Growth And Physiological Characteristics Of Mixed Cunninghamia Lanceolata And Phoebe Chekiangensis Seedlings Under Nitrogen Deposition

A greenhouse experiment was conducted,in which the conifer tree species Cunninghamia lanceolata and the broadleaved tree species Phoebe chekiangensis were grown in monocultures and in a mixture under two levels of N deposition:0 and 45 kg·ha^-1·yr^-1.The plant growth,root architecture,biomass allocation and photosynthetic physiology were determined after 6-month treatments.This study aimed to explore the differences of growth and physiological adaptation mechanisms of C.lanceolata and P.chekiangensis to nitrogen deposition,providing support for regional vegetation restoration,especially the project of converting coniferous to breadleave forest.The results showed that:（1）There was a positive interspecific interaction between C.lanceolata and P.chekiangensis in mixture.However,the positive interspecific interaction was weakened by N deposition.The seedling height and crown width was higher in mixture than in monoculture,while the opposite trend was observed under N deposition.Interspecific competition under N-fertilized treatment was negatively correlated with growth of C.lanceolata and P.chekiangensis.（2）Mixed cultivation inhibited root growth of C.lanceolata and P.chekiangensis and changed their biomass allocation strategy.Under N-unfertilized treatment,total root length and root surface area of C.lanceolata and P.chekiangensis seedlings were lower in mixture than those in monoculture.In a mixture,N deposition reduced the input to underground parts in C.lanceolata,while it increased the biomass allocation to underground parts in P.chekiangensis.（3）Mixed cultivation promoted the photosynthetic capacity of P.chekiangensis to some extent,but did not threaten the physiological state of C.lanceolata.For C.lanceolata,mixed cultivation decreased its net photosynthetic rate,but increased its maximum photochemical efficiency of PSII（F_v/F_m）and potential activity of PSII（F_v/F₀）.Whether or not N-fertilized,mixed cultivation promoted photosynthesis of P.chekiangensis.（4）Simulated nitrogen deposition can promote the physiology of C.lanceolata and P.chekiangensis.In mixture,gas exchange parameters and nitrogen content in leaves of C.lanceolata were higher than that in monoculture in N treatment.Specific leaf area of P.chekiangensis in mixture was increased compared with that in N-unfertilized mixture,indicating N addition promoted P.chekiangensis to distribute more resource to photosysthesis,leading to high P_n.