Background and aims

Priming effect (PE) plays a crucial role in driving soil organic carbon (SOC) decomposition and it is strongly affected by C addition types and nitrogen (N) addition. However, the understanding of the strength and microbial mechanisms of PE in response to specific root exudates (glucose and oxalic acid) and N addition remains inadequate.

Methods

In this study, we carried out a 60-day incubation experiment using simulated root exudates (i.e., glucose and oxalic acid) and inorganic N in coniferous and broad-leaved forest soils to estimate their effects on PE and microbial mechanisms.

Results

Oxalic acid addition resulted in positive PE through “co-metabolism” (i.e., the accelerated microbial decomposition of native SOC), which was supported by an increase in microbial biomass C (MBC), and the activities of enzyme involved in the C and N metabolism in both forest soils. In contrast, N addition significantly lowered positive PE by moderating N mining, as supported by the decreased ratios of fungi: bacteria (F: B), oxidase activities: hydrolase activities (O: H), and C: N enzyme activities, and increased CO₂ derived from root exudate per MBC. These results indicated that stoichiometric decomposition increased with the partial preferential use of the root exudate. The pattern of increased ratios of F: B, O: H, and C: N enzymes with incubation time revealed the dominance of microbial N mining.

Conclusion

Collectively, our results demonstrate that shifts in driving PE from stoichiometric decomposition to microbial N mining over time predominantly depend on N availability, thereby providing insightful evidence for accurately assessing soil C dynamics for future climate change.

中文翻译：

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针叶林和阔叶林土壤中两种模拟根系分泌物和氮添加下微生物机制的变化调节碳启动效应

 背景和目标

启动效应（PE）在驱动土壤有机碳（SOC）分解中起着至关重要的作用，并且它受到碳添加类型和氮（N）添加的强烈影响。然而，对 PE 响应特定根系分泌物（葡萄糖和草酸）和氮添加的强度和微生物机制的了解仍然不足。

 方法

在本研究中，我们使用模拟根系分泌物（即葡萄糖和草酸）和针叶林和阔叶林土壤中的无机氮进行了 60 天的培养实验，以评估它们对 PE 和微生物机制的影响。

 结果

添加草酸通过“共代谢”（即加速微生物分解天然 SOC）产生正 PE，这得到了微生物生物量 C (MBC) 的增加以及参与 C 和 N 的酶活性的支持。两种森林土壤的新陈代谢。相比之下，氮添加通过抑制氮开采显着降低了正 PE，真菌：细菌 (F: B)、氧化酶活性：水解酶活性 (O: H) 和 C: N 酶活性比率下降证明了这一点，并且增加了CO ₂来源于每个MBC 的根分泌物。这些结果表明，随着部分优先使用根系分泌物，化学计量分解增加。 F:B、O:H 和 C:N 酶的比例随培养时间增加的模式揭示了微生物氮开采的主导地位。

 结论

总的来说，我们的结果表明，随着时间的推移，推动PE从化学计量分解向微生物氮开采的转变主要取决于氮的可用性，从而为准确评估未来气候变化的土壤碳动态提供了富有洞察力的证据。