Effects of experimental early canopy closure on the growth and reproduction of spring ephemeral Erythronium japonicum in a montane deciduous forest

Abstract

Spring leaf flush and changes in the understory radiation in montane deciduous forests are major determinants of the life cycle of spring ephemerals, which complete their epigeous growth before canopy closure in spring. We compared the growth, carbon allocation, and reproduction of a spring ephemeral, Erythronium japonicum (Balrer) Decne., between the ambient (control) and early shade treatments in the field during the flowering (early-May), fruiting (mid- May), and fruit ripening periods (late-May), under the assumption of early spring canopy closure due to climate change. Carbon allocation was investigated using a 13C labelling experiment. Both sterile (non-flowering) and fertile (flowering) E. japonicum under the shade treatment showed higher specific leaf area and earlier leaf senescence than those in the ambient conditions (p < 0.05). The flowering E. japonicum concentrated on biomass allocation to the aboveground vegetative organs prior to fruiting and to reproductive and storage organs from fruiting. E. japonicum used carbohydrates stored during the previous year for vegetative growth, while the current-year photosynthates were used for the current-year reproduction. Carbon allocation to fruit began earlier under the shade treatment, demonstrating that E. japonicum allocated the current-year photosynthates more to reproduction than to vegetative organs under the early shade conditions. However, the seed size (p = 0.012) and germination rate (p = 0.008) were significantly lower under the shade treatment than under the ambient conditions, implying a potential decrease in viable seed production in the shorter high-light period. The earlier leaf flush could be a critical threat to the population maintenance of spring ephemerals such as E. japonicum.