Biomass and Its Allocation Changes of Pinus yunnanensis Seedlings under Phosphorus Stress and Different Planting Treatments

To reveal responses of mixed plantation of Pinus yunnanensis and Alnus nepalensis to phosphorus stress,growth,biomass and allocation of P.yunnanensis seedlings were measured through sand culture experiments in green house.Hoagland nutrient solution was used and 3 levels of P concentrations(0 mg·L-1,31 mg·L-1 and 62 mg·L-1) were designed.The results were as follows.(1) Under P stress,height,diameter,root length,shoot biomass,root biomass and total biomass of P.yunnanensis seedlings were lower than those of the control when mixed or not mixed with A.nepalensis.Differences with the control were not remarkable(P0.05)under low P stress(31 mg·L-1),and remarkable(P0.05) under the absence of P(0 mg·L-1).With the increase of P stress,root mass/shoot mass ratio of P.yunnanensis seedlings increased.(2) Under P stress,the height,diameter,root length,shoot biomass,root biomass,total biomass and root mass/shoot mass ratio of P.yunnanensis seedlings decreased with the increase of individuals of A.nepalensis mixed.It was concluded that biomass of P.yunnanensis seedlings would decrease under P stress.Besides,shoot and root mass would be re-allocated to adapt the stress.In the re-allocation,the decrease of root mass would strengthen competition of shoots growing with those of A.nepalensis.Mixed A.nepalensis in seedlings would affect the growth of P.yunnanensis seedlings,but benefit to the growth of A.nepalensis.