SEED-GERMINATION RESPONSE TO POLYETHYLENE-GLYCOL SOLUTION DEPTH

Osmotic solutions of polyethylene glycol (PEG) are commonly used to co ntrol water potential in seed germination studies. PEG reduces the wat er potential of osmotic solutions but may limit oxygen availability to germinating seeds. The purpose of this study was to determine whether seed immersion in PEG solution had a detrimental effect on total germ ination percentage and germination rate of six grass species. Boutelou a curtipendula, Cenchrus ciliaris, Panicum coloratum, Eragrostis lehma nniana, Pseudoroegneria spicata and Leymus cinereus seeds were germina ted over the water potential range of 0 to -1.5 MPa at PEG solution de pths of 0, 1, 3, or 5 mm. Total germination percentage and germination rate were generally greatest at 1 mm depth even in the pure water tre atments. Reduced germinability at 0 mm depth may have been caused by t he lower hydraulic conductivity of the medium. Reduced germinability a t 3 and 5 mm depth may have been caused by decreased oxygen availabili ty to the seeds. A reduction in germination was also apparent at 3 and 5 mm depth in pure water treatments, indicating that oxygen diffusion between the seeds and the air/solution interface was more important t o oxygen availability than was the presence or absence of PEG per se.