9409395 Watson Persistence of plant populations in nature is partly due to their success at sexual reproduction --i.e., their production of seeds. Among the determinants of plant reproductive success are (1) their schedules of reproduction through time, or life histories, and (2) the amount of resources available to them at critical points in the expression of these life histories. Because plants grow and reproduce by building new leaves and flowers, the expression of a plant's life history is the result of on-going developmental decisions about the type of structures it makes. And because a structure cannot both be vegetative and flowering, there is an inherent trade-off between plant growth and reproduction. The trade-off between growth and reproduction is complicated be the interaction between (1) the expression of the plant's developmental program, which specifies when and what type of new structures may be made, and (2) the efficiency of a particular type of structure in resource accumulation. Some structures will add to the plant's future growth potential, others detract, thus influencing the course of subsequent development and reproductive success. In producing vegetative structures, for example, plants may increase their lifetime seed production through increases in plant size and vigor. Little is known about how the interaction between developmental program and resource use actually results, mechanistically, in the expression of a particular life history. The interactions between developmental program, seasonal patterns of resource uptake and use, and life history in the herbaceous perennial, mayapple (Podophyllum peltatum) will be studied. Mayapple is an ideal plant for such studies because each year its rhizome faces a simple developmental decision whether to produce a reproductive shoot or a single leaf; only one such structure is made. Longterm studies of native populations are used to (1) construct a developmental timetable for shoot type determination, (2) examine the interaction between the degree and pattern of resource uptake and use and shoot determination, and (3) determine whether differences in the timing of developmental events, as manifested by different clones, affect longterm demography and, hence, fitness. This study also will reveal at what points selection may act to alter the timing of developmental events, thus contributing to understanding of how different life histories evolve -- a critical issue for plants facing rapidly changing environments, as well as for the modification of crop plants for higher productivity.
