Abstract Physiological and yield evaluation of perennial forage plants grown in intercropping in the semiarid region is indispensable in the search for higher efficiency of the agricultural and livestock production systems. In this context, an experiment was carried out at the Experimental Station of the National Institute of the Semiarid Region - INSA, in the municipality of Campina Grande, Paraíba, Brazil, to evaluate the physiological efficiency and yield of prickly pear and gliricidia in intercropping. Treatments were distributed in randomized blocks, with six replicates, being represented by four spacings between gliricidia plants: S1 (1.0 m), S2 (1.5 m), S3 (2.0 m) and S4 (3.0 m) x 2.30 m between rows. Prickly pear was planted in double rows of 1.5 m x 0.8 m x 0.5 m. The analyzed variables were initial, maximum and variable fluorescence chlorophyll a, variable/initial fluorescence ratio, potential quantum yield and the fresh matter yield of both crops. Density planting of gliricidia up to 4,348 plants ha-1 increases its photochemical efficiency and yield, but reduces light energy capture by prickly pear in intercropping, whereas its yield is not influenced by cultivation density. Regardless of gliricidia density, prickly pear yield was not influenced.

RESUMEN El nopal forrajero Oreja de Elefante Mexicano está ampliamente incorporado a la cadena productiva animal de la región noreste de Brasil. Sin embargo, faltan estudios sobre la dinámica fisiológica de este cactus. Por lo anterior, se realizó este estudio en la Estação Experimental Prof. Ignácio Salcedo del Instituto Nacional do Semiárido (INSA), en Campina Grande, estado de Paraíba, Brasil. El objetivo del estudio fue evaluar la absorción de CO2 y los niveles de eficiencia en el uso del agua in Opuntia stricta (Haw.) durante diferentes estaciones e horas de evaluación. Los tratamientos se distribuyeron utilizando un arreglo factorial de 24×2, que correspondió a la evaluación de los procesos de intercambio de gases durante 24 horas en la época de lluvias (junio) y sequía (diciembre). Los parámetros evaluados fueron la conductancia estomática, la tasa de transpiración y absorción de CO2, la concentración interna de CO2, la eficiencia instantánea de uso del agua y la eficiencia intrínseca de uso del agua. Los resultados revelaron que el intercambio de gases en el nopal forrajero son más intensos durante la estación de lluvias, con buena estabilidad, que los bajos niveles de intercambio durante la estación época de sequía. Independientemente de la estación, la absorción de CO2 alcanzó su pico entre las 24:00 y las 2:00. Además, este intervalo de tiempo es el más adecuado para realizar análisis en condiciones de campo.

ABSTRACT The forage cactus Mexican Elephant Ear is widely incorporated into the animal productive chain of the northeast region of Brazil. However, there is a lack of studies on the physiological dynamics of this cactus. Therefore, this study was conducted at the Estação Experimental Prof. Ignácio Salcedo of the Instituto Nacional do Semiárido (INSA), in Campina Grande, State of Paraíba, Brazil. The aim of this study was to evaluate CO2 uptake and water-use efficiency levels in Opuntia stricta (Haw.) during different seasons and evaluation times. The treatments were distributed using a 24×2 factorial arrangement, which corresponded to the evaluation of gas exchange processes for 24 hours in the rainy (June) and dry (December) seasons. The evaluated parameters were stomatal conductance, transpiration and CO2 uptake rate, internal CO2 concentration,instantaneous water-use efficiency and intrinsic water-use efficiency. The results revealed that gas exchange in the forage cactus was more intense during the rainy season, with good stability, than the low exchange levels during the dry season. Regardless of the season, the CO2 uptake peaked between 24:00 and 02:00. In addition, this range of time is the most suitable to conduct analyses under field conditions.