Dynamic characteristics of refractory substances during litter decomposition of Chinese fir at different developmental stages

<bold>Objective</bold> This study aims to explore the dynamic characteristics of refractory substances（lignin，cellulose，total phenols，tannins）during the decomposition of Chinese fir litter at different developmental stages，and provide a theoretical basis for a comprehensive understanding of nutrient cycling barriers in Chinese fir forests. <bold>Method</bold> Taking the middle-aged（18-year-old），mature（30-year-old）and over-mature（42-year-old）Chinese fir plantations at three developmental stages in Xinkou Teaching Forest Farm of Fujian Agriculture and Forestry University in Sanming，Fujian Province as the research object，indoor decomposition experiments were conducted using litter branches and litter branches with leaves，respectively.Different types of litter were sampled on days 0，15，30，72，118，172 and 264，respectively. <bold>Result</bold> （1）The initial content of lignin and cellulose in different types of litter showed a higher content in litter branches compared with litter branches + leaves，and increased significantly with the development of the stand.The initial content of tannins showed a lower content in litter branches，with the lowest content observed in the young stand.（2）In the process of decomposition for 0-264 days，the overall pattern of lignin release-enrichment-release was observed for both types of litter at different developmental stages，while cellulose showed an overall enrichment-release pattern.Total phenols and tannins showed a slight enrichment in the initial 0-30 days，followed by a release pattern.（3）At the end of the 264 day experiment，the release of refractory substances from fallen branches showed the following order：total phenols&gt;cellulose&gt;lignin&gt;tannins，with release rates of 62.56%，32.75%，20.96%，and 15.33%，respectively.The release of refractory substances from fallen branches and leaves followed the order：total phenols&gt;cellulose&gt;tannins&gt;lignin，with release rates of 76.25%，37.32%，22.05%，and -3.52% respectively.（4）Correlation analysis showed that the release rate of lignin was significantly negatively correlated with the release rate of tannin and total phenols（<italic>P</italic>&lt;0.05），and the release rate of total phenols was significantly positively correlated with the release rates of cellulose and tannins. <bold>Conclusion</bold> There are interaction relationships among the release of different refractory substances，and there is an antagonistic effect between lignin release and tannin，total phenol release；as well as a synergistic effect between total phenol release and cellulose，tannin release.It is suggested that broad-leaved trees with low leaf lignin content should be planted in pure Chinese fir forest to improve the substrate quality of litter，thus accelerating the rate of litter decomposition and nutrient cycling and improving the soil fertility level of Chinese fir plantations.