title: Photosynthetically active radiation and carbon gain drives the southern orientation of Myrtillocactus geometrizans fruits.
abstract: The equatorial orientation of reproductive structures is known in some columnar cacti from extratropical deserts. It has been hypothesised that photosynthetically active radiation (PAR) interception is the main reason for this orientation, because of its key effect on nocturnal CO2uptake. However, there are no studies addressing both the effect of PAR and its consequence, carbon gain, on fruit orientation. Accordingly, we tested whether PAR and carbon gain could explain the southern fruit orientation of Myrtillocactus geometrizans, an inter-tropical columnar cactus. We studied three populations of M. geometrizans in Mexico. For each population, azimuth of fruits, total daily PAR, nocturnal acid accumulation (NAA) and fruit production were measured. The relationships between rib orientation and number of fruits, as well as total daily PAR, were evaluated using periodic regressions. The effect of total daily PAR and NAA on number of fruits was assessed using generalised linear models. During spring, mean fruit orientation had a south azimuth for three populations. Likewise, rib orientation had a significant effect on fruit production, with the south-facing ribs having the maximum number of fruits. Total daily PAR was highest in the south-facing ribs, at least for those in the northern and central populations. Furthermore, during spring, there was a significant positive effect of total daily PAR and NAA on fruit production. Our results provide strong evidence that the higher carbon gain in equatorial ribs, through a highest interception of PAR, would be the responsible factor for equatorial orientation of fruits in an inter-tropical columnar cactus.
authors.affiliation: Doctorado en Ciencias Biológicas y de la Salud, Universidad Autónoma Metropolitana-Iztapalapa, Ciudad de México, México.|Departamento de Biología, Universidad Autónoma Metropolitana-Iztapalapa, Ciudad de México, México.
authors.forename: A
authors.initials: A
authors.lastname: Ponce-Bautista
authors.affiliation: Departamento de Biología, Universidad Autónoma Metropolitana-Iztapalapa, Ciudad de México, México.
authors.forename: P L
authors.initials: PL
authors.lastname: Valverde
authors.affiliation: División de Ciencias Ambientales, Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, SLP, México.
authors.forename: J
authors.initials: J
authors.lastname: Flores
authors.affiliation: Departamento de Biología, Universidad Autónoma Metropolitana-Iztapalapa, Ciudad de México, México.
authors.forename: A
authors.initials: A
authors.lastname: Zavala-Hurtado
authors.affiliation: Departamento de Biología, Universidad Autónoma Metropolitana-Iztapalapa, Ciudad de México, México.
authors.forename: F
authors.initials: F
authors.lastname: Vite
authors.affiliation: Departamento de Biología, Universidad Autónoma Metropolitana-Iztapalapa, Ciudad de México, México.
authors.forename: G
authors.initials: G
authors.lastname: López-Ortega
authors.affiliation: Departamento de Biología, Universidad Autónoma Metropolitana-Iztapalapa, Ciudad de México, México.
authors.forename: M A
authors.initials: MA
authors.lastname: Pérez-Hernández
mesh_terms: D029421:Cactaceae / Q000502:physiology* / Q000528:radiation effects; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D005638:Fruit / Q000502:physiology* / Q000528:radiation effects; D008800:Mexico; D010788:Photosynthesis / Q000528:radiation effects*; D012621:Seasons; D013472:Sunlight
chemical_list: D002245:Carbon Dioxide; D002244:Carbon
keywords: Columnar cactus; fruit orientation; nocturnal acid accumulation; photosynthetically active radiation