Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
Department of Earth Science, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.
Sci Rep. 2021 Mar 18;11(1):6202. doi: 10.1038/s41598-021-85506-w.
The boreal forest is among the largest terrestrial biomes on earth, storing more carbon (C) than the atmosphere. Due to rapid climatic warming and enhanced human development, the boreal region may have begun transitioning from a net C sink to a net source. This raises serious concern that old biogenic soil C can be re-introduced into the modern C cycle in near future. Combining bio-decay experiments, mixing models and the Keeling plot method, we discovered a distinct old pre-bomb organic carbon fraction with high biodegradation rate. In total, 34 ± 12% of water-extractable organic carbon (WEOC) in podzols, one of the dominating boreal soil types, consisted of aged (~ 1000 year) labile C. The omission of this aged (i.e., ΔC depleted) WEOC fraction in earlier studies is due to the co-occurrence with ΔC enriched modern C formed following 1950s nuclear bomb testing masking its existence. High lability of aged soil WEOC and masking effects of modern ΔC enriched C suggests that the risk for mobilization and re-introduction of this ancient C pool into the modern C cycle has gone undetected. Our findings have important implications for earth systems models in terms of climate-carbon feedbacks and the future C balance of the boreal forest.
北方森林是地球上最大的陆地生态系统之一，储存的碳（C）比大气还多。由于气候迅速变暖以及人类活动的加剧，北方地区可能已经开始从净碳汇向净碳源转变。这引发了人们的严重担忧，即古老的生物成因土壤碳可能在不久的将来重新被引入到现代碳循环中。通过生物降解实验、混合模型和基林（Keeling）图法，我们发现了一个明显的具有高生物降解率的古老（~1000 年）前爆炸有机碳（pre-bomb organic carbon）的特征。总的来说，在北方土壤类型之一的灰化土中，有 34±12%的水可提取有机碳（WEOC）是由老化（即ΔC 耗尽）的易生物降解 C 组成。在早期研究中，由于与 20 世纪 50 年代核爆炸试验后形成的 ΔC 富集现代 C 同时存在，这种古老的（即 ΔC 耗尽）WEOC 组分被忽略了，这掩盖了它的存在。老化土壤 WEOC 的高生物可降解性和现代 ΔC 富集 C 的掩蔽效应表明，这种古老碳库向现代碳循环中迁移和重新引入的风险尚未被发现。我们的发现对地球系统模型在气候-碳反馈和北方森林未来碳平衡方面具有重要意义。
