Light, temperature and burial depth effects on Rumex obtusifolius seed germination and emergence

Trials were carried out to investigate the effects of light and temperature on germination of Rumex obtusifolius L. After several months of storage, s eeds gradually lost dormancy and became photosensitive. Thermal optima for germination were between 20 degreesC and 25 degreesC in light or in darknes s. At lower temperatures there was a greater demand for light, so that the greatest differences in germination percentage (between low and high temper atures) were found within the 10-15 degreesC temperature range. The calcula ted thermal minima (x-intercept method) in light and darkness were 8.3 degr eesC and 6.1 degreesC respectively. Daily temperature fluctuation increased germination even after seed irradiation with far-red light, suggesting a l ower demand for the far-red-absorbing form of phytochrome. Seed burial inhi bited germination in proportion to depth; however, germination inhibition w as independent of seed phytochrome photo-equilibrium, which had been divers ified by seed pretreatment with light. Seedlings did not emerge when seeds were buried >8 cm deep. Recovery of ungerminated seeds showed that excessiv e burial did not impede seedling emergence but rather prevented seed germin ation. However, this induction of dormancy was lost once germination proces ses were activated (24-48 h at 20 degreesC) that made germination irreversi ble. Temperature was also involved in inhibition, and low temperature (< 15 degreesC) induced the least inhibition. This is discussed in terms of proc esses of respiration and fermentation in buried seeds.