Sustained drought and concomitant high temperature may reduce photosynthesis and cause tree mortality. Possible causes of reduced photosynthesis include stomatal closure and biochemical inhibition, but their relative roles are unknown in Amazon trees during strong drought events. We assessed the effects of the recent (2015) strong El Niño drought on leaf-level photosynthesis of Central Amazon trees via these two mechanisms. Through four seasons of 2015, we measured leaf gas exchange, chlorophyll a fluorescence parameters, chlorophyll concentration, and nutrient content in leaves of 57 upper canopy and understory trees of a lowland terra firme forest on well-drained infertile oxisol. Photosynthesis decreased 28% in the upper canopy and 17% in understory trees during the extreme dry season of 2015, relative to other 2015 seasons and was also lower than the climatically normal dry season of the following non-El Niño year. Photosynthesis reduction under extreme drought and high temperature in the 2015 dry season was related only to stomatal closure in both upper canopy and understory trees, and not to chlorophyll a fluorescence parameters, chlorophyll, or leaf nutrient concentration. The distinction is important because stomatal closure is a transient regulatory response that can reverse when water becomes available, whereas the other responses reflect more permanent changes or damage to the photosynthetic apparatus. Photosynthesis decrease due to stomatal closure during the 2015 extreme dry season was followed 2 months later by an increase in photosynthesis as rains returned, indicating a margin of resilience to one-off extreme climatic events in Amazonian forests.

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-The objective of this work was to evaluate the development and quality of clonal seedlings of teak (Tectona grandis) grown in substrate with two types of biochar. The assay was carried out in a randomized complete block design, with ten treatments and four replicates: CS, commercial substrate, composed of pine bark and vermiculite at a ratio of 4:1; NS, nursery substrate composed of carbonized rice husk and coconut fiber at 1:1; and the remaining treatments were composed of the inclusions of biochar (BC) or activated biochar (BCA) in the CS, at the proportions of 25, 50, 75, and 100%. The development and quality parameters of seedlings were evaluated 90 days after striking the minicuttings in the substrates. BCA substrate additions at 25, 50, and 100% allowed for a development of height and stem diameter comparable to that of the NS. Biochar without the activation procedure does not improve quality parameters of seedlings, in comparison with the commercial substrate. The use of 25% activated biochar added to the commercial substrate is enough to improve seedling growth performance to the same level as that provided by the already validated NS.Index terms: Tectona grandis, agroindustrial waste, biochar activity, pyrolysis, seedling quality. Biochar na composição de substratos para a produção de mudas de tecaResumo -O objetivo deste trabalho foi avaliar o desenvolvimento e a qualidade de mudas clonais de teca (Tectona grandis) cultivadas em substrato com dois tipos de biochar. O ensaio foi realizado em delineamento de blocos ao acaso, com dez tratamentos e quatro repetições: SC, substrato comercial, composto de casca de pinus e vermiculita à proporção de 4:1; SV, substrato do viveiro, composto de casca de arroz carbonizada e fibra de coco a 1:1; e o restante dos tratamentos foi composto de inclusões de biochar (B) e biochar ativado (BA), nas proporções de 25, 50, 75 e 100% do SC. Os parâmetros de desenvolvimento e qualidade das mudas foram avaliados 90 dias após o plantio das estacas nos substratos. A adição de 25, 50 e 100% de BA possibilitou o desenvolvimento em altura e diâmetro do coleto comparável ao proporcionado pelo SV. O biochar sem o procedimento de ativação não melhora os parâmetros de qualidade das mudas, em comparação ao substrato comercial. A adição de biochar ativado na proporção de 25% já é suficiente para melhorar o crescimento das mudas para o mesmo nível proporcionado pelo já validado SV.Termos para indexação: Tectona grandis, resíduo agroindustrial, atividade do biochar, pirólise, qualidade de mudas.

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RESUMOA castanheira-da-amazônia (Bertholletia excelsa Bonpl.) é uma espécie exigente de luz, pois em floresta nativa, a espécie depende da formação de clareiras para alcançar o tamanho reprodutivo e em plantios florestais demonstra rápido crescimento inicial quando exposta a altos níveis de irradiância. No entanto, os aspectos ecofisiológicos dessa espécie sob condições contrastantes de irradiância não foram investigados. Nesse estudo, além das características de crescimento, objetivou-se analisar pela primeira vez o grau de plasticidade das respostas ecofisiológicas de Bertholletia excelsa quando submetida a ambientes de irradiância contrastantes. Plantas jovens de Bertholletia excelsa foram cultivadas em três condições de irradiância: baixa (20-300 µmol m -2 s -1 ), moderada (800-1000 µmol m -2 s -1) e alta (1900-2100 µmol m -2 s -1 ). Foram analisadas características de crescimento, trocas gasosas, teores de pigmentos cloroplastídicos e, no fim do experimento, o acúmulo e partição de biomassa. Plantas jovens de Bertholletia excelsa demonstraram maior acúmulo de biomassa, crescimento e fotossíntese quando expostas aos ambientes de moderada e alta irradiância. A condição de baixa irradiância estimulou maior partição de biomassa para a parte aérea em contraposição ao sistema radicular e maior concentração foliar de pigmentos cloroplastídicos. Bertholletia excelsa possui plasticidade fisiológica sob condições contrastantes de irradiância, sendo o maior crescimento e acúmulo de biomassa, em ambientes de moderada e alta irradiância, promovidos pelo melhor desempenho fotossintético, ao passo que o balanço positivo de carbono sob baixa irradiância é assegurado pelo investimento em estruturas de interceptação e captação de energia. Palavras-chave: Castanheira-da-amazônia; trocas gasosas; crescimento inicial; espécie arbórea tropical. ABSTRACTBrazil nut (Bertholletia excelsa Bonpl.) is a light-demanding species, because in natural forest, the species depending of formation of clearings for reach reproduction size and in forest plantation, showing fast initial growth when exposed to high levels of irradiance. However, the ecophysiological traits of this species under contrasting conditions of irradiance were not investigated. In this study, in addition to growth traits, we investigated for first time the degree of plasticity of ecophysiological response of Bertholletia excelsa when subjected to contrasting irradiance environments. Young plants of Bertholletia excelsa were cultivated under three conditions of irradiance: low (20-300 µmol m -2 s -1

As a preparatory study for future hyperspectral missions that can measure canopy chemistry, we introduce a novel approach to investigate whether multi-angle Moderate Resolution Imaging Spectroradiometer (MODIS) data can be used to generate a preliminary database with long-term estimates of chlorophyll. MODIS monthly chlorophyll estimates between 2000 and 2015, derived from a fully coupled canopy reflectance model (ProSAIL), were inspected for consistency with eddy covariance fluxes, tower-based hyperspectral images and chlorophyll measurements. MODIS chlorophyll estimates from the inverse model showed strong seasonal variations across two flux-tower sites in central and eastern Amazon. Marked increases in chlorophyll concentrations were observed during the early dry season. Remotely sensed chlorophyll concentrations were correlated to field measurements (r 2 = 0.73 and r 2 = 0.98) but the data deviated from the 1:1 line with root mean square errors (RMSE) ranging from 0.355 μg cm-2 (Tapajós tower) to 0.470 μg cm-2 (Manaus tower). The chlorophyll estimates were consistent with flux tower measurements of photosynthetically active radiation (PAR) and net ecosystem productivity (NEP). We also applied ProSAIL to mono-angle hyperspectral observations from a camera installed on a tower to scale modeled chlorophyll pigments to MODIS observations (r 2 = 0.73). Chlorophyll pigment concentrations (Chl A+B) were correlated to changes in the amount of young and mature leaf area per month (0.59 ≤ r 2 ≤ 0.64). Increases in MODIS observed Chl A+B were preceded by increased PAR during the dry season (0.61 ≤ r 2 ≤ 0.62) and followed by changes in net carbon uptake. We conclude that, at these two sites, changes in LAI, coupled with changes in leaf chlorophyll, are comparable with seasonality of plant productivity. Our results allowed the preliminary development of a 15-year time series of 4 chlorophyll estimates over the Amazon to support canopy chemistry studies using future hyperspectral sensors.