Annals of Botany

The flowers that bloom in the spring

One of the botanical pleasures of my spring-time visits to West Virginia has been the sighting of Trillium erectum and T. grandiflorum* in the Kanawha State Forest. These beautiful plants are typical of those woodland species that sprout from underground organs (e.g. rhizomes) after winter and flower while the canopy is still open. This provides the context for the research of Ida and Kudo at Sapporo, Japan (pp. 435–446), working with another Trillium species, T. apetalon. The authors are mindful that the trees themselves are affected by environmental conditions such that the length of the high-irradiance period from snow-melt to canopy closure is variable from year to year. Thus, in their work on plants in the field, the authors subjected some plants to artificial shading to mimic a shorter period of canopy openness. As expected, maximum photosynthesis occurred during the high irradiance period. Use of ¹³C showed that photosynthate was initially allocated mainly to the shoot and leaves, promoting growth, and then to the rhizome, laying down provision for over-wintering and for the next year’s shoot and flowers. Translocation to the developing fruit did not occur until after canopy closure when the photosynthetic rate was very low. In plants that were shaded during the normal flowering and active growth period, mimicking early canopy closure, the switch between allocation to rhizome and allocation to fruit occurred early, as if the reduction in irradiance/canopy closure acts as a signal for changing the main sink for photosynthate. Seed production was reduced in the early-shaded plants. It was also clear that early shading reduced flower production in the following year, presumably because of reduced allocation to the reserves in the rhizome. Overall, this strategy of prioritizing the shoot and then the rhizome over seed production ensures that the existing plant is more likely to survive while retaining some potential for propagation by seeds that can be expanded in years when canopy closure is delayed.

* For descriptions, see West Virginia Wildlife Magazine http://www.wvdnr.gov/Wildlife/Magazine/Archive/05spring/elegance_spring_trilliums.shtm