EFFECT OF HYPOXIA ON BURIED WEED SEED-GERMINATION

Trials were carried out in order to investigate the effect of hypoxia on seed germination of Datura stramonium L. in Petri dishes and when b uried at various depths in soil. Hypoxia was found to cause a decrease in germination capacity and germination rate. This inhibition was par tially alleviated by daily exchange of hypoxic gas surrounding the see ds during incubation. Similarly, seed scarification allowed maintenanc e of a higher germination capacity under conditions of low oxygen avai lability, showing that the seed coat was only partially gas permeable. Oxygen deficiency led to a decrease in respiratory capacity. However, this was probably compensated for by induction of fermentation metabo lism. The possibility of removing the final products of fermentation e xerts a decisive influence on seed germination, especially in an envir onment such as soil, where their diffusion into the surrounding enviro nment is restricted. Thus daily nitrogen flushing partially eliminated this inhibition, even under conditions of low external oxygen availab ility. It was therefore postulated that the main depth-derived inhibit ion was not caused directly by oxygen deficiency but by the increasing difficulty in eliminating toxic fermentation products, which was foun d to be proportional to the degree of hypoxia. Finally, incubation for several days under completely anaerobic conditions induced secondary dormancy. This was probably due to an ecological adaptation mechanism that prevents germination under conditions that are unfavourable for s urvival.