Response characteristics of on seed germination and seedling growth of the invasive plant Sorghum halepense

In recent years, the invasive plant Sorghum halepense has spread rapidly in Hainan Island, causing serious harm to crops, such as corn, sugarcane, and sorghum. S. halepense has invaded habitats or regions with different water conditions and has caused disasters. To reveal the physiological and ecological mechanisms whereby S. halepense adapts to drought, the polyethylene glycol (PEG)-simulated drought method and the pot water control method were adopted in this study. Seven PEG-6000 mass concentrations (0, 2.5%, 5%, 7.5%, 10%, 12.5%, and 15%) and four soil field water capacities (100%, 80%, 60%, and 40%) were set up to study seed germination characteristics, seedling morphological characteristics, biomass allocation, and physiological indices under different drought stress intensities. The highest germination rate of S. halepense seeds was 73% under mild drought stress (2.5% PEG), and the lowest germination rate was 4% under severe drought stress (15% PEG). The germination index, vigor index, and radicle and germ length decreased, and the radicle and germ length first decreased and then increased with increasing PEG concentrations. The seedling height, leaf number, specific leaf area, relative chlorophyll content, aboveground biomass, and total biomass of pseudosorghum seedlings decreased, but the underground biomass and root-shoot ratio increased with the increasing drought stress intensity. The seedling height, leaf number, relative chlorophyll content, aboveground biomass, and total biomass of S. halepense seedlings significantly decreased (P < 0.05), but the underground biomass and root-shoot ratio significantly increased ( P < 0.05) with field water capacities of 60% and 40%. These results indicated that mild drought stress was beneficial, as it enhanced the seed germination and did not affect the seedling growth of S. halepense. Moreover, the results showed S. halepense is partially tolerant to drought stress, which may be one of the reasons for its adaptability to various habitats.