Modeling the effect of silicon and calcium availability on the future sustainability of Arctic permafrost carbon pools based on laboratory and field experiments

自工业化开始以来，全球平均温度观测值有所增加，北方高纬度地区的增长率特别高。更温暖的条件有可能使目前储存在北方永久冻土中的大量有机碳库（估计为1330-1580千万亿立方米）退化，对全球气候可能产生严重后果。北极永久冻土生态系统内的碳循环以及碳库的可持续性不仅受温度条件的控制。以CO2或CH 4形式排放到大气中的碳的量在很大程度上取决于其他环境边界条件，如土壤的水分含量、温度或pH值。此外，有机物的质量（例如，营养物的含量、营养物化学计量和碳化合物）起着主导作用，其中磷（P）是非常重要的。在这方面，其他次要化学元素的潜在影响在很大程度上被忽视了。更具体地说，有两种元素对海洋系统的碳固定和周转非常重要，即硅（Si，对硅藻的碳固定很重要）和钙（Ca，对颗石藻的碳固定很重要）。然而，对于陆地和半水生系统，只有少数研究分析了硅和钙含量和碳周转率之间的联系，甚至更少的结果尚未公布的冻土，尽管潜在的重要性，目前和未来的碳循环过程。硅被证明是动员P从土壤结合位点，因此增加P的可用性，而钙是已知的，以减少P的可用性，形成不溶性的Ca-P相。该项目的目的是限制与硅和钙的可用性相关的竞争过程的净效应，以及它们对磷可用性的影响，对降解永冻土中有机物矿化的影响，并量化气候变化的潜在反馈。我们将在现场和实验室中进行操作实验，这将把增强的Si和/或Ca含量（模拟永久冻土解冻期间的动员）与土壤中分解/矿化速率的变化以及永久冻土生态系统中CO2/CH 4排放的相关变化联系起来。这些结果随后将被用来测试，如果考虑硅和钙的可用性可以提高性能的过程为基础的模型相比，泛北极碳通量观测。结合预测模拟的融化深度与数据的垂直分布的硅和钙池，我们将进一步估计如何硅和钙的可用性可能会受到影响，通过增加融化深度在未来的气候变化。综上所述，这些结果将允许评估硅和钙的可用性对碳通量的影响，在多年冻土土壤，和他们的贡献之间的反馈多年冻土碳循环过程和未来的气候变化。

Globally averaged temperature observations have increased since the onset of industrialization, and increase rates have been particularly high at the northern high latitudes. Warmer conditions threaten to degrade the vast pool of organic carbon currently stored in the in northern permafrost soils (estimated at 1330-1580 petagram), with potentially drastic consequences for global climate. The carbon cycle within Arctic permafrost ecosystems, as well as the sustainability of carbon pools, is not only controlled by temperature conditions. The amount of carbon emitted to the atmosphere in form of CO2 or CH4, depend strongly on other environmental boundary conditions such as moisture content, temperature, or pH of the soil. Also the quality of the organic matter (e.g. content of nutrients, nutrient stoichiometry and carbon compounds) plays a dominant role, with phosphorus (P) being of high importance. The potential influence of other, minor chemical elements have been largely neglected in this context. More specifically, two elements have been shown to be highly important for carbon fixation and turnover in marine systems, i.e. silicon (Si, important for C-fixation by diatoms) and calcium (Ca, important for C-fixation by coccolithophores). For terrestrial and semiaquatic systems, however, only few studies have analyzed links between Si and Ca content and carbon turnover rates, and even fewer results have yet been published for permafrost soils despite the potential importance for current and future carbon cycle processes. Silicon was shown to mobilize P from soil binding sites, therefore increasing P availability, whereas Ca is known to decrease P availability by forming insoluble Ca-P phases. The aim of this project is to constrain the net effect of competing processes linked to the availability of Si and Ca, and their effect on P availability, on the mineralization of organic matter in degrading permafrost soils, and quantify potential feedbacks with climate change. We will execute manipulation experiments both in-situ and in the laboratory, which will link enhanced Si and/or Ca contents (mimicking mobilization during permafrost thaw) to changes in decomposition/mineralization rates in the soil, and related shifts in CO2/CH4 emissions from permafrost ecosystems. These results will subsequently be used to test if the consideration of Si and Ca availability can improve the performance of a process-based model when compared against pan-Arctic carbon flux observations. Combining prognostic simulations of thaw depth with data on the vertical distribution of Si and Ca pools, we will furthermore estimate how Si and Ca availability may be affected through increases in thaw depth under future climate change. Taken together, these results will allow assessing the impact of Si and Ca availability on carbon fluxes in permafrost soils, and their contribution to the feedbacks between permafrost carbon cycle processes and future climate change.