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Abstract:Plants are composed of modules that may be integrated to varying degrees. To examine the extent of integration for photosynthate in female Oemleria cerasiformis (H. & A.) Landon at different times during reproduction, we defoliated terminal branch systems at two scales (0.25 and 1.0 m) just after flowering. Fruit set and mass in the current year were unaffected by defoliation, indicating that developing fruits were strong sinks that could effectively draw on photosynthate from leaves at least 1 m away. In the subsequent year, however, defoliated branches grew very little and produced few flowers and almost no fruits, indicating that storage, growth, and the initiation of flowers and fruit did not utilize carbon resources from leaves only 0.25 m away. Thus, there is no single module size for photosynthate in O. cerasiformis. Because fruits are a strong sink that can draw carbon resources from a considerable distance, high fruit set followed by adverse conditions can lead to generalized resource depletion within a plant, which may result in mortality and contribute to the male-biased sex ratios often observed in O. cerasiformis.
Key words: costs of reproduction, defoliation, fruit set, fruit mass, integrated physiological units.
Resume : Les plantes sont constituees de modules qui peuvent etre integres a differents degres. Afin d'examiner l'etendue de l'integration pour les photosynthetats, a differents etapes de la reproduction, chez l'Oemleria cerasiformis (H. & A.) Landon femelle, les auteurs ont defolie les systemes de branches terminales, a deux echelles (0,25 et 1,0 m), juste apres la floraison. Dans l'annee courante, la mise a fruit et leur masse n'ont pas ete affectees par la defoliation, ce qui indique que les fruits en developpement sont de puissants puits qui peuvent effectivement absorber les photosynthetats a partir des feuilles, sur au moins 1 m de distance. Au cours de l'annee subsequente, cependant, les branches defoliees poussent tres peu et produisent moins de fleurs et presque pas de fruits, ce qui indique que les reserves, la croissance et l'initiation des fleurs et des fruits n' utilisent pas les sources de carbone a partir des feuilles situees a seulement 0,25 m de distance. Ainsi il n'y a pas de dimension de module unique pour les photosynthetats chez l'O. cerasiformis. Parce que les fruits constituent un puissant...