Soil element patterns and carbon turnover at the micro-scale (20-250 µm)

土壤有机质在不同尺度上呈非均匀分布，并以微团聚体的形式稳定分布，但微团聚体结构对土壤有机质储存和周转时间的影响一直未得到研究人员的重视。本项目旨在结合电子探针分析制图技术（EPMA）和三维激光烧蚀同位素比值监测（LA-ICP-MS和LA-IRMS），阐明4-20 μ m微聚集体中SOM、其同位素特征和邻近其他元素的时空格局。使用模式识别和地统计学工具进行的后续数据评估将使我们能够回答以下问题：(i)不同年龄和来源的微聚集体（微观实验、拓扑序列、时间序列）中SOM的空间格局在多大程度上遵循确定性模式；（ii）微聚集体中SOM的周转时间和生物可及性在多大程度上影响C和N的空间异质性；（iii）成土氧化铁和粘土矿物如何控制微团聚体热点中SOM的积累和周转。我们假设微团聚体年龄越老，随机过程对土壤有机质动力学的解释作用越弱，从而为这些微团聚体在养分生物地球化学循环和碳周转中的作用提供了线索。

Soil organic matter (SOM) is heterogeneously distributed at different scales and stabilized in microaggregates, but the role of microaggregates¿ architecture for SOM storage and turnover time has eluded researchers. This project aims at combining electron microprobe analyses mapping techniques (EPMA) and a three dimensional laser-ablation isotope ratio monitoring (LA-ICP-MS and LA-IRMS) to elucidate the spatio-temporal patterns of SOM, its isotopic signature and adjacent other elements in microaggregates down to a size of 4-20 ¿m. The subsequent data evaluation using pattern recognition and geostatistical tools will allow us to answer the following questions (i) to which extent does the spatial pattern of SOM within microaggregates of different age and provenience (microcosm experiment, toposequence, chronosequence) follow a deterministic pattern, ii) to which extent does turnover time and bioaccessibility of SOM within microaggregates affect spatial heterogeneity of C and N, and (iii) how do pedogenic iron oxides and clay minerals control the accumulation and turnover of SOM in microaggregates¿ hot spots. We hypothesize that the older the microaggregates are, the less relevant are stochastic processes to explain the dynamics of SOM, thus providing a clue to the role of these microstructures for the biogeochemical cycling of nutrients and C turnover.