Extreme preformation, the initiation of leaves or inflorescences more than one year 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. The cost of storing carbohydrates for the next year’s spring growth may be reduced by allocating carbohydrate directly from photosynthesizing leaves to the growth of preforming organs which will mature in subsequent years. Allocation of resources to preforming organs has, however, previously been unstudied in plants with multi-year patterns of preformation. Populations of A. rossii in the southern Rockies have been observed to initiate leaves and inflorescences two years before the year of maturation and function. Allocation to preforming organs in A. rossii was studied by means of a labeled carbon pulse chase experiment. Plants were labeled by exposure to a 13CO2 enriched atmosphere for one photoperiod during the 1998 summer growing season. Plants were then harvested and analyzed by mass spectrometry over the course of the subsequent thirteen months to determine the distribution of the 13C label. During the summer growing season carbon is allocated directly to preforming organs and rhizomes from the mature leaves. Additional allocation of carbohydrate into preforming organs occurs in autumn after these leaves have stopped photosynthesizing. Existing preformed organ primordia do not subsequently receive additional inputs of labeled carbon from rhizomes in the second year of development. Newly initiated organ primordia initiated in the second year do not receive any of the labeled carbon initially allocated to storage in the rhizome the previous year.

Key words: Acomastylis rossii (Rosaceae), alpine, carbon allocation, preformation