The purpose of this study is to evaluate the relationship between Si and NH4+ toxicity in the context of the nutrition, physiology, and production of sugar beet grown using hydroponics. We hypothesized that NH4+ affects the physiology of the plant, accumulation of nutrients, and dry matter, with the possibility for Si to mitigate this toxicity. The experimental design used was completely randomized, in a factorial scheme of 2 × 5, corresponding with the absence and presence of Si (2 mmol L −1) and five concentrations of NH4+ with four replicates. The following series of physiological evaluations were carried out: photosynthesis, stomatal conductance, transpiration, with the use of an infrared gas analyzer (LICOR, Inc., LI-6400), the dry biomass, N and Si accumulation, and Si use efficiency in the roots. Accumulation of N and photosynthesis in the leaves was higher in the presence of Si. An increase of NH4+ increased transpiration, especially in the plants cultivated without the incorporation of Si. Stomatal conductance was lower in the presence of Si. Dry matter was reduced when plants were exposed to higher concentrations of NH4+, showing a greater reduction in the root than in the aerial part. The use of NH4+ equal to or higher than 15 mmol L −1 damaged the photosynthesis. Transpiration and stomatal conductance were less affected in the presence of Si and in the accumulation of N and Si in the roots. Dry matter was reduced when plants were exposed to higher concentrations of NH4+, and this effect was mitigated in the presence of Si. Keywords Abiotic stress. Ammoniacal nitrogen. Beneficial element. Vegetables Highlights The negative effects caused by the toxicity of NH 4 + in sugar beet plants, up to concentrations of 15 mmol L −1 , can be mitigated by the presence of Si.

Global warming is predicted to cause more intense extreme events such as heat waves, flooding and severe droughts, producing significant effects on agriculture. In tropics, climate change will severely impact livestock production affecting water availability, forage quality and food for cattle. We investigated the isolated and combined effects of soil water deficit (wS) and + 2°C increase in canopy temperature (eT) on leaf gas exchange, chlorophyll fluorescence, carbohydrate content, forage quality and in vitro dry matter digestibility (IVDMD) of a field‐grown C4 tropical forage grass Panicum maximum Jacq. using a temperature‐free air‐controlled enhancement (T‐FACE) system. The wS and eT treatments showed no effects on photosystem II photochemistry. However, wS under ambient temperature decreased net photosynthesis rate (A), stomatal conductance (gs) and maximum rate of carboxylation of Rubisco (Vcmax), leading to a reduced starch content in leaves. A 16% reduction in leaf dry mass (LDM) and reduction in forage quality by increasing fibers, reducing crude protein (CP) and decreasing the IVDMD was also observed by effect of wS. Warming under adequate soil moisture (eT) significantly increased LDM by 25% but reduced the forage quality, increasing the lignin content and reducing starch, CP and digestibility. The combined wSeT treatment reduced A, gs, Vcmax and the forage quality. When compared to control, the lignin content in leaves increased by 43, 28 and 17% in wS, eT and wSeT, respectively, causing a significant reduction in IVDMD. We concluded that despite physiological mechanisms to acclimate to warming, both warming and water deficit will impair the quality and digestibility of C4 tropical pastures.

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BACKGROUND: High concentrations of ammonium as the sole nitrogen source may result in physiological and nutritional disorders that can lead to reduced plant growth and toxicity. In this study, we hypothesized that ammonium toxicity in radish seedlings (Raphanus sativus L.) might be mitigated by the incorporation of silicon (Si) into applied nutrient solution. To examine this possibility, we conducted a hydroponic experiment to evaluate the effects of five concentrations of ammonium (1, 7.5, 15, 22.5, and 30 mmol L −1) on the photosynthesis, green color index, stomatal conductance, transpiration, instantaneous wateruse efficiency, and biomass production of radish in the absence and presence (2 mmol L −1) of Si. The experimental design was a randomized block design based on a 2 × 5 factorial scheme with four replicates. RESULTS: The highest concentration of applied ammonium (30 mmol L −1) was found to reduce the photosynthesis, transpiration and total dry biomass of radish seedlings, independent of the presence of Si in the nutrient solution. However, at lower ammonium concentrations, the application of Si counteracted these detrimental effects, and facilitated the production of seedlings with increased photosynthesis, greater instantaneous water-use efficiency, and higher total dry biomass compared with the untreated plants (without Si). Transpiration and stomatal conductance were affected to lesser extents by the presence of Si. CONCLUSION: These findings indicate that the addition of Si to nutrient solutions could provide an effective means of alleviating the unfavorable effects induced by ammonium toxicity at concentrations of less than 30 mmol L −1 .

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Con el objetivo de evaluar la asociación entre diferentes formas de aplicación de microorganismos eficientes y la inoculación con Rhizobium en el comportamiento morfológico y productivo del frijol común se desarrolló un experimento en la Cooperativa de Créditos y Servicios “Mártires de Taguasco”, Sancti Spíritus, Cuba, de octubre de 2012 a febrero de 2013 y se utilizó el cv. Cuba cueto. Fueron evaluados dos factores, el primero fue la utilización de Rhizobium (sin y 1 kg/46 kg de semilla) y el segundo fue cuatro formas de aplicación de microorganismos eficientes, sin (0), al surco (100 mg/L), foliares (100 mg/L) y la asociada (surco más la foliar). Los indicadores morfológicos y productivos que se determinaron fueron: promedio de hojas por plantas, altura de las plantas (cm), legumbres por plantas, granos por legumbres, masa de 100 granos (g/100 semillas) y rendimiento (t/ha). Los resultados mostraron que la aplicación asociada al surco más la foliar de microorganismos eficientes comparadas con las otras formas, incrementó los parámetros morfológicos y productivos evaluados como la producción de hojas, altura de la planta, legumbres por planta, granos por legumbre, la masa de 100 semillas y el rendimiento del grano en 153,23 % cuando no fueron inoculadas con Rhizobium y 100,00 % con la inoculación en relación al tratamiento control.