Interactions Between Seedlings of Agave Deserti and the Nurse Plant Hilaria Rigida

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.Wiley is collaborating with JSTOR to digitize, preserve and extend access to Ecology This content downloaded from 128.163.Abstract. Seedlings of the succulent crassulacean acid metabolism (CAM) plant Agave deserti in the northwestern Sonoran Desert were found only in sheltered microhabitats, nearly all occurring under the canopy of a desert bunchgrass, Hilaria rigida. Apparently because soil surface temperatures can reach 71 0C in exposed areas, seedlings were generally located near the center or on the northern side of this nurse plant. Both species have shallow root systems, about half of the roots of H. rigida and all those for seedlings of A. deserti occurring above soil depths of 0.08 m.To examine competition for water between the nurse plant and an associated seedling, a three-dimensional model for root water uptake was developed. The model divided the soil into 17 concentric sheaths each subdivided radially into eight wedges and vertically into nine layers. Predicted pre-dawn soil water potentials at the mean root depth and total shoot transpiration agreed well with field measurements. Simulated annual water uptake by a seedling of A. deserti was reduced 50% when the seedling was moved from an exposed location to the center of the nurse plant. Shading by the nurse plant reduced total daily photosynthetically active radiation (PAR) by up to 74% compared with an exposed seedling. On the other hand, soil nitrogen under the canopy of H. rigida was 60% higher than in exposed locations. Assuming that the effects of nitrogen, temperature, PAR, and soil water on net CO2 uptake are multiplicative, the predicted net CO2 uptake by a seedling of A. deserti under the nurse plant was only -45% of that for an exposed seedling. Thus, although the nurse plant facilitates seedling establishment by reducing maximum soil surface temperatures and provides a microhabitat with higher soil nitrogen levels, its shading and competition for water reduce seedling growth.

Efeitos da seca sazonal e disponibilidade de luz na sobrevivência e crescimento de Bowdichia virgilioides em duas fitofisionomias típicas dos cerrados do Brasil Central

“…Entretanto, os valores de DFF medidos no cerradão foram superiores aos valores medidos abaixo do dossel ou em pequenas clareiras de florestas tropicais (Osunkoya et al 1993, Fetcher et al 1994, provavelmente devido a menor biomassa arbórea do cerradão, quando comparado a florestas tropicais. No campo sujo, a cobertura herbácea apresentou altura máxima de 50 cm e os valores de DFF mantiveram-se na mesma faixa dos valores medidos abaixo do dossel de gramíneas no deserto de Sonora, Estados Unidos (Franco & Nobel 1988). Portanto, pequenas mudanças no tamanho da planta podem levar a um rápido aumento na DFF incidente e, consequentemente, no potencial de assimilação de CO2, resultando numa maior oferta de carbono para o crescimento.…”

Factores ambientales relacionados con la cobertura de Agave angustifolia (Asparagaceae) en el matorral costero de Yucatán, México

“…Aunque la sombra parcial reduce la tasa fotosintética de agaves adultos y juveniles, en otras especies del género, las plántulas originadas a partir de semillas requieren de sombra parcial para poder sobrevivir y crecer en ambientes cálidos y secos (Jordan y Nobel, 1979;Franco y Nobel, 1988). En el caso de Agave angustifolia, para individuos más pequeños, las tasas de fotosíntesis y crecimiento son mayores en individuos que reciben 50% de la luz ambiental total que las iluminadas con mayor o menor intensidad (Cervera, datos sin publicar).…”

“…En las poblaciones de Chuburná y San Benito ha habido poco reclutamiento de plántulas menores a 5 cm de diámetro de copa, lo que es común para especies longevas en ambientes semiáridos y cálidos (Franco y Nobel, 1988;Arias-Medellín et al, 2016;Zepeda et al, 2017).…”

Positive associations between macroalgal species in a rocky intertidal zone and their effects on the physiological performance of Ulva lactuca

“…These positive interactions frequently have been reported in stressful habitats, such as deserts (e.g. Franco & Nobel 1988, Valiente-Banuet et al 1991, Tirado & Pugnaire 2003, high-mountain ecosystems (e.g. Callaway et al 2002, Cavieres et al Positive associations between macroalgal species in a rocky intertidal zone and their effects on the physiological performance of Ulva lactuca ABSTRACT: Positive interactions become more important as physical stress increases.…”