Characteristics of soil organic matter within an erosional landscape under agriculture in Northeast China: stock, source, and thermal stability
Characteristics of soil organic matter within an erosional landscape under agriculture in Northeast China: stock, source, and thermal stability
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DOI：
10.1016/j.still.2020.104927
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发表时间：
2021-05
影响因子：
6.5
通讯作者：
Wencan Zhang;A. Gregory;W. R. Whalley;T. Ren;Weida Gao
中科院分区：
文献类型：
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作者：
Wencan Zhang;A. Gregory;W. R. Whalley;T. Ren;Weida Gao
土壤有机质的储量、来源和稳定性等特征对于了解侵蚀区土壤功能和碳循环具有重要意义。本研究采用稳定同位素（13 C和14 C）和热重分析（TG）技术，对东北某坡地3个部位（坡肩、坡背和坡脚）的土壤有机质和团聚体进行了研究。大约80年前，在转换为C4玉米为主的可耕地作物之前，该田地最初被C3草地植物占据。从0-120厘米土壤剖面中每隔20厘米采集土壤样品。137 Cs分析表明，肩、背部位的侵蚀速率分别为0.21 cm/yr-1和0.08 cm/yr-1。与肩位相比，在脚位的表土和底土层中发现了更大比例的小的大团聚体（2-0.25 mm）和微团聚体（0.25-0.053 mm）。肩位和背位土壤有机碳含量和储量均显著低于足位。更大的热不稳定SOM的浓度和存储观察到在脚的位置相比，肩和背部的位置。C4来源的有机碳和热不稳定的有机质的比例之间的正相关关系表明，大多数热不稳定的有机质是C4-来自最近的玉米（年轻的SOC），而最稳定的有机质组分是C3-来自以前的草地植被（老SOC）。然而，老SOC的不稳定有机质也是总的热不稳定有机质的重要组成部分，特别是在深层土壤层（低于40厘米）在所有采样点。与微团聚体和粉砂+粘粒（<0.053 mm）相比，小团聚体具有更高的SOC含量、δ 13 C和热不稳定性有机质比例，以及更年轻的SOC年龄，但在40-60 cm深度的底部除外。由于团聚体的质量占32-50%的散装土壤，约有一半的热不稳定和总的SOC被存储为协会与粉砂+粘土组分在侵蚀和沉积点。我们的研究结果表明：（1）在沉积位置，热不稳定有机质和总有机质的含量较高;（2）与新碳源相比，侵蚀坡面，尤其是深层土壤中，老有机质对热不稳定有机质的贡献较大;（3）侵蚀和沉积位置土壤团聚体和粉粒+粘粒组分对有机碳的固存作用相当。
The characteristics of soil organic matter (SOM) such as stocks, sources and stability, are important for understanding soil functioning and C cycling in an eroding field. In this study we investigated the characteristics of SOM in bulk soil and aggregates collected from three positions (shoulder, back, and foot) on a sloping field in Northeast China using stable and radioactive isotope (13C and14C) and thermogravimetry (TG) techniques. The field had originally been populated with C3grassland plants before conversion to C4corn dominated arable cropping approximately 80 years ago. Soil samples were collected from 0–120 cm soil profiles in 20 cm depth intervals. Erosion rates were estimated by137Cs analysis to be 0.21 cm yr–1and 0.08 cm yr–1at the shoulder and back positions, respectively. A greater proportion of small macroaggregates (2–0.25 mm) and microaggregates (0.25–0.053 mm) were found in the topsoil and subsoil layers at the foot position compared with the shoulder position. The concentration and storage of soil organic C (SOC) in the bulk soil was significantly lower at the shoulder and back positions compared with the foot position. Greater thermal-labile SOM concentration and storage were observed at the foot position compared with the shoulder and back positions. Positive relationships between C4-derived SOC and the proportion of thermal-labile SOM suggested that most thermal-labile SOM was C4-derived from the recent corn (young SOC), while most stable SOM fractions were C3-derived from previous grassland vegetation (old SOC). However, labile SOM from old SOC was also an important part of total thermal-labile SOM, particularly in deep soil horizons (below 40 cm) at all sampling positions. Small macroaggregates had a greater SOC content,δ13C, and thermal-labile SOM proportion, and younger SOC age, compared with microaggregates and silt + clay (<0.053 mm) fractions, except at the 40–60 cm depth at the foot position. As the mass of aggregates accounted for 32–50% of the bulk soil, about half of thermal-labile and total SOC were stored as associations with silt + clay fractions at erosional and depositional points. Our results indicated that: (1) more thermal-labile and total SOM were stored at depositional position, (2) compared with new carbon sources, old SOM contributed to a large proportion of thermal-labile SOM on an eroding slope, particularly in deep soil, and, (3) soil aggregates and silt + clay fractions had equivalent roles in SOC sequestration in both erosional and depositional locations.