Biogeochemical mechanisms of C and P cycles in paddy driven by the FeIII-FeII redox wheel in dynamic redox environment

水稻田周期性地被淹和排水，这导致土壤中氧化还原条件的强烈波动。在还原条件下，土壤中的三价铁矿物通过铁还原作用被微生物溶解，而铁氧化剂则在输氧水稻根系周围形成三价铁菌斑。这些铁相与P和C化合物具有独特的相互作用，这些化合物控制这两种元素的循环。因此，该项目的目标是进一步了解氧化还原敏感性铁矿物与P和C之间形成缔合的过程和机制。该建议基于三个主要假设：（1）土壤溶液中溶解的P浓度控制微生物溶解释放的亚铁是否被构建到根周围的三价铁斑块或亚铁磷酸盐矿物蓝铁矿中。每个铁相形成铁还原和氧化细菌的热点。(2)微生物溶解三价铁/磷复合物导致蓝铁矿的形成，因此大部分释放的磷是植物无法获得的。由于铁/磷络合物或蓝铁矿的形成，磷的有效性低，刺激了溶磷微生物和磷矿化微生物的活性。(3)钙钛矿沉积的有机碳直接与三价铁斑块和蓝铁矿矿物共生。根源有机碳和斑块处陡峭的氧梯度为活跃的铁和甲烷循环相关微生物提供了栖息地。该假说将由中德联合体进行验证，结合Fe，P和C同位素标记技术的经验，从土壤矿物学，生物学和微生物的角度阐明土壤地球化学相互作用。具体过程将分别用同位素标记的Fe、P和C研究假设（1）、（2）和（3）。在德国进行温室盆栽试验以检验（1）和（2），在中国进行温室盆栽试验和田间试验以检验（3）。为了评估矿物相的形成和转化机制，包括相关的P和C，将应用MC-ICP-MS，XPS，NanoSIMS，33 P放射性成像，穆斯堡尔谱，XRD和ICP-OES。微生物过程和关键类群将通过16 S rRNA、16 S rRNA基因和功能性P-循环相关基因扩增子高通量测序、MPN富集和分离、类群特异性定量PCR、基因表达分析以及基于原位RNA和PLFA的稳定同位素探测来确定。这个中德研究团队设想更好地了解氧化还原过程，相关的三价铁和二价铁相，以及微生物对水稻土中C积累和P有效性的影响。

Paddy rice fields are periodically flooded and drained, which leads to strongly fluctuating redox conditions in the soils. Under reducing conditions, ferric iron minerals in the bulk soil are subjected to microbial dissolution by iron reduction, while ferric iron plaques are formed by iron oxidizers around oxygen-transporting rice roots. These iron phases have distinctive interactions with P and C compounds, which control the cycling of both of these elements. Thus, the objective of the proposed project is to gain further knowledge on the processes and mechanisms that govern the formation of associations between redox-sensitive iron minerals and P as well as C. The proposal is based on three major hypothesises: (1) The dissolved P concentration in the soil solution controls whether ferrous iron that is released from microbial dissolution is built into ferric iron plaques around roots or into the ferrous phosphate mineral vivianite. Each of the iron phases forms hot spots for iron reducing and oxidizing bacteria. (2) The microbial dissolution of ferric iron/P complexes leads to formation of vivianite, so that most of the released P is not plant accessible. Low P-availability due to ferric/P complexes or vivianite formation stimulate the activity of P-solubilizing and P-mineralizing microorganisms. (3) Rhizodeposited organic C is directly associated with ferric iron plaques and vivianite minerals. Both the root-derived organic C and the steep oxygen gradient at plaques provide the habitat for active iron and methane cycling associated microbes. The hypotheses will be tested by a Sino-German consortium, integrating experiences in isotope labelling techniques of Fe, P, and C to elucidate biogeochemical interactions from soil mineralogical, biological, and microbiological perspectives. The specific processes will be studied with isotope labeled Fe, P, and C for hypothesises (1), (2), and (3), respectively. Greenhouse pot experiments to test (1) and (2) will be conducted in Germany, and greenhouse pot experiments as well as field experiments adressing (3) will be conducted China. To assess the mechanisms concerning the formation and transformation of mineral phases, including the associated P and C, MC-ICP-MS, XPS, NanoSIMS, 33P radioimaging, Mössbauer spectroscopy, XRD, and ICP-OES will be applied. Microbial processes and key taxa will be determined with 16S rRNA, 16S rRNA gene and functional P-cycle associated gene amplicon high throughput sequencing, MPN enrichments and isolation, taxon-specific quantitative PCR, gene expression analyses, as well as in situ-like RNA- and PLFA-based stable isotope probing. This Sino-German research team envisions a better understanding on the impact of redox processes, associated ferric and ferrous iron phases, as well as microbial key players on C accumulation and P availability in paddy soils.