EXTREME PREFORMATION IN ALPINE POLYGONUM-VIVIPARUM - AN ARCHITECTURALAND DEVELOPMENTAL ANALYSIS

Preformation, the initiation of organs one or more years prior to matu ration and function, is reported to be common and crucial for plant su rvival in arctic and alpine environments, yet the phenomenon is remark ably little studied. in order to understand the role of preformation i n the ecology and evolution of tundra species. this investigation take s a developmental and architectural approach to the analysis of plant growth and reproduction in the alpine perennial Polygonum viviparum L. Analyses show that the extent and duration of preformation in P., viv iparum are extraordinary. Four years are required for each leaf and in florescence to progress from initiation to functional and structural m aturity. This single salient feature of development has profound conse quences for basic architecture, dynamics of resource allocation, and t he timing of plant responses to environmental variation. As a conseque nce of the protracted duration of leaf and inflorescence development, five cohorts of primordia, initiated in successive years, are borne si multaneously by an individual plant. In the year prior to maturation l eaves reach 30% of their maximum size, and the maximum potential repro ductive output of each inflorescence is determined. Thus, developmenta l processes that affect final morphology and resource allocation occur at least 1 yr before functional maturity. From the developmental and architectural models constructed for P. viviparum, a I-yr delay in mea surable plant responses to environmental variation is predicted. The m odels also apply generally to arctic and alpine species and provide a mechanistic explanation for observed patterns of productivity at the c ommunity and ecosystem scale.