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In or Out of Equilibrium? How Microbial Activity Controls the Oxygen Isotopic Composition of Phosphate in Forest Organic Horizons With Low and High Phosphorus Availability
Frontiers in Environmental Science ( IF 4.6 ) Pub Date : 2020-09-29 , DOI: 10.3389/fenvs.2020.564778
Chiara Pistocchi , Éva Mészáros , Emmanuel Frossard , E. K. Bünemann , Federica Tamburini

While there are estimates of the abiotic processes contribution to soil phosphorus (P) availability, less is known about the contribution of biological processes. Two main enzymatic processes involved in soil P cycling are known to alter the oxygen isotopic composition of phosphate (δ18O-P), each in a different way, through the cleavage of the P–O bond: the intracellular P turnover and the organic P hydrolysis. The former induces isotopic equilibration between phosphate and water and is considered the major process affecting soil available P via microbial P release. The latter induces depleted δ18O-P in the phosphate released from the mineralization of organic P. We studied P dynamics in organic horizons of two contrasting soils (low- and high-P availability) from temperate beech forests. We labeled the soil with 18O-enriched water and followed changes in the δ18O-P of different soil P pools in the presence or absence of added leaf litter during 3 months of incubation. δ18O-P values of almost all P pools progressively increased indicating oxygen incorporation from the enriched soil water into phosphate via the above-mentioned enzymatic processes. δ18O-P of available P increased more in the P-rich soil than in the P-poor soil and approached the isotopic equilibrium between phosphate and water, revealing the impact of microbial P release into the available P pool. However, in the P-poor soil, the available P brought the isotopic signature induced by phosphatase enzymes, indicating that it was mostly originated from the hydrolysis of organic P. Therefore, under P-limiting conditions, the isotopic effect of organic P hydrolysis can outweigh the isotopic equilibrium effect. Finally, two independent isotopic approaches with 33P and δ18O-P provided very similar estimates of P exchanged between the available P and other inorganic soil pools. This suggests that δ18O-P can be successfully used to trace P fluxes, provided that the underlying processes do not break the P–O bonds of the phosphate molecule.

中文翻译:

处于平衡状态还是处于平衡状态?微生物活动如何控制磷含量低和高的森林有机层中磷酸盐的氧同位素组成

虽然估计了非生物过程对土壤磷 (P) 有效性的贡献,但对生物过程的贡献知之甚少。已知参与土壤 P 循环的两个主要酶促过程通过 P-O 键的断裂以不同的方式改变磷酸盐 (δ18O-P) 的氧同位素组成:细胞内 P 周转和有机 P 水解. 前者诱导磷酸盐和水之间的同位素平衡,被认为是通过微生物磷释放影响土壤有效磷的主要过程。后者导致有机磷矿化释放的磷酸盐中 δ18O-P 耗尽。我们研究了来自温带山毛榉森林的两种对比土壤(低磷和高磷可用性)有机层中的磷动态。我们用富含 18O 的水标记土壤,并在 3 个月的孵化过程中跟踪不同土壤 P 池中 δ18O-P 在是否添加落叶的情况下的变化。几乎所有 P 库的 δ18O-P 值都逐渐增加,表明氧气通过上述酶促过程从富集的土壤水中吸收到磷酸盐中。富磷土壤中有效磷的δ18O-P比贫磷土壤增加更多,接近磷酸盐和水的同位素平衡,揭示了微生物磷释放到有效磷库中的影响。然而,在贫磷土壤中,有效磷带来了磷酸酶诱导的同位素特征,表明其主要来源于有机磷的水解。因此,在限磷条件下,有机磷水解的同位素效应大于同位素平衡效应。最后,使用 33P 和 δ18O-P 的两种独立同位素方法提供了非常相似的可用 P 和其他无机土壤池之间交换的 P 估计值。这表明 δ18O-P 可以成功地用于追踪 P 通量,前提是基础过程不会破坏磷酸盐分子的 P-O 键。
更新日期:2020-09-29
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