o crescimento, a concentração de carboidratos em folhas e colmos e as trocas gasosas. Concluiu-se que o efeito do etefom em cana-de-açúcar é genótipo-dependente, estimulando o acúmulo de sacarose no colmo e o suprimento de fotoassimilados pela fonte na variedade responsiva (IACSP95-5000). Tais efeitos não são associados à restrição do crescimento. Em relação à aplicação dos tratamentos de déficit hídrico e etefom associados, a variedade responsiva apresenta aumento no teor de sacarose no colmo nos mesmos níveis apresentados quando apenas etefom é aplicado, de modo que os tratamentos não apresentam efeitos aditivos na maturação da cana-de-açúcar.

Guilherme Garcia Roberto, Camila Cunha, Cristina Rodrigues Gabriel Sales, Neidiquele Maria Silveira, Rafael Vasconcelos Ribeiro, Eduardo Caruso Machado& Ana Maria Magalhães de Andrade Lagôa

Aquaporins (AQPs) are proteins that facilitate the transport of water, small neutral solutes and gases across membranes and have an important role in plant physiology and drought stress responses. The sugarcane (Saccharum spp.) transcriptome was searched for AQPs, also known as major intrinsic proteins. Phylogenetic analysis based on nucleotide sequences identified 33 isoforms that fit into four AQP subfamilies previously described for monocotyledonous: 13 plasma membrane intrinsic protein (PIPs), 11 tonoplast intrinsic proteins (TIPs), six nodulin 26-like intrinsic proteins (NIPs) and three small basic intrinsic proteins (SIPs). Among the PIPs, five proteins were classified as PIP1 type and eight were classified as PIP2 type. The expression profiles of three PIP2 isoforms (ShPIP2;1, ShPIP2;5 and ShPIP2;6), which are counterparts of previously described isoforms involved in drought stress in leaves of higher plants, were aligned with monocots and dicot PIP2 protein sequence showing high identity with maize proteins. Furthermore, the transcript abundance of these three genes was evaluated through quantitative PCR (qPCR) in two sugarcane genotypes (‘IACSP94-2094’ and ‘IACSP97-7065’) subjected to water deficit under field and greenhouse conditions. ShPIP2;1, ShPIP2;5 and ShPIP2;6 isoforms were responsive to water deficit and their expression patterns were dependent on genotype, experimental condition and duration of drought stress. Taken together, our results show that the three APQs have their expression in leaves changed under drought, suggesting that these proteins constitute an important target for functional characterization in sugarcane, particularly focusing the performance of plants under varying water availability.

Larissa Mara de Andrade, Paula Macedo Nóbile, Rafael Vasconcelos Ribeiro, João Felipe Nebó Carlos de Oliveira, Antonio Vargas de Oliveira Figueira, Luis Tadeu Marques Frigela, Daniel Nunes, Dilermando Perecin, Michael dos Santos Brito, Regina Célia de Matos Pires, Marcos Guimarães de Andrade Landell & Silvana Creste

Low water availability and high temperatures occur under field conditions and we hypothesize that the critical temperature for photochemical damage (TC) in common bean (Phaseolus vulgaris L.) plants is increased by the occurrence of previous water deficit in a genotype-dependent manner. Five common bean cultivars A320, A222, Carioca, BAT477 and Ouro Negro were evaluated. Thirty days after seedlings emergence, one group of plants was exposed to water deficit for ten days and rehydrated and another one was maintained well hydrated during the experimental period. The minimum chlorophyll fluorescence (FO) was monitored in leaf discs exposed to temperatures ranging from 25 to 45 oC and the TC values estimated. The previous water deficit did not affect TC, which varied between 38.8 and 43.8 oC when considering all cultivars and water regimes. Under well-watered conditions, BAT477 (41.9 oC) and Carioca (43.8 oC) presented higher TCthan Ouro Negro (38.8 oC). Our findings indicate a significant genotypic variation in thermal tolerance in Phaseolus vulgaris, an important crop trait to be considered in breeding programs.

Rafael Vasconcelos Ribeiro, Mauro Guida dos Santos, Carlos Pimentel, Eduardo Caruso Machado& Ricardo Ferraz de Oliveira

This study assessed the photosynthesis, biomass, and phytoenergy production in sugarcane plants subjected to water deficit during the initial stages of development. We hypothesize that the limitations imposed by water deficit on photosynthesis proportionally affect carbon balance, growth, and partitioning of phytoenergy in sugarcane. This study was carried out during 5 months in a growth chamber and water deficit was induced by maintaining soil moisture at 20 % of the maximum water holding capacity (WHC). As control, one group of plants was maintained at 100 % WHC. Water deficit reduced the carboxylation of Rubisco and PEPCase significantly, which were the main limiting factors for photosynthesis. As consequence, the daily leaf carbon balance was significantly reduced by drought. The total accumulated dry matter in well-watered plants was 3.6 times higher than in drought-stressed ones. Water deficit reduced the energy accumulated in sugarcane plants by approximately threefold. Regardless of water regime, a large fraction of the converted energy was not found in stalks. Under water deficit, less than 20 % of the energy is stored in stalks. Since only a tiny fraction of solar energy is used for the production of first generation ethanol, our study reinforces the importance of evaluating strategies to optimize the use of sugarcane, for example, harvesting plant organs other than stalks.

Alexandrius M. Barbosa, K. A. Guidorizi, T. A. Catuchi, T. A. Marques, Rafael Vasconcelos Ribeiro& Gustavo M. Souza

Despite of the agronomic importance for water management, few studies of sugarcane roots have been performed under field conditions during the crop cycle. The aim of this study was to determine the cumulative root density (LA), root distribution on soil profile and the effective rooting depth (ERD) for three sugarcane cultivars using the minirhizotron method. A field experiment was done with sugarcane cultivars IACSP94-2094, IACSP94-2101 and SP79-1011 grown under subsurface drip fertigation. Soil chemical and physical characteristics were also evaluated. Root evaluations were taken at 38, 58, 123, 185 and 205 days during the second ratoon, considering the soil profile until 0.8 m depth. The highest LA and root growth rates were found up to 0.4 m soil layer for all cultivars. Root growth rate varied during the crop cycle, with the highest values being found between 38 and 58 days after ratoon (DAR). There was a genotypic variation in root growth, with IACSP94-2101 showing the highest LA of 12.9 mm cm–2. The total root length observed around the tube (0.16892 m2) was 10.8, 5.9 and 2.5 m up to 0.8 m depth for IACSP94-2101, SP79-1011 and IACSP94-2094, respectively at 205 DAR. The effective rooting depth varied during the cycle for IACSP94-2094, but all cultivars presented an effective depth of 0.4 m at 205 DAR.

Augusto Yukitaka Pessinatti Ohashi, Regina Célia de Matos Pires, Rafael Vasconcelos Ribeiro& André Luiz Barros de Oliveira Silva

Water deficit is an important exogenous factor that enhances the influx of sucrose into sugarcane (Saccharum spp.) stem internodes during ripening, when photosynthetic ability in supplying sinks is essential. The aim of this study was to test the hypothesis that drought tolerance in sugarcane is associated with an effective antioxidant protection during the ripening phase that might maintain a favorable redox balance in chloroplasts and protect photosynthesis under drought conditions. Two commercial sugarcane varieties, IACSP94-2094 (tolerant) and IACSP96-2042 (sensitive), with contrasting behavior under water deficit, were subjected to water withholding during the ripening stage. Our results revealed that the tolerant variety was less affected by water deficit, maintaining photosynthesis for a longer period and showing a faster recovery after rehydration as compared to the sensitive one. As consequence, the tolerant variety faced lesser excess of light energy at PSII. The maintenance of photosynthesis under water deficit and its fast recovery after rehydration resulted in the lower leaf H2O2 concentration and favorable redox status in the drought-tolerant genotype, which was associated with stimulation of superoxide dismutase during ripening. Our results also revealed that ferric superoxide dismutase isoforms were strongly enhanced under drought conditions, playing an important role in chloroplast redox homeostasis.

Cristina Rodrigues Gabriel Sales, Paulo Eduardo Ribeiro Marchiori, R. S. Machado, A. V. Fontenele, Eduardo Caruso Machado, Joaquim Albenisio Gomes Silveira& Rafael Vasconcelos Ribeiro

The aim of this study was to evaluate the differential sensitivity of sugarcane genotypes to H2O2 in root medium. As a hypothesis, the drought tolerant genotype would be able to minimize the oxidative damage and maintain the water transport from roots to shoots, reducing the negative effects on photosynthesis. The sugarcane genotypes IACSP94-2094 (drought tolerant) and IACSP94-2101 (drought sensitive) were grown in a growth chamber and exposed to three levels of H2O2 in nutrient solution: control; 3 mmol L−1 and 80 mmol L−1. Leaf gas exchange, photochemical activity, root hydraulic conductance (Lr) and antioxidant metabolism in both roots and leaves were evaluated after 15 min of treatment with H2O2. Although, root hydraulic conductance, stomatal aperture, apparent electron transport rate and instantaneous carboxylation efficiency have been reduced by H2O2 in both genotypes, IACSP94-2094 presented higher values of those variables as compared to IACSP94-2101. There was a significant genotypic variation in relation to the physiological responses of sugarcane to increasing H2O2 in root tissues, being root changes associated with modifications in plant shoots. IACSP94-2094 presented a root antioxidant system more effective against H2O2 in root medium, regardless H2O2 concentration. Under low H2O2 concentration, water transport and leaf gas exchange of IACSP94-2094 were less affected as compared to IACSP94-2101. Under high H2O2 concentration, the lower sensitivity of IACSP94-2094 was associated with increases in superoxide dismutase activity in roots and leaves and increases in catalase activity in roots. In conclusion, we propose a general model of sugarcane reaction to H2O2, linking root and shoot physiological responses.

Karina I. Silva, Cristina Rodrigues Gabriel Sales, Paulo Eduardo Ribeiro Marchiori, Neidiquele Maria Silveira, Eduardo Caruso Machado& Rafael Vasconcelos Ribeiro

Photosynthetic modulation by sugars has been known for many years, but the biochemical and molecular comprehension of this process is lacking. We studied how the exogenous sucrose supplied to leaves could affect sugar metabolism in leaf, sheath and stalk and inhibit photosynthesis in four-month old sugarcane plants. Exogenous sucrose 50 mM sprayed on attached leaves strongly impaired the net CO2 assimilation (PN) and decreased the instantaneous carboxylation efficiency (PN/Ci), suggesting that the impairment in photosynthesis was caused by biochemical restrictions. The photosystem II activity was also affected by excess sucrose as indicated by the reduction in the apparent electron transport rate, effective quantum yield and increase in non-photochemical quenching. In leaf segments, sucrose accumulation was related to increases in the activities of soluble acid and neutral invertases, sucrose synthase and sucrose phosphate synthase, whereas the contents of fructose increased and glucose slightly decreased. Changes in the activities of sucrose hydrolyzing and synthesizing enzymes in leaf, sheath and stalk and sugar profile in intact plants were not enough to identify which sugar(s) or enzyme(s) were directly involved in photosynthesis modulation. However, exogenous sucrose was able to trigger down-regulation in the Rubisco abundance, activation state and enzymatic activity. Despite the fact that PN/Ci had been notably decreased by sucrose, in vitro activity and abundance of PEPCase did not change, suggesting an in vivo modulation of this enzyme. The data reveal that sucrose and/or other derivative sugars in leaves inhibited sugarcane photosynthesis by down-regulation of Rubisco synthesis and activity. Our data also suggest that sugar modulation was not exerted by a feedback mechanism induced by the accumulation of sugars in immature sugarcane stalk.

Ana Karla Moreira Lobo, Marcio de Oliveira Martins, Milton Costa Lima Neto, Eduardo Caruso Machado, Rafael Vasconcelos Ribeiro& Joaquim Albenisio Gomes Silveira

Wood contains a large amount of air, even in functional xylem. Air embolisms in the xylem affect water transport and can determine plant growth and survival. Embolisms are usually estimated with laborious hydraulic methods, which can be prone to several artefacts. Here, we describe a new method for estimating embolisms that is based on air flow measurements of entire branches. To calculate the amount of air flowing out of the branch, a vacuum was applied to the cut bases of branches under different water potentials. We first investigated the source of air by determining whether it came from inside or outside the branch. Second, we compared embolism curves according to air flow or hydraulic measurements in 15 vessel‐ and tracheid‐bearing species to test the hypothesis that the air flow is related to embolism. Air flow came almost exclusively from air inside the branch during the 2.5‐min measurements and was strongly related to embolism. We propose a new embolism measurement method that is simple, effective, rapid and inexpensive, and that allows several measurements on the same branch, thus opening up new possibilities for studying plant hydraulics.

Luciano Pereira, Paulo R. L. Bittencourt, Rafael S. Oliveira, Mauro B. M. Junior, Fernanda V. Barros, Rafael Vasconcelos Ribeiro& Paulo Mazzafera

The role of photorespiration in plants under drought is not well understood. It can act both as an alternative electron sink and a source of reactive oxygen species (ROS). In this study, we evaluated in which stage of water deficit the energy dissipation by thermal processes and photorespiration act as photoprotective mechanisms, alleviating the photodamage in photosystem II (PSII) of Jatropha curcas plants. The experiment lasted 20 days; every 5 days (0, 5, 10, 15, and 20 days), measurements of gas exchange, chlorophyll fluorescence, and biochemical analysis were performed. On the 10th day of treatment, re-hydration in a separate group of drought-stressed plants was applied. The electron flow used for ribulose bisphosphate (RuBP) carboxylation (JC) progressively decreased with time of exposure to increasing drought. On the other hand, the electron flow used for RuBP oxygenation (JO) decreased during 5–10 days of exposure to water deficit and was significantly enhanced from 10 to 20 days. The JC/JO ratio was lower in plants exposed to drought compared to non-stressed plants. In addition, the photorespiration and the PR/PN and JT/PN ratios also were stimulated by drought. The non-photochemical quenching coefficient (NPQ) and relative energy excess level at PSII (EXC) in drought-stressed plants significantly increased between 5 and 10 days of treatment compared to control plants. Leaf H2O2 content was enhanced in plants exposed to water deficit reaching their concentrations more elevated in the period of 15–20 days when compared to control. In addition, the drought stress stimulated ascorbate peroxidase activity. On the other hand, the glycolate oxidase (GO) activity intensely increased, while catalase activity progressively decreased with increasing water deficit. In general, our results reveal that both excessive energy dissipation as heat and photorespiration play important roles in protecting the photosynthetic apparatus from photoinhibition.

Evandro Nascimento Silva, Joaquim Albenisio Gomes Silveira, Rafael Vasconcelos Ribeiro& Suyanne A. Vieira

Tomato (Solanum lycopersicum) shows three growth habits: determinate, indeterminate and semi-determinate. These are controlled mainly by allelic variation in the SELF-PRUNING (SP) gene family, which also includes the “florigen” gene SINGLE FLOWER TRUSS (SFT). Determinate cultivars have synchronized flower and fruit production, which allows mechanical harvesting in the tomato processing industry, whereas indeterminate ones have more vegetative growth with continuous flower and fruit formation, being thus preferred for fresh market tomato production. The semi-determinate growth habit is poorly understood, although there are indications that it combines advantages of determinate and indeterminate growth. Here, we used near-isogenic lines (NILs) in the cultivar Micro-Tom (MT) with different growth habit to characterize semi-determinate growth and to determine its impact on developmental and productivity traits. We show that semi-determinate genotypes are equivalent to determinate ones with extended vegetative growth, which in turn impacts shoot height, number of leaves and either stem diameter or internode length. Semi-determinate plants also tend to increase the highly relevant agronomic parameter Brix × ripe yield (BRY). Water-use efficiency (WUE), evaluated either directly as dry mass produced per amount of water transpired or indirectly through C isotope discrimination, was higher in semi-determinate genotypes. We also provide evidence that the increases in BRY in semi-determinate genotypes are a consequence of an improved balance between vegetative and reproductive growth, a mechanism analogous to the conversion of the overly vegetative tall cereal varieties into well-balanced semi-dwarf ones used in the Green Revolution.

Mateus Henrique Vicente, Agustin Zsögön, Ariadne Felicio Lopo de Sá, Rafael Vasconcelos Ribeiro& Lázaro E. P. Peres

The aim of this study was to evaluate if endophytic bacteria inoculants would be beneficial to the sugarcane varieties IACSP94-2094 and IACSP95-5000, promoting changes in photosynthesis and plant growth. The plants, obtained from mini stalks with one bud, were treated with two bacteria mixtures (inoculum I or II) or did not receive any inoculum (control plants). The inocula did not affect shoot and root dry matter accumulation as compared to the control condition (plants with native endophytic bacteria). However, photosynthesis and electron transport rate (ETR) increased in IACSP94-2094 treated with the inoculum II, whereas the inoculum I enhanced photosynthesis and stomatal conductance in IACSP95-5000. The inoculum II caused increase in leaf sucrose concentration of IACSP94-2094 and decrease in IACSP95-5000 leaves. Leaf nitrogen concentration was not affected by treatments, but bacteria inoculation increased nitrate reductase activity in IACSP95-5000, and the highest activity was found in plants treated with the inoculum II. We can conclude that bacteria inoculation changed sugarcane physiology, improving photosynthesis and nitrate reduction in a genotype-dependent manner, without promoting plant growth under non-limiting conditions.

Fernanda Castro Correia Marcos, Raquel de Paula Freitas Iório, Adriana Parada Dias da Silveira, Rafael Vasconcelos Ribeiro, Eduardo Caruso Machado& Ana Maria Magalhães de Andrade Lagôa

Developing genotypes with enhanced performance under phosphorus (P) deficiency can be described as an approach to improving production sustainability. This study investigated the physiological responses of sugarcane varieties to varying P availability and the plant traits contributing to P efficiency (shoot dry matter production under low P availability). Sugarcane varieties IACSP94-2101, IACSP95-5000, RB86-7515, IAC91-1099, IACSP94-2094 and IAC87-3396 were grown under low (25 mg P kg−1 soil) and high (400 mg P kg−1 soil) P supply, and the leaf gas exchange, photochemical activity, plant growth and P uptake were evaluated. The sugarcane varieties responded distinctly to a low P supply, as indicated by differences in root and shoot growth, leaf area, net CO2 assimilation, photosynthetic P utilization efficiency, leaf P concentration and P uptake. The following ranking was obtained for P efficiency: IACSP94-2094 = IACSP95-5000 > IAC87-3396 = RB86-7515 = IACSP94-2101 = IAC91-1099. Greater leaf area, net CO2 assimilation and P acquisition efficiency were combined in the more P-efficient varieties but not in the less efficient ones. Although it was not possible to separate cause and effect, such finding might be explained by the positive effect of improved leaf P concentration on leaf area and net CO2 assimilation, which in turn contributed to sustaining improved plant performance under a low P supply.

Fernando C. Bachiega Zambrosi, Rafael Vasconcelos Ribeiro, Paulo Eduardo Ribeiro Marchiori, Heitor Cantarella & Marcos Guimarães de Andrade Landell