-The objective of this work was to evaluate the physiological and anatomical traits of plants of a cacao (Theobroma cacao) clone in response to water deficit after leaf application of silicon. A randomized complete block design was used, with four replicates, in a 2x3 factorial arrangement of two water regimes (irrigated or nonirrigated) and three silicon concentrations (0.0, 1.5, and 3.0 mg mL -1 ) applied in wettable SiO 2 powder. The plants were evaluated 20 days after the irrigation regimes were applied. The use of SiO 2 increased the stability of cell membranes and the photochemical efficiency of the plants under water deficit. The 1.5 mg mL -1 concentration of SiO 2 increased photosynthetic rate, water use efficiency, and carboxylation efficiency, besides mitigating the effect of oxidative stress. Stomatal density was reduced in nonirrigated plants under the highest concentration of Si. The 1.5 mg mL -1 concentration of Si is considered optimal for the photosynthetic metabolism of young cacao plants under soil water limitation.Index terms: Theobroma cacao, anatomy, antioxidant enzymes, drought, photochemistry, SiO 2 . Aplicação foliar de silício em plantas jovens de cacau submetidas à deficiência hídricaResumo -O objetivo deste trabalho foi avaliar as características fisiológicas e anatômicas de plantas de um clone de cacau (Theobroma cacao) em resposta ao deficit hídrico após a aplicação foliar de silício. Utilizou-se o delineamento de blocos ao acaso, com quatro repetições, em arranjo fatorial 2x3, com dois regimes hídricos (irrigado e não irrigado) e três concentrações de silício (0, 1,5 e 3,0 mg mL -1 ) aplicadas como pó molhável de SiO 2 . As plantas foram avaliadas 20 dias após a aplicação dos regimes de irrigação. O uso de SiO 2 aumentou a estabilidade das membranas celulares e a eficiência fotoquímica das plantas sob deficit hídrico. A concentração de 1,5 mg mL -1 de SiO 2 aumentou a taxa fotossintética, a eficiência do uso da água e a taxa de carboxilação, além de ter mitigado o efeito do estresse oxidativo. A densidade estomática foi reduzida em plantas não irrigadas sob a maior concentração de Si. A concentração de 1,5 mg mL -1 de Si é considerada ótima para o metabolismo fotossintético de plantas jovens de cacau sob limitação de água no solo.Termos para indexação: Theobroma cacao, anatomia, enzimas antioxidantes, seca, fotoquímica, SiO 2 .

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Based on reports that variables related to photosynthesis (net assimilatory ratio and chloroplast pigments) are more plastic than the morphological and biochemical variables in a climax tropical species, Cariniana estrellensis, under contrasting irradiance, we hypothesised that plasticity of gas exchange variables is higher in relation to growth, biochemical and anatomical variables. Plants that were 14 months old were subjected to 200 up to 2000 lmol m -2 s -1 of photo synthetically active radiation (PAR) for 140 days. Growth increased up to 1400 lmol m -2 s -1 PAR and then decreased at 2000 lmol m -2 s -1 PAR (full sunlight). This was related to the rate of photosynthesis (A) which showed the same tendency as photosystem II performance index (PI ABS ). The greater thickness of the secondary xylem at 1400 lmol m -2 s -1 PAR indicated a higher water conductance capacity. The decrease in specific leaf area, elongation of mesophyll cells, and increase in stomatal density observed at higher irradiances were associated with higher leaf fructose and sucrose concentrations. We concluded that the better growth in partial shade was due to higher photosynthetic capacity. On the other hand, photosynthesis was inhibited equally in full sun and deep shade. The high adjustment capacity of C. estrellensis to wide amplitudes of irradiance was provided by greater plasticity of gas exchange variables in relation to growth, anatomical, and biochemical variables.

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The existing inconsistent data on the irradiance needs of Brazilwood plants Paubrasilia echinata (Lam.) Gagnon,H.C.Lima and G.P.Lewis. can be explained by their phenotypical variations. While small-leaf morphotypes grows better in the shade, not tolerating environments with high irradiance, a recently discovered population of medium morphotype presents different behavior: better performance under direct sunlight and limited growth in the shade. In order to understand the physiological mechanisms of the medium morphotype in response to the available irradiance, this study was performed to characterize the oxidative stress metabolism, photochemical and biochemical photosynthesis efficiency, as well as anatomical adjustments of leaves of the medium morphotype of P. echinata under different intensities of irradiance. The analyses were performed at direct sunlight condition (2000 µmol m-2.s-1) and within a dense ombrophilous forest with 80% shading (192 µmol m-2.s-1). Growth, leaf anatomy, chloroplast pigments, photochemical (chlorophyll a fluorescence), and biochemical (gaseous exchanges) efficiency, soluble carbohydrates, and antioxidants were measured. The results showed that the higher efficiency in light energy uptake, paired with better photochemical performance and better CO2 fixation in plants under direct sunlight resulted in higher concentration of soluble sugars and growth. The energy that should have been used in photochemical and/or biochemical reactions of shaded plants was dissipated in the form of heat, re-emitted as fluorescence or translocated to the production of antioxidant defense compounds of the secondary metabolism. Therefore, the medium morphotype of P. echinata presents an ecological profile of sun-tolerant or pioneer species, and as such, it is recommended its planting in full sunlight. These results differ from previous studies on small morphotype of P. echinata and suggest the need for a taxonomic reconstruction of this species, which is essential to adequate management practices in Atlantic rainforest recovery programs.

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<p>A ocorrência de <em>Cariniana legalis </em>(Mart.) Kuntze (Lecythidaceae) em florestas secundárias em diferentes fases de regeneração sugere que essa espécie seja mais resistente a pleno sol em relação a <em>Paratecoma peroba </em>(Record. &amp; Mell) Kuhlm. (Bignoniaceae) encontrada no interior da floresta primária densa. O objetivo desse trabalho foi caracterizar a plasticidade das variáveis de crescimento, anatômicas e estruturais de parede celular de <em>C. legalis </em>e <em>P. peroba</em>. Como o caule é forte dreno em arbóreas, foi elaborada a hipótese que as plasticidades das ligninas e dos monossacarídeos das hemiceluloses são maiores em relação às variáveis de crescimento e anatômicas, especialmente em <em>C. legalis, </em>mais resistente a pleno sol, como sugere seu hábito ecológico. Plantas jovens, com 14 meses de idade, foram submetidas a 20 e 100% de luminosidade solar por 60 dias. Diferente do esperado, a plasticidade das ligninas foi inferior a das variáveis de crescimento e anatômicas para as duas espécies<em>. </em>A composição das hemiceluloses de <em>C. legalis </em>não foi influenciada pela luminosidade. Em <em>P. peroba</em>, a proporção de arabinose foi menor a pleno sol. Concluímos que a indicação de maior resistência de <em>C. legalis </em>a pleno sol foi associada ao índice de plasticidade das taxas de assimilação líquida e de crescimento relativo (≥ 0,6), densidade estomática (≥ 0,3) e ligninas (≤ 0,2).</p>

-(Relationships of N, P, and K with the chlorophyll fluorescence, leaf nutrient accumulation, and soluble carbohydrate concentration in the stem of Caesalpinia echinata Lam.). The aim of this study was to evaluate the effect of N, P, and K in the accumulation of these elements in the leaf and their relations with the chlorophyll a fluorescence parameters and with the concentration of soluble carbohydrates in stems of young plants of Caesalpinia echinata. Eight-month-old plants were grown in polyethylene pots. which received N, P, and K in isolated form ((NH 4 ) 2 SO 4 , P 2 O 5 , KCl) and the combined form NPK in the ratio 10:10:10 and 04:14:08. The pots were arranged in randomized blocks. The applications were repeated each 90 days during 450 days. The results demonstrated that C. echinata is more responsive to N. Plants showed higher leaf N concentrations and positive correlation with the concentration of chlorophyll a and b. However, the treatments did not influence the potential quantum yield of PSII (FV/FM) and the performance index (PITOTAL). The concentration of sucrose in the stem bark was higher than that of secondary xylem and superior in fertilizers rich in P (P and NPK 04:14:08) suggesting increased demand of substrate for forming the wood in these treatments, which could result in more resistant stems and higher survival of the plants under field conditions. Keywords: Brazilwood, fluorescence, nutrients, soluble carbohydrates RESUMO -(Relações do N, P e K com a fluorescência da clorofila, teores de nutrientes foliares e carboidratos solúveis do caule de Caesalpinia echinata Lam.). Esse trabalho foi realizado com o objetivo de avaliar o efeito de suplementação de N, P e K no acúmulo foliar desses elementos e suas relações com os parâmetros da fluorescência da clorofila a e com a concentração de carboidratos solúveis em caules de plantas jovens de Caesalpinia echinata Lam. Plantas com oito meses de idade foram cultivadas em vasos que receberam N, P e K na forma isolada ((NH 4 ) 2 SO 4 , P 2 O 5 , KCl) e combinada na proporção 10:10:10 e 04:14:08, distribuídos em blocos inteiramente casualizados. As aplicações foram repetidas a cada 90 dias durante 450 dias. Os resultados demonstraram que C. echinata é mais responsiva ao N. As plantas apresentaram maiores concentrações de N foliar e correlação positiva com a concentração das clorofilas a e b. No entanto, os tratamentos não influenciaram no rendimento quântico potencial do FSII (FV/FM) e no índice de desempenho (PITOTAL). A concentração da sacarose na casca do caule foi maior do que do xilema secundário e superior nas adubações fosfatada e em NPK 04:14:08 sugerindo maior demanda de substrato para a formação da madeira nesses tratamentos, o que poderia resultar em caules mais resistentes e maior capacidade de sobrevivência das plantas em condições de campo. Palavras-chave: carboidratos solúveis, fluorescência, nutrientes, pau-brasil IntroduçãoEstudos recentes têm demonstrado que as arbóreas nativas tropicais respondem à aplicação de N, P e K ap...