FOR 1806: The Forgotten Part of Carbon Cycling: Organic Matter Storage and Turnover in Subsoils (SUBSOM)

FOR 1806：碳循环中被遗忘的部分：底土中的有机物储存和周转（SUBSOM）

• 批准号: 207213200
• 金额: --
• 依托单位: Max-Planck-Institut für Biogeochemie (MPI-BGC)
• 依托单位国家: 德国
• 项目类别: Research Units
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/207213200?language=en
• 关键词: 1806; Forgotten; Part; Carbon; Cycling

This project focusses on the storage and turnover of organic matter (OM) in subsoils. 40-60 percent of the globally total carbon pool is fixed in the deeper soil from 30 cm up to 2 m depth. The organic carbon analysed in deeper soil horizons showed a high 14C-age of several thousand years. This suggests that OM was accumulated in subsoils over a very long time and, therefore, appears to be very stable. Thus subsoil OM was not considered to be relevant for global C-cycle. Nevertheless, fresh C-inputs due to dissolved OM and bioturbation reach the subsoil and consequently lead to soil organic matter (SOM) decomposition. To enhance the understanding of the turnover mechanisms the Research Unit raised the following hypotheses: (1) Subsoil OM largely consists of recalcitrant compounds that are the least degradable end-products of numerous metabolic and biochemical processes and which, thus, accumulate during the degradation of fresh biomass inputs. (2) The annual inputs of fresh OM into the subsoil are so low that their sequestration in the subsoil does not significantly contribute to pool size changes or 14C activity over centuries. (3) Old SOM in subsoils is more strongly bound to pedogenic minerals and, thus, is more effectively stabilised against biodegradation. This is because C-limited subsoil environments provide a larger sorption site density than topsoils with less competition effects among organic matter components during sorptive interactions. (4) The high radiocarbon age of bulk subsoil OM is caused by a small fraction of fossil or geogenic C. The mean residence time of OM in subsoil is thus grossly overestimated. (5) Microbial densities in subsoils are low and activities are limited by environmental factors like low partial O2 pressures and low temperatures so that SOM is mineralised at extremely low rates. (6) Microbial communities and activities are limited to very few hot spots where fresh OM is supplied with SOM, roots, exudates or burrowing animals. Large parts of the bulk soil are so sparsely populated that even potentially degradable OM can persist. Within ten subprojects the hypotheses will be studied in the field and in laboratory experiments, which follow a common experimental design to refer the elevated data to each other. Overall, the Research Unit aims to develop a conceptual model to enhance the knowledge of OM storage and turnover processes in the subsoil considering soil physical, chemical and biological parameters.

该项目的重点是底土中有机物（OM）的储存和周转。全球总碳库的40- 60%固定在30厘米至2米深的深层土壤中。深层土壤中的有机碳分析表明，14 C年龄高达几千年。这表明OM在很长一段时间内积累在底土中，因此似乎非常稳定。因此，底土有机质被认为与全球碳循环无关。然而，新鲜的C-输入由于溶解OM和生物扰动到达底土，从而导致土壤有机质（SOM）的分解。为了加深对周转机制的理解，研究单位提出了以下假设：（1）底土有机质主要由柠檬酸盐化合物组成，这些化合物是许多代谢和生物化学过程的最难降解的最终产物，因此，在新鲜生物量输入的降解过程中积累。(2)新鲜有机质的年度输入到底土是如此之低，他们在底土中的封存并没有显着的贡献池大小的变化或14 C活动几个世纪以来。(3)底土中的旧SOM与成土矿物的结合更强，因此更有效地稳定了生物降解。这是因为碳有限的底土环境提供了一个更大的吸附位点密度比表土之间的有机质组分在吸附相互作用的竞争效应较小。(4)大量底土有机质的高放射性碳年龄是由一小部分化石碳或地源碳造成的。因此，OM在底土中的平均停留时间被严重高估。(5)底土中的微生物密度低，活动受到环境因素的限制，如低分氧压和低温，因此SOM以极低的速率矿化。(6)微生物群落和活动仅限于极少数热点，其中新鲜OM与SOM、根、渗出物或穴居动物一起供应。大部分的散装土壤人口稀少，甚至可能降解的有机质可以持续存在。在10个子项目中，将在实地和实验室实验中研究假设，这些实验遵循共同的实验设计，将升高的数据相互参考。总体而言，研究股的目标是开发一个概念模型，以提高有机质的存储和周转过程中的底土考虑土壤物理，化学和生物参数的知识。