Abstract: With a randomized block design by changing above-ground litter and nitrogen addition rate, we studied the main effects and interactive effects of nitrogen addition and litter manipulation on soil nitrogen in a mixedPinus tabuliformis andQuercus wutaishanica forest. Litter manipulation included complete removal of all litter (Litt_nil), double of fine woody litter (Litt_woody), double of leaf litter (Litt_leaf), and double of mixed leaf and fine woody litter (Litt_mix), and the nitrogen addition rates were 0 (N₀), 5 (N₅) and 10 g·m^-2·a^-1 (N₁₀). We collected the surface soil from 0-5 cm in growing season (August) after 5 years of treatment, analyzed the soil and microbial variables correlated with soil N, including soil water content (SWC), soil pH, soil organic carbon (SOC), soil total nitrogen (TN), NH₄⁺-N, NO₃^--N, microbial biomass nitrogen (MBN), N-acetyl glucosaminidase (NAG), protease and urease activities. The results showed that NH₄⁺-N was the main form of soil inorganic nitrogen, ranging from 64.53% to 87.02%. Nitrogen addition and litter manipulation did not change soil pH, and significantly higher SWC, TN, SOC, NH₄⁺-N, soil inorganic nitrogen, MBN, and NAG were found in the plots of Litt_leaf and Litt_mixcompared to those in the plots of Litt_woody and Litt_nil. The protease and urease activities were not influenced by litter manipulation. Furthermore, TN, NO₃^--N contents and urease activity were significantly influenced by nitrogen addition, and TN decreased with increasing nitrogen rate. NO₃^--N content increased and then decreased in Litt_nil and Litt_woody treatment, but increased with increasing nitrogen rate in Litt_leaf and Litt_mix treatment. The urease activity showed a trend of descending after ascending with increasing nitrogen rate. Moreover, there were no interactive effects between litter manipulation and nitrogen addition on any of the variables. This study also indicated that leaf litter input improved soil quality.

Key words: quality, growth, Chinese chive., carbon-nitrogen metabolism, light quality