Aims

Plant inputs are the primary organic carbon source that transforms into soil organic matter (SOM) through microbial processing. One prevailing view is that lignin plays a major role in the accumulation of SOM. This study investigated lignin decomposition using wood from different genotypes of Populus tremula as the model substrate. The genotypes naturally varied in lignin content and composition, resulting in high and low lignin substrates.

Methods

The wood was inoculated with fresh soil and decomposition was interpreted through mass loss and CO₂ produced during a 12-month lab incubation. Detailed information on the decomposition patterns of lignin was obtained by Two-dimensional Nuclear magnetic resonance (2D NMR) spectroscopy on four occasions during the incubations.

Results

The lignin content per se did not affect the overall decomposition and ~ 60% of the mass was lost in both substrates. In addition, no differences in oxidative enzyme activity could be observed, and the rate of lignin decomposition was similar to that of the carbohydrates. The 2D NMR analysis showed the oxidized syringyl present in the initial samples was the most resistant to degradation among lignin subunits as it followed the order p-hydroxybenzoates > syringyl > guaiacyl > oxidized syringyl. Furthermore, the degradability of β–O–4 linkages in the lignin varied depending on the subunit (syringyl or guaiacyl) it is attached to.

Conclusions

Our study demonstrates that lignin contains fractions that are easily degradable and can break down alongside carbohydrates. Thus, the initial differences in lignin content per se do not necessarily affect magnitude of SOM accumulation.

中文翻译：

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揭示木质素化学对分解的动力学，以了解其对土壤有机质积累的贡献

 目标

植物输入是通过微生物加工转化为土壤有机质 （SOM） 的主要有机碳源。一种普遍的观点是木质素在 SOM 的积累中起主要作用。本研究使用来自不同基因型的 Populus tremula 的木材作为模型基质研究了木质素分解。基因型在木质素含量和组成方面自然变化，导致高和低木质素底物。

 方法

用新鲜土壤接种木材，并通过质量损失和 12 个月的实验室培养期间产生的 CO₂ 来解释分解。在孵育过程中，通过二维核磁共振 （2D NMR） 波谱四次获得木质素分解模式的详细信息。

 结果

木质素含量本身不会影响整体分解，两种基材中损失了 ~ 60% 的质量。此外，未观察到氧化酶活性的差异，木质素分解的速率与碳水化合物的分解速率相似。二维核磁共振分析显示，初始样品中存在的氧化丁香酯在木质素亚基中是最耐降解的，因为它遵循对羟基苯甲酸盐 > 丁香酯 > 愈创木酰 > 氧化丁香酯的顺序。此外，木质素中 β-O-4 键的降解性取决于它所连接的亚基（丁香酰或愈创木酰基）。

 结论

我们的研究表明，木质素含有易于降解的馏分，可以与碳水化合物一起分解。因此，木质素含量本身的初始差异不一定会影响 SOM 积累的大小。