耕作干扰下喀斯特土壤有机碳损失主要途径及其影响因素

西南喀斯特生态系统原生土壤有机碳(SOC)含量较高,但在开垦后急剧损失,然而目前对SOC损失过程、途径和机制仍缺乏充分认知。本研究基于不同频率翻耕处理(分别隔6、4、2、1个月翻耕一次,以免耕为对照)的原位控制试验,以土壤团聚体为切入点,通过对土壤CO_2排放和可溶性有机碳(DOC)淋失通量进行为期一年的连续监测,探讨了SOC损失的主要途径及其影响因素。结果发现:翻耕导致表层(0～10 cm)土壤SOC和5～8 mm粒级团聚体显著降低;一年后,各翻耕处理平均损失15.4%～27.6%的SOC,土壤DOC淋失量仅占SOC损失量的0.05%～0.10%,而土壤以CO_2形式释放的碳占SOC损失总量的22.7%～35.5%,是土壤碳损失的重要途径之一;SOC损失量与Ca~(2+)、Mg~(2+)淋失总量均呈显著正相关,说明在岩溶作用下以HCO_3-形式淋失是SOC损失的另一重要途径;土壤CO_2排放速率与5～8 mm粒级团聚体含量呈显著负相关,说明翻耕干扰导致5～8 mm团聚体崩解、受团聚体保护的闭蓄态SOC释放后迅速矿化是喀斯特SOC损失的主要机制。

Pathways and influencing factors of soil organic carbon loss under tillage disturbance in karst area, China

Soil organic carbon (SOC) content is relatively high in natural karst ecosystems of southwest China, but a substantial SOC loss would occur rapidly once cultivated. However, the pathways and underlying mechanisms responsible for SOC loss upon disturbance are still unknown. Based on an in-situ experiment with treatments of tillage at different frequencies (tilled every 6, 4, 2, and 1 month(s), no-till treatments as control), this study took soil aggregates as the key point and investigated the pathways and influencing factors of SOC loss via monitoring soil CO2 fluxes and dissolved organic carbon (DOC) leaching fluxes for 1 year. Tillage managements significantly reduced the 5~8 mm aggregate content and SOC concentration. Approximately 15.4%~27.6% of SOC was lost from the surface soil (0~10 cm) during this year. DOC loss via leaching contributed only 0.05%~0.10% of the total SOC loss, whereas CO2-C loss accounted for about 22.7%~35.5% of total SOC loss, supporting that CO2 emission was one of the important ways of C loss. Besides, SOC losses were significantly and positively correlated with both Ca2 and Mg2 losses via leaching, indicating that HCO3--C leaching induced by karstification was another important way of SOC loss. Soil CO2 fluxes were significantly and negatively correlated with 5~8 mm aggregate contents, suggesting that the disruption of 5~8 mm aggregates induced by tillage led to the failure of SOC protection by aggregates, thereby accelerating SOC mineralization. This study revealed the mechanisms responsible for SOC loss induced by tillage in a calcareous soil of southwest China.