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(American Journal of Botany. 2005;92:700-708.)
© 2005 Botanical Society of America, Inc.

Ecology

Does cladode inclination restrict microhabitat distribution for Opuntia puberula (Cactaceae)?1

Lugui Sortibrán2,5, Clara Tinoco-Ojanguren3, Teresa Terrazas4 and Alfonso Valiente-Banuet2

2Instituto de Ecología, UNAM, Departamento de Ecología de la Biodiversidad, Apartado Postal 70-275, C. P. 04510, México, D. F. México; 3Instituto de Ecología, UNAM, Departamento de Ecología de la Biodiversidad, Unidad Regional Noroeste, Apartado Postal 1354, Hermosillo, Sonora, C. P. 83000, México; 4Programa de Botánica, Colegio de Posgraduados, Montecillo, Estado de México, C. P. 56230, México

ABSTRACT

In contrast with other Opuntia species, most of the cladodes of Opuntia puberula have a horizontal position. This study explores whether the horizontal cladodes are an adaptive trait to increase light interception in the understory or are a neutral trait, and if this characteristic may prevent its distribution in full sun habitats. Cladode inclination angle and its effect on light interception, cladode temperature, and carbon gain are characterized, and anatomical and physiological traits of upper and lower cladode surfaces are described. Inclination angle was under 50° for 95% of the cladodes, and the frequency of low inclination angles increases as light availability decreases. Nocturnal acid accumulation increased with total daily PPFD intercepted, but no significant differences were detected between typical horizontal cladodes and the few vertical cladodes. Chlorophyll content differed in the upper and lower surfaces of horizontal cladodes; however, chlorenchyma thickness, stomatal conductance, and nocturnal acid accumulation were similar between surfaces. The horizontal position of O. puberula cladodes, which is anatomically determined, restricts it to shaded habitats, where the plants do not overheat, but seems to have no effect on carbon gain.

Key Words: Cactaceae • carbon gain • cladode position • light interception • Opuntia puberula • plant architecture • Tehuacán Valley • temperature






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