Seedling expression of cross-generational plasticity depends on reproductive architecture.

Through adaptive cross-generational plasticity, stressed plants can alter their offspring in specific ways that promote seedling success. As yet, very little is known about the expression of such plasticity, and whether it varies within a plant due to offspring position. The effects of parental light deprivation on distinct reproductive structures were tested in the annual Polygonum hydropiper, which produces both long terminal racemes and inconspicuous axial inflorescences. Inbred replicate parents from four genetic lines were grown in full greenhouse sunlight and simulated shade, and the initial mass, germination rate, and seedling growth traits of their terminal and axial offspring measured under uniform growth chamber conditions. Although parent light environment did not significantly influence seedlings from axial achenes, growth traits of those from terminal achenes were significantly enhanced as a result of parental light deprivation. In shaded conditions where resources are limiting, P. hydropiper plants appear to prioritize terminal achenes through increased provisioning as well as specific growth changes. These results show that the expression of cross-generational plasticity may vary depending on architectural position of offspring on the maternal plant.