A long-term Warming Experiment to elucidate Soil Organic Matter dynamics in a subarctic forest Ecosystem (AWESOME)

气候变化导致土壤明显变暖，加速和增加了土壤有机质(SOM)的分解。这可能成为最强大的气候-碳循环反馈机制之一，因为这一过程可能会排放大量二氧化碳。然而，由于全球变暖，所有生态系统的土壤是否会成为二氧化碳的来源，仍然是高度不确定的。土壤有机质周转所涉及的各种生物地球化学过程对气候变暖的响应还没有得到足够详细的了解。这也是由于与土壤变暖相关的实验困难和障碍。尤其是长期和深层土壤变暖的观测资料很少，这妨碍了对气候变暖开始后新的稳定状态的可靠估计。此外，当只应用一种实验土壤变暖水平时，无法调查与变暖强度有关的临界点。在AWEW项目中，我们将利用加拿大育空地区的自然地热土壤变暖梯度，获得关于自养和异养生物与矿物土壤基质因气温上升而产生的复杂相互作用的基本见解。初步结果表明，在亚北极落叶林下地热变暖的土壤中，有机碳减少了22%，而土壤氮素存量保持不变。然而，随着变暖的加剧，与矿物相关的有机质组分中的氮被发现更稳定。已经确定了四种不同的升温强度，总温度范围约为8摄氏度，并于2019年夏季启动了标记凋落物的现场微观世界实验。该项目的最终目的是在百年尺度的亚北极变暖森林土壤中建立一个新的有机物质循环的概念框架，未来可能会在其他生态系统中进行测试。植被和碳输入、微生物生理学、群落组成和适应以及有机质质量的变化将是该项目的重点。气候变暖对土壤水文(水分)和矿物学(风化)的影响将作为整个变暖梯度的解释变量进行评估。在与几个合作伙伴的合作下，通过使用土壤科学和微生物学的最新方法以及理想的研究地点，这一令人敬畏的项目有望在一个与21世纪高度相关的主题上取得重大进展。这些结果将与另一项地热变暖实验(在冰岛)的结果进行比较，以阐明差异和共同点，并提出一个更一般的框架，说明长期变暖对土壤生物地球化学循环的影响。

Climate change is leading to a pronounced warming of soils, which is accelerating and increasing the decomposition of soil organic matter (SOM). This could become one of the strongest Climate-Carbon Cycle feedback mechanisms, since this process could emit large amounts of CO2. However, it is still highly uncertain, if soils in all ecosystems will become a CO2 source due to global warming. The warming response of the various biogeochemical processes involved in SOM turnover are not understood in sufficient detail. This is also due to experimental difficulties and barriers related to soil warming. Especially long-term and deep-soil warming observations are scarce, which hampers reliable estimates of new steady-state situations after the onset of warming. Also tipping points related to warming intensity cannot be investigated when only one level of experimental soil warming is applied. In the AWESOME project, we will make use of a natural, geothermal soil warming gradient in the Canadian Yukon Territory to gain essential insights on the complex interplay of autotrophic and heterotrophic organisms and the mineral soil matrix as affected by increasing temperature. First results showed that organic carbon was reduced by up to 22% in the geothermally warmed soils under subarctic deciduous forest, while the soil nitrogen stock remained constant. However, nitrogen was found to be more stabilized in the mineral associated organic matter fraction with increased warming. Four different warming intensities with a total temperature range of approximately 8°C are already established and an in-situ microcosm experiment with labeled litter was initiated in summer 2019. The ultimate aim of the project is to establish a new conceptual framework of organic matter cycling in century-scale warmed subarctic forest soils that could potentially tested in other ecosystems in the future. Changes in vegetation and carbon inputs, microbial physiology, community composition and adaptation as well as organic matter quality will be the focus of the project. Warming effects on soil hydrology (moisture) and mineralogy (weathering) will be evaluated as explanatory variables across the whole warming gradient. In cooperation with several partners, by using state of the art methods in soil science and microbiology, as well as an ideal research site, the AWESOME project is expected to bring about significant progress in a topic that will be highly relevant in the 21st century. The results will be compared to findings from another geothermal warming experiment (on Iceland) to elucidate differences and commonalities and come up with a more generic framework of long-term warming effects on biogeochemical cycling in soils.