Sequestration of microbial, aged and pyrogenic N during paddy soil development

虽然水稻土的氮素利用效率较低，但该研究单元一期的研究结果表明，水稻土可能在微生物残留物和老化氨基酸中封存了大量的氮素。此外，我们还观察到烧焦有机质的积累，其对总氮含量的贡献尚不清楚。我们认为主要是细菌将氮隔离在细胞壁上。虽然这一过程在表层土壤中是有效的，但在底土中似乎缺乏有效的氮储存机制。这些过程在多大程度上也适用于不同母质和不同气候条件下形成的水稻土，目前尚不清楚。因此，子项目将继续使用氨基糖和氨基酸对映体结合化合物特异性同位素测量来阐明在水稻土形成和保存过程中这些可水解的SON形式的微生物转化和自然老化。另外，我们会尽量识别黑色的N表格。我们特别致力于确定(i)不同水稻土剖面中SON的特征分解模式，（ii）不同氨基酸库、不可水解氮和微生物残氮积累，以及（iii）不同土壤类型中可水解氮的转化率。利用生物标志物对氮循环进行评估（iv）在短期内利用15N尿素施肥后土壤氨基糖的15N含量，(v)在中长期内通过Δ14C追踪不同矿物学水稻土微生物残留物和氨基酸中的炸弹C。

Although paddy soils exhibit low N use efficiency, the results from the 1st phase of this Research Unit suggested that they may sequester significant amounts of N in microbial residues and aged amino acids. In addition, we observed an accumulation of charred organic matter with yet unknown contribution to total N content. We suggest that mainly bacteria sequester N in their cell walls. While this process is efficient in the surface soils, in subsoils an effective mechanism for N storage seems to be missing. To which degree such processes also hold true for paddy soils formed from different parent materials and under different climatic regimes is unclear. Subproject will thus continue to use amino sugars and amino acid enantiomers in combination with compound-specific isotopic measurements to elucidate the microbial transformation and natural ageing of these hydrolysable SON forms during paddy soil formation and preservation. Besides, we will try to identify black N forms. In particular we aim at identifying (i) characteristic SON decomposition patterns within the different paddy soil profiles, (ii) pools of different amino acid, non-hydrolyzable N and microbial residue N accumulation, and (iii) the transformation rates of hydrolysable N in dependency of soil type. The N-cycling using biomarkers is assessed (iv) in the short-term using the 15N content of soil amino sugars after fertilizing with 15N urea, and (v) in the medium – to long-term by Δ14C tracing of bomb C in microbial residues and amino acids in the paddy soils of different mineralogy.