Objective To study the variation of soil nitrogen (N)-cycling enzyme activities and rhizosphere effect during the development of Chinese fir (Cunninghamia lanceolata) plantation and its driving factors.

Method Rhizosphere and non-rhizosphere soils were collected from Chinese fir plantation with the ages of 7, 15, 24 and 34. The enzyme activities regulating soil nitrogen cycling (β-glucosidase (BG), acetyl-β-D-glucosaminidase (NAG), proteolytic enzyme (PRO), urease (URE), leucine aminopeptidase (LAP) and nitrate reductase (NR)) were measured. Redundancy analysis (RDA) and Pearson correlation were conducted to explore the relationship between soil nitrogen-cycling enzyme activities and the soil physico-chemical properties.

Result Forest age and rhizosphere had significant effects on soil N-cycling enzyme activities (P<0.05). The enzyme activities regulating soil nitrogen cycling in the non-rhizosphere soil decreased at first and then increased with the increase of forest age. The activities of BG, NAG, PRO, URE and LAP in rhizosphere soil were significantly higher than those in non-rhizosphere soil (P<0.05). The difference of NR activity between rhizosphere and non-rhizosphere soil varied with forest age. The NR activity in rhizosphere soil was significantly higher than that of non-rhizosphere soil in 15- and 24-years-old Chinese fir plantations (P<0.01). The rhizosphere effects of soil NR activities in 15-years-old Chinese fir plantation were significantly higher than those in 7-years-old and 34-years-old Chinese fir plantations (P<0.05). The key factors regulating soil N-cycling enzyme activities in rhizosphere and non-rhizosphere soil were C/N and ammonium nitrogen content.

Conclusion Soil N-cycling enzyme activities was the lowest in middle-age Chinese fir plantations in mid-subtropical China, indicating that nitrogen may still be one of the main limiting factors in the fast-growing stage of Chinese fir plantations. In the future, we should focus on the middle-age Chinese fir plantation, so as to meet the nitrogen demand of Chinese fir and achieve the purpose of sustainable management.