Changes in litter and nutrient inputs into soil could have significant consequences on forest carbon (C) dynamics via controls on the structure and microbial utilization of soil organic C (SOC). In this study, we assessed changes in physical fractions (250–2000 μm, 53–250 μm, and < 53 μm soil aggregates) and chemical fractions (labile, intermediate and recalcitrant pools) of SOC in the top 20 cm mineral soil layer and their influences on microbial substrate utilization after eight years of experiment in a mixed pine-oak forest. The litter treatments included: control (Lcon), litter removal (Lnil), fine woody litter addition (Lwoody), leaf litter addition (Lleaf) and a mix of leaf and fine woody litter (Lmix). Nitrogen (N) addition (application rates of 0, 5 and 10 g N m−2 year−1, respectively) was also applied. We found that complete removal of forest-floor litter (Lnil) significantly reduced the pool sizes of all SOC fractions in both the physical and chemical fractions compared with treatments that retained either leaf litter (Lleaf) or mixture of leaves and fine woody materials (Lmix). The type of litter was more important in affecting SOC fractions than the quantity of inputs; neither the level of N addition rate nor its interaction with litter treatment had significant effects on both physical and chemical SOC fractions. Microbial respiration differed significantly among the treatments of varying litter types. However, the effectiveness of microbial C utilization inferred by microbial C use efficiency and biomass-specific respiration was not affected by either the litter treatments or N addition. These results suggest that despite significant changes in SOC composition due to long-term treatments of forest-floor litter and N addition in this mixed pine-oak forest of temperate climate, microbial C utilization strategies remain unaffected.

中文翻译：

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长期凋落物类型处理改变了松橡混交林中土壤碳组成但不改变微生物碳利用

通过控制土壤有机碳 (SOC) 的结构和微生物利用，凋落物和土壤养分输入的变化可能对森林碳 (C) 动态产生重大影响。在本研究中，我们评估了顶部 20 cm 矿质土壤层中 SOC 的物理组分（250-2000 μm、53-250 μm 和 < 53 μm 土壤团聚体）和化学组分（不稳定、中间和顽固池）的变化和在松橡混交林中进行八年试验后，它们对微生物底物利用的影响。凋落物处理包括：控制 (Lcon)、凋落物去除 (Lnil)、细木本凋落物添加 (Lwoody)、落叶添加 (Lleaf) 以及树叶和细木本凋落物的混合 (Lmix)。还应用了氮 (N) 添加量（分别为 0、5 和 10 g N m-2 year-1 的施用率）。我们发现，与保留落叶物 (Lleaf) 或叶子与细木材料的混合物 (Lmix) 的处理相比，完全去除森林地面凋落物 (Lnil) 显着降低了物理和化学部分中所有 SOC 部分的池大小）。在影响 SOC 分数方面，凋落物的类型比输入的数量更重要；N 添加率的水平及其与凋落物处理的相互作用对物理和化学 SOC 分数都没有显着影响。微生物呼吸在不同垫料类型的处理之间存在显着差异。然而，由微生物碳利用效率和生物量特定呼吸推断的微生物碳利用的有效性不受凋落物处理或氮添加的影响。