Soil respiration (Rs), a critical component of the global carbon (C) cycle, is sensitive to changes in nitrogen (N) deposition. However, the temporal dynamics of the effects of long-term (≥ five years) N addition and its cessation on Rs in forests remain uncertain. We conducted a continuous field experiment, which included three years of N cessation after seven years of N addition at different rates (0, 30, 60, and 90 kg N∙ha−1∙yr−1), in a subtropical Moso bamboo forest to explore the response of Rs and its components, determine the influence of biotic and abiotic factors to long-term N addition, and identify any legacy effects. We found a two-phase pattern of Rs, with a significant increase in the first two years across three N addition rates and a constant significant increase in the last five years across low and medium N addition; however, Rs did not change under high N addition. The nitrogen addition legacy effects significantly increased Rs and autotrophic respiration but reduced heterotrophic respiration, which could persist for at least three years. The mechanism underlying the temporal variation in Rs and its components was related to the increase in fine root biomass and changes in soil microbial biomass and bacteria to fungi ratio. These findings have advanced our understanding of soil CO2 dynamics in subtropical forests under N deposition. Moreover, they reveal that the legacy effects of long-term N addition should be incorporated into global C cycle modeling to reflect the persistent effects of N deposition on forest ecosystem C budgets.

中文翻译：

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长期氮添加对亚热带毛竹林土壤呼吸具有正遗传效应


土壤呼吸 （Rs） 是全球碳 （C） 循环的关键组成部分，对氮 （N） 沉积的变化很敏感。然而，长期（≥ 5 年）氮添加及其停止对森林 Rs 影响的时间动态仍不确定。我们在亚热带毛竹林进行了一项连续的田间试验，包括以不同速率（0、30、60 和 90 kg N∙ha−1∙yr−1）添加 7 年后 3 年停止施氮，以探究 Rs 及其成分的响应，确定生物和非生物因子对长期氮添加的影响， 并识别任何遗留效果。我们发现了 Rs 的两阶段模式，前两年在三个 N 添加速率中显着增加，而在过去五年中低 N 添加量中持续显着增加;然而，在高 N 添加下 Rs 没有变化。氮添加遗留效应显着增加了 Rs 和自养呼吸，但减少了异养呼吸，异养呼吸可以持续至少三年。Rs 及其组分时间变化的机制与细根生物量的增加以及土壤微生物生物量和细菌与真菌比的变化有关。这些发现促进了我们对氮沉降下亚热带森林土壤 CO2 动态的理解。此外，他们揭示了长期氮添加的遗留效应应纳入全球碳循环建模，以反映氮沉积对森林生态系统碳预算的持续影响。