Objective  Litter is an important part of nutrient cycle in the forest ecosystem. The decomposition of litter and its accompanying nutrient release and soil organic matter structure is an important aspect of the operation of forest ecosystem. Taking measures to accelerate the decomposition of litter has very important theoretical and practical significance for accelerating the return of nutrients and promoting forest growth.

  Method  Taking 4 kinds of thinning intensity of Larix principis-rupprechtii plantation in Saihanba Mechanical Forest Farm in Hebei Province of northern China as the research object, the litter was laid out by the litter decomposition bag method. 8 physical and chemical nutrient indexes, including residual rates of litter, organic matter, total carbon (C), total nitrogen (N), total phosphorus (P) and total potassium (K) etc., were determined under 4 thinning intensities of 0 (CK), 15%, 20% and 30%, respectively (hereinafter referred to as CK, 15%, 20% and 30%, respectively). Two-factor ANOVA and Duncan multiple comparison methods were used to study the decomposition rate and nutrient dynamics of Larix principis-rupprechtii litter.

  Result  (1) Thinning significantly reduced the residual rate of Larix principis-rupprechtii litter. By September 2015, the residual rates were: CK > 30% > 20% > 15%. (2) The decomposition rate of Larix principis-rupprechtii litter under different thinning intensities was 15% > 30% > 20% > CK, among which, little difference was found in decomposition rate between 30% and 20% thinning intensity . (3) The intensity and time of thinning have a significant interaction on organic matter, C, N and P, while the residual rate of K was hardly affected by the intensity of thinning. There was a strong positive correlation between N and P in the litter of Larix principis-rupprechtii and the decomposition rate (P < 0.01). With the increase of time, the process of leaching-enrichment or enrichment occurred in N residue in litter, the process of leaching-enrichment-release or enrichment-release occurred in P residue, and the process of release-enrichment occurred in K residue. (4) The correlation between C/N, C/P and decomposition rate in Larix principis-rupprechtii litter was extremely significant. Among them, the decomposition rate was negatively correlated with C/N value and significantly negatively correlated with C/P value. At the end of the experiment, the C/N and C/P decreased more significantly under 15% and 20% thinning intensities than CK and 30% thinning intensities, which is more conducive to litter decomposition. them, the decomposition rate was negatively correlated with C/N value and significantly negatively correlated with C/P value. At the end of the experiment, the C/N and C/P decreased more significantly under 15% and 20% thinning intensities than CK and 30% thinning intensities, which is more conducive to litter decomposition.

  Conclusion  Thinning has a significant effect on the decomposition of Larix principis-rupprechtii litter in Saihanba. Among them, 15% thinning intensity can promote the decomposition of Larix principis-rupprechtii litter to the maximum extent.