Mass budgets and stable isotope ratios of Ca and Mg in ecosystems along a 120 yr-old glacial retreat chronosequence in the subtropical Gongga mountains

植被演替对冰川退缩产生的裸露土壤的稳定对于减少山区的滑坡、侵蚀和水风险至关重要。植被生长速度的主要驱动因素是风化作用从基质中释放钙和镁等营养物质并将其转移到植物中。我们建议确定在中国亚热带冰川退缩的时间序列中，在不到100年的时间里，植被快速演替为森林，钙和镁从底物释放并融入生物循环的速率。为了量化这些速率，我们将通过测定所有主要生态系统区室（矿质土壤、有机层、植被）中Ca和Mg总储量的变化，以及使用空间-时间替代方法沿着大约120年的时间序列从裸露土壤到短距离的完整森林的总体沉积速率，来建立质量平衡。为了阐明观测到的储量变化背后的过程，我们将开发一种利用46Ca和43Ca的双峰来确定44/42Ca同位素比率的新方法，并在我们的实验室建立一种确定26/24Mg比率的新方法，并测量岩石、土壤、植物和生态系统溶液中Ca和Mg的稳定同位素比率。由于风化、植物吸收、吸附或淋滤等过程都反映在稳定同位素比率的变化中，我们期望通过同时建立质量预算和测定Ca和Mg的稳定同位素比率来提高对过程的理解。

The stabilization of bare soil originating from glacial retreat by vegetation succession is crucial for reducing landslide, erosion, and water risks in mountainous areas. A major driver of the speed of vegetation establishment is the release of nutrients like Ca and Mg from the substrate by weathering and their transfer to the plants. We propose to determine the rates with which release from substrate and incorporation into biological cycling of Ca and Mg occur at a subtropical glacial retreat chronosequence with fast vegetation succession to a forest in less than 100 yr in China. To quantify these rates, we will establish mass balances by determining the change of the total stocks of Ca and Mg in all major ecosystem compartments (mineral soil, organic layer, vegetation) and bulk deposition rates along a ca. 120-yr chronosequence reaching from bare soil to full forest at a short distance using a space-for-time-substitution approach. To elucidate the processes behind the observed stock changes, we will develop a new method to determine 44/42Ca isotope ratios using a double spike of 46Ca and 43Ca and establish a published method to determine 26/24Mg ratios in our laboratory and measure stable isotope ratios of Ca and Mg in rocks, soils, plants, and ecosystem solutions. Because processes like weathering, plant uptake, adsorption, or leaching are reflected by changes of the stable isotope ratios, we expect an improved process understanding by the simultaneous establishment of mass budgets and determination of stable isotope ratios of Ca and Mg.