Quantitative influence and underlying mechanisms of nutrient stoichiometry on mineralization of native Soil organic C (SOC) and straw C in different aggregate classes from cultivated and non-cultivated soils are still unclear. Soil samples (Mollisols) from a native woodlot and a farmland converted from woodlot were sieved into three aggregate classes (mega-aggregates (6.3-2 mm), macro-aggregates (2-0.25 mm), and micro-aggregates (< 0.25 mm)) and incubated (180 days) under different nutrient rates (nil, low, and high supplies of N and P) with or without 13C-enriched straw amendment. Significantly higher percentage of native SOC was mineralized from mega- and macro-aggregates (65.8-82.2%) compared with micro-aggregates (48.3-52.0%) in woodlot soil. Nutrient addition significantly increased aggregate-associated C in both soils with straw, and the increase was greater in farmland than in woodlot soil and in large-sized aggregates than in micro-aggregates. These results suggested that large aggregates serve as a C reservoir of labile C, while micro-aggregates that contained C was not easily mineralized even with abundant nutrients. Differences of C mineralization among aggregate size classes were significant in woodlot soil but not in farmland soil. Depletion of SOC was greater with increasing nutrient addition rates in farmland aggregates without straw, while the depletion in woodlot aggregates showed no difference among nutrient treatments, suggesting that microbial activity was nutrient-limited in farmland aggregates. The results improved our knowledge on SOC mineralization in response to residue-nutrient management in different aggregate classes from cultivated and non-cultivated soils, which have important implications for strategies to improve soil fertility or mitigate climate change via increased SOC.

中文翻译：

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受土壤化学计量影响的来自天然和耕作土壤的聚集体中的碳封存

养分化学计量对耕地和非耕地不同团聚体中天然土壤有机碳（SOC）和秸秆碳矿化的定量影响和潜在机制尚不清楚。来自原生林地和从林地转化而来的农田的土壤样品（Mollisol）被筛分为三个聚集体类别（巨型聚集体（6.3-2 毫米）、宏观聚集体（2-0.25 毫米）和微聚集体（< 0.25 毫米） )) 并在不同营养比率（零、低和高 N 和 P 供应）下孵育（180 天），有或没有富含 13C 的秸秆改良剂。与林地土壤中的微团聚体 (48.3-52.0%) 相比，从大型团聚体和大型团聚体 (65.8-82.2%) 矿化的天然 SOC 的百分比显着更高。养分添加显着增加了两种秸秆土壤中与团聚体相关的 C，农田增加量大于林地土壤，大团聚体大于微团聚体。这些结果表明，大团聚体作为不稳定 C 的 C 库，而含有 C 的微团聚体即使有丰富的营养也不容易矿化。C矿化在林地土壤中的骨料大小等级之间存在显着差异，而在农田土壤中则不显着。没有秸秆的农田团聚体随着养分添加率的增加，SOC 的消耗更大，而林地团聚体的消耗在养分处理之间没有差异，这表明农田团聚体中的微生物活动是养分有限的。