Effects of burial and substrate characteristics on the germination ecology of a rare coastal pioneer species, Amaranthus pumilus.

Abstract

The limited information available regarding the germination ecology of the federally threatened coastal pioneer, Amaranthus pumilus (Raf. Amaranthaceae), may be an obstacle to the development of sound species management and conservation plans. We investigated the effects of seed burial depth, sand versus shell substrate, and the presence or absence of soil microorganisms on seed germination and seedling emergence of A. pumilus in a controlled, growth chamber environment. Burial treatments consisted of forty seeds each, planted at 0, 2, 4, and 6 cm and incubated for 26 days. Effects of substrate and soil microorganisms were tested using a factorial combination of sand versus shell with sterilized versus unsterilized substrate. Each treatment consisted of 35 seeds, planted in petri dishes and incubated for 18 days. Germination and emergence decreased with increasing burial depth. At 4 cm of burial, above-ground emergence was delayed approximately six days relative to 0 and 2 cm of burial. At 6 cm of burial, few seeds germinated and none emerged. Viability of seeds that niether emerged nor germinated was reduced relative to that of other treatments. Substrate type and sterilization had no observable effects of seed germination or emergence of seedlings. Long-term studies will be required to determine the effects of these factors on seedling development and survival to adulthood. The equivalence of germination and emergence on sand versus shell substrate conflicts with field observations that indicate preferential establishmnet of A. pumilus on sand. Differences noted in the field may be due to the lower water retention capacity of shell substrate, a factor that was not tested in this experiment. Ecosystem-level issues, such as habitat degradation and loss, are of critical and immediate importance to species persistance. However, conservation and restoration efforts will be facilitated by an improved understanding of the environmental factors that influence individual growth and survival.