Seed Dormancy and Soil Seed Bank Persistence in the Federally Endangered Short’s Bladderpod (Physaria globosa)
Noah Dell, Missouri Botanical Garden, Geoff Call, United States Fish and Wildlife Service, Matthew A. Albrecht, Missouri Botanical Garden
Short’s bladderpod (Physaria globosa) was recently listed as federally endangered due to population decline across its range in Tennessee and Kentucky. However, little is known about the biology of the species and the potential mechanisms underlying range-wide declines. In short-lived mustards, seed dormancy and seed bank persistence can play an important role in regulating population dynamics and response to disturbance. To address the recovery plan objective of enhancing knowledge of Short’s Bladderpod to facilitate the development of scientifically sound management plans, we conducted laboratory experiments and a seed burial study to examine what environmental cues promote dormancy break and whether or not seeds form a persistent seed bank. A majority of seeds are in primary dormancy when dispersed in summer. Germination percentages are generally low, and long cold stratification times are needed to break dormancy. Seeds that were cold stratified at 2°C for 12 weeks and then incubated in a 20/10°C alternating temperature regime achieved the highest average germination percentage (24%). Warm stratification with or without alternating wet/dry cycles did not improve germination percentages over cold stratification treatments. However, constant imbibition in warm temperatures may have promoted viability loss, as germination percentages were lower than seeds kept at warm temperatures with alternating wet/dry cycles. Results from the seed burial study were consistent with those in laboratory experiments and indicate a cold stratification requirement for dormancy-break. Germination of buried seeds was greater in light than darkness and varied seasonally: 0% and 1% in dark and light conditions, respectively, in October following dispersal, 7% and 21% in January, 23% and 36% in March, 9% and 10% in June, and 4% and 8% in October in the year following dispersal. Seeds that afterripened in ambient indoor conditions for up to one year germinated to low (< 2%) percentages, indicating dry storage does not substitute for cold stratification in breaking seed dormancy. The germination niche of P. globosa can be defined by physiological dormancy, a long cold stratification period at low temperatures for dormancy break, formation of a persistent soil seed bank, and annual dormancy/non-dormancy cycling in buried seeds. Results from this study shed light on Short’s bladderpod regeneration biology and have implications for population management.