Long‐term geothermal warming reduced stocks of carbon but not nitrogen in a subarctic forest soil
Long‐term geothermal warming reduced stocks of carbon but not nitrogen in a subarctic forest soil
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DOI：
10.1111/gcb.15754
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发表时间：
2021-06
影响因子：
11.6
通讯作者：
Tino Peplau;J. Schroeder;E. Gregorich;C. Poeplau
中科院分区：
文献类型：
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作者：
Tino Peplau;J. Schroeder;E. Gregorich;C. Poeplau
全球变暖加速了土壤有机质（SOM）的分解。在预测响应变暖的净SOM动态时，由于实验限制，存在相当大的不确定性。长期的原位全剖面土壤变暖研究尤其罕见。本研究利用加拿大育空地区长期的自然地温梯度，研究了森林生态系统对SOM的变暖效应。沿此热序列取样的土壤显示升温高达7.7℃；取样深度80 cm，分析土壤有机碳（SOC）和氮(N)含量，并估算土壤有机碳储量和组分。利用埋置茶袋和温度记录仪观察了1年期间潜在凋落物分解率与土壤温度和深度的关系。表层土壤（0 ~ 20 cm）和底土（20 ~ 80 cm）的有机碳对气候变暖的响应相似。土壤温度与全剖面有机碳储量呈负相关，最暖样地与对照样地总损失27%，相对损失3%℃−1。有机碳损失仅限于颗粒有机物质（POM）和溶解有机碳（DOC）组分，其净全剖面消耗。POM - C的损失占总SOC损失的最大份额。与有机碳相比，N并未因变暖而从土壤中流失，而是在土壤中重新分配，在粉土和粘土中积累较多（+40%）。这表明在与矿物相关的有机物中积累的微生物对氮的固定作用。这些结果证实，土壤变暖加速了整个剖面的有机碳周转，表层土壤和底土中碳都有损失。由于氮储量随气候变暖保持不变，SOM的化学计量发生了显著变化，这可能通过微生物代谢的变化影响碳循环。
Global warming is accelerating the decomposition of soil organic matter (SOM). When predicting the net SOM dynamics in response to warming, there are considerable uncertainties owing to experimental limitations. Long‐term in situ whole‐profile soil warming studies are particularly rare. This study used a long‐term, naturally occurring geothermal gradient in Yukon, Canada, to investigate the warming effects on SOM in a forest ecosystem. Soils were sampled along this thermosequence which exhibited warming of up to 7.7℃; samples were collected to a depth of 80 cm and analysed for soil organic carbon (SOC) and nitrogen (N) content, and estimates made of SOC stock and fractions. Potential litter decomposition rates as a function of soil temperature and depth were observed for a 1‐year period using buried teabags and temperature loggers. The SOC in the topsoil (0–20 cm) and subsoil (20–80 cm) responded similar to warming. A negative relationship was found between soil temperature and whole‐profile SOC stocks, with a total loss of 27% between the warmest and reference plots, and a relative loss of 3%℃−1. SOC losses were restricted to the particulate organic matter (POM) and dissolved organic carbon (DOC) fractions with net whole‐profile depletions. Losses in POM‐C accounted for the largest share of the total SOC losses. In contrast to SOC, N was not lost from the soil as a result of warming, but was redistributed with a relatively large accumulation in the silt and clay fraction (+40%). This suggests an immobilization of N by microbes building up in mineral‐associated organic matter. These results confirm that soil warming accelerates SOC turnover throughout the profile and C is lost in both the topsoil and subsoil. Since N stocks remained constant with warming, SOM stoichiometry changed considerably and this in turn could affect C cycling through changes in microbial metabolism.