Many plant populations fluctuate between years of high and low seed production. These fluctuations, often called mast-seeding, have typically been attributed to fluctuations in resource availability.
Recent theoretical models show that mast-seeding could also be due to the dynamics of resource allocation within individuals, synchronized among individuals by pollen limitation in low flowering years. This "pollen coupling" mechanism appears to explain synchronous, alternate-year flowering in a perennial wildflower, Astragalus scaphoides. Our past research shows that plants are more pollen limited in low-flowering years, and that pollen coupling models fit to data for this species predict alternate-year flowering in the absence of environmental forcing. Here, we present tests of two additional components of pollen coupling. First, we directly tested whether preventing fruit set caused plants to flower in successive years.
Removing flowers in 2005, a high flowering year, caused these plants to flower again in 2006. Because few other plants flowered in 2006, these plants did not set seed, and flowered again in 2007. We also directly measured resource depletion by quantifying N, P, and nonstructural carbohydrates before flowering, after fruiting, and at the end of the season in plants with flowers removed.