Lignin's role in litter and soil organic carbon (SOC) decomposition remains contentious. Lignin decomposition was traditionally thought to increase during mid-stage litter decomposition, when cellulose occlusion by lignin began to limit mass loss. Alternatively, lignin decomposition could be greatest in fresh litter as a consequence of co-metabolism, and lignin might decompose faster than bulk SOC. To test these competing hypotheses, we incubated 10 forest soils with C4 grass litter (amended with 13 C-labeled or unlabeled lignin) over two years and measured soil respiration and its isotope composition. Early lignin decomposition was greatest in five of ten soils, consistent with the co-metabolism hypothesis. However, lignin decomposition peaked 6-24 months later in the other five soils, consistent with the substrate-limitation hypothesis; these soils were highly acidic. Rates of lignin, litter, and SOC decomposition tended to converge over time. Cumulative lignin decomposition was never greater than SOC decomposition; lignin decomposition was significantly lower than SOC decomposition in six soils. Net nitrogen mineralization predicted lignin decomposition ratios relative to litter and SOC. Although the onset of lignin decomposition can indeed be rapid, lignin still presents a likely bottleneck in litter and SOC decomposition, meriting a reconsideration of lignin's role in modern decomposition paradigms.

中文翻译：

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木质素滞后、超前或限制凋落物和土壤有机碳的分解

木质素在凋落物和土壤有机碳 (SOC) 分解中的作用仍然存在争议。传统上认为木质素分解在垃圾分解中期阶段会增加，此时木质素对纤维素的吸留开始限制质量损失。或者，由于共同代谢，木质素在新鲜垫料中的分解可能最大，并且木质素的分解速度可能比散装 SOC 快。为了测试这些相互竞争的假设，我们在两年内用 C4 草屑（用 13 C 标记或未标记的木质素修正）培养了 10 个森林土壤，并测量了土壤呼吸及其同位素组成。早期木质素分解在十种土壤中的五种中最大，这与共代谢假设一致。然而，其他五种土壤的木质素分解在 6-24 个月后达到峰值，这与基质限制假设一致；这些土壤酸性很强。木质素、凋落物和 SOC 分解的速率随着时间的推移趋于收敛。累积木质素分解永远不会大于 SOC 分解；在六种土壤中木质素分解显着低于 SOC 分解。净氮矿化预测了木质素相对于凋落物和 SOC 的分解率。尽管木质素分解的开始确实可以很快，但木质素仍然可能是垃圾和 SOC 分解的瓶颈，值得重新考虑木质素在现代分解范式中的作用。净氮矿化预测了木质素相对于凋落物和 SOC 的分解率。尽管木质素分解的开始确实可以很快，但木质素仍然可能是垃圾和 SOC 分解的瓶颈，值得重新考虑木质素在现代分解范式中的作用。净氮矿化预测了木质素相对于凋落物和 SOC 的分解率。尽管木质素分解的开始确实可以很快，但木质素仍然可能是垃圾和 SOC 分解的瓶颈，值得重新考虑木质素在现代分解范式中的作用。