Soil microorganisms are primary decomposers driving carbon and nutrient cycling in terrestrial ecosystems. One prevailing view is that fungi, rather than bacteria, play a predominant role in litter decomposition. However, the roles of bacteria and factors that restrict their activity during decomposition remain unclear. We hypothesized that the limiting activity of bacterial decomposers is associated with litter size beyond chemical quality. To address this gap, we conducted a 180-d decomposition microcosm experiment to investigate the effect of fragment size (large, 1–2 mm; middle, 0.18–0.28 mm; small, <0.07 mm) of oak and pine litters on bacterial or fungal decomposition. Bacterial and fungal decomposition were accelerated with fragment size decrease, suggesting that an interface effect existed between microbial decomposers and litter. Generally, the decomposition ability of bacteria was more sensitive to changes in fragment size compared to fungi. Fungi resulted in faster decomposition of large fragments than bacteria. For small oak litter fragments, bacteria showed faster decomposition than fungi, whereas the opposite was true for small pine litter. Therefore, the decomposition dominance of bacteria and fungi was regulated by fragment size and influenced by the chemical quality of litter, especially the lignin:N ratio. The contrasting decomposition dominances of bacteria versus fungi were likely attributed to filamentous fungi penetrating litter interiors and forming mycelial bridges between scattered litters. Bacteria resided on litter surfaces and even formed biofilms. Consistent with the findings of the microcosm experiment, the proportion of small fragments was greater in the fresh litter layer than in the decomposed layer in the field, and greater in the pine forest than in the oak forest, suggesting the fresh, large, and low-quality litter was preferentially fragmented by fungi. Consequently, the dominance of fungi and bacteria during litter decomposition in the conventional view should be revisited considering the litter size.

中文翻译：

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扩大界面扭转了垃圾分解过程中真菌对细菌的主导地位


土壤微生物是驱动陆地生态系统中碳和养分循环的主要分解者。一种流行的观点是，真菌而不是细菌在垃圾分解中发挥着主要作用。然而，细菌的作用以及在分解过程中限制其活性的因素仍不清楚。我们假设细菌分解剂的限制活性与化学质量之外的产仔数有关。为了解决这一差距，我们进行了 180 天的分解微观实验，以研究橡树和松树凋落物碎片尺寸（大，1-2 毫米；中，0.18-0.28 毫米；小，<0.07 毫米）对细菌或真菌分解。随着碎片尺寸的减小，细菌和真菌的分解加速，表明微生物分解者和凋落物之间存在界面效应。一般来说，与真菌相比，细菌的分解能力对碎片大小的变化更敏感。真菌比细菌更快地分解大碎片。对于小橡木垃圾碎片，细菌比真菌分解得更快，而对于小松树垃圾则相反。因此，细菌和真菌的分解优势受到碎片大小的调节，并受到凋落物化学质量（尤其是木质素：N 比率）的影响。细菌与真菌的分解优势的对比可能归因于丝状真菌穿透垃圾内部并在分散的垃圾之间形成菌丝桥。细菌驻留在垃圾表面，甚至形成生物膜。 与微观实验的结果一致，田间新鲜凋落物层中小碎片的比例大于腐烂层中的小碎片比例，松林中小碎片的比例大于橡树林中的比例，这表明小碎片的比例新鲜、大、低。 -优质垫料优先被真菌破碎。因此，考虑到垃圾的大小，应重新审视传统观点中真菌和细菌在垃圾分解过程中的主导地位。