Resumo -O objetivo deste trabalho foi avaliar a interferência da adubação potássica em parâmetros fisiológicos de duas cultivares de soja, sob diferentes regimes hídricos. O experimento foi realizado em condições de casa de vegetação, em Presidente Prudente, SP. Utilizou-se o delineamento experimental inteiramente casualizado, em arranjo fatorial 2x2x3, com as cultivares BR-16 (tolerante ao estresse hídrico) e Embrapa 48 (suscetível), regimes hídricos com reposição diária de água de 100% (controle) e de 40% da capacidade de campo, e três níveis de suplementação com K (0, 90 e 180 mg dm -3). Duas semanas após a imposição da restrição hídrica, foram avaliados: conteúdo relativo de água, potencial fotossintético e rendimento de biomassa. As plantas que se desenvolveram sob restrição hídrica tiveram sua capacidade fotossintética reavaliada após 12 horas de reidratação. Em condições de restrição hídrica, a adubação potássica não interferiu significativamente nos parâmetros fisiológicos e de crescimento avaliados. A suplementação com potássio promoveu melhor eficiência dos parâmetros fisiológicos, no regime sem deficiência hídrica, nas duas cultivares, e as principais variáveis influenciadas pelo nutriente foram: condutância estomática, taxa máxima de carboxilação da Rubisco e assimilação máxima de CO 2 . A suplementação com K melhora a recuperação fotossintética das plantas após a reidratação, especialmente na cultivar Embrapa 48.Termos para indexação: Glycine max, biomassa, deficit hídrico, fotossíntese, nutrição. Physiological responses of soybean cultivars to potassium fertilization under different water regimesAbstract -The objective of this work was to evaluate the interference of potassium fertilization on the physiological parameters of soybean cultivars under different water regimes. The experiment was carried out in greenhouse at Presidente Prudente, SP, Brazil. The experimental design was a completely randomized block in a 2x2x3 factorial arrangement, with the soybean cultivars BR-16 (tolerante ...) and Embrapa 48 (suscept...), water regimes with daily replacements of 100% (control) and 40% of the field capacity, and three levels of K supplementation (0, 90, and 180 mg dm -3). Relative water content, photosynthetic potential, and biomass yield were evaluated two weeks after the initiation of water restriction. Plants grown under water restriction had their photosynthetic potential reevaluated after 12 h of rehydration. Under water restriction conditions, potassium fertilization did not significantly affect the assessed growth and physiological parameters. Supplementation with potassium promoted a better efficiency of the physiological parameters, in water deficit control, in both cultivars, and the main variables influenced by the nutrient were: stomatal conductance, maximum rate of Rubisco carboxylation, and maximum CO 2 assimilation. Potassium supplementation improves photosynthetic recovery of plants after rehydration, especially in the Embrapa 48 cultivar.Index terms: Glycine max, biomass, water deficit...

This study assessed the photosynthesis, biomass, and phytoenergy production in sugarcane plants subjected to water deficit during the initial stages of development. We hypothesize that the limitations imposed by water deficit on photosynthesis proportionally affect carbon balance, growth, and partitioning of phytoenergy in sugarcane. This study was carried out during 5 months in a growth chamber and water deficit was induced by maintaining soil moisture at 20 % of the maximum water holding capacity (WHC). As control, one group of plants was maintained at 100 % WHC. Water deficit reduced the carboxylation of Rubisco and PEPCase significantly, which were the main limiting factors for photosynthesis. As consequence, the daily leaf carbon balance was significantly reduced by drought. The total accumulated dry matter in well-watered plants was 3.6 times higher than in drought-stressed ones. Water deficit reduced the energy accumulated in sugarcane plants by approximately threefold. Regardless of water regime, a large fraction of the converted energy was not found in stalks. Under water deficit, less than 20 % of the energy is stored in stalks. Since only a tiny fraction of solar energy is used for the production of first generation ethanol, our study reinforces the importance of evaluating strategies to optimize the use of sugarcane, for example, harvesting plant organs other than stalks.

The objective of this study was to identify how changes in the photosynthetic network would be linked to the homeostasis modulation of a drought tolerant sugarcane cultivar subjected to severe water deficit. Moreover, we tested the potential effect of phosphorus supply on the plant physiological responses to drought, because such element is essential to photosynthetic processes. This study was carried out in a greenhouse, where sugarcane plants (Saccharum spp.) cv. RB 86-7515 were grown. One singlenode stalk segment was planted in plastic pots (20 L) filled with soil (red-yellow ultisol). Soil fertilization was performed according to the chemical analysis, except for the phosphorus (P) supply. Plants were subjected to the original P concentration in soil (36 mg dm -3 ) or supplied with 50 mg P2O 5 dm -3 using CaH 4 (PO 4 ) 2 . Plants were irrigated daily until the beginning of drought treatment. After 90 days of shoot emergence, the water deficit was started at the phenological phase II (tillering). Plants were irrigated with the equivalent to 100% (control) or 10% (water deficit) of daily water requirement based on the evapotranspiration. Light response curves of leaf gas exchange and other physiological and growth variables were performed in each treatment. Data were subjected to analysis of variance and the mean values were compared by Tukey's test (p \ 0.05). To assess changes in system network, we evaluated the occurrence of photosynthetic system modulation under distinct water regimes and phosphorus supplying via the concept and measurement of global connectance, C g . Set of results from coefficient of variation (CV) and C g analyses indicated adjustments in the relationships among the elements of the leaf gas exchange network that support the high drought tolerance of the sugarcane cultivar RB 86-7515 and such adjustments enabled the homeostasis of both photosynthesis and plant growth under water deficit. Moreover, P supply improved the sugarcane acclimation capacity by affecting plant characteristics related to water status and photosynthetic performance and causing network modulation under water deficit.

-The objective of this work was to evaluate the effect of plant densities and sidedressed nitrogen (N) rates on nutrition and productive performance of the common bean cultivars IPR 139 and Pérola. For each cultivar, a randomized complete block experimental design was used in a split-plot arrangement, with three replicates. Plots consisted of three plant densities (5, 7, and 9 plants ha -1 ) and subplots of five N rates (0, 30, 60, 120, and 180 kg ha -1 ). Aboveground dry matter, leaf macro-and micronutrient concentrations, yield components, grain yield, and protein concentration in grains were evaluated. Lower plant densities (5 and 7 plants m -1 ) increased aboveground dry matter production and the number of pods per plant and did not reduce grain yield. In the absence of N fertilization, reduction of plant density decreased N concentration in common bean leaves. Nitrogen fertilization linearly increased dry matter and leaf N concentration, mainly at lower plant densities. Regardless of plant density, the N supply linearly increased grain yield of cultivars IPR 139 and Pérola by 17.3 and 52.2%, respectively.Keywords: Phaseolus vulgaris. Nitrogen. Plant population. Mineral nutrition. Grain yield. DENSIDADE DE PLANTAS E ADUBAÇÃO NITROGENADA NA NUTRIÇÃO E PRODUTIVIDADE DE CULTIVARES DE FEIJÃORESUMO -O objetivo do trabalho foi avaliar o efeito da densidade de plantas na fileira e de doses de nitrogênio (N) em cobertura na nutrição e desempenho produtivo das cultivares de feijão comum IPR 139 e Pérola. Para cada cultivar, o delineamento experimental utilizado foi em blocos ao acaso, em parcelas subdivididas e três repetições. As parcelas consistiram de três densidades de plantas (5, 7 e 9 plantas m -1 de fileira) e as subparcelas de cinco doses de N (0, 30, 60, 120 e 180 kg ha -1 ). Foram avaliadas: matéria seca da parte aérea, teores de macro e micronutrientes na folha diagnose, componentes da produção, produtividade de grãos e teor de proteína nos grãos. Menores densidades de plantas (5 e 7 plantas m -1 ) proporcionaram maior produção de MS e número de vagens por planta e não reduziram a produtividade de grãos. Na ausência da adubação nitrogenada, a redução da densidade de plantas diminuiu o teor de N nas folhas do feijoeiro. A adubação nitrogenada aumentou linearmente a produção de matéria seca e o teor de N nas folhas do feijoeiro, principalmente sob as menores densidades de plantas. Independentemente da densidade de plantas, o fornecimento de N aumentou linearmente a produtividade de grãos das cultivares IPR 139 e Pérola em 17,3 e 52,2%, respectivamente.Palavras-chave: Phaseolus vulgaris. Nitrogênio. População de plantas. Nutrição mineral. Produtividade de grãos.

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