Abstract: Increased atmospheric nitrogen (N) deposition is a serious threat to the structure and function of ecosystems globally. Soil fauna is sensitive to environmental changes, and increased nitrogen deposition may profoundly influence soil faunal communities. We conducted a field experiment with different N addition treatments (0, 5, 10, 15 and 30 g N·m^-2·a^-1, respectively) to examine the effects of N deposition on the structure of soil faunal communities in poplar (Populus deltoides cv. I₃₅) plantations with different ages (7, 11, 18 years old) in a coastal area of eastern China in May 2012. Our results showed that the individual density of soil fauna increased significantly with increasing the stand age, but 11 years old poplar plantations had the greatest number of soil fauna group. The individual density of soil fauna decreased after an initial increase with the increasing N level, and it was the highest at the addition of 15 g N·m^-2·a^-1. Furthermore, the diversity of soil fauna was significantly correlated with soil TOC and TN. Significant effect of N addition on the diversity of soil fauna community was found only in 11 years old poplar plantation. Shannon diversity index and Pielou index showed a decreasing trend with the increasing N concentration, but Simpson index was completely opposite. In conclusion, N addition may cause great effects on the structure of soil fauna community through altering soil nutrition condition. Moderate N addition had a promoting effect on soil fauna community, but high N addition had a negative effect.

Key words: cucumber, reactive oxygen species, salt-alkaline stress, AsA-GSH cycle, antioxidation