Effects of nitrogen addition on interspecific competition between tea plants and the invasive weed Alternanthera philoxeroides

【Objective】The present paper aimed to explore the impact of nitrogen addition on competition between tea plants（Camellia sinensis） and the invasive weed Alternanthera philoxeroides, providing theoretical basis for improving the quality and efficiency of weed control in tea gardens and green tea production under global environment change.【Method】By setting up the three-factors potted experiment that containing nitrogen treatment（control and nitrogen addition）, planting method（mono and mixed culture） and species trait（tea plants and A. philoxeroides）, the heterogeneity responses of tea plant variety Xinyang 10 and the accompanying invasive weed A. philoxeroides in terms of biomass, morphology, nutrients, pigments, and photosynthetic fluorescence were analyzed. 【Result】The maximum stem length, area of root, area of leaf, biomass, total carbon（C） content, carbon/nitrogen ratio（C∶N）, chlorophyll index（Chla） and flavonoid index（Flav） of tea plants were extremely significantly（P＜0.01, the same below） higher than those of A. philoxeroides, while the total nitrogen（N）, nitrogen balance index（NBI）, anthocyanin index（Anth） and steady-state light adaptation photochemical quenching coefficient（qP-Lss） of A. philoxeroides were significantly（P＜0.05,the same below） or extremely significantly higher than those of tea plants. Nitrogen addition significantly increased the maximum stem length by 1.14 times but decreased the root-shoot ratio of A. philoxeroides by 67.28%; while nitrogen addition significantly decreased the total nitrogen of tea plants and A. philoxeroides by 29.79% and 6.03%, but increased the C∶N of tea plants by 39.47%. Nitrogen addition significant decreased the maximum light quantum efficiency（F_v/F_m） of A. philoxeroides by 19.62%, decreased the maximum fluorescence（F_m） and steady-state light actual quantum efficiency（QY-Lss） of A.philoxeroides by 22.56% and 48.36% in the monocultures, as well as decreased the QY-Lss of tea plants and A. philoxeroides in mixed cultures by 68.99% and 56.19%. 【Conclusion】Tea variety Xinyang 10 has the higher individual competitive advantage, photosynthetic efficiency and secondary defense ability in dealing with competition, while A. philoxeroides has a higher nitrogen absorption capacity, stress resistance and photosynthetic activity. Nitrogen addition relatively improves the competitive advantage of tea plants in photosynthetic physiology, but intensifies the competition for aboveground resources by A. philoxeroides.