Natural 13C abundance as a tracer for studies of soil organic matter dynamics

A method for measuring the long- and medium-term turnover of soil organic matter is described. Its principle is based on the variations of 13C natural isotope abundance induced by the repeated cultivations of a plant with a high 13C/12C ratio (C4 photosynthetic pathway) on a soil which has never carried any such plant. The 13C/12C ratio in soil organic matter being about equal to the 13C/12C ratio of plant materials from which it is derived, changing the 13C content of the organic inputs to the soil (by altering vegetation from C3 type into C4 type) is equivalent to a true labelling in situ of the organic matter. Two cases of continuous corn cultivation (Zea mays: δ13C = −12%.) on soils whose initial organic matter average δ13C is −26%. were studied. The quantity of organic carbon originating from corn (that is the quantity which had turned-over since the beginning of continuous cultivation) was estimated using the 13C natural abundance data. After 13 yr, 22% of total organic carbon had turned-over, in the system studied. Particle size fractions coarser than 50μm on the one hand, and finer than 2μm on the other. contained the youngest organic matters. The turnover rate of silt-sized fractions was slower

硫酸参与喀斯特流域（北盘江）风化过程的碳同位素证据

在碳酸盐岩地区，流域侵蚀过程中硫酸是否参与，对于我们正确理解流域化学风化速率，以及流域侵蚀对大气CO2的消耗和全球碳循环等都有重要的意义。本工作在前期工作（乌江）的基础上，对贵州喀斯特地区的河流(北盘江)和支流的水化学特征以及水体溶解无机碳同位素组成进行了初步研究，研究结果证实硫酸参与了该喀斯特流域岩石/土壤化学风化过程。