Ion and Nutrient Status in Rhizospheres of Poplar Stands at Different Ages

This project was aimed to study the amount of ions and some nutrients in the rhizospheres of hybrid poplar (Populus deltoides Bartr. cv. ‘Lux’). Three poplar stands at different ages (3,6,12 years old) were located in Dongta Forest Farm (8 km away from the Yellow Sea),Dongtai City,Jiangsu Province. Samples of rhizospheres were taken from the topsoil (0～20 cm) and subsoil (21～40 cm) under three average trees of each stand. The total ion in rhizospheres is higher in all stands. In most rhizospheres, ion accumulations were statistically obvious. Higher ion accumulations in subsoil rhizospheres were associated with stronger water-absorbing function of the deep root,the nutrient-absorbing function of the root in topsoil made the ion accumulation at a low rate.The accumulation of K+ in rhizosphere was the highest and the most obvious one in all the ions. K+ accumulation in rhizospheres of trees on salty soil were possibly induced by the excessive K+ transported to the rhizospheres by mass flow. Na+ was obviously accumulated in some rhizospheres. Ca2+ and Mg2+ did not vary greatly between rhizospheres and non-rhizospheres. The differences of HCO3- fluctuated within 10% between rhizospheres and non-rhizospheres. Cl- was accumulated in rhizospheres in summer and in topsoil, but not in other conditions. SO42- was not highly accumulated in the rhizospheres of the most stands. Soil pH of rhizospheres in all sites were lower than those of the non-rhizospheres. In subsoil,a greater decrease of pH in the rhizospheres were observed comparing with the topsoil. Hydrolysable N,available P and soluable K were found accumulated in all sites.