Seed Germination Characteristics Of Tropical Pioneer Tree Species In Seasonal Rainforest In Xishuangbanna, Southwest China

Four common pioneer tree species (Ficus hispida, F. semicordata, Trema orientalis, Mallotus paniculatus) and one climax tree species (F. altissima) were studied to examine the effects of different light and temperature treatments on their seed germination in incubator with the purpose of understanding their response to forest microenvironment.Experiments to test the effect of temperature on seed germination of F. altissima, F. hispida & F. semicordata were conducted at 35/25, 35/20, 30/20, 25/15 and 30℃under fluorescent light. Neutral-density black plastic film was used to determine the effect of light intensity on germination at 30℃. Tests of the effect of R/FR ratio on germination were set at 23/20℃and 30℃, and R/FR ratio gradients were created by filtering incandescent light through setting 2, 4 and 6 layers of green plastic films respectively. The seeds of T. orientalis & M. paniculatus were incubated under the same temperature gradient with Ficus seeds. Treatments as H2SO4 scarification, bird digestion, GA3 treatment, were designed to break the dormancy of M. paniculatus seeds. All the experiments were carried out in incubator with 14 h light / 10 h dark treatments. The results show that:1. The seeds of F. altissima, F. hispida & F. semicordata were photoblastic, germinating only in light, while the seeds of T. orientalis & M. paniculatus showed a positive germination response to temperature fluctuation independent of light.2. R/FR ratio showed significant impact on the seed germination of F. hispida & F. semicordata, followed by temperature then light intensity. Germination could be induced by very low PPFD though delayed.3. Although the final germinations of F. altissima, F. hispida & F. semicordata were high in all temperature treatments under fluorescent light, mean times to germinate (MTG) differed among temperature treatments.4. The seed germination of F. hispida & F. semicordata at 23/20℃and 0.42 R/FR ratio was inhibited. While much higher and earlier germination was recorded at 30℃under the light with 0.42 R/FR ratio. In addition, the R/FR ratio of 0.34 could significantly inhibit the seed germination of F. hispida & F. semicordata at 30℃. The seed germination of F. altissima showed a neutral response to R/FR & 23/20℃.5. Though the seed coat of M. paniculatus is water-permeable, the seeds of M. paniculatus showed both physical dormancy and physiological dormancy.6. High and highly fluctuating temperature induced the seed germination of T. orientalis & M. paniculatus, while low and constant temperature inhibited the seed germination.7. Temperature played the main role in controlling seed germination of T. orientalis, while illumination may also induce seed germination.8. The seed germination of M. paniculatus showed positive responses to seed coat scarification, bird digestion and GA3 treatment.