Objective This study aimed to reveal the influence mechanisms of vegetation restoration on soil carbon, nitrogen and phosphorus stocks of Larix gmelinii var. principis-rupprechtii plantations in Saihanba, and to provide a basis for precise improvement of carbon sequestration and fertility maintenance function.

Method In this study, L. gmelinii var. principis-rupprechtii plantations with different years of recovery (15, 25, 36, 52 year) were compared against the degraded sandy land used as controls in Saihanba. Soil carbon, nitrogen and phosphorus stocks (0-1 m) and associated environmental factors were measured. Variation in soil carbon, nitrogen and phosphorus stocks and its influencing factors during vegetation restoration will be clarified.

Result (1) Soil carbon, nitrogen and phosphorus stocks of L. gmelinii var. principis-rupprechtii plantations during different vegetation recovery years are (211.5 ± 46.1) t/ha, (16.0 ± 3.1) t/ha, (5.8 ± 0.8) t/ha. Soil carbon, nitrogen and phosphorus stocks increased with increasing vegetation recovery years (P < 0.05). Soil carbon and phosphorus stocks reached maximum at 36 years, while soil nitrogen stocks at 52 years were significantly higher than other vegetation recovery years. (2) Soil and vegetation factors together explained 84.46%, 82.73% and 65.29% of the variation in soil carbon, nitrogen and phosphorus stocks, respectively; and soil clay content individually explained 25.79%, 28.08% and 34.16% of the variation. Vegetation belowground biomass individually explained 58.67%, 54.65% and 31.13% of the variation in soil carbon, nitrogen and phosphorus stocks. (3) Structural equation models demonstrated that vegetation recovery years had no significant direct effect on soil carbon, nitrogen and phosphorus stocks. Vegetation recovery years indirectly increased soil carbon, nitrogen and phosphorus stocks by increasing vegetation belowground biomass (58.6%, 53.0% and 35.3%), and indirectly increased soil phosphorus stocks through affecting soil texture (by increasing vegetation belowground biomass and litter biomass, 38.3%).

Conclusion Vegetation recovery years increased soil carbon, nitrogen and phosphorus stocks through indirect pathways mediated by soil texture and vegetation belowground biomass. Therefore, for practice and management of plantations, it is necessary to strengthen the management of soil texture and maintenance of vegetation belowground biomass as well as to focus on the long-term soil carbon sequestration and fertility maintenance function.