HANNAN, GARY L. Department of Biology, Eastern Michigan University, Ypsilanti, MI, 48197. - Size-related changes in biomass allocation to male and female function in a wind-pollinated annual plant.
Platystemon californicus is a self-compatible,
perfect-flowered, wind-pollinated annual plant exhibiting strict
modular architecture (solitary flower per node) and extreme
variability in numbers of stamens and carpels within flowers. Theory
predicts that wind-pollinated species should allocate an increasing
proportion of resources to male function as plants become larger. I
found that larger plants produced more massive flowers (300-400%
increase) and invested proportionally more resources (estimated as
biomass) in stamens than in carpels than did flowers of smaller
plants. Carpels represented less than 20% of the biomass contained in
stamens at anthesis. Total flower biomass at anthesis and allocation
to stamens vs. carpels also change at successively formed nodes. The
first flower on a plant (the only flower produced by the smallest
plants) produced fewer stamens and carpels and had a lower ratio of
stamens to carpels than did subsequently produced flowers. Allocation
shifts without a change in architecture suggest that changes in
resource availability occur at successive nodes as plants grow larger.
If resource availability influences allocation patterns within flowers
and if carbon is a limiting resource, then carbon distribution
patterns among nodes or carbon fixation rates at independent nodes
must change during plant development. Such changes have been found in
crop plants, but many models of resource allocation ignore
demand-driven changes in carbon transport or photosynthetic rate and
assume a constant resource pool.
Key words: architecture, Papaveraceae, Platystemon, reproduction, resource allocation, sex allocation