|Abstract or Summary
- Field and growth chamber studies were conducted to ascertain
the effects of some environmental factors on the persistence of viable
buried seed of Agrostis tenuis, Avena fatua, Lolium multiflorum,
Lolium perenne, and Poa annua.
Through the use of a population model, specific effects of environment
on parameters of viability and nonviability were studied.
The parameters of viability included seed quiescence and terminal
dormancy. In situ germination and nonviability among ungerminated
seed plus their composite, total nonviability, comprised the parameters
Of the five species studied, only buried seed of L. perenne was
found to be nonpersistent. Variation in the degree of persistence was
found among different seed lots of L. multiflorum.
Quiescence among buried seed of the persistent species was
greater at deeper burial depths. Nonviability among buried seed was
found to be less extensive at deeper burial depths.
Seed samples of persistent species recovered from burial under
perennial ryegrass plant cover displayed higher levels of terminal
dormancy than similar samples recovered from indigenous weed,
wheat and alfalfa plots.
Low soil temperature and high soil moisture, characteristic of
winter conditions in western Oregon, were effective in maintaining
viability of buried seed. These conditions were also found to be conducive
to the induction of secondary seed dormancy. The depletion
of viable, buried seeds through in situ germination occurred at intermediate
soil temperatures and soil moisture. Such conditions prevail
in western Oregon during autumn and spring periods. High temperature
and soil moisture percentage was found to increase non-viability among ungerminated seed.
Seed quiescence played an important role in persistence during
the early stages of seed burial. With the progression of time,
terminal dormancy played an increasingly important role as a mode
of buried seed persistence.
In situ germination was the principle mode of buried viable
seed depletion in A. fatua, L. multiflorum, L. perenne, and P.
annua. Nonviability among ungerminated seed was found to be the
principle mode of viable seed depletion in A. tenuis.