The pattern of carbon allocation supporting growth of preformed shoot primordia in Acomastylis rossii (Rosaceae).

Extreme preformation, the initiation of leaves or inflorescences more than 1 yr before maturation and function, is common in arctic and alpine habitats. This extended pattern of development provides a potential means to alleviate an apparent asynchrony between carbon supplied by photosynthesis in the summer and carbon demanded by growth in the spring. Allocation of resources to preforming organs has not been studied in herbs with multi-year patterns of preformation. Acomastylis rossii (Rosaceae) in the southern Rockies initiates leaves and inflorescences 2 yr prior to their maturation and function. Allocation to preforming organs in A. rossii was studied by means of a labeled carbon pulse chase experiment. During the summer, carbon is allocated directly to preforming organs and rhizomes from the mature leaves. Additional allocation of carbohydrate into preforming organs occurs in autumn after photosynthesis by mature leaves has ceased. Organ primordia initiated in the second year do not receive a substantial quantity of the labeled carbon from reserves stored in the rhizome the previous year. We conclude that concurrent photosynthesis is the primary source of carbon for preformation development.