Abiotic and biotic reactions operate side by side in the cycling of phosphorus (P) in the environment, but the relative roles of these two reactions vary both spatially and temporally. In biotic reactions, the uptake and release of P are catalyzed by enzymes and thus change phosphate oxygen isotope ratios, while in abiotic reactions, the absence of hydrolysis-condensation reactions results in no apparent changes in isotope composition, except short-term kinetic isotope effect due solely to preferential ion exchange. Therefore, isotope method could be a promising tool to differentiate relative roles of these two reactions in the environment but the relationship of concentration and isotope exchange at the biota-water interface is largely unknown. In this study, we aimed to develop a process-based isotope model underpinning the competition of abiotic (sorption, desorption, and ion exchange) and biotic (uptake, metabolism, and release) reactions during uptake and recycling of ferrihydrite-bound P by E. coli. Our model comprises equations describing the partitioning relationship among different P pools and their corresponding oxygen isotope compositions and is based exclusively on oxygen isotope exchange at multiple sites including mineral surface, aqueous phase, and bacterial cells. The process-based model adequately reproduced the measured concentration and isotope compositions over time. Furthermore, parametric and sensitivity analyses using the model indicated that the rate of biological uptake of P was the major factor controlling the changes of phosphate isotope composition. In conclusion, our model provides new insights into a mechanistic aspect of isotope exchange and could be potentially useful for future efforts to understand the interplay of biotic and abiotic factors on phosphorus cycling in natural environments.

中文翻译：

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影响矿物质-水-生物群界面中磷酸盐氧同位素比率的生物和非生物过程的建模

非生物和生物反应在环境中磷（P）的循环中并排运行，但是这两个反应的相对作用在空间和时间上都不同。在生物反应中，P的吸收和释放被酶催化，从而改变了磷酸盐中氧的同位素比，而在非生物反应中，不存在水解-缩合反应，除了短期的动态同位素作用外，同位素组成没有明显变化。仅由于优先离子交换。因此，同位素方法可能是区分这两种反应在环境中的相对作用的有前途的工具，但是在生物-水界面的浓度和同位素交换之间的关系却鲜为人知。在这项研究中，大肠杆菌。我们的模型包括描述不同P池及其对应的氧同位素组成之间分配关系的方程式，并且仅基于氧同位素在多个位置的交换，这些位置包括矿物质表面，水相和细菌细胞。基于过程的模型会随着时间的推移充分再现所测得的浓度和同位素组成。此外，使用该模型进行的参数和敏感性分析表明，磷的生物吸收速率是控制磷酸盐同位素组成变化的主要因素。总之，我们的模型为同位素交换的机理提供了新的见解，并且对于未来了解自然环境中磷循环中生物因子和非生物因子之间相互作用的研究可能具有潜在的帮助。