Most Amazonian soils are highly weathered and poor in nutrients. Therefore, photosynthesis and plant growth should positively respond to the addition of mineral nutrients. Surprisingly, no study has been carried out in situ in the central Amazon to address this issue for juvenile trees. The objective of this study was to determine how photosynthetic rates and growth of tree saplings respond to the addition of mineral nutrients, to the variation in leaf area index of the forest canopy, and to changes in soil water content associated with rainfall seasonality.We assessed the effect of adding a slow-release fertilizer. We determined plant growth from 2010 to 2012 and gas exchange in the wet and dry season of 2012. Rainfall seasonality led to variations in soil water content, but it did not affect sapling growth or leaf gas exchange parameters. Although soil amendment increased phosphorus content by 60 %, neither plant growth nor the photosynthetic parameters were infl uenced by the addition of mineral nutrients. However, photosynthetic rates and growth of saplings decreased as the forest canopy became denser.Even when Amazonian soils are poor in nutrients, photosynthesis and sapling growth are more responsive to slight variations in light availability in the forest understory than to the availability of nutrients. Therefore, the response of saplings to future increases in atmospheric [CO 2 ] will not be limited by the availability of mineral nutrients in the soil.

Optical characteristics, contents of photosynthetic pigments, total soluble sugars, and starch, rates of gas exchange, chlorophyll (Chl) a fluorescence, and leaf water relations were analysed in three Vitis vinifera L. cultivars, Tinto Cão (TC), Touriga Nacional (TN), and Tinta Roriz (TR), grown in Mediterranean climate. Chl content was significantly lower in TC than in TN and TR leaves, while the Chl a/b ratio was higher. TR had the lowest net photosynthetic rate, stomatal conductance, and contents of soluble sugars and starch than TN and TC. In spite of low Chl content, TC showed the lowest photon absorbance and the highest photochemical efficiency of photosystem 2. TC had the lowest predawn and midday leaf water potential. The capability for osmotic adjustment was similar among cultivars and the calculated modulus of elasticity was higher in TC leaves. The typical lighter green leaves of TC seemed to be an adaptive strategy to high irradiance and air temperature associated to water stress.

RESUMO -Na Floresta Amazônica, a fotossíntese e o crescimento das árvores podem ser limitados pela disponibilidade de nutrientes. O objetivo deste trabalho foi determinar o efeito do conteúdo de nitrogênio (N) e fósforo (P) foliar na fotossíntese e a eficiência do uso destes nutrientes nas taxas fotossintéticas, bem como avaliar o efeito da luminosidade no crescimento em 10 espécies florestais da Amazônia Central. Os dados foram coletados em janeiro de 2008. A capacidade fotossintética (A pot ) foi positivamente relacionada com o conteúdo de N e P, mas a capacidade fotossintética da folha foi responsiva apenas quanto à eficiência no uso do P. Os conteúdos de N e P aumentaram com a irradiância do sub-bosque. Observou-se relação positiva entre o conteúdo de N e a relação N/P, mas a razão N/P não teve efeito na eficiência do uso do P. A área foliar específica Correlacionou negativamente com N e P, e a eficiência no uso do N diminuiu com o aumento da razão N/P, que não teve efeito na eficiência do uso do P. O crescimento em diâmetro aumentou com a luminosidade do sub-bosque. Conclui-se que as arvoretas têm alta sensibilidade às variações no ambiente luminoso e o P é utilizado de forma altamente eficiente nas espécies estudadas.Palavras-chave: Área foliar específica; Irradiância do sub-bosque; Teor de nutrientes foliar GROWTH AND PHOTOSYNTHETIC USE EFFICIENCY OF NITROGEN AND PHOSPHORUS IN SAPLINGS OF AMAZONIAN TREE SPECIES

The adjunctive use of biofeedback systems with exoskeletons may accelerate post-stroke gait rehabilitation. Wearable patient-oriented human-robot interaction-based biofeedback is proposed to improve patient-exoskeleton compliance regarding the interaction torque’s direction (joint motion strategy) and magnitude (user participation strategy) through auditory and vibrotactile cues during assisted gait training, respectively. Parallel physiotherapist-oriented strategies are also proposed such that physiotherapists can follow in real-time a patient’s motor performance towards effective involvement during training. A preliminary pre-post controlled study was conducted with eight healthy participants to conclude about the biofeedback’s efficacy during gait training driven by an ankle-foot exoskeleton and guided by a technical person. For the study group, performance related to the interaction torque’s direction increased during (p-value = 0.07) and after (p-value = 0.07) joint motion training. Further, the performance regarding the interaction torque’s magnitude significantly increased during (p-value = 0.03) and after (p-value = 68.59×10-3) user participation training. The experimental group and a technical person reported promising usability of the biofeedback and highlighted the importance of the timely cues from physiotherapist-oriented strategies. Less significant improvements in patient–exoskeleton compliance were observed in the control group. The overall findings suggest that the proposed biofeedback was able to improve the participant-exoskeleton compliance by enhancing human-robot interaction; thus, it may be a powerful tool to accelerate post-stroke ankle-foot deformity recovery.

Resumo -O objetivo deste trabalho foi determinar as mudanças fisiológicas que ocorrem em acariquara (Minquartia guianensis) durante o processo de aclimatação à alta irradiância, bem como a estratégia de aclimatação dessa espécie. Plantas mantidas em baixa irradiância foram transferidas para alta irradiância por 290 dias. Durante esse período, foi medida a relação entre fluorescência variável e máxima (F v /F m ), em folhas desenvolvidas à sombra e, após a senescência prematura por foto-oxidação, em folhas aclimatadas ao sol. Ao final do experimento, foram determinadas as características fotossintéticas e anatômicas da folha. A exposição à alta irradiância causou, logo após a transferência, forte fotoinibição e foto-oxidação parcial da folhagem, mas não provocou a morte da planta. Folhas produzidas no ambiente ensolarado apresentaram valores de F v /F m similares aos do controle. A fotossíntese saturada por luz e a fotossíntese saturada por CO 2 foram 90 e 50% maiores em plantas aclimatadas à alta irradiância. A velocidade máxima de carboxilação da rubisco e a taxa máxima de regeneração da ribulose bisfosfato seguiram a mesma tendência. Folhas produzidas ao sol apresentaram maior densidade estomática e maior espessura foliar. A produção de folhas novas é a principal estratégia de aclimatação da acariquara à alta irradiância.Termos para indexação: Minquartia guianensis, características da folha, características fotossintéticas, fluorescência da clorofila, fotoinibição. Acclimation of manwood seedlings to full sunlightAbstract -The aim of this work was to determine the physiological changes that occur in manwood (Minquartia guianensis) during the acclimation process to high irradiance, and also to determine the acclimation strategy of this species. Plants kept in low light were transferred to high irradiance for 290 days. During this period the ratio between variable fluorescence and maximum fluorescence (F v /F m ) was measured in leaves developed in the shade, and after premature senescence due to photooxidation, in sun-acclimated leaves. At the end of the experimental period the anatomic and photosynthetic characteristics of leaves were determined. Exposure to high irradiance caused, just after transferring, strong photoinhibition and partial photooxidation, but did not cause plant death. Leaves produced in sunny environment showed F v /F m similar to that of control plants. Light-saturated photosynthesis and CO 2 saturated-photosynthesis were 90 and 50% higher in plants acclimated to high irradiance. The maximum carboxylation velocity of rubisco and the maximum rate of ribulose bisphosphate regeneration followed the same trend. Leaves produced under sunlight had higher stomatal density and increased leaf thickness. The production of new leaves is the main acclimation strategy to high irradiance in manwood.

RESUMOLight and soil water availability may limit carbon uptake of trees in tropical rainforests. The objective of this work was to determine how photosynthetic traits of juvenile trees respond to variations in rainfall seasonality, leaf nutrient content, and opening of the forest canopy. The correlation between leaf nutrient content and annual growth rate of saplings was also assessed. In a terra firme rainforest of the central Amazon, leaf nutrient content and gas exchange parameters were measured in five sapling tree species in the dry and rainy season of 2008. Sapling growth was measured in 2008 and 2009. Rainfall seasonality led to variations in soil water content, but it did not affect leaf gas exchange parameters. Subtle changes in the canopy opening affected CO 2 saturated photosynthesis (A pot , p = 0.04). Although A pot was affected by leaf nutrient content (as follows: P > Mg > Ca > N > K), the relative growth rate of saplings correlated solely with leaf P content (r = 0.52, p = 0.003). At present, reduction in soil water content during the dry season does not seem to be strong enough to cause any effect on photosynthesis of saplings in central Amazonia. This study shows that leaf P content is positively correlated with sapling growth in the central Amazon. Therefore, the positive effect of atmospheric CO 2 fertilization on long-term tree growth will depend on the ability of trees to absorb additional amount of P.Key words: canopy opening, mineral nutrition, potential nutrient use efficiency, rainfall seasonality. O crescimento de arvoretas correlaciona-se com a fotossíntese e teor de fósforo foliar na Amazônia central A disponibilidade de luz e o conteúdo de água do solo podem limitar a fixação de carbono de árvores em florestas tropicais. O objetivo deste trabalho foi determinar como as características fotossintéticas de árvores juvenis (arvoretas) respondem às variações na sazonalidade das chuvas, teor de nutrientes da folha e a abertura do dossel da floresta. Avaliou-se também a correlação entre o crescimento anual das arvoretas e o teor de nutrientes na folha. Parâmetros de trocas gasosas e teor foliar de nutrientes foram mensurados, na estação seca e chuvosa de 2008, em cinco espécies de árvores numa floresta de terra-firme na Amazônia central. O crescimento anual das arvoretas foi mensurado em 2008 e 2009. A sazonalidade das chuvas causou variações na umidade do solo, mas não afetou os parâmetros de trocas gasosas. Mudanças sutis na abertura de dossel afetaram a fotossíntese saturada por CO 2 (A pot , p = 0.04). Embora A pot tenha sido afetado pelos teores de nutrientes da folha (nesta ordem: P > Mg > Ca > N > K), a taxa de crescimento relativo das arvoretas correlacionou-se apenas com o conteúdo de P foliar (r = 0.52, p = 176 Ricardo Antonio Marenco et al. Ricardo Antonio

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