Abstract: [Objective] Pokeweed (Phytolacca americana) is an invasive plant specie sand now widely distributed in China. This paper explores the ecophysiological mechanism of pokeweed invasion and its advantages over the accompanying species in terms of their energy use efficiency, and usage of water, nitrogen and other resources, in order to provide a reference for risk assessment of pokeweed and the comprehensive prevention and control. [Method] This experiment was performed in the coastal protection forest belt in northern Yantai. In this study, the photosynthetic performance parameters of pokeweed and its accompanying species Amorpha fruticosa at the margins of the forest were measured with a TPS-1 photosynthetic system under both low and high light environment to study the ecophysiological mechanism of invasion. Light use efficiency and water use efficiency were calculated according to the related parameters. The chlorophyll fluorescence parameters were detected by using a Handy-PEA system. The total nitrogen content of leaves was analysed with the vario Micro cube element analyzer. The gross calorific value was evaluated with a C2000 oxygen bomb calorimeter, and the leaf photosynthetic nitrogen use efficiency and construction cost were thus calculated. [Result] Under both high and low light conditions, the apparent quantum efficiency (AQY), maximum net photosynthetic rate (P_max), chlorophyll content, maximum quantum efficiency of photosystemⅡ (F_v/F_m) and photosynthetic performance index on energy absorption basis (PI_ABS) in pokeweed were significantly higher than those of its accompanying species A. fruticosa (P<0.05). However, the light compensation point and chlorophyll a/b ratio were significantly lower than those in A. fruticosa (P<0.05). The Light use efficiency (LUE), and photosynthetic nitrogen-use efficiency (PNUE) in pokeweed were significantly higher than those in A. fruticosa (P<0.05); the water use efficiency (WUE) of pokeweed was lower than that in A. fruticosa under high light, but higher uder low light condition. The mass-based (CC_mass) and area-based (CC_area) leaf construction cost were all significantly lower in pokeweed than in its accompanying species A. fruticosa under both high and low light condition (P<0.05). Additionally, the difference of the photosynthetic performance indices, resource efficiency indicators and leaf construction cost of pokeweed and A. fruticosa were both higher under high light than under low light condition. Explanation: under low light, the photosynthetic capacity, resource use efficiency, the material and energy use policy in pokeweed were more advantageous over the accompanying species.[Conclusion] Compared with the accompanying native species, pokeweed has higher photosynthetic capacity, higher efficient use of resources and lower construction cost (material and energy consumption), which could facilitate it a high growth rate and competitiveness. This was particularly advantageous for pokeweed when the resources and light were insufficient.

Key words: pokeweed (Phytolacca americana), invasion mechanism, photosynthetic performance, construction cost, competitiveness