Objectives Cunninghania lanceolata (Chenshan-red-fir) is a national forest tree fine variety with national protected geographical indication. Soil fertility affects the growth of forest trees, study on soil nutrients content, enzyme activities and fertility status both in rhizosphere which is a place for exchange of plant and soil materials and in non-rhizosphere soil of different ages can further understand soil nutrients with evolution of the age, also can provide a theoretical basis for nutrient and scientific management ofC. lanceolata.

Methods Soil nutrient contents including soil organic matter (SOM), total N, P and K, alkali hydrolysable N and available P and K and enzyme activities (including calatase, protease, sucrase, urease and phosphatase) in rhizosphere and non-rhizosphere soil ofC. lanceolata with different ages in the Chenshan Forest Farm of Anfu County, Jiangxi were determined and analyzed, and soil fertility was evaluated by using the principal component analysis (PCA).

Results The stand age of the tree had a significant effect on soil nutrients and enzyme activities, while there were not significant differences of soil alkali hydrolysable N, total N and total P in rhizosphere and non-rhizosphere. The trends of soil nutrients and enzyme activities with changes of the age in rhizosphere and non-rhizosphere were in good agreements, which meant the rhizosphere was affected by both plant roots and soil. With the stand age increased, the SOM, total N and K, alkali hydrolysable N and available K, and the activities of protease, urease and phosphatase decreased first and then increased with the minima in 10 year, while the trend of available P was on the contrary, and the total P decreased. Contrary to the activity of sucrase, the activity of calatase showed a trend of decrease, increase and decrease. The rhizosohere effects of SOM, alkali hydrolysable N and enzyme activities were positive effects, while those of others were negative effects except for the total N and available P in 20 and 40 years, respectively. The rhizosphere effects of SOM and available P were different among the ages (P < 0.05). The integrated fertility indices (IFI) ofC. lanceolata (Chenshan-red-fir) were from –1.408 to 2.238, the trend of the IFIs (rhizosphere and non-rhizosphere) was in the order: 5 a (2.238, 2.413) > 40 a (–0.313, 0.065) > 20 a (–0.773, –1.019) > 10 a (–1.203, –1.408). The IFIs of rhizosphere were greater than those of non-rhizosphere in 5 and 40 years, mainly caused by PC2 (mainly include sucrase) and PC3 (mainly include available P and total P), while in 10 and 20 years, the change was just the opposite for the reason of PC1 (mainly include SOM, alkali hydrolysable N, total N, urease and protease).

Conclusions Along with the stand age increasing, soil fertility will be declined, and reach the lowest at the tenth year. Although restored gradually afterwards, but will not reach the level in the 5th year. Therefore, nitrogen and phosphorous fertilizers should be applied appropriately for preventing soil degradation in the process of tree growth, particularly before and after the 10th year.