Effects of seed stratification on germination of four weedy rangeland forbs

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Abstract
Many rangeland weeds exhibit physiological seed dormancy that is released by cold winter temperatures. Species vary in their cold stratification requirements, leading to variation in the amount and timing of weed germination in the spring. We performed a replicated growth chamber study testing the impacts of stratification duration (0, 2, 4, 6, or 12 wk) on germination of common evening primrose ( Oenothera biennis L.), Baldwin’s ironweed ( Vernonia baldwinii Torr.), tall goldenrod ( Solidago altissima L.), and hollow Joe-pye weed [ Eutrochium fistulosum (Barratt) E.E. Lamont]. Species (P < 0.001), stratification treatment (P < 0.001), and the interaction between species and stratification treatment (P < 0.001) jointly impacted the probability of germination. Stratification did not influence germination of O. biennis , although non-stratified seeds took longer to germinate. For V. baldwinii , positive effects of stratification were similar regardless of stratification duration (2 to 12 wk), although seeds stratified for 12 wk germinated fastest. Dissection revealed that most stratified V. baldwinii seeds failing to germinate did not appear to be viable. Germination of S. altissima was maximized at 4 wk of stratification, although seeds stratified for 12 wk again germinated fastest. In E. fistulosum , germination was maximized at 12 wk of stratification and time to germination decreased with increasing stratification duration. Overall, these results show flexible stratification requirements in these rangeland weeds, although longer stratification periods are generally associated with greater and faster germination. These data may be useful in predicting the timing of weed emergence to help guide management operations.

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