Light, oxygen, and temperature requirements for Typha latifolia seed germination

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Abstract
Typha latifolia L. seed germination required high temperatures, low O2 concentration, and relatively long exposure to light to induce high percentages of seed germination. A greater percentage of seeds germinated at 35 °C than at lower temperatures. Less than 10% of the seeds germinated at 15 °C and none at 10 °C. For submerged seeds exposed to red light (R), maximum germination was achieved when the O2 concentration in the water was reduced to between 2.3 and 4.3 mg L−1 at 30 °C. Seeds were most sensitive to R when imbibed for 6–24 h. At least 10 h of continuous R (2.5 × 10−8 W m−2) was needed for maximum germination. However, when seeds were exposed to light of the same intensity for four 30-min periods over a 12-h span, the effect was nearly the same as 12 h of continuous light. The germination percentage after the intermittent irradiation was nine times that produced by a single 2-h exposure. Five minutes of far-red light (FR) reversed the effect of 6 h of R to the level of dark controls. The photoreversible effect of FR was less pronounced for seeds imbibed prior to illumination. When spans of R and FR were alternated (FR–R–FR, R–FR–R, FR–R–FR–R, R–FR–R–FR), repeated reversibility was observed. However, FR was progressively less effective in reversing the effect of R.