The molecular diversity of soil organic matter (SOM) is recognised as a key factor influencing soil organic carbon (SOC) accumulation, and the molecular diversity of SOM may change as SOC content changes during land use change. However, the relationship between SOM molecular diversity and SOC before and after natural wetland reclamation remains unclear. Here, we selected seven groups of natural wetland–reclaimed wetlands for spatially paired sampling. SOM molecular diversity was assessed using pyrolysis–gas chromatography–mass spectrometry (py-GC/MS), and factors driving changes in SOM molecular diversity (including microbial community characteristics, enzyme activities, carbon mineralisation rate and soil environmental factors) were investigated. The results showed that molecular diversity (Shannon diversity, Richness) tended to increase with increasing organic carbon content in both wetland and paddy soils. And the soil mineralisation rate decreased with the increase of molecular diversity. This suggests that the relationship between molecular diversity and organic carbon content is not decoupled, even in anaerobic or cyclic anaerobic environments. Therefore, the molecular diversity of soil organic matter can be used as an indicator of the sustainability of soil carbon pools. Microbial biomass and enzyme activity characteristics were important factors influencing soil carbon dynamics and molecular diversity. Molecular diversity decreases with a loss of soil organic carbon after wetland reclamation. Compared to those in natural wetlands, the relative proportions of both aliphatic and alkyl compounds decreased, and the relative proportions of nitrogenous compounds increased in paddy field soils. In addition, the rate of soil carbon mineralisation increases despite the presence of a greater proportion of recalcitrant carbon (phenols and aromatics) in paddy soils. Our results also suggest a positive role for molecular diversity in suppressing soil mineralization rates. Our study provides a molecular diversity-based perspective for understanding wetland soil organic carbon dynamics under the influence of reclamation.

中文翻译：

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开垦导致土壤有机碳损失和分子复杂性：从自然湿地到开垦湿地的证据


土壤有机质 （SOM） 的分子多样性被认为是影响土壤有机碳 （SOC） 积累的关键因素，在土地利用变化过程中，土壤有机质的分子多样性可能随着 SOC 含量的变化而变化。然而，自然湿地复垦前后 SOM 分子多样性与 SOC 之间的关系仍不清楚。在这里，我们选择了七组天然湿地-开垦湿地进行空间配对采样。使用热解-气相色谱-质谱 （py-GC/MS） 评估 SOM 分子多样性，并研究驱动 SOM 分子多样性变化的因素 （包括微生物群落特征、酶活性、碳矿化速率和土壤环境因素）。结果表明，湿地和水稻土的分子多样性 （Shannon diversity， Richness） 随着有机碳含量的增加而增加。土壤矿化速率随分子多样性的增加而降低。这表明分子多样性和有机碳含量之间的关系并不是解耦的，即使在厌氧或循环厌氧环境中也是如此。因此，土壤有机质的分子多样性可以作为土壤碳库可持续性的指标。微生物生物量和酶活性特性是影响土壤碳动态和分子多样性的重要因素。分子多样性随着湿地复垦后土壤有机碳的损失而降低。与自然湿地相比，稻田土壤中脂肪族和烷基化合物的相对比例均有所降低，含氮化合物的相对比例增加。 此外，尽管水稻土壤中存在更大比例的顽固碳（酚类和芳烃），但土壤碳矿化的速度会增加。我们的研究结果还表明，分子多样性在抑制土壤矿化速率方面起着积极作用。我们的研究为理解围垦影响下的湿地土壤有机碳动态提供了一种基于分子多样性的视角。