Effects of simulated nitrogen deposition on the seeding growth, photosynthetic characteristics and allelopathic potential of invasive plant Ipomoea cairica (L.) Sweet

Ipomoea cairica (L.) Sweet (Convolvulaceae), one of the world's most invasive weeds, has caused serious damage in southern China. To better understand the effects of elevated nitrogen deposition on biomass allocation, photosynthetic characteristics and allelopathic potential of I. cairica, a simulated nitrogen deposition experiment was conducted. I. cairica seedlings were exposed to three nitrogen treatments using NH4NO3 solutions (low N, 50 kg N ha(-1) yr(-1); medium N, 100 kg N ha(-1) yr(-1); and high N, 150 kg N ha(-1) yr(-1)) for 50 days. Photosynthetic characteristics (net Photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (E) and Water Use Efficiency (WUE)), chlorophyll fluorescence parameters (Fo, Fm, Fv/Fm, and Fv/Fo) in leaves of I. cairica were measured. Compared to the control, high N significantly increased the total biomass, the percentage of biomass allocated to stem, leaves area and stem length by 14.8, 20.0%, 68.7%, and 29.0%, respectively. Simulated nitrogen deposition had promoting effect on the photosynthesis rate of I. cairica, especially I. cairica treatment with medium N and high N. Phytotoxicity of leaf litter leachates from I. cairica showed the stronger phototoxic effects under the medium N or high N treatment. Our results indicate that increased atmospheric nitrogen input might benefit the invasiveness of this species.