Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin, 150081, P.R. China.
University of the Chinese Academy of Sciences, Beijing, 100039, P.R. China.
Sci Rep. 2020 Jun 3;10(1):9041. doi: 10.1038/s41598-020-66038-1.
Evaluation of soil organic carbon (SOC) dynamics is often limited by the complexity of soil matrix. Quantitative information on the distribution of SOC within aggregate hierarchy will help elucidate the carbon flow in soil matrix. However, this knowledge still needs to be documented. Soils were sampled from a surface Mollisol with plots under 100 years of continuous cropping, 31 years of simulated overgrazing to severely degraded bareland, and grassland restoration from cropped soil. A combined density and chemical fractionation procedure within water-stable aggregate was utilized to quantify the distribution of OC after long-term different land use patterns. Results showed that grassland significantly increased total SOC and mean aggregate associated OC compared to initial soil in 1985 with total SOC (g kg soil) from 46.1 to 31.7 and mean aggregate associated OC (g kg aggregate) from 31.6 to 44.7. Converting cropland to grassland also enhanced the formation of macroaggregates (>0.25 mm) (from 34.7% to 52.2%) and increased the OC concentrations in density and humic fractions by 48.3%-75.9% within aggregates. But the proportions of OC in density and humic fractions to SOC only increased in macroaggregates in grassland. Alternatively, converting cropland to bareland caused substantial depletion of total SOC, macroaggregates and their associated OC concentrations. The SOC (g kg soil) and mean aggregate associated OC (g kg aggregate) significantly decreased from 31.7 to 25.7 and from 31.6 to 26.2, respectively. While the OC concentration of density and humic fractions within aggregates in bareland did not show significant decreases. Principal component analysis demonstrated that the soils were developed by contrasting land use changes, with the grassland soil being more associated with labile OC fractions within macroaggregats and bareland soil more associated with recalcitrant OC fractions within microaggregates and silt-clay units. These findings highlighted the favorable preservation of plant-derived carbon within soil aggregates, particularly in the labile OC fractions within macroaggregates under high plant inputs with 31 years of grassland conversion. For the cropland and bareland soils without organic inputs, more OC was stabilized within fine aggregates via organo-mineral interactions, tending to be more recalcitrant.
土壤有机碳（SOC）动态的评估通常受到土壤基质复杂性的限制。定量了解 SOC 在团聚体层次结构中的分布情况，将有助于阐明土壤基质中的碳流动。然而，这方面的知识仍有待进一步阐述。本研究从表层黑钙土中采集了土壤样本，该土壤经历了以下三种土地利用方式：100 年连续耕作、31 年模拟过度放牧导致的严重退化裸地以及从耕作土壤恢复为草地。采用水稳性团聚体中的联合密度和化学分馏程序，定量描述了长期不同土地利用方式下 OC 的分布情况。结果表明，与 1985 年初始土壤相比，草地显著增加了总 SOC 和平均团聚体结合 OC，总 SOC（g kg-1 土壤）从 46.1 增加到 31.7，平均团聚体结合 OC（g kg-1 团聚体）从 31.6 增加到 44.7。将耕地转换为草地还增加了大团聚体（>0.25 mm）的形成（从 34.7%增加到 52.2%），并使团聚体内密度和腐殖质分数中的 OC 浓度增加了 48.3%-75.9%。但是，只有在草地的大团聚体中，OC 在密度和腐殖质分数中占 SOC 的比例才会增加。相反，将耕地转换为裸地会导致总 SOC、大团聚体及其结合 OC 浓度大量减少。SOC（g kg-1 土壤）和平均团聚体结合 OC（g kg-1 团聚体）分别从 31.7 下降到 25.7 和从 31.6 下降到 26.2。而裸地中团聚体内密度和腐殖质分数中的 OC 浓度并没有明显下降。主成分分析表明，土壤是由对比鲜明的土地利用变化形成的，草地土壤与大团聚体中易分解的 OC 分数更相关，而裸地土壤与微团聚体和粉砂-粘粒单元中更难分解的 OC 分数更相关。这些发现强调了在高植物输入条件下，经过 31 年的草地转化，植物源碳在土壤团聚体中得到了良好的保存，特别是在大团聚体中易分解的 OC 分数中。对于没有有机投入的耕地和裸地土壤，更多的 OC 通过有机-矿物相互作用稳定在细团聚体中，倾向于更难分解。
