Bottom-up effects of nutrient availability on flower production, pollinator visitation, and seed output in a high-Andean shrubReportar como inadecuado




Bottom-up effects of nutrient availability on flower production, pollinator visitation, and seed output in a high-Andean shrub - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.

Resumen

Soil nutrient availability directly enhances vegetative growth, flowering, and fruiting in alpine ecosystems. However, the impacts of nutrient addition on pollinator visitation, which could affect seed output indirectly, are unknown. In a nutrient addition experiment, we tested the hypothesis that seed output in the insect-pollinated, self-incompatible shrub, Chuquiraga oppositifolia Asteraceae of the Andes of central Chile, is enhanced by soil nitrogen N availability. We aimed to monitor total shrub floral display, size of flower heads capitula, pollinator visitation patterns, and seed output during three growing seasons on control and N addition shrubs. N addition did not augment floral display, size of capitula, pollinator visitation, or seed output during the first growing season. Seed mass and viability were 25-40% lower in fertilised shrubs. During the second growing season only 33% of the N addition shrubs flowered compared to 71% of controls, and a significant 50% enhancement in vegetative growth occurred in fertilised shrubs. During the third growing season, floral display in N addition shrubs was more than double that of controls, received more than twice the number of insect pollinator visits, and seed output was three- to four-fold higher compared to controls. A significant 50% enhancement in vegetative growth again occurred in N addition shrubs. Results of this study strongly suggest that soil N availability produces strong positive bottom-up effects on the reproductive output of the alpine shrub C. oppositifolia. Despite taking considerably longer to be manifest in comparison to the previously reported top-down indirect negative effects of lizard predators in the same study system, our results suggest that both bottom-up and top-down forces are important in controlling the reproductive output of an alpine shrub.



Autor: Muñoz, Alejandro A.; - Celedón Neghme, Constanza; - Cavieres, Lohengrin A.; - Kalin Arroyo, Mary T.; -

Fuente: http://repositorio.uchile.cl/



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