Abstract：
Subsoil stores the majority of soil organic carbon (SOC), and plays a vital role in the global carbon cycle in terrestrial ecosystems and in regulating climate change. Response of SOC decomposition to temperature warming (TR) is a crucial parameter to predict SOC dynamics under global warming. However, it remains unknown how TR varies across the whole soil profile and responds to exogenous C and N inputs. To assess this, we designed a novel incubation system to measure SOC-derived CO2 efflux across the whole soil column (i.e., 60 cm length), allowing manual addition of 13C-labeled glucose and ammonium nitrate, and incubated it under ambient or warmed temperatures (+4 °C). We found that C addition significantly increased TR in 0-20 cm, 20-40 cm and 40-60 cm by 64.3 %, 68.1 % and 57.2 %, respectively. However, the combined addition of C and N decreased TR by 11.1 % - 15.3 % compared to without anything addition (CK) in the whole soil profile. The effect of N on TR ranged from -22.8 % to -40.4 % in the whole soil profile, and was significantly lower in topsoil than in subsoil. Furthermore, sole N addition significantly promoted TR compared to CK by 79.0 % and 94.7 % in 20-40 cm and 40-60 cm subsoil, only 9.8 % in 0-20 cm topsoil. These results together suggested that TR is sensitive to increasing C availability in the whole soil profile and increasing N availability in 20-60 cm subsoil. Random forest model indicated that soil enzyme activities (explained 21.3 % of the variance) and DOC (explained 11.1 % of the variance) dominantly governed TR in topsoil, but N availability displayed a predominant control of TR in subsoil. Overall, our results suggested that increased C and N availability under climate warming scenarios could further increase the risk of carbon loss especially in subsoil with substrate deficiency, but labile C (e.g., root exudation) input under climate warming and N enrichment could reduce SOC decomposition and benefit for C sequestration by decreasing TR.
摘要：
底土储存了大部分土壤有机碳(SOC)，并在陆地生态系统的全球碳循环和调节气候变化中起着至关重要的作用。SOC分解对温度变暖（TR）的响应是预测全球变暖下SOC动态的关键参数。然而,目前尚不清楚TR在整个土壤剖面中如何变化，以及如何响应外源C和N输入。为了评估这一点，我们设计了一种新颖的孵育系统来测量整个土壤柱的SOC衍生CO2外排(即，长度60厘米），允许手动添加13C标记的葡萄糖和硝酸铵，并将其在环境温度或温热温度(+4°C)下孵育。我们发现，在0-20厘米内添加C显著增加TR，20-40厘米和40-60厘米增长64.3%，68.1%和57.2%，分别。然而,在整个土壤剖面中，与不添加任何元素（CK）相比，C和N的组合添加使TR降低了11.1％-15.3％。在整个土壤剖面中，N对TR的影响范围为-22.8％至-40.4％，表土中显着低于底土。此外，在20-40厘米和40-60厘米的底土中，单一N的添加显着提高了TR比CK的79.0％和94.7％，在0-20厘米的表土中只有9.8％。这些结果共同表明，TR对整个土壤剖面中C的有效性增加和20-60cm底土中N的有效性增加敏感。随机森林模型表明，表层土壤中的土壤酶活性（解释了21.3％的方差）和DOC（解释了11.1％的方差）主要控制TR，但是氮的有效性显示了对底土TR的主要控制。总的来说,我们的结果表明，在气候变暖的情景下，增加碳和氮的可利用性可以进一步增加碳损失的风险，特别是在底土缺乏，但不稳定的C(例如，气候变暖和氮富集下的根系渗出）输入可以通过降低TR来减少SOC分解并有利于碳固存。
