Potential allelopathic effects of Xanthium italicum Moretti on wheat.
The allelopathic potential of invasive Xanthium italicum Moretti on seedling growth of wheat (Triticum aestivum Linn) was investigated. Aqueous (0.05 g/ml) and ethanol (1 mg/ml) extracts reduced root elongation of wheat seedlings by 71 and 87%, respectively; chloroform fraction of the ethanol extract exhibited the strongest phytotoxic effect as compared to other fractions, inhibiting root growth of wheat seedlings by 95% at 1 mg/ml. Incorporation of X. italicum plant residues (20, 50 and 100 g/kg soil) into soils affected not only photosynthetic pigment content, but also photosynthetic parameters of wheat seedlings. Chlorophyll a, b and carotenoid contents of wheat seedlings decreased significantly when plant residues were applied at 100 g/kg soil. Net photosynthetic rate (Pn), transpiration rate (Tr) and stomatal conductivity (gs) decreased greatly when seedlings were treated with plant residues at 20, 50 and 100 g/kg soil, whereas CO2 concentration (Ci) increased significantly at 50 and 100 g plant residue/kg soil. Shoot length, fresh and dry weight were also significantly affected starting from 20 g plant residue/kg soil treatment in a dose-dependent manner. Furthermore, our results indicated that soil conductivity, soil pH and soil nutrients were unlikely responsible for the aforementioned changes. Our results suggest that allelopathy might contribute to the invasion success of X. italicum, and its invasion could possibly pose potential threat to wheat production in China.