The lifespan of fine roots plays an important role in forest productivity. On the basis of minirhizotron technology, this study focused on the annual dynamics of different order fine roots in successive rotation poplar plantations and analyzed their survival. The results showed that the cumulative survival rates of poplar fine roots were significantly different among root orders. The lifespan of higher order roots (3rd-5th order) was longer than that of lower order roots (1st-2nd order), and their cumulative survival rate was also higher. Furthermore, there was a significant difference in the lifespan of poplar fine roots between two plantations (the first and second generations). There were more live roots, dead roots, and total roots in the second rotation forest than in the first. The median lifespan of fine roots was 90±16 d in the second rotation poplar plantation, whereas it was 102±22 d in the first rotation plantation. The root number and the proportion of roots of each order in the second rotation poplar plantation were significantly higher than those in the first rotation plantation. However, the cumulative survival rate of lower order roots was significantly higher, whereas that of higher order roots was significantly lower, in the first rotation poplar plantation. The lifespan of poplar fine roots was responsive to soil environments, with the lifespan of the first order roots being significantly correlated with soil available nitrogen (r=-0.861) and that of the second order roots being significantly correlated with phenolic acid content (r=0.870). The lifespan of the higher order roots also showed some correlation with soil physical properties and nutrient conditions. The findings of this study indicate that the accumulation of phenolic acids and a decreased soil nutrient availability might influence fine root lifespan and turnover of poplar trees and lead to a loss of net primary productivity in poplar plantations, thereby providing an important insight into the mechanism of declining poplar plantation productivity.