The carbon pools of forest soils play a vital role in global carbon sequestration and emissions. Forest management can regulate the sequestration and output of forest soil carbon pools to a certain extent; however, the kinetics of the effects of forest density on soil carbon pools require further investigation. We established sample plots with stand density gradients in three different aged Larix principis-rupprechtii plantations and quantified the soil respiration, soil organic carbon (SOC), soil dissolved organic carbon (DOC), microbial biomass carbon (MBC), light fraction organic carbon (LFOC), and readily oxidized carbon (ROC). During the growth and development of plantations, stand density is an essential factor that impacts soil respiration and its associated elements. Moderate density was observed to promote both the soil and heterotrophic respiration rates and the sequestration of MBC and LFOC, whereas it inhibited the sequestration of ROC. The soil, heterotrophic, and autotrophic respiration rates of older forest stands were relatively rapid, whereas the contents of SOC, MBC, LFOC, DOC, and ROC were higher and more sensitive to changes in stand density. The MBC, LFOC, and ROC in soil labile organic carbon were closely related to both the soil and heterotrophic respiration, but not the SOC. Among them, the LFOC and MBC played the roles of “warehouse” and “tool” and were significantly correlated with soil and heterotrophic respiration. The ROC, as a “raw material”, exhibited a significantly negative correlation with the soil and heterotrophic respiration. When the soil and heterotrophic respiration rates were rapid, the ROC content in the soil maintained the low level of a “dynamically stabilized” state. The stand density regulated heterotrophic respiration by affecting the soil labile organic carbon, which provided an essential path for the stand density to regulate soil respiration.

中文翻译：

---

林分密度对不同年龄落叶松人工林土壤呼吸和不稳定有机碳的影响

森林土壤的碳库在全球碳固存和排放中起着至关重要的作用。森林经营可以在一定程度上调节森林土壤碳库的封存和输出；然而，森林密度对土壤碳库影响的动力学需要进一步研究。我们在三个不同年龄的落叶松人工林中建立了林分密度梯度的样地，并量化了土壤呼吸、土壤有机碳 (SOC)、土壤溶解有机碳 (DOC)、微生物生物量碳 (MBC)、轻质有机碳 ( LFOC) 和易氧化碳 (ROC)。在人工林的生长和发展过程中，林分密度是影响土壤呼吸及其相关元素的重要因素。观察到中等密度可促进土壤和异养呼吸速率以及 MBC 和 LFOC 的隔离，而它抑制 ROC 的隔离。老林分的土壤、异养和自养呼吸速率相对较快，而 SOC、MBC、LFOC、DOC 和 ROC 的含量较高，对林分密度变化更敏感。土壤不稳定有机碳中的 MBC、LFOC 和 ROC 与土壤和异养呼吸密切相关，但与 SOC 无关。其中，LFOC和MBC起到“仓库”和“工具”的作用，与土壤和异养呼吸显着相关。ROC作为“原料”，与土壤和异养呼吸呈显着负相关。当土壤和异养呼吸速率较快时，土壤中的 ROC 含量保持在“动态稳定”状态的低水平。林分密度通过影响土壤不稳定有机碳来调节异养呼吸，这为林分密度调节土壤呼吸提供了重要途径。