14C AMS as a tracer to study carbon dynamics resulting from paddy management under different climatic conditions in different soil types

995研究单元的第一阶段“水稻土演化的生物地球化学”显示，水稻表层土壤中来源于母质(浙江慈溪附近的河口沉积物，中国)的碳被来自最近大气的有机碳非常快速地替换；非水稻表层土壤中的碳替换速度较慢。在底土中有机碳(OC)浓度恒定或降低的情况下，增加底土中的14C浓度，证明了在稻田和非稻田中，原有的河口有机碳被从上方运输所取代，尽管在稻田下的速度较慢。我们假设，在水稻土中发现的OC和14C的测量浓度分布代表了从上面输入年轻碳、其矿物稳定以及矿化和淋溶之间的动态平衡的快照。这些碳通量又取决于新鲜光合作用的输入、降雨/灌溉、温度、耕盘的渗透性(如果有的话)、土壤微生物、土壤矿物质组成和稻田管理。在第二阶段，我们将重点关注不同的母质和相关的气候区域，从而产生不同的主要土壤类型(阿克苏/费拉尔索、西兰迪克安多索、阿卢安多索和变性土)，将土壤类型和气候的影响与管理的影响分开。考虑到慈溪的有机碳快速更替，这是印尼西莫村地区的一个很短的时间序列，在西莫村地区，水稻种植的开始是由1908年、1965年和2006年的灌溉渠修建确定的，这一点特别重要。

Phase 1 of Research Unit 995, “Biogeochemistry of paddy soil evolution”, showed a very fast replacement of carbon, originating from the parent material (estuarine sediments near Cixi, Zhejiang Province, China), with organic carbon derived from the recent atmosphere in paddy top soils; carbon replacement in non-paddy top soils was slower. Increasing 14C concentrations in the subsoil at constant or decreasing organic carbon (OC) documented the replacement of original estuarine OC by transport from above in both paddies and non-paddies, though at a slower pace under paddies. We hypothesize that measured concentration profiles in OC and 14C, found in paddy soils, represent snapshots of the dynamic balance between import of young carbon from above, its mineral stabilisation, and mineralisation and leaching. These carbon fluxes, in turn, depend on the input of fresh photosynthate, rainfall/irrigation, temperature, permeability of the plough pan (if any), soil microbes, soil mineral composition, and paddy management. In the second phase we will focus on different parent materials and correlated climatic regions, resulting in different main soil types (Acrisols/Ferralsols, Silandic Andosols, Aluandic Andosols, and Vertisols), to separate the influence of soil type and climate from that of management. Considering the rapid OC replacement at Cixi, a short Indonesian chronosequence from the Simo village area, where the onset of paddy cultivation is defined by the construction of irrigation canals in the years 1908, 1965 and 2006, is of special importance.