EFFECTS OF ENDOGENOUS NITRATE CONTENT OF SISYMBRIUM-OFFICINALE SEEDS ON GERMINATION AND DORMANCY

The nitrate content of seeds of the annual Sisymbrium officinale was r aised by weekly nitrate fertilizations of the seeding mother plants. N itrate content and germination of the seeds produced were positively c orrelated. Seed lots with different endogenous nitrate contents were b uried at 10 cm in sandy loam. At regular intervals seeds were exhumed and germination was tested. Both the initial differences in endogenous nitrate content and the differences of germination rapidly diminished during burial because nitrate rapidly leached from the seeds. The sen sitivity of exhumed seeds to applied nitrate strongly varied during th is 1-year study. Sensitivity to nitrate was low in December and had in creased in January-February probably because of low winter temperature s. A cold pretreatment in Petri dishes also strongly increased sensiti vity to nitrate. Endogenous nitrate content of seeds collected in the field was much lower than reported in this study and therefore the dif ferences in seed-nitrate content in the field probably are of limited ecological significance. A high endogenous nitrate content will stimul ate germination only temporarily. In contrast, the changes in sensitiv ity in nitrate seem ecologically important because they will restrict germination of S. officinale to seasons suitable for survival of the s eedlings.