C3 and C4 plants, as their intermediates, respond differently to short-term changes in environmental conditions. This difference is linked to contrasting levels of phenotypic plasticity and photosynthetic apparatus specialization. Phenotypic plasticity is an underexplored topic although its understanding is crucial to predict plant behaviour in future climatic scenarios. In this research, the phenotypic plasticity of anatomical traits and its influence to carbon uptake efficiency was studied in plants with different photosynthetic types, under contrasting water regimes. Oryza sativa cvs. Soberana (droughtsensitive) and Douradão (drought-tolerant) (C3), Homolepis isocalycia (C3 proto-Kranz) and Andropogon gayanus (C4), grown at three water treatments (100, 75 and 50% of substrate water holding capacity), were phenotyped for leaf anatomy and gas-exchange parameters. The results showed that plasticity trends indicated different strategies between O. sativa cultivars to deal with water shortage, explaining their classification as drought-sensitive or tolerant. We also mapped typical characteristics of C3-C4 intermediate plant, H. isocalycia, mainly in the ratio mesophyll:bundle sheath cells and hypothesize how it may influence photosynthesis. Finally, we have confirmed previous claims that C4 carbon uptake advantages may be limited under severe drought conditions, as A. gayanus have drastically reduced its photosynthetic rates at lower water levels. By studying C3-C4 intermediates, this study may also be a starting point to unravel the trade-offs of anatomical changes during the evolutionary process from C3 to C4 photosynthesis, and also improve the understanding of their impact in carbon uptake in different water conditions.

Sugarcane productivity is severely affected by the occurrence of water deficit in the field, causing inhibition of growth and sugar production. Evaluating physiological responses of sugarcane under water deficit conditions is essential to understand physiological variables responsible for reaching homeostasis. Therefore, we analysed physiological traits of two sugarcane genotypes, RB835486 (Tolerant) and RB855453 (Susceptible), under water deficit conditions: well‐watered (WW‐Control), water deficit (WD) and rewatered (RW). The physiological response was evaluated using linear regression and multivariate analysis. Some characteristics such as water potential in leaves, photosynthesis, chlorophyll fluorescence, chlorophyll index, sucrose and starch contents did not show differences between the genotypes under water deficit conditions. However, the tolerant genotype showed increased reducing sugars content in the leaves, whereas the susceptible genotype had increased non‐photochemical quenching (qN). After rewatering, the susceptible sugarcane genotype showed higher electron transport rate (ETR) and efficiency of PSII (Y). Multivariate analysis revealed that non‐photochemical quenching and reducing sugars in the leaves were physiological variables responsible for reaching homestasis under water deficit conditions. Therefore, the reducing sugars concentration should be considered a physiological variable responsible for the adjustment made by the tolerant sugarcane genotype when submitted to water deficit.

The phenotype of an individual emerges of an interaction of its genotype and the environment in which it is located. Phenotypic plasticity (PP) is the ability of a specific genotype in presenting multiple phenotypes in response to the environment. Past and current methods for quantification of PP present limitations, mainly in what concerns a systemic analysis of multiple traits. This research proposes an integrative index for quantifying and evaluating PP. The Multivariate Plasticity index (MVPi) was calculated based on the Euclidian distance between scores of a Canonical Variate Analysis. It was evaluated for leaf physiological traits in two cases using Brazilian Cerrado species and sugarcane varieties, grown under diverse environmental conditions. The MVPi presented sensitivity to plant behaviour from simple to complex genotype-environment interactions and was able to inform coarse and fine changes in PP. It was correlated to biomass allocation, showing agreement between plant organizational levels. The new method proved to be elucidative of plant metabolic changes, mainly by explaining PP as an integrated process and emergent property. We recommend the MVPi method as a tool for analysis of phenotypic plasticity in the context of a systemic evaluation of plant phenotypic traits.

increase of Al leaf content as a function of Al concentration in the nutrient solution. Plants grown in 1 mM Al showed a remarkable increase of K leaf content, net photosynthesis, stomatal conductance, and transpiration, while in 4 mM Al there were reductions of N, P, and K contents, gas exchange characteristics, and height. H. impetiginosus did not have mechanisms of avoidance, compartmentalization, or resistance to high Al concentrations. Indeed, this species showed a hormetic response, with low Al concentrations stimulating and high Al concentrations inhibiting plant responses.

Limited water availability in reforestation areas can compromise plant growth and development, especially for plants at early stages. In this context, the exogenous application of growth regulators, such as brassinosteroids (BRs), can be used to mitigate the negative effects of water restriction. The aim of this study was to evaluate the effect of the application of BRs (90% brassinolide + a brassinosteroid) on initial growth, gas exchange, leaf water potential and leaf anatomy in yellow Ipê (Handroanthus serratifolius), under water restriction conditions. Throughout the experimental period, plants were maintained in two different water regimes: WR1-plants maintained at 100% of the pot capacity; WR2-plants rehydrated with 50% of the evapotranspiration from the previous day. BRs were applied on three occasions during the experimental period, in five concentrations: C1, 0 g/L (application of distilled water); C2, 0.25 g/L; C3, 0.5 g/L; C4, 0.75 g/L; and C5, 1.00 g/L. The dry mass, root:shoot ratio, water status and leaf anatomy traits were evaluated at the end of the experimental period and were analysed in two-level factorial scheme (2WR  5BRs concentrations). The plant height, number of leaves, gas exchange and leaf chlorophyll content were evaluated four times during the experimental period and were analysed in a split-split-plot design (two WR  five BRs concentrations  four evaluation times). The differences between the means were evaluated by analysis of variance (ANOVA). Pairs of means were separated using the standard error of the difference between the means (SED) and the Fisher's protected least significant difference test (LSD) at p < .05. In addition, all variables were subjected to regression analysis, being the variables evaluated over time, analysed through a two-stage modelling approach. The results obtained indicate that the water deficit led to reductions in growth and gas exchange parameters, regardless of the exogenous application of the regulator; therefore, higher concentrations (C4 and C5) were the most harmful for the maintenance of metabolic and photosynthetic activity. The exogenous application of BRs in H. serratifolius plants attenuated the effects of water limitation on the leaf water potential, but was not able to mitigate for the negative effects in growth, gas exchange and leaf anatomy.

RESUMONeste estudo foram avaliados os efeitos do nitrato (NO 3 -), amônio (NH 4 + ) e da ausência de nitrogênio (N) na fotossíntese, no processo fotorrespiratório e no metabolismo antioxidante de plantas jovens de seringueira. As plantas foram cultivadas em areia, irrigadas com solução nutritiva de Bolle-Jones, com N na concentração de 8mM nas proporções + proportions: 8/0, 0/8 and 0/0, respectively. The gas exchange, chlorophyll a fluorescence, photorespiration and antioxidant enzyme activities (SOD, CAT and APX) in leaves were evaluated. The net CO 2 assimilation rate (A) and the electron transport rate (ETR) were higher in NO 3 -treated plants. Lowest ETR and higher photorespiratory activity were observed in plants treated with NH 4 + . SOD activity was higher in leaves of plants treated with both N sources. Lower CAT and higher APX activities were found in NO 3 -treated plants. Plants grown in the absence of N showed lowest values of A. We observed that the different N sources significantly affected the photosynthetic process and that NH 4 + favored photorespiratory process in rubber plants.

No abstract

A necessidade da destinação correta do lodo de esgoto doméstico vem atraindo pesquisas para sua utilização como componente de substrato para mudas arbóreas. Uma das características que permitem essa utilização é a sua composição rica em matéria orgânica e elementos minerais essenciais. Objetivou-se avaliar a viabilidade da utilização de diferentes proporções de lodo de esgoto doméstico na composição do substrato para aroeira e sua influência no crescimento das mudas. A aroeira foi cultivada durante 180 dias em diferentes substratos: T1- 100% Terra Vegetal (T); T2- 100% Sedimento Arenoso (A); T3- 20% Lodo de Esgoto (LE) + 80% A; T4- 60% LE + 40% A; e T5- 100% LE. As variáveis de crescimento foram analisadas mensalmente, enquanto a eficiência do fotossistema II (Fv/Fm) a cada 60 dias. Ao final do experimento foram determinadas as concentrações de carboidratos, proteínas, clorofila total, além da razão entre a biomassa de raiz e da parte aérea. Plantas cultivadas em 100% A apresentaram menores valores para as características de crescimento e bioquímicas avaliadas. Nas proporções de 20% e 60% LE, as plantas alcançaram maior altura, diâmetro do caule e número de folhas, assim como elevados teores de açúcares e clorofila. Entretanto, na concentração de 100% LE, aos 180 dias, as plantas apresentaram redução em altura e número de folhas. Apesar disso, o lodo de esgoto doméstico demonstrou ser viável para composição de substrato para mudas de aroeira em proporções que podem variar desde 20% até 100%.