软土中含有大量的土壤有机碳（SOC），极易受到气候变化的影响；因此，气候变化可以间接影响土壤团聚体稳定性，但影响团聚体稳定性的主导因素仍存在争议。这里，从2004年开始进行从高纬度到低纬度地区的土壤移栽试验，以研究变暖主导的气候变化（约3-4.7℃）对表层（0-20 cm）土壤OC组分数量和分子组成、团聚稳定性变化及其潜在机制的影响。原位确定了不同的初始土壤有机质（SOM）含量：50.6 g kg -1 (SOM5)、58.8 g kg -1 (SOM6) 和 108.9 g kg -1 (SOM11)土壤和移植土壤中以模拟变暖。15 年变暖主导的气候变化并未使较低 SOM 的 Mollisol（SOM5 和 SOM6）中的 SOC 含量发生明显变化，但较高 SOM Mollisol（SOM11）中的 SOC 含量增加了 13.3%。就不稳定OC组分而言，变暖主导的气候变化使溶解有机碳（DOC）含量显着增加20.1%~47.7%，但易氧化有机碳（EOC）和微生物量碳（MBC）含量减少22.1%~33.6%。无论采取何种处理方式，变暖主导的气候变化都会降低土壤团聚体稳定性，平均重量直径（MWD）和几何平均直径（GMD）减少41.7%–79.3%，分形维数（D）增加28.6%–58.5%。对于分层组织的土壤团聚体，变暖主导的气候变化增加了游离微团聚体（Fm-POM）以及非团聚淤泥+粘土大小有机物（nA-MOM）内颗粒有机物的比例和OC含量。然而，气候变化降低了大团聚体 (mM-MOM) 内微团聚体中淤泥 + 粘土大小部分的比例和 OC 含量。重要的是，变暖主导的气候变化增加了 mM-MOM、Fm-POM 和 nA-MOM 组分中碳水化合物的含量，并减少了木质素的含量。因此，我们推测，大团聚体和 nA-MOM 组分中矿物缔合的化学保护以及游离微团聚体中 POM 吸留的物理保护可能是软土长期气候变化下 SOC 稳定的主要机制。长期变暖主导的气候变化结果表明，对较高的SOM软土中的SOC含量、DOC、碳水化合物C、游离微团聚体相关C和非聚集粉土+粘土尺寸相关C有积极影响，但对EOC、MBC、木质素C、大团聚体内微团聚体C和聚集体稳定性产生负面影响。这些变量都导致了土壤团聚体稳定性的降低，并可能作为软土中由变暖主导的气候变化的敏感指标，进而影响农田生态系统的碳通量以应对进一步的气候变化。木质素 C、大团聚体 C 内的淤泥 + 粘土大小的微团聚体以及团聚体稳定性。这些变量都导致了土壤团聚体稳定性的降低，并可能作为软土中由变暖主导的气候变化的敏感指标，进而影响农田生态系统的碳通量以应对进一步的气候变化。木质素 C、大团聚体 C 内的淤泥 + 粘土大小的微团聚体以及团聚体稳定性。这些变量都导致了土壤团聚体稳定性的降低，并可能作为软土中由变暖主导的气候变化的敏感指标，进而影响农田生态系统的碳通量以应对进一步的气候变化。
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Warming-dominated climate change impacts on soil organic carbon fractions and aggregate stability in Mollisols
Mollisols contain high amounts of soil organic carbon (SOC), which is highly susceptible to climate change; thus, climate change could indirectly influence soil aggregate stability, but the dominant factor affecting aggregate stability remains controversial. Here, a soil transplanting test from high-latitude to low-latitude locations was initiated in 2004 to investigate the influences of warming-dominated climate change (approximately 3–4.7 ℃) on the quantity and molecular composition of OC fractions in surface (0–20 cm) soils, aggregate stability changes and underlying mechanisms. Different initial soil organic matter (SOM) contents of 50.6 g kg−1 (SOM5), 58.8 g kg−1 (SOM6), and 108.9 g kg−1 (SOM11) were established in situ soils and in transplanted soils to simulate warming. The 15-year warming-dominated climate change presented no noticeable change in the SOC content in the lower SOM Mollisols (SOM5 and SOM6) but increased the SOC content by 13.3% in the higher SOM Mollisol (SOM11). In terms of labile OC fractions, warming-dominated climate change significantly increased the dissolved organic carbon (DOC) content by 20.1%–47.7% but reduced the easily oxidizable organic carbon (EOC) and microbial biomass carbon (MBC) contents by 22.1%–33.6%. Irrespective of any treatment, warming-dominated climate change decreased soil aggregate stability, as evidenced by the reduction in mean weight diameter (MWD) and geometric mean diameter (GMD) of 41.7%–79.3% and an increase in fractal dimension (D) of 28.6%–58.5%. For hierarchically organized soil aggregates, warming-dominated climate change increased the proportion and OC content of particulate organic matter inside free microaggregates (Fm-POM) as well as nonaggregated silt + clay-sized organic matter (nA-MOM). However, climate change decreased the proportion and OC content of silt + clay-sized fractions inside microaggregates within macroaggregates (mM-MOM). Of importance, warming-dominated climate change increased the amount of carbohydrates and decreased the amount of lignin in the mM-MOM, Fm-POM, and nA-MOM fractions. Therefore, we speculated that chemical protection by mineral association within macroaggregates and nA-MOM fractions and physical protection by the occlusion of POM within free microaggregates might be the primary mechanisms for SOC stabilization under long-term climate change in Mollisols. The long-term warming-dominated climate change results demonstrated a positive effect on SOC content in higher SOM Mollisols, DOC, carbohydrate C, free microaggregate-associated C and nonaggregated silt + clay-sized associated C but exhibited a negative effect on EOC, MBC, lignin C, silt + clay-sized inside microaggregates within macroaggregates C and aggregate stability. These variables all contributed to the reduction in soil aggregate stability and might act as sensitive indicators of warming-dominated climate change in Mollisols, which in turn affect farmland ecosystem C fluxes in response to further climate change.
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