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.

Water deficiency during the dry seasons influences the relationship between water and gas exchange in tropical grasses, reducing their productive potential. In addition, the phosphorus (P) deficiency Brazilian soils adds to the set of factors limiting crop production. In this context, the objective of this study was to evaluate the responses of different tropical forage species to phosphorus supplementation as mitigating the damage caused by water stress. Seeds of Urochloa brizantha cv. MG-4, Urochloa decumbens cv. Basilisk, Panicum maximum cv. Áries, Panicum maximum cv. Tanzânia and Paspalum atratum cv. Pojuca were germinated in pots containing 10 liters of red-yellow Acrisol type soil. Experiments were conducted by combining levels of phosphorus, 8,0 and 100,0 mg of P dm-3, with two irrigation regimes, 100 and 40% replacement of transpired water. The biometric parameters, photosynthetic capacity, leaf water potential and soil chemical characteristics were evaluated, and the data was submitted to analysis of variance (ANOVA, p < 0.05), and subsequently the means were compared using a Tukey test (p < 0.05). The results showed for tropical grasses grown under water stress, there is a clear mitigating effect of phosphorus supplementation, especially on the maintenance of biomass growth.

Photosynthetic process of common bean plants (Phaseolus vulgaris L.) was evaluated from short-term root flooding and recovery conditions. Common bean plants (BRS Expedito genotype) were grown in single plastic pots (1 L), containing soil as substrate. At the early reproductive stage (R1), distilled water was added up to 20 mm above the soil surface to flood the root system of plants for 1 day. The flooding was maintained by fitting a second pot without holes. After 1 day of flooding, the pots without holes were removed to drain water and recover the plants. Control plants were kept under normoxia. Chlorophyll a fluorescence transient, gas exchange, glycolate oxidase, antioxidative enzymes, reactive oxygen species (ROS) and lipid peroxidation were measured in leaves upon flooding (1 day) and recovery (1, 3 and 7 days) conditions. Root flooding (1 day) induced decrease (two-fold) in CO 2 assimilation rate and did not recover even after 7 days of normoxic conditions was re-established, besides limited transpiration rate and decreases in stomatal conductance. Moreover, the continuous light energy absorption by chlorophylls induced an increase in fluorescence and heat and impaired the connectivity between photosystems I and II, leading to ROS formation. The antioxidative enzyme system induced upon flooding and recovery conditions did not deal efficiently with ROS, which led to oxidative damage (lipid peroxidation) in leaves of common bean. Therefore, short-term root flooding impairs photosynthetic process recovery of common bean plants upon re-establishment of normoxic conditions. Keywords Antioxidative enzymes Á Oxidative damage Á Phaseolus vulgaris L. Á Photosynthesis Á Waterlogging 1 Introduction Climate changes are increasing flooding events since the 1950 0 s worldwide (Bailey-Serres et al. 2012; Limami et al. 2014; Pedersen et al. 2017), especially in the 28 million hectares of flood-prone located in Cerrado and lowlands in the South of Brazil (Jackson and Colmer 2005), due to increases in heavy rainfall (IPCC 2014). Currently, the lowland areas are mainly occupied with rice cropping system (Garcia et al. 2020), and food production by small farmers, such as common bean (Phaseolus vulgaris L.). Common bean

This study aimed to assess the capacity of two methods of application of salicylic acid (SA) to mitigate the effects of water deficit during the vegetative growth of tomato (Solanum lycopersicum L.) plants comparatively evaluated by growth, physiological and biochemical responses. Under greenhouse conditions, a combination of two factors was tested. The first was SA application: without SA, seed priming with SA, and soil drench with SA solution at 19 days after seedling emergence. The second factor, water limitation (20, 30, 40, and 100% of water holding capacity of the substrate) was applied 28 days after seedling emergence for 5 days. Results showed that plant growth and photosynthetic activity were significantly inhibited by the water deficit. On the other hand, water use efficiency, activities of superoxide dismutase, ascorbate peroxidase, catalase and contents of malondialdehyde, hydrogen peroxide and osmoprotectants were significantly increased by water deficit. Seed priming with SA induced increases in leaf area, root dry weight and root/shoot ratio under drought conditions. Soil drench with SA induced improvements in CO 2 assimilation rate and stomatal conductance in well-irrigated plants. Even when, in general, the activity of antioxidant enzymes was not increased by the application of SA, the cellular redox homeostasis was maintained through increases in the contents of proline and total soluble sugars from the degradation of starch. Seed priming with SA is a suitable technique to mitigate the damaging effects of severe water deficit while maintaining plant growth.