Abstract: For understanding the features of light-demanding seed germination of Eupatorium adenophorum, the influences of light qualities (different colors, red/far-infrared light) and light intensity on seedling sprouting of this weed were studied in this paper. Lights of different colors have significantly influence on the parameters of seedling sprouting, i.e., yellow light, orange light and red light, which have longer wavelength, were more suitable for facilitating seed germination rate (74.3%-83.3%), while the shorter wavelength lights (<570 nm, violet, blue and green lights) had significant lower seed germination rates (62.3%-66.7%)(p<0.05). Light intensity had markedly more regularity on seed germination and seedling status than the color of the light. Under the condition of darkness, germination rate was 22%. Along with the light enhancement both in transmittance and lux, exponential increases in seed germination (r²=0.96) and root length (r²=0.98) were observed, while height of seedlings exponentially decreased (r²=0.99); a linear increase in fresh mass was simultaneously observed (r²=0.70). Appropriate radiation of red light (630 nm) and far-infrared light (730 nm) can break and cause dormancy. The exposure amount of red light linearly related with germination increase with reference to dark control (r²=0.98), while the amount of far-infrared light was linearly correlated with germination decrease with reference to control (r²=0.92). This indicates that light-demanding seed germination of E.adenophorum is a phytochromes-induced process. E.adenophorum generally runs rampant in barren and disturbed lands and light sensitive germination should be partially responsible for that. The ecological control of this weed should consider light regulation, in particular the light quality (such as afforestation decreases red light/far-infrared ratio) to decrease seed germination.

Key words: light quality, light quantity, red/far-infrared light alternating process, germination rate