Vulnerability of carbon in Cryosols – substrate-microorganisms-aggregate interactions

永久冻土融化可能是最重要的自然过程，作为对全球变暖的响应，它可能将碳(C)从陆地生态系统转移到大气中，从而启动对气候变化的正反馈。虽然已经对未来几十年的碳损失作出了若干估计，但冻土融化后土壤发育的主要过程尚未得到计算。根据冰的丰富度和土壤的排水情况，永久冻土退化可能导致更湿或更干的情况。在这些情景下，不同环境条件的演变将严重影响生物化学过程，改变微生物群落组成，导致不同的有机物（OM）分解和潜在的OM稳定过程。基于干湿两种情景下冻土融化的概念框架，CRYOVULCAN的主要目标是对比研究干湿两种情景下冻土的分解和稳定化。我们的主要假设是，化学和生物衰减过程将部分补偿永久冻土融化造成的有机碳（OC）损失。在(1)干燥、含氧“生锈”的情况下，我们假设化学和生物稳定过程更加明显，导致聚集和矿物-有机结合，并部分补偿OC损失。在(2)潮湿、缺氧“苍白”的情况下，由于厌氧菌的漆酶和过氧化物酶效率较低，低氧可能导致微生物分解木质素的能力降低。我们已经组建了一个捷克-德国跨学科联盟，在土壤科学，土壤微生物学和宏基因组学方面具有互补的专业知识，这将面临现场和实验室实验的独特结合的挑战。在野外，我们的研究是基于在两种不同情景下对完整的永久冻土和正在退化的土壤的比较。采用先进的分子、生物标志物和光谱技术，研究微生物群落组成、细胞外酶和亚转录组对不同土壤环境条件的响应以及土壤中OM物种的稳定性。原位13C标记实验将进一步了解微生物利用和新鲜底物的命运，取决于环境条件。最后，具体的培养实验将确定冻融循环对OM加工的影响，以及在干燥情况下增加根渗出物在矿物-有机复合物形成中的作用，以及在潮湿情况下木质素分解潜力。因此，CRYOVULCAN将有助于了解土壤水文制度对退化的永久冻土中有机质稳定的影响的迫切需要，这将控制在一个更温暖的世界中向大气释放的温室气体的量。

Permafrost thawing is likely the most important natural process that may translocate carbon (C) from terrestrial ecosystems to the atmosphere as response to global warming, thus initiating a positive feedback to climate change. While several estimates on C losses have been made for the next decades, major processes in soil development after permafrost thawing have not been accounted yet. Depending on ice richness and soil drainage, permafrost degradation can result in wetter or drier conditions. Contrasting environmental conditions evolving under these scenarios will critically influence biotic-chemical processes shifting the microbial community composition, leading to different organic matter (OM) decomposition and potential OM stabilization processes. Based on a conceptual framework on permafrost thaw under dry and wet scenario, the main objective of CRYOVULCAN is to comparatively investigate OM decomposition and stabilization under these two scenarios. Our main hypothesis is that chemical and biological attenuation processes will partly compensate for the organic carbon (OC) losses caused by permafrost thaw. Under (1) a dry, oxic "rusty" scenario we hypothesize chemical and biological stabilization processes to be more pronounced, leading to aggregation and mineral-organic associations and partly compensate for the OC losses. Under (2) a wet, anoxic "pale" scenario low oxygen likely leads to a reduction of the microbial ability to decompose particularly lignin due to less efficient laccases and peroxidases of anaerobes. We have assembled a Czech-German interdisciplinary consortium with complementary expertise in soil science, soil microbiology and metagenomics, which will face the challenge by a unique combination of field and laboratory experiments. In the field, our studies are based on a comparison of intact permafrost soils with soils undergoing degradation under the two contrasting scenarios. Employing state-of-the art molecular, biomarker and spectroscopic techniques, the response of the microbial community composition, extracellular enzymes, metatranscriptomes on the different soil environmental conditions and the respective stabilization of OM species in the soils will be investigated. An in-situ 13C labeling experiment will further inform about the microbial utilization and fate of fresh substrate, depending on the environmental condition. Finally, specific incubation experiments will identify the impact of freeze-thaw cycles in OM processing, as well as the role of increasing root exudation in the formation of mineral-organic complexes in the dry scenario and the lignin decomposition potential in the wet scenario. CRYOVULCAN will thus contribute to the urgently needed knowledge on the effect of the soil hydrological regime on OM stabilization in degraded permafrost soils, which will control the magnitude of greenhouse gases release to the atmosphere in a warmer world.