Dynamic characteristics of soil aggregate stability and related carbon and nitrogen pools at different developmental stages of plantations in northern China

The carbon and nitrogen reserves of forest soil play a key role in combating global climate change. Afforestation is considered an effective measure for increasing carbon and nitrogen reserves in terrestrial forest ecosystems. However, the mechanisms governing how different developmental stages of plantations affect soil carbon and nitrogen stability and storage remain unclear. In this study, we selected three developmental stages of the Larix principis-rupprechtii plantations: medium mature forest (30 yr), near mature forest (40 yr) and mature forest (50 yr). We studied the distribution and stability of soil aggregates at distinct developmental stages, the distribution of carbon and nitrogen pools related to aggregates, and their relationship to environmental factors. We found that with increasing forest age, the soil sand particles became finer. In each developmental stage, the proportion of aggregates >0.25 mm reached more than 85%. The concentrations of carbon and nitrogen in the soil aggregates were lower in the near mature forest (40 a) than in the medium mature forest (30 a), but reached a maximum in the mature forest (50 a). There were significant positive correlations between soil carbon and nitrogen concentrations and soil relative water content (RWC), forest age, and stand density. Soil texture strongly affected the distribution of aggregates. TOC/TN was mainly influenced by aggregate distribution, which was most vulnerable to environmental factors. Environmental factors have a significant negative impact on soil texture, and the path coefficient was -0.812. Environmental factors indirectly affected the concentrations of soil carbon and nitrogen by influencing the distribution and stability of soil aggregates. Therefore, different developmental stages of plantations strongly affected forest carbon and nitrogen pools by changing the soil structure and environmental factors. This study provides a basis for understanding the mechanisms of forest soil carbon and nitrogen storage.