Role of short-term cold stratification on seed dormancy break and germination of alien species in southeastern China.
Do short periods of relatively low temperatures during winter in subtropical zones promote seed dormancy break and germination of alien species and thus facilitate their spread? To help answer this question, we tested the germination responses to moist storage at low temperatures of seeds of 21 alien species from southeastern China. For each species, fresh seeds and seeds stored dry at room temperature and wet at 15 °C and wet at 4 °C for 30 days were tested for germination at 25 and 25/15 °C in a 12-h daily photoperiod. Fresh seeds of Bidens pilosa, Eclipta prostrata, Hyptis suaveolens, and Talinum paniculatum germinated to 89-96.7% at both test temperatures, those of Ageratum conyzoides, Mikania micrantha, and Wedelia trilobata to 53-83% at one or both temperatures, and those of the other 14 species to 0-39% at one or both temperatures. A 30-day cold stratification pretreatment at 4 °C increased the germination percentage of seeds of Lantana camara and Solanum torvum, but they germinated to only 10.7-21.3% and 2-30.7%, respectively. However, germination speed of seeds of five species increased following moist storage at 4 °C, and that of four species increased following storage at 15 °C. Seeds of 14 species began germinating during wet storage at 15 and/or 4 °C. B. pilosa germinated to 87.3 and 57% at 15 and 4 °C, respectively, and the other 13 species to 0.3-22.3% at 15 °C. Thus, the short periods at 4 and/or 15 °C increased germination percentages of two species and the rate of six species and permitted early germination of 14 species, leading to the conclusion that the short cool periods during winter in the subtropical zone of China may contribute to the success of alien plant species in this region.