Abstract: Chenshan red fir (Cunninghamia lanceolata) is an endemic tree species in Jiangxi Province granted with national geographical protection status, but the relationship between plants and soils were not well understood. In the current study, different tree ages (5, 10, 20 and 40 years) of C. lanceolata were selected to examine the contents of soil organic carbon (SOC) and different nitrogen forms in the rhizosphere and nonrhizosphere soils and their relationships. The results showed that the pH value of rhizosphere soil was slightly lower than that of nonrhizosphere soil, while SOC and nitrogen contents were higher. SOC and nitrogen contents of rhizosphere and nonrhizosphere soil decreased initially with the increasing plantation age, but increased thereafter. The rhizosphere effects of SOC, total N and organic N increased initially with plantation age and then decreased, but that of nitrate and ammonium firstly increased and then kept relatively stable. The rhizosphere effects on pH and alkaline hydrolysis N experienced little change. The rhizosphere effects of different N forms on soil pH and SOC were in order of total N>inorganic N>alkaline hydrolysis N. In terms of the rhizosphere effect, the influences of alkaline hydrolysis N and total N on pH and SOC were the greatest. The proportion of nitrate increased with the plantation age compared with that of ammonium. More attentions should be paid to the N loss caused by soil denitrification and subsequent soil nutrient decline. At age about 10 years, forest soil organic matter and N pools should be replenished so as to prevent the soil fertility decline.

Key words: Erguna, Inner Mongolia, soil organic nutrient, urea, semi arid grassland, enzyme activity, glucose