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The main objective was to evaluate the effects of seasonal variations in air temperature, soil water content, and irradiation on the net rate of C 0 2 uptake for Agave tequilana growing in a warm subtropical environment (Amatitan, Jalisco, Mexico) and in a temperate subtropical environment (Arandas, Jalisco, Mexico). At Amatitan, the lowest value of positive daily net C 0 2 uptake (141 mmol/m2/d) occurred at the end of the summer rainy season and the highest values during the winter (578 and 921 mmol/m2/d); at Arandas, the lowest value (188 mmol/m2/d) occurred at midsummer and the highest values at the end of the summer (763 mmol/m2/d) and in late winter (572 mmol/m2/ d). The highest values of daily net C02 uptake in both localities reflected prolonged daily periods of net C 0 2 uptake that included both daytime and nighttime assimilation accompanied by high rates of nocturnal net C 0 2 uptake due to moderate nighttime air temperatures. High temperatures in the summer reduced daily net C 0 2 uptake at both localities but in late summer, the nighttime temperatures at Arandas were moderate, which lead to high daily net C 0 2 uptake. Leaf succulence allowed substantial daily net C 0 2 uptake when the soil water content was relatively low during the winter and the spring (January-March). Indeed, appreciable daily net C 0 2 uptake occurred throughout the year for A. tequilana at both localities, indicating that this CAM plant species can sequester carbon even during prolonged dry periods. RESUMENEl objetivo principal de Cste trabajo fue evaluar el efecto de la variacidn estacional en la temperatura del aire, el contenido de humedad en el suelo y la irradiacibn en la asimilaci6n neta diaria de C 0 2 en plantaciones cultivadas de Agave tequilanu que crecen en un ambiente d i d o subtropical (Amatitin, Jalisco, MCxico) y en un ambiente remplado subtropical (Arandas, Jalisco, MCxico). En la localidad de Amatitin 10s valores positivos mis bajos de asimilaci6n neta diaria de C 0 2 (141 mmol/m2/d) heron registrados a finales del period0 de lluvias en verano y 10s valores mis altos durance el invierno (578 y 921 mmol/m2/d), mientras que en Arandas 10s valores mis bajos (188 mmol/m2/d) se presentaron a mediados del verano, registrindose 10s mis altos a finales de verano (763 mmol/m2/d) y a finales de invierno (572 mmol/m2/d). Los valores mas altos de asimilaci6n neta diaria de C02 en ambas localidades reflejaron periodos prolongados de asimilaci6n neta diaria de C 0 2 , que incluyeron ranro asimilaci6n diurna como nocturna, las altas tasas de asimilacibn nocturna de C 0 2 se debieron a temperaturas nocturnas moderadas. Las altas temperaturas durante el verano reducen la asimilaci6n neta diaria de COZ en ambas localidades, sin embargo a finales de verano las temperaturas nocturnas de Arandas fueron moderadas, permitiendo alta asimilaci6n neta diaria de C02. La suculencia de la hoja permiti6 que ocurriera una importante asimilaci6n neta diaria de C02 cuando el contenido de humedad en el suelo h e relativamente bajo durante el in...

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Daughter cladodes significantly hasten the effects of drought on mother cladodes by competition for the water supply and thus decrease daily carbon gain by mother cladodes, mainly by inhibiting phase IV of CAM.

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