THE MEANING AND MEASUREMENT OF REPRODUCTIVE EFFORT IN PLANTS WITH SPECIFIC REFERENCE TO AGROPYRON REPENS (RESOURCE ALLOCATION, CURRENCY OF ALLOCATION, ALLOMETRY, GROWTH ANALYSIS)

Reproductive effort, or the proportion of an organism's resources allocated to reproduction is a crucial aspect of an organism's life history and the optimal allocation of resources to reproduction in different environments has been the subject of much theorizing. Adequate tests of these theories have been hampered by the difficulties involved in assessing reproductive effort: (1) what structures and activities should be considered part of reproduction, (2) what resource should be used as the currency of allocation, and (3) does resource allocation to reproduction necessarily reflect the "effort" involved in reproduction? The first of these problems was addressed using allometric relationships between plant parts in vegetative plants, and time dependent models of activity rates in these plants to delineate which structures and activities in reproductive plants were vegetative in character and which were reproductive. There were both genotypic and environmentally induced differences in the proportion of resources allocated to ancillary reproductive structures and activities; therefore, methods of assessing reproductive effort based upon biomass allocation to flowers and fruits may not be indicative of total resource allocation to reproduction. With regard to the question of what currency to use, carbon may be most suitable because of its important energetic role in plants. It was shown that the respiratory cost of plant growth increased as the concentration of nitrogen and phosphorus increased and furthermore, that the respiratory cost per unit of nutrient increased as the nutrients became less available. Carbon allocation will, therefore, tend to reflect the allocation of these nutrients, particularly as these nutrients become more limiting. With regard to the third problem, the cost of reproduction in terms of lost vegetative growth was compared to the amount of resources allocated to reproduction. Genotypic and environmentally induced differences in the relationship between these two measures suggest that differences among plants in the resources allocated to reproduction will not necessarily reflect differences in the cost of reproduction. To test current theory, it will be necessary not only to consider resources allocated to propagules, but also the total resources allocated to reproduction, and the effect of this allocation on vegetative activity.