The aim of this work was to compare gas exchanges from leaf to whole plant scales, in two Ethiopian accessions (‘E083’ and ‘E027’), and two bred cultivars (Iapar 59 and Catuaí 99) of Arabica coffee (Coffea arabica L.) cultivated under irrigated and rainfed conditions. Variations in gas exchanges were evaluated over four phenophases (leaf expansion – BE1 and BE2, and berry harvesting – BH1 and BH2), covering the first two production years in the coffee life cycle. We addressed the following questions: Are gas exchanges modified by water availability at leaf and/or plant scales? Do bred cultivars and wild accessions differ in their physiological responses to water availability and phenophases? Photosynthesis (A), stomatal conductance (gs), and transpiration (E) were measured on the recently fully expanded leaves at the upper canopy stratum. The functional-structural plant modelling (FSPM) was used to integrate A at whole plant photosynthesis (A”p), based on 3D virtual trees constructed under VPlants modelling platform. Despite high A values of ‘E083’ overall phenophases, a strong decline in A”p under rainfed condition was observed due to lower plant leaf area as compared to irrigated condition. Catuaí 99 and ‘E083’ were more sensitive to drought than Iapar 59 and ‘E027’, considering photosynthesis at leaf and plant scales. At the last BH2 phenophase, A, gs, E, and carboxylation efficiency were similar between irrigated and rainfed conditions for all genotypes, suggesting some acclimation of leaf gas exchange to the environment. However, A”p benefited by water management in all phenophases as plant leaf area increased. These findings revealed the need to develop methodologies for structural and functional analyses at plant scale, an important step towards the realistic responses of plants and orchards to the surrounding environment.

Miroslava Rakocevic, Evelyne Costes, Eliemar Campostrini, José C. Ramalho & Rafael V. Ribeiro

Local adaptation is common in plant species, and knowing whether a population is locally adapted has fundamental and applied relevance. However, local adaptation in tropical plants remains largely less studied, and covering this gap is not simple since reciprocal transplantation – the gold standard for detecting local adaptation – is not feasible for most species. Here, we combined genetic, climatic and phenotypic data to investigate ecotypic differentiation, an important aspect of local adaptation, in coastal and inland populations of the orchid Epidendrum fulgens Brongn., a long-lived tropical plant for which reciprocal transplantation would not be feasible. We used nine microsatellite markers to estimate genetic divergence between inland and coastal populations. Moreover, occurrence data and climate data were used to test for differences in the realized niche of those populations. Finally, we assessed saturated water content, leaf specific area, height, and stomatal density in common garden and in situ to investigate the effects of ecotypic differentiation and plasticity on the phenotype. Coastal and inland groups' niches do not overlap, the former occupying a wetter and warmer area. However, this differentiation does not seem to be driven by ecotypic differentiation since there was no positive correlation between genetic structure and climate dissimilarity. Moreover, specific leaf area and leaf saturated water content, which are important phenotypic traits related to soil fertility and drought stress, were rather plastic. We conclude that ecotypic differentiation is absent, since phenotypic plasticity is an important mechanism explaining the niche broadness of this species.

T. M. de Lima, S. F. da Silva, J. Sánchez-Vilas, W. L. S. Júnior, J. L. S. Mayer, R. V. Ribeiro & F. Pinheiro.

Premise: Salt tolerance has rarely been investigated regionally in the neotropics and even more rarely in Orchidaceae, one of the largest families. Therefore, investigating local adaptation to salt spray and its physiological basis in Epidendrum fulgens, a neotropical orchid species, brings important new insights. Methods: We assessed the degree of salt tolerance in E. fulgens by testing whether coastal populations are more tolerant to salt, which could point to local adaptation. To understand the physiological basis of such salt tolerance, we exposed wild-collected individuals to salt spray for 60 days, then measured leaf expansion, osmotic potential, sodium leaf concentration, chlorophyll leaf index, chlorophyll fluorescence, relative growth rate, and pressure–volume curves. Results: There is no local adaptation to salt spray since both inland and coastal plants have a high tolerance to salt stress. This tolerance is explained by the ability to tolerate high concentrations of salt in leaf tissues, which is related to the high succulence displayed by this species. Conclusions: We showed an unprecedented salt tolerance level for an orchid species, highlighting our limited knowledge of that trait beyond the traditional studied groups. Another interesting finding is that salt tolerance in E. fulgens is linked to succulence, is widespread, and is not the result of local adaptation. We suggest that E. fulgens and its allied species could be an interesting group to explore the evolution of important traits related to tolerance to salt stress, like succulence.

Thales M. de Lima, Simone F. Silva, Rafael V. Ribeiro, Julia Sánches-Vilas & Fabio Pinheiro.

In almost all species of the genus Passiflora, the plants in the juvenile stage produce leaves with a different morphology when compared to adult plants. During the juvenile stage, Passiflora organensis typically has variegated leaves, and in adult plants leaves are non-variegated and have extrafloral nectaries. Studies have shown that variegation in plants is not just a color change, but has adaptive functions that can benefit plants. We show here that the variegated leaves observed in P. organensis in the juvenile stage occur due to a mechanism in which intercellular spaces are present between the epidermis and palisade parenchyma cells in the adaxial side of the leaves. We also show that both the green and the white-silverish sectors of the leaves contain well-developed chloroplasts, with no significant differences in the efficiency of Photosystem II. We hypothesize that leaf variegation in P. organensis represents an adaptation to protect juvenile plants from herbivores and environmental stresses.

Tatiana S. Moraes, Mônica L. Rossi, Rafael V. Ribeiro, Adriana P. Martinelli & Marcelo C. Dornelas.

Considerable attention has been paid to addressing methodological concerns related to measurements of embolism in conduits of angiosperm xylem. A fast, easy and cheap method is based on gas extraction measurements from dehydrating samples to obtain pneumatic vulnerability curves (VCs). Here, we tested the assumption that cutting open conduits leads to gas-filled lumina when these are cut in air at fairly high water potentials, which is required to detect embolism in intact conduits. We performed VCs with the Pneumatron for 12 angiosperm species and extracted sap from cut-open vessels in branches of nine species under early stages of branch dehydration. The optical method was applied to Citrus plants as an alternative reference method to estimate embolism resistance. We found an increase in gas discharge during early stages of dehydration, which affected the pneumatic VCs for most of the species studied. Xylem sap residue was not absorbed immediately by surrounding tissue in cut-open conduits in six of the nine species but gradually disappeared over time during progressive dehydration. The amount of gas discharged increased until all residual sap was absorbed, and was not related to embolism. We conclude that residual xylem sap in cut-open conduits affects early stages of pneumatic VCs and represents a novel artifact that can easily be corrected for. Yet, it remains unclear why exactly the air–water meniscus in cut-open conduits did not fully withdraw to the conduit end wall in most species. By analyzing the slope of VCs over time, we could improve estimations of embolism resistance, as evidenced by a strong agreement between the pneumatic and the optical methods. Since residual sap in cut-open conduits of some species could slightly underestimate embolism resistance, we propose to apply a correction for this artifact based on the high time-resolution measurements taken with a Pneumatron.

Marcela T. Miranda, Luciano Pereira, Gabriel S. Pires, Xinyi Guan, Luciano M. Silva, Swetlana Kreinert, Eduardo C. Machado, Steve Jansen & Rafael V. Ribeiro.

Neste trabalho testou-se a hipótese de que o estresse hídrico reduz a fotossíntese da cana-de-açúcar impondo limitações de origem estomática e mesofílica e modificando a via de descarboxilação nas células da bainha do feixe vascular. Para tanto se mediu as trocas gasosas, a fluorescência da clorofila a, a atividade das enzimas envolvidas na descarboxilação e na fixação do CO2 na fotossíntese – fosfoenolpiruvato carboxilase (PEPC), ribulose-1,5-bisfosfato carboxilase/oxigenase (Rubisco), enzima málica dependente de nicotinamida adenina dinucleotídeo fosfato (NADP-ME), enzima málica dependente de nicotinamida adenina dinucleotídeo (NAD-ME) e fosfoenolpiruvato carboxiquinase (PEPCK). Com a redução do potencial hídrico foliar devido à baixa disponibilidade de água, houve redução na assimilação de CO2, na condutância estomática, na transpiração e na eficiência do uso da água, bem como na eficiência fotoquímica do fotossistema II. A descarboxilação de CO2 na cana-de-açúcar ocorreu com a participação das três descarboxilases; todavia, a atividade PEPCK foi mantida sob estresse hídrico, enquanto as atividades da NADP-ME e NAD-ME foram reduzidas. A Rubisco teve sua atividade diminuida sob estresse hídrico, enquanto que a PEPC não foi afetada. Após o período de reidratação do substrato, as plantas recuperaram-se atingindo valores de fotossíntese muito próximos dos apresentados em plantas bem hidratadas. Como conclusão, a fotossíntese em cana-de-açúcar sob deficiência hídrica é limitada pela disponibilidade de substrato devido ao fechamento estomático, assim como pela menor atividade fotoquímica e menor atividade da Rubisco. O déficit hídrico também evidenciou a flexibilidade do mecanismo de descaboxilação de CO2 nas células da bainha do feixe vascular, com aumento da contribuição relativa da enzima PEPCK.

Daniela F. São Pedro Machado, Norma M. Erismann, Yolanda E. A. G. Boza, Rose Marry A. Godim-Tomaz, Eduardo C. Machado & Rafael V. Ribeiro.

Embolism resistance of xylem tissue varies among species and is an important trait related to drought resistance, with anatomical attributes like pit membrane thickness playing an important role in avoiding embolism spread. Grafted Citrus trees are commonly grown in orchards, with the rootstock being able to affect the drought resistance of the whole plant. Here, we evaluated how rootstocks affect the vulnerability to embolism resistance of the scion using several rootstock/scion combinations. Scions of ‘Tahiti’ acid lime, ‘Hamlin’, ‘Pera’ and ‘Valencia’ oranges grafted on a ‘Rangpur’ lime rootstock exhibit similar vulnerability to embolism. In field-grown trees, measurements of leaf water potential did not suggest significant embolism formation during the dry season, while stomata of Citrus trees presented an isohydric response to declining water availability. When ‘Valencia’ orange scions were grafted on ‘Rangpur’ lime, ‘IAC 1710’ citrandarin, ‘Sunki Tropical’ mandarin or ‘Swingle’ citrumelo rootstocks, variation in intervessel pit membrane thickness of the scion was found. The ‘Rangpur’ lime rootstock, which is known for its drought resistance, induced thicker pit membranes in the scion, resulting in higher embolism resistance than the other rootstocks. Similarly, the rootstock ‘IAC 1710’ citrandarin generated increased embolism resistance of the scion, which is highly relevant for citriculture.

Marcela T. Miranda, Gabriel S. Pires, Luciano Pereira, Rodrigo F. de Lima, Simone F. da Silva, Juliana L. S. Mayer, Fernando A. Azevedo, Eduardo C. Machado, Steven Jansen & Rafael V. Ribeiro

Sucrose yield in sugarcane is a complex process regulated by both environmental and endogenous factors. However, the metabolic balance driving vegetative growth and sucrose accumulation remains poorly understood. Herein, we carried out a comprehensive assessment of carbohydrate dynamics throughout the crop cycle in two sugarcane varieties varying in biomass production, evaluating the carbon metabolism in both leaves and stalks. Our data revealed that the decline in photosynthetic rates during sugarcane maturation is associated not only to accumulation of sugars in leaves but also due to stomatal and non-stomatal limitations. We found that metabolic processes in leaves and stalks were intrinsically linked. While IACSP94-2094 had higher stalk sucrose concentration than IACSP95-5000, this latter produced more biomass. Compared to IACSP95-5000, IACSP94-2094 showed higher sucrose phosphate synthase (SPS) activity in leaves and stalks, along with lower soluble acid invertase (SAI) activity in leaves during the maximum growth stage. Interestingly, IACSP94-2094 also exhibited higher stalk SPS activity and lower stalk SAI activity than IACSP95-5000 during maturation. High biomass production by IACSP95-5000 was associated with higher sucrose synthase (SuSy) and SAI activity in leaves and higher SuSy and soluble neutral invertase (SNI) activity in stalks when compared to IACSP94-2094 during the maximum growth. Despite the contrasting strategies, both varieties displayed similar total sucrose yield, a balance between sucrose concentration and biomass production. This phenomenon implies the presence of a compensatory mechanism in sugarcane, with high biomass production compensating low sucrose accumulation and vice versa.

Tamires da S. Martins, José R. Magalhães Filho, Larissa P. Cruz, Daniela F. S. P. Machado, Norma M. Erismann, Rose M. A. Gondim-Tomaz, Paulo E. R. Marchiori, André L. B. O. Silva, Eduardo C. Machado & Rafael V. Ribeiro

In Coffea arabica, there is a small genetic distance between wild and bred genotypes. However, coffee genotypes express differential acclimation to multiple drought cycles, allowing them to successfully deal with water-limiting conditions. We hypothesized that bred coffee cultivars have a plant structure less sensitive to drought than wild genotypes. Plant and leaf architecture were analyzed over the coffee strata of two cultivars (Iapar 59 and Catuaí 99) and two wild Ethiopia accessions (‘E083’ and ‘E027’) grown under rainfed conditions and irrigation. During two consecutive productive years, evaluations were taken at leaf and berry expansion (BE1 and BE2) and harvest (BH1 and BH2) phenophases. The plant canopy was divided into up to four strata of 40 cm of thickness. Topological and geometric coding of coffee trees was performed in three botanical scales – metamers, branches, and plants in multiscale tree graphs (MTGs), following the VPlants modeling platform. Leaf and branch area per plant increased with tree structure development, being always significantly higher in irrigated than in rainfed plants over all phenophases. The individual leaf area was the least sensitive to water regime in Catuaí 99, while the 2nd order axis elevation – angle in relation to horizontal plane, ranging from 0° to 90° – of bred cultivars was less sensitive to drought than in ‘E083’. This finding partially corroborated our hypothesis that orchestrated reprograming of leaf/branch responses over the vertical plant profile were less sensitive to water availability in cultivars than in wild accessions. Leaves of 2nd to 4th-order branching were roughly plagiophile, while the 1st-order leaves were classified as extremophiles. When the coffee leaves were planophile, irrespective of genotype, this pattern was found at the lowest, 1st plant stratum, and the newest developed 4th stratum. Such responses were not obligatorily related to water regime, similar to branch elevation – with exception of ‘E083’, very sensitive to drought. Taken together, our data suggest that the leaf and branch elevations in C. arabica were more influenced by light distribution through the canopy profile – i.e., self-shading – than by water availability.

Miroslava Rakocevic, Fabio T. Matsunaga, Ricardo A. A. Pazianotto, José C. Ramalho, Evelyne Costes & Rafael V. Ribeiro

This commentary reports the challenges faced and lessons learned during the formation of the first large-scale tropical garden inside a building with native tree species in Brazil. This garden, set entirely over cement slab, is inside the Albert Einstein Education and Research Center (AEERC) – Campus Cecília and Abram Szajman in São Paulo city, and comprises 11 tree species, ten of which are native to the Atlantic Forest. The indoor environment, in the shape of an atrium, is controlled and isolated from the external environment, which imposes a unique and new habitat for those tree species, especially considering that this garden is shared with people during their daily activities. Over one year, we followed the growth and development of 95 trees and noticed that the acclimation potential varied among species as well as the susceptibility to pest and disease outbreaks and low temperature (due to an imbalance in the air conditioning system), which were identified as the main limiting factors. Among the species monitored, Lafoensia glyptocarpa was the most sensitive to mites, aphids and mealybugs, and effective and rapid phytosanitary management was crucial for maintaining a healthy garden. Aspidosperma polyneuron, Eriotheca candolleana, Holocalyx balansae, Poecilanthe parviflora and Euterpe edulis were the species with the most acclimation potential to the new environment, which was based on leaf area development. On the other hand, poor acclimation was observed for Calycophyllum spruceanum, which was replaced two years after the initial planting. As an important lesson, continuous monitoring of both plants and the environment is needed to enhance our knowledge and management of indoor tropical gardens.

Rafael V. Ribeiro, Nathalia Fonseca, Manoel D. L. Neto, Isabel Duprat & Maria A. Delbin

Abiotic stresses are among the primary environmental variables that have consistently posed challenges to agricultural production worldwide. In the last decades, our understanding of how plants sense environmental cues has greatly expanded. This encompasses the mechanisms that convert environmental stress signals into cellular signaling pathways and gene transcription networks. Moreover, emerging evidence indicates that plants have the capacity to retain memories of past stressful experiences and use such capacity to enhance their responses under recurrent stresses. Priming, through prior exposure to a triggering factor, improves plant tolerance to subsequent biotic or abiotic stresses and has been proposed as the basis for plant stress memory. Priming-induced stress memory can persist in the current generation or even in the progeny. The significance of stress memory in enhancing abiotic stress tolerance is well-established in several important crops, and the capacity of plants to retain stress-related memories has been linked to diverse plant mechanisms. In this review, we revisit the recent literature reporting the mechanistic underpinnings of abiotic stress memory in important crops. We outline the underlying processes related to acquisition of stress memory, occurring at molecular, physiological, biochemical, and morphological levels. Here, we addressed the methods for studying plant memory over the last ten years, giving special attention to growth conditions, phenological stages and the techniques for inducing crop memory. Enhancing our comprehension of stress memory-related mechanisms would open up a range of possibilities for developing stress-resistant genotypes through molecular breeding or biotechnological methods or even stress-resistant crop fields due to improved management practices.

Maria D. Pissolato, Tamires S. Martins, Yutcelia C. G. Fajardo, Gustavo M. Souza, Eduardo C. Machado & Rafael V. Ribeiro

The effect of environmental gradients on the remarkable diversity of mountain-associated plants and on the species' abilities to cope with climate change transcends species-specific strategies. For instance, our understanding of the impact of thermal gradients on ecological divergences in populations of widely distributed species is limited, although it could provide important insights regarding species' response to climate change. Here, we investigated whether populations of an endemic species broadly distributed across an elevation gradient employ unique or multiple divergent ecological strategies according to specific environmental conditions. We hypothesised that populations employ distinct strategies, producing a tolerance-avoidance trade-off related to the thermal conditions they experience across elevations. We conducted our research with 125 individuals of Pitcairnia flammea (Bromeliaceae) sampled from various elevations spanning from sea level to ~2200 m and cultivated under the same conditions. To assess specific ecological strategies of P. flammea populations across elevations, we examined leaf temperature, heat and cold tolerances, as well as other structural/morphological, optical, physiological and biochemical leaf traits. We majorly observed that water-saving traits diminish as elevation increases while membrane fluidity, majorly associated with unsaturated and very-long-chain lipids, enhances. Low-elevation individuals of P. flammea invest in water storage tissues, which likely prevent excessive water loss through the intense transpiration rates under warming periods. Conversely, high-elevation plants exhibit increased membrane fluidity, a possible response to the stiffening induced by low temperature. Our results revealed a tolerance-avoidance trade-off related to thermal strategies of populations distributed across an elevation gradient. Low-elevation plants avoid excessive leaf temperature by investing in water-saving traits to maintain transpiration rates. High-elevation individuals, in turn, tend to invest in membrane properties to tolerate thermal variations, particularly cold events. Our findings challenge the conventional notion that plants' vulnerability to warming depends on species-specific thermal tolerance by showing diverse thermal strategies on populations across an elevation gradient.

Cleber J. N. Chaves, Tami C. Cacossi, Taynara S. Matos, João P. S. P. Bento, Lucas N. Gonçalves, Simone F. Silva, Marcus V. da Silva- Ferreira, Douglas F. Barbin, Juliana L. S. Mayer, Alessandra Sussulini, Rafael V. Ribeiro & Clarisse Palma- Silva