Background and aims

It is known that nitrogen (N) input modulates the rhizosphere priming effect (RPE); however, the magnitude and driving mechanisms of priming under increasing rates of fertilizer application remain unclear.

Methods

¹⁵N-urea (control, 75 (N75), 150 (N150), 225 (N225), and 300 (N300) kg N ha⁻¹) was applied to a plant (maize)-soil (rice paddy) system and the RPE was monitored during the trumpet period (the most active stage) of plant growth.

Results

Addition of N decreased soil-derived CO₂ emission by 21.1–49.3% in the presence of plants. The RPE declined following N input in the control−N150 as a result of low microbial C:N imbalance, which decreased enzyme activities due to low microbial N mining and microbial activation, and high microbial metabolic efficiency (MME). In contrast, the RPE increased following N input in the N150 − N300, which was attributed to the high microbial C:N imbalance causing low MME, rather than the promotion of microbial N mining or microbial activation mechanisms. The microbial C:N imbalance was the result of N competition between microorganisms and plants.

Conclusions

Thus, the combination of enzyme activities and MME mediates N-regulated RPE, while N competition drives the switching of RPE mechanisms.

中文翻译：

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施氮对根际启动的影响

背景和目标

众所周知，氮的输入会调节根际启动效应（RPE）。然而，在肥料施用量增加的情况下，引发的数量和驱动机制仍不清楚。

方法

^将15 N尿素（对照，75（N75），150（N150），225（N225）和300（N300）kg N ha ^-1）施用于植物（玉米）-土壤（稻田）系统，在植物生长的喇叭期（最活跃的阶段）期间对RPE进行了监测。

结果

在植物存在下，氮的添加使土壤衍生的CO ₂排放降低了21.1–49.3％。由于微生物C：N失衡低，RPE随对照N150中的N输入而下降，这是由于微生物低氮开采和微生物活化以及高微生物代谢效率（MME）而降低了酶活性。相反，在N150-N300中输入N后，RPE升高，这归因于微生物C：N的高度失衡导致MME降低，而不是促进了微生物N的开采或微生物激活机制。微生物C：N失衡是微生物与植物之间N竞争的结果。

结论

因此，酶活性和MME的组合介导了N调节的RPE，而N竞争推动了RPE机制的转换。