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，在北部高纬度地区，增幅尤其大。气候变暖有可能使目前储存在北部永久冻土土壤中的大量有机碳池（估计在1330-1580千兆位）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CH4形式排放到大气中的碳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，有机质的质量（如养分含量、营养化学计量和碳化合物）也起主导作用，其中磷(P)非常重要。在这种情况下，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，有两种元素已被证明对海洋系统中的碳固定和循环非常重要，即硅（Si，对硅藻固定碳很重要）和钙（Ca，对球石藻固定碳很重要）。然而，对于陆地和半水生系统，只有很少的研究分析了Si和Ca含量与碳周转率之间的联系，尽管永久冻土对当前和未来的碳循环过程具有潜在的重要性，但发表的结果甚至更少。硅被证明可以从土壤结合位点调动磷，从而增加磷的有效性，而钙则通过形成不溶性钙-磷相来降低磷的有效性。该项目的目的是限制与硅和钙的有效性相关的竞争过程的净效应，以及它们对磷有效性的影响，对退化的永久冻土中有机质的矿化的影响，并量化与气候变化有关的潜在反馈。我们将在现场和实验室进行操作实验，将Si和/或Ca含量的增加（模拟永久冻土融化期间的动员）与土壤中分解/矿化率的变化以及永久冻土生态系统中CO2/CH4排放的相关变化联系起来。这些结果随后将用于测试与泛北极碳通量观测相比，考虑Si和Ca可用性是否可以改善基于过程的模式的性能。结合融深的预测模拟和Si和Ca库的垂直分布数据，我们将进一步估计在未来气候变化下，Si和Ca可用性如何通过融深的增加而受到影响。综上所述，这些结果将有助于评估Si和Ca有效性对永久冻土中碳通量的影响，以及它们对永久冻土碳循环过程与未来气候变化之间反馈的贡献。

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.