Land-use affecting organic carbon and its active components in soil aggregates in China

ABSTRACT Due to large-scale wetland reclamation, the typical wetland had been conversed to different wetland use types (upland field, paddy field, and artificial forest) in the Sanjiang Plain. However, there are scarce data regarding soil aggregates and active organic carbons during land-use transition. Here, soil aggregates and the changes in content and storage of active organic carbon [total organic carbon (TOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and readily oxidized carbon (ROC)] were studied under three land-uses reclaiming wetlands as an upland field, paddy field, and artificial forest in Heilongjiang Province, China. The results showed that soil aggregate structure changed significantly under the three land-uses, of which the largest decrease of mean weight diameter (MWD) occurred in the upland field. Under the three land-use types, the content and storage of TOC and each active organic carbon in soil aggregates with different size fractions significantly decreased compared with that in the wetland. In addition, the proportion of the 1–2 mm soil aggregate was significantly lower than that of other particle sizes, which resulted in the lowest storage of TOC and active organic carbon at 1-2 mm and was found in the wetland, and different land-use types; small aggregates (<0.25 mm) with a small proportion were ignored in calculating organic carbon content and storage. The TOC and active organic carbon content in various soil aggregates varied significantly in different land-use types; the paddy field was most similar to the wetland because of seasonal flooding factors. In soil aggregates with various size fractions, the paddy field presented small changes in the TOC, DOC, and MBC content, and the ROC content was significantly lower than that in the upland field and the artificial forest land-use types. The TOC, DOC, and MBC content in the upland field and the artificial forest were significantly reduced compared with that in the paddy field due to the decrease of water content in the soil. In the artificial forest, which had less human disturbance, organic carbon content was less affected than in long-term cultivated upland fields due to its abundant plant root systems and large input of organic matter. The upland field could seriously affect the structure of soil aggregates and organic carbon in the wetlands and had the most negative impact on the wetland ecosystem.

摘要 由于大规模湿地开垦，三江平原典型湿地已被转换为旱地、稻田与人工林等不同土地利用类型。然而，当前针对土地利用转型过程中土壤团聚体及活性有机碳的相关数据仍较为匮乏。本研究以中国黑龙江省将湿地开垦为旱地、稻田及人工林的三种土地利用场景为研究对象，系统分析了土壤团聚体特征，以及总有机碳（total organic carbon, TOC）、溶解性有机碳（dissolved organic carbon, DOC）、微生物生物量碳（microbial biomass carbon, MBC）与易氧化有机碳（readily oxidized carbon, ROC）的含量与储量变化。研究结果显示，三种土地利用方式下土壤团聚体结构均发生显著改变，其中旱地的平均重量直径（mean weight diameter, MWD）降幅最大。相较于原生湿地，三种土地利用类型下不同粒径团聚体中的总有机碳及各活性有机碳的含量与储量均显著降低。此外，1–2 mm粒径土壤团聚体的占比显著低于其他粒径，使得该粒径下总有机碳与活性有机碳储量在湿地及各土地利用类型中均处于最低水平；而占比较低的微团聚体（<0.25 mm）在有机碳含量与储量的计算过程中常被忽略。不同土地利用类型下，各粒径团聚体中的总有机碳与活性有机碳含量存在显著差异；受季节性淹水因素影响，稻田与原生湿地的特征最为相似。在各粒径团聚体中，稻田的总有机碳、溶解性有机碳与微生物生物量碳含量变化幅度较小，但其易氧化有机碳含量显著低于旱地与人工林。由于土壤含水量下降，旱地与人工林的总有机碳、溶解性有机碳与微生物生物量碳含量相较于稻田均显著降低。在人为干扰较少的人工林中，得益于发达的植物根系与大量有机质输入，其有机碳含量受影响程度低于长期耕作的旱地。整体而言，旱地开垦会严重破坏湿地土壤团聚体结构与有机碳特征，对湿地生态系统造成的负面影响最为显著。