Abstract: High-yield maize was planted in a preceding 7-year-old alfalfa land for four consecutive years, and the vertical distribution of root, physiological characteristics of root and yield of maize were measured. The results showed that the maize yield and the root dry weight at the silking and milking stages decreased with the cultivation years, and the difference of the root dry weight in the different years were more obvious with the increase of soil depth. The percentage of root biomass at the 0-20 cm soil layer to the total root biomass (0-60 cm) increased with the cultivation years. The root activity and SOD activity at the silking and milking stages decreased with the cultivation years. The POD activity of maize roots at the silking stage decreased with the cultivation years except for the 20-60 cm soil layer. The MDA contents of maize roots in different soil layers at the milking stage increased with the cultivation years, and the differences among the different cultivation years were more obvious with increasing the soil depth.

Key words: N-fixing tree species, enzyme activity, Chinese fir, PLFA