The effects of high root temperatures on nodulation, nitrogen (N) fixation, and dry matter production of ‘Lee’ soybean [Glycine max (L.) Merr.] plants inoculated with 13 different strains of Rhizobium japonicum were studied in the greenhouse. Plants were grown in vermiculite, and their root systems were submerged in thermostatically controlled water baths. A treatment without inoculation in which 12 mM of KNO3 was supplied with the nutrient solution was included.Increasing root temperatures from 28 to 40°C had a detrimental effect on the number of nodules, the specific nitrogenase activity, the N content, and the dry weight of tops and roots of inoculated plants. The magnitude of this effect was highly dependent on the rhizobial strain.For some strains, higher nodule weights and higher total nitrogenase (C2H2 reduction) activity were found at 33 than at 28°C, whereas for other strains, these variables declined with increasing temperatures. It appeared that, with increasing temperatures, the processes determining nodule initiation became susceptible at lower temperatures than those associated with nodule growth.When plants formed nodules under nonlimiting temperatures and then were transferred to stressing root temperatures, appearance of additional nodules, N fixation, and plant growth were restricted by high root temperature. These results indicate that the detrimental effect of increasing root temperatures on inoculated plants is due in part to the reduction in number of nodules formed and also to limitations imposed on other processes of the soybean‐Rhizobium association.The growth of plants supplied with combined N was also adversely affected by continuous high root temperatures. However, while a temperature of 34°C restricted the growth of plants depending on N fixation, it was stimulatory for the growth of plants supplied with combined N. Therefore, the effect of temperatures near 34°C on the growth of nodulated plants without combined N was due mainly to the effect on the symbiotic system and not on other physiological processes of the plant.The response of different Rhizobium strains in symbiosis with soybean plants to increasing temperature was related to their response to temperature in pure culture and modified the adverse effect of temperature on plant development. Therefore, pure culture screening of R. japonicum may be a useful tool to aid in the selection of strains better suited for soil environments where high temperature is a limiting factor for the symbiosis.
This study examined the effect of high root temperatures on nodulation, dinitrogen fixation, and growth of five soybean [Glycine max (L.) Merr.] cultivars associated with either of two Rhizobium japonicum strains of contrasting temperature tolerances. In each of three greenhouse experiments, soybeans growing in pots containing vermiculite were submitted to root temperatures of 28, 33, and 37 C or 28, 33, and 35 C by submerging the pots in thermostatically controlled water baths. In the first experiment, cvs. ‘Hutton’ and ‘Ransom’ were inoculated with either strain USDA 110 or 587, while in the second experiment the same strains were used to inoculate cvs. ‘Gasoy‐17’ and ‘Bragg.’ In a third experiment cvs. Bragg, Gasoy‐17, ‘Lee,’ and Ransom were grown in association with strain 587. Plants were harvested 34 days after germination. The superiority in high temperature tolerance of strain 587 over USDA 110, found in earlier work with cv. Lee, was confirmed for cvs. Gasoy‐17, Hutton, and Ransom. Results with cultivar Bragg were inconsistent for the two experiments in which that genotype was included. The results indicate that soybean genotype influences the response of the symbiotic system to high root temperatures. Gasoy‐17 and Lee appeared to be more tolerant to high root temperature than the other cultivars. That characteristic was enhanced when Gasoy‐17 was associated with the tolerant strain 587. Selection of soybean cultivars with tolerance to high root temperature in symbiotic association with R. japonicum appears to be a feasible alternative to overcome high soil temperature stress and needs to be done in conjunction with strain selection.
Objetivo: Analizar la validez, confiabilidad y baremos de la escala de satisfacción con la vida (SWLS) por Vázquez, Duque y Hervás (2013) en estudiantes universitarios de la ciudad de Bogotá. Método: Participaron en el estudio 121 universitarios de ambos sexos entre los 18 y 45 años. Se utilizó como instrumento para esta investigación la versión traducida y adaptada al español del SWLS por Vázquez, Duque y Hervás (2013). El estudio fue de corte transversal, de tipo instrumental y con un método psicométrico. Resultados: El análisis factorial denota un solo factor que explica el 62,3 % de la varianza total acumulada, modelo que fue confirmado con ecuaciones estructurales y que concuerda con la propuesta teórica de la escala, así como un alfa de Cronbach general de 0,839, correlaciones positivas entre todos los reactivos y apropiada concordancia entre los elementos y el puntaje total corregido. Conclusiones: La Escala de satisfacción con la vida (SWLS) muestra una alta confiabilidad, apropiada consistencia interna entre los reactivos, correlaciones entre elementos y el puntaje total corregido, y concordancia en la estructura factorial con la versión original, lo que indica una adecuada validez de constructo, con apropiada confiabilidad y consistencia en la muestra de estudiantes universitarios, recomendando su aplicación en esta muestra.
A study was conducted to examine the growth responses of different Rhizobium japonicum strains to increasing temperatures, determine the degree of variability among strains in those responses, and identify temperature-related growth characteristics that could be used to select temperature-tolerant strains. Each of 42 strains was grown in liquid culture for 96 h at 19 incubation temperatures ranging from 27.4 to 54.1°C in a temperature gradient apparatus. Growth was estimated by measuring the change in optical density over time. Strains differed in their responses to increasing temperatures. Three characteristic temperatures were determined for each strain: the temperature giving the maximum optical density at 96 h (optimum temperature), the maximum temperature allowing a continuous increase in optical density during the 96-h period (maximum permissive temperature), and the maximum temperature allowing growth of the cultures after they were transferred to a uniform incubation temperature of 28°C (maximum survival temperature). The three characteristic temperatures varied among strains and had the following ranges: optimum temperature, from 27.4 to 35.2°C; maximum permissive temperature, from 29.8 to 38.0°C; and maximum survival temperature, from 33.7 to 48.7°C. Significant positive correlations were found between maximum permissive temperature and optimum temperature and between maximum permissive temperature and maximum survival temperature. Eight strains which had the highest maximum permissive temperature, optimum temperature, and maximum survival temperature were considered tolerant of high temperatures and were able to grow at temperatures higher than those previously reported for the most tolerant R. japonicum strains. The strains were of diverse geographical origin, but the response to high temperatures was not related to their origin. Evaluation of the temperature responses in pure culture may be useful in the search for R. japonicum strains better suited to environments in which high soil temperature is a limiting factor.
Dentro de los constructos que se han estudiado en los últimos años como predictores del desempeño académico se encuentra el factor grit. En la presente investigación se realizaron dos estudios con el objetivo de adaptar y validar la escala Grit-O a un contexto colombiano, así como determinar la validez de criterio de la escala Grit-S por medio del desempeño académico en estudiantes universitarios. En el primer estudio (n = 500) se realizó un análisis factorial exploratorio a través de un método de extracción de mínimos cuadrados no ponderados y un análisis factorial confirmatorio a través de un método de extracción de máxima verosimilitud. Los análisis arrojaron adecuados índices de validez y confiabilidad para las dos escalas (Grit-O y Grit-S) —siendo Grit-S la que presentó mejores índices de ajuste—, y la distribución de ítems por factor de la escala coincidió con la validación original. Sin embargo, los dos factores —perseverancia en el esfuerzo y consistencia en el interés— no se agruparon bajo el constructo grit. En el segundo estudio (n = 89) se observó la relación existente entre la puntuación obtenida en la escala Grit-S y diferentes indicadores de desempeño académico —promedio, número de materias perdidas, entre otros—. Para esto, se realizó un análisis de correlación y de regresión lineal múltiple, tras lo cual se encontraron correlaciones moderadas entre el puntaje total de la escala Grit-S y sus dos componentes con las medidas de desempeño académico. En el análisis de regresión se encontró que el puntaje total de la escala es mejor predictor del desempeño académico (.016**) que el puntaje de cada uno de los componentes de la escala por separado. Al final, en la discusión se comparan los hallazgos con validaciones realizadas en otros países y se dan algunas recomendaciones respecto al uso de la escala.
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