桂西北喀斯特峰丛洼地不同植被恢复方式下土壤有机碳组分变化特征

植被恢复被认为是提升退化区域土壤有机碳（SOC）固持的有效措施。然而，喀斯特脆弱生态系统植被人工恢复和自然恢复模式下SOC不同组分变化特征、稳定性和固持能力的研究还较缺乏。以典型喀斯特峰丛洼地为研究区，以耕地为对照，以恢复15年的人工恢复（人工林）和自然恢复（耕地撂荒后植被自然演替为灌丛）为研究对象，分析不同植被恢复模式下SOC、颗粒态有机碳（POC）、矿质结合态有机碳（MOC）、易氧化态有机碳（ROC）、惰性碳指数（RI）和SOC相对固持能力（SCS_capacity）变化特征。结果发现：（1）人工林和灌丛SOC、POC和ROC含量显著高于耕地，且灌丛POC和ROC含量显著高于人工林，MOC则在三者之间差异不显著；（2）与耕地相比，人工林和灌丛RI显著下降，但SCS_capacity差异不显著。研究表明，桂西北喀斯特峰丛洼地植被恢复15年后主要提升土壤活性碳组分，且自然恢复比人工恢复更有利于于提升土壤活性碳组分；然而，耕地退耕后短期内土壤碳稳定性并未增加，强调植被恢复后避免再次毁林开荒对于维持土壤碳固持的必要性。

Responses of soil organic carbon fractions to different vegetation restoration in a typical karst depression

Vegetation restoration is an effective strategy to improve soil organic carbon (SOC) sequestration in the degraded ecosystems. However, the responses of SOC fractions, stabilization, and sequestration capacity to the managed and natural vegetation restoration in the karst region are poorly understood. Here, using cropland as a control, we compared the managed plantation and naturally recovered shrubland after 15 years of vegetation restoration in a typical subtropical karst depression. The SOC, particulate organic carbon (POC), mineral-associated organic carbon (MOC), readily oxidizable carbon (ROC), recalcitrant index (RI), and relative sequestration capacity (SCS_capacity) were measured. We found that the contents of SOC, POC, and ROC in both plantation and shrubland were significantly higher than those in the cropland, whereas MOC showed no significant difference among the three land-use types. We also found that the contents of POC and ROC in the shrubland were significantly higher than those in the plantation. Furthermore, compared with cropland, the RI in the plantation and shrubland were significantly decreased, whereas the relative sequestration capacity of SOC showed no significant differences. Our results indicated that vegetation restoration over a relatively short period (15 years) mainly improved the active SOC fractions. Moreover, the natural vegetation restoration was more beneficial to the active SOC fraction accumulation than the managed vegetation restoration. However, the decreased soil carbon stabilization following vegetation restoration emphasizes the necessity of avoiding human disturbances of the vegetation restoration sites to maintain soil carbon sequestration.