ABSTRACT

This study investigated the effect of land-use and management change (LUMC) on carbon (C) and nitrogen (N) dynamics after 15–40 years. LUMC constituted change from rice paddies to chestnut orchard, wetland, and buckwheat upland fields in Shonai region, Yamagata Prefecture, Northeast Japan. Soil samples were collected from the top – (0–15 cm) and sub-layers (15–30 cm) for analysis of soil organic C (SOC) and its δ¹³C value, total N (TN), and their stocks. C decomposition (Dec-C) and net N mineralization (Net Min-N) were determined according to the production of CO₂ and NH₄⁺ + NO₃^– by aerobic incubation and CO₂ + CH₄ and NH₄⁺ by anaerobic incubation, respectively. The results reveal that 40 years after change from rice paddy to orchard and wetland, the SOC and TN contents in the top-layer were not significantly altered. However, in buckwheat upland fields and in the parking area where vegetation was absent, the SOC content decreased significantly. Conversion of rice paddies to amur silver grass wetland altered the soil δ¹³C the most, leading to an increase of 5.1‰ and 2.9‰ for the top – and sub-layers, respectively. In general, the incubation experiment results revealed that a change to orchard and wetland did not significantly decrease the Dec-C and Net Min-N. Whereas, the change from rice paddies to parking area significantly decreased the Dec-C and Net Min-N in both aerobic and anaerobic conditions. We conclude that LUMC over decades had various effects on the SOC and TN contents and stocks as well as their mineralization potentials.

摘要

本研究调查了 15-40 年后土地利用和管理变化 (LUMC) 对碳 (C) 和氮 (N) 动态的影响。LUMC 构成了日本东北部山形县庄内地区从稻田到栗园、湿地和荞麦高地的变化。从顶层 (0–15 cm) 和亚层 (15–30 cm) 收集土壤样品，用于分析土壤有机碳 (SOC) 及其 δ ¹³ C 值、总氮 (TN) 及其储量。C 分解 (Dec-C) 和净 N 矿化 (Net Min-N) 是根据 CO ₂和 NH ₄ ⁺ + NO ₃ ^–通过好氧培养和 CO ₂ +  CH ₄和 NH _{4 的产生确定的}⁺分别通过厌氧培养。结果表明，从稻田转为果园和湿地40年后，表层土壤SOC和TN含量未发生显着变化。然而，在荞麦高地和没有植被的停车区，SOC含量显着下降。将稻田转化为阿穆尔银草湿地改变了土壤 δ ¹³C 最大，导致顶层和子层分别增加 5.1‰和 2.9‰。总的来说，孵化实验结果表明，改变果园和湿地并没有显着降低 Dec-C 和 Net Min-N。而从稻田到停车区的变化显着降低了有氧和厌氧条件下的 Dec-C 和 Net Min-N。我们得出的结论是，几十年来 LUMC 对 SOC 和 TN 含量和储量以及它们的矿化潜力产生了各种影响。