Isotope geochemical determination of phosphorus weathering sources and fluxes in forest ecosystems

森林生态系统中磷风化源和通量的同位素地球化学测定

• 批准号: 240870574
• 负责人: Professor Dr. Friedhelm von Blanckenburg
• 金额: --
• 依托单位: Forstliche Versuchs- und Forschungsanstalt Baden-Württemberg (FVA)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/240870574?language=en
• 关键词: Isotope; geochemical; determination; phosphorus; weathering

The primary source of phosphorus, an essential nutrient to all terrestrial ecosystems, is its release by weathering of rock. As rock weathering is an inherently slow process, the rate at which phosphorus is supplied to ecosystems is ultimately limited by the rock weathering rate, and by the ability of soils to retain the released phosphorus. Forest ecosystems respond to slow supply by increasing their phosphorus recycling rate. Hence a full quantification of the phosphorus cycle through ecosystems requires knowing these initial release rates. Yet such rates are still not generally available. This project will make use of several innovative isotope geochemical tools to determine these fluxes at four upland “Level 2” sites of the DFG Priority Programme “Ecosystem Nutrition”. 1) In two sites of granitoid/gneissic bedrock, the rare in situ-produced cosmogenic isotope 10Be will be used in combination with element mass balances to determine phosphorus fluxes and quantify phosphorus depletion in soil. 2) In two sites underlain by volcanic substrates that do not contain the quartz required for measuring in situ-produced 10Be we will use the a new system to obtain the same parameters: the 10Be(meteoric)/9Be isotope ratio in combination with weathering mass balances. 3) We will measure the radiogenic 87Sr/86Sr isotope ratio in primary phosphorus-containing minerals such as apatite, in soil water, in the exchangeable soil phase, and in tree stem wood and leaves to determine phosphorus sources. To evaluate the retention behavior of phosphorus in soils we will compare these primary fluxes with the phosphorus discharge by streams and groundwater and the preferential flow paths this discharge takes as determined in other SPP projects. Ultimately, we will close the phosphorus flux loop determine the ecosystems‘ phosphorous recycling efficiency by comparing litterfall fluxes with phosphorus weathering fluxes, and the sensitivity of fluxes ad recycling to change by comparing the dissolved phosphorus discharge with the primary input flux through weathering.

磷的主要来源是岩石风化释放的磷，磷是所有陆地生态系统的基本营养物质。由于岩石风化是一个固有的缓慢过程，向生态系统供应磷的速度最终受到岩石风化速度和土壤保留释放的磷的能力的限制。森林生态系统通过提高磷的循环利用率来应对供应缓慢的问题。因此，要全面量化生态系统中的磷循环，就需要知道这些初始释放率。然而，这样的费率仍然不是普遍可用的。该项目将利用几种创新的同位素地球化学工具，在DFG优先方案“生态系统营养”的四个高地“2级”地点确定这些通量。1)在两处花岗岩/片麻质基岩中，稀有的原位生成的宇宙成因同位素10Be将与元素质量平衡相结合，以确定土壤中的磷通量和定量土壤中的磷消耗。2)在火山基岩下的两个地点，我们将使用一种新的系统来获得相同的参数：10Be(大气)/9Be同位素比值，结合风化物质平衡，这两个地点不含现场生产的10Be所需的石英。3)测定磷灰石等原生含磷矿物、土壤水、可交换土相、树干木材和树叶中的放射性~(87)Sr/~(86)Sr同位素比值，以确定磷的来源。为了评估磷在土壤中的滞留行为，我们将把这些主要通量与河流和地下水的磷排放以及其他SPP项目确定的这种排放所采取的优先流动路径进行比较。最终，我们将通过比较凋落物通量和磷风化通量来确定生态系统的磷循环效率，并通过比较风化过程中溶解的磷排放和初级输入通量来确定通量和再循环对变化的敏感度。