Plants react to changes in light and hydrological conditions in terms of quantity and composition of chloroplastidic pigments, which affects the photosynthetic properties and consequently the accumulation of plant biomass. Thus, the chloroplastidic pigment concentration and chlorophyll a fluorescence of three Amazonian species (Bertholletia excelsa, Carapa guianensis e Dipteryx odorata) were investigated in sun and shade leaves form the tree crown collected during two distinct periods of precipitation (dry and rainy seasons). Pigment contents were determined by spectrophotometry and fluorescence variables were determined using a portable fluorometer. The results demonstrated that the species showed high concentrations of Chl a, Chl b e Chl total during the wet season in relation to the dry season, especially in shade leaves. A higher concentration of carotenoids was found in B. excelsa, when compared with leaves of C. guianensis and D. odorata. In leaves of B. excelsa and D. odorata no significant difference was found in relation to the photochemistry of photosystem II (Fv/Fm) between the wet and dry seasons. In conclusion, the three species react differently to variations in the light and precipitation conditions regarding light capture, aspects that might be considered in the management of forest plantations.

The significance of phenological characteristics, stomatal conductance of the leaves, and stem water storage fluctuations for the regulation of xylem sap flow in an evergreen (Carapa guianensis Aubl.), in a semideciduous (Swietenia macrophylla King), and in a deciduous (Cedrela odorata L.) Meliaceae species was studied in a 7-year-old plantation near Manaus, Brazil. The study responds to the increasing demand for knowledge on the water relations of highly exploited timber trees of the Amazon. Xylem sap flow measurements indicated that the daily sap flow of Carapa (3.8 l day -1 tree -1 to 16.4 l day -1 tree -1 ) exceeded the daily sap flow of Swietenia (2.4 l day -1 tree -1 to 7.0 l day -1 tree -1 ) and Cedrela (1.6 l day -1 tree -1 to 11.6 l day -1 tree -1 ) during the entire year, although the highest flux densities were measured in Cedrela. The decrease in xylem sap flow observed in periods with low soil water potentials and high atmospheric vapor saturation deficits was more pronounced in the deciduous (Cedrela) and semi-deciduous species (Swietenia) than the evergreen species (Carapa). Carapa, which has the highest daily sap flow, had the highest biomass and sapwood portion. The high flux densities measured in Cedrela most likely result from the large earlywood vessels in this species. The seasonal variation of xylem sap flow of the three species was correlated with the stomatal conductance of the leaves measured by infiltration experiments. Stem water storage fluctuations in Carapa and Swietenia were predominantly due to transpiration; in Cedrela it was predominantly due to evaporative water loss on the stem surface during dry periods.

O feijão-caupi (Vigna unguiculata) é uma das principais culturas alimentares nas regiões Norte e Nordeste do Brasil, que concentram a maior área cultivada e produção desta leguminosa. A produtividade, nestas regiões, é de cerca de 300 kg ha -1 (Medeiros et al. 2008), não muito diferente daquela obtida no continente africano, maior região produtora, onde se registra produtividade média de 380 kg ha -1 (Ishaya et al. 2008). Segundo Silva et al. (2000) e Ishaya et al. (2008), dentre os fatores que interferem, negativamente, na cultura, o manejo inadequado das plantas daninhas que ocorrem nas áreas de cultivo contribui para a redução de produtividade. Além ABSTRACT RESUMO disso, algumas espécies de plantas daninhas servem como hospedeiros alternativos de doenças que atacam o feijão-caupi, como ocorre com a guanxuma (Sida rhombifolia), malva-sedosa (Waltheria indica), mussambê (Cleome affinis) e mela-bode (Herissantia crispa) (Assunção et al. 2006).Nesse contexto, o uso de herbicidas, como um dos componentes de programas de manejo integrado de plantas daninhas, na cultura do feijão-caupi, permite elevada eficácia de controle, com redução de custos de produção. Entretanto, dois aspectos devem ser considerados, no que se refere ao emprego de herbicidas, nessa cultura: a inexistência de herbicidas registrados no Brasil, para controle de plantas daninhas, o que impede recomenda-

RESUMONas últimas décadas, considerável parcela da floresta amazônica tem sido transformada em pastagens que, em função da baixa fertilidade natural dos solos e do manejo deficiente, decrescem rapidamente em produtividade e são abandonadas, dando lugar a uma sucessão secundária arbórea adaptada à baixa disponibilidade de nutrientes. O objetivo deste estudo foi obter informações sobre a eficiência no uso dos nutrientes por espécies arbóreas freqüentes nesses ambientes degradados, após calagem e aplicação de fosfato. O experimento realizado numa área de sucessão secundária com seis anos de idade, consistiu na aplicação de quatro tratamentos: controle; aplicação de fósforo (P); aplicação de fósforo e calcário (P+Cal); e aplicação de fósforo, calcário e gesso (P+Cal+G). As determinações das taxas de fotossíntese, bem como as coletas de amostras de solo e de folhas foram realizadas oito meses após a aplicação dos tratamentos. A aplicação do corretivo e do fosfato favoreceu o desempenho das espécies nos tratamentos P+Cal e P+Cal+G. Bellucia grossularioides acumulou mais N, P e Zn, enquanto que Laetia procera acumulou mais Ca e Mn. Vismia japurensis foi a espécie mais eficiente no uso dos nutrientes, em função dos altos valores da taxa fotossintética; apresentou baixos teores foliares de P quando comparada com Bellucia grossularioides, sugerindo ser uma espécie bem adaptada a ambientes com baixa disponibilidade de nutrientes, como ocorre em áreas degradadas na Amazônia. PALAVRAS-CHAVEÁreas degradadas, sucessão secundária, trocas gasosas, calcário, fósforo, gesso. (P+Cal); and phosphorus, lime and gypsum addition (P+Cal+G). Leaf gas exchange, soil and leaf nutrient concentration were determined eight months after the treatment application. There was a significant response by species to the addition of phosphorus and lime (P+Cal and P+Cal+G). The species, Bellucia grossularioides accumulated more N, P and Zn in the leaves, while Laetia procera accumulated more Ca and Mn. The species Vismia japurensis had higher nutrient use efficiency, as a function of the higher photosynthetic rates. Vismia japurensis presented lower P concentrations than Bellucia grossularioides, suggesting that is well adapted to environments low in nutrients, as this species often occurs in degraded areas in Amazonia. Nutrient use efficiency for pioneer species grown on abandoned pastures in central Amazonia ABSTRACT Large areas of Amazonian forest have been converted to pastures over the last two decades. Low soil fertility and mismanagement results in a rapid decline in net primary productivity leading the pastures to be abandoned, and woody vegetation adapted to low nutrient conditions colonize the areas. The objective of this study was to examine nutrient use efficiency, following liming (calcium) and phosphorus addition by three of the most frequent colonizing species. The experiment conducted on a six year-old secondary forest, consisted of four treatments: control; phosphorus addition (P); phosphorus and lime addition

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RESUMOO objetivo deste trabalho foi investigar a influência da variação de temperatura foliar associada à suspensão de irrigação sobre as trocas gasosas de plantas jovens de taxi-branco (Sclerolobium paniculatum Vogel). O estudo foi realizado em casa de vegetação na área experimental da Embrapa Amazônia Ocidental. As plantas cresceram em casa de vegetação e depois de quatro meses de aclimatização foram submetidas a três regimes hídricos (mantidas irrigadas até a capacidade de campo do solo, irrigação suspensa por oito e 14 dias). Foram avaliados os parâmetros fisiológicos de trocas gasosas, taxa de assimilação líquida de CO 2 (A), transpiração foliar (E), condutância estomática (g s ) e eficiência no uso da água (EUA) os quais foram obtidos por meio do medidor portátil de fotossíntese (CI-340, CID, Inc.). Os resultados mostraram que houve redução das taxas de assimilação líquida de CO 2 em função da elevação da temperatura foliar e da suspensão da irrigação. Após oito dias de suspensão da irrigação houve redução das taxas de assimilação líquida de CO 2 fotossintéticas em 62, 65, 75, 58, 50 e 64% e aos 14 dias esta redução foi de 80, 85, 85, 84, 86 e 93% em comparação as plantas mantidas irrigadas, nas temperaturas de 25, 30, 35, 40, 45 e 50°C, respectivamente. O comportamento das taxas de transpiração foliar foi inversamente proporcional às taxas de fotossíntese líquida, mostrando incremento em função do aumento da temperatura foliar. O comportamento fisiológico de trocas gasosas de Sclerolobium paniculatum apresentou variações tanto em relação ao efeito da temperatura foliar, quanto da suspensão de irrigação. Palavras-chave: Sclerolobium paniculatum; fotossíntese; estresse hídrico. ABSTRACTThe study aimed to investigate the influence of leaf temperature variation associated with irrigation suspension on gas exchange of seedlings of Sclerolobium paniculatum Vogel. The study was carried out in a greenhouse at experimental area of Embrapa, Amazônia Ocidental. Plants were grown in a greenhouse and, after four months were subjected to three treatments (irrigated maintained until the field capacity, irrigation suspended for eight and 14 days). We evaluated the physiological parameters of gas exchange, net assimilation rate of CO 2 (A), leaf transpiration (E), stomatal conductance (g s ) and water use efficiency (WUE) which were obtained through a photosynthesis portable meter (CI-340, CID, Inc). The results showed reduction of net assimilation rate of CO 2 depending on the elevation of the leaf temperature and without irrigation. After eight days without irrigation, decreased rates of photosynthetic assimilation of CO 2 in 62, 65, 75, 58, 50 and 64%, and after 14 days the reduction was 80, 85, 85, 84, 86 and 93% compared to plants irrigated maintained at temperatures of 25, 30, 35, 40, 45 and 50 °C, respectively. The leaf transpiration was inversely proportional to rates of net photosynthetic assimilation of CO 2 , which has increased with an increased leaf temperature. The physiological behavior of gas exchange of ...

Weeds negatively affect cowpea plants, causing reduced growth, delayed development and yield loss. The aim of this study was to assay selectivity and effectiveness of weed control herbicides in cowpea cropping field conditions. For selectivity evaluation, the herbicide S-metolachlor, was used pre-emergence (PRE), and carfentrazone-ethyl, clethodim, fenoxaprop-p-ethyl, fluazifop-p-butyl and quizalofop-p-ethyl post-emergence (POST). In effectiveness evaluation, S-metolachlor (PRE), and carfentrazone-ethyl (POST), S-metolachlor in PRE and fluazifop-p-butyl (POST), clethodim, carfentrazone-ethyl and clethodim, fenoxapropp- ethyl, carfentrazone-ethyl and fenoxaprop-p-ethyl, fluazifop-p-butyl, carfentrazone-ethyl and fluazifop-pbutyl, quizalofop-p-ethyl and carfentrazone-ethyl and quizalofop-p-ethyl (POST). Two controls were included, one with weeding at 15 and 35 days after sowing (DAS) and the other without weed control. Carfentrazone-ethyl caused mild phytotoxicity in plants seven days after application, but did not reduce yield (2337 kg ha-1). The levels of weed control and productivity obtained with S-metolachlor alone or in association with carfentrazoneethyl or fluazifop-p-butyl, associated or not with carfentrazone-ethyl, were similar to those obtained with weeds. Spraying with carfentrazone-ethyl alone resulted in low control effectiveness and reduced yield (1511 kg ha-1). Weed interference during the crop cycle reduced yield by 77% (531 kg ha-1). The selectivity and effectiveness obtained with the herbicides should be considered as an agronomic and economically-viable.

Climatic factors of a region determine the critical periods of corn crop development and affect the sowing planning in order to reduce the negative effects on yield. This study aimed to evaluate the agronomic performance of eight corn genotypes and two sowing dates in the edaphoclimatic conditions of Manaus, Amazonas. Four experiments were carried out in the agricultural years 2016/2017 and 2017/2018, conducted in two sowing periods under harvest season and off-season conditions each year. The sown of the harvest season and off-season were made in October and March, respectively. The experiments were conducted in a randomized block design, with eight genotypes (four varieties - BR 106, BR 5011 Sertanejo, BRS 4103, and BRS Caimbé; and four hybrids - AG 1051, BRS 1055, BRS 3040, and BRS 3046), and four replicates evaluated in two sowing periods for each year. The data were submitted to individual variance analysis for each sowing period, joint for each year, and to the means comparison test. Corn cultivation at the Manaus region could be carried out both during the harvest season, sowing at the beginning of the rainy period (October), and in the off-season, with sowing near the end of the rainy period (March). Hybrids have higher yield potential than open-pollinated varieties for both grain and green ear cultivation, regardless of sowing, harvest, or off-season.