Carbon (C) and nitrogen (N) represent the commonest limiting nutrients for microbial growth in terrestrial ecosystems. However, most of our understanding of how C:N ratios modulate microbial growth comes from short-term growth assays under controlled conditions. Four levels of N additions including control (CK, 0 kg·hm− 2·a− 1), low N (LN, 50 kg·hm− 2·a− 1), medium N (MN, 100 kg·hm− 2·a− 1), and high N (HN, 150 kg·hm− 2·a− 1) inputs were applied monthly in a pine forest (Pinus tabulaeformis). Three C management practices were further conducted in each N additions plot, namely aboveground litter and belowground root removal (LRR), aboveground litter removal (LR), and intact soils (non-removal, NR). Soil bacterial richness, diversity, community composition and soil properties were measured. MN and HN significantly increased the relative abundance of copiotrophic taxa, but decreased that of oligotrophic taxa. Bacterial richness and diversity were not altered by N enrichment. LRR significantly increased the relative abundance of Gemmatimonadetes while decreased that of Actinobacteria. C management did not affect bacterial richness and community structure but LR significantly decreased bacterial diversity. Structural equation modeling showed that N addition induced the decrease in soil pH was responsible for the changes in the bacterial community structure. C management exhibited a direct negative effect on bacterial diversity and had an indirect positive effect on it via increasing soil moisture and microbial biomass C:N ratio. The findings highlight the contrasting impacts of N addition and C management on soil bacterial communities and emphasize the regulation of above- and below-ground C substrate supplies on the N responses of soil bacterial communities.

中文翻译：

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碳管理实践调节土壤细菌群落以响应松林中的氮添加

碳 (C) 和氮 (N) 是陆地生态系统中微生物生长最常见的限制性营养素。然而，我们对 C:N 比率如何调节微生物生长的大部分理解来自受控条件下的短期生长测定。四种氮添加水平，包括对照（CK，0 kg·hm- 2·a- 1）、低氮（LN，50 kg·hm- 2·a- 1）、中氮（MN，100 kg·hm- 2） ·a− 1) 和高 N (HN, 150 kg·hm− 2·a− 1) 投入每月在松树林（Pinus tabulaeformis）中施用。在每个 N 添加地块中进一步进行了三种碳管理实践，即地上凋落物和地下根去除 (LRR)、地上凋落物去除 (LR) 和完整土壤（非去除，NR）。测量了土壤细菌丰富度、多样性、群落组成和土壤特性。MN 和 HN 显着增加了营养类群的相对丰度，但降低了寡营养类群的相对丰度。N 富集不会改变细菌丰富度和多样性。LRR 显着增加了 Gemmatimonadetes 的相对丰度，同时降低了放线菌的相对丰度。C 管理不影响细菌丰富度和群落结构，但 LR 显着降低了细菌多样性。结构方程模型表明，N添加引起土壤pH值的降低是细菌群落结构变化的原因。C 管理对细菌多样性产生直接的负面影响，并通过增加土壤水分和微生物生物量 C:N 比对其产生间接积极影响。