Department of Soil Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Federated Co-operatives Limited, Saskatoon, Saskatchewan, Canada.
PLoS One. 2020 Feb 24;15(2):e0229172. doi: 10.1371/journal.pone.0229172. eCollection 2020.
Phosphorus (P) fertilizers are crucial to achieve peak productivity in agricultural systems. However, the fate of P fertilizers via microorganism incorporation and the exchange processes between soil pools is not well understood. 18Oxygen-labelled phosphate (18O- Pi) can be tracked as it cycles through soil systems. Our study describes biological and geochemical P dynamics using a tandem mass spectrometry (MS/MS) method for the absolute quantification of 18O- Pi. Soil microcosms underwent three treatments: (i) 18O- Pi, (ii) unlabelled phosphate (16O- Pi) or (iii) Milli-Q control, dissolved in a bio-stimulatory solution. During a 6-week series the microcosms were sampled to measure P by Hedley sequential fractionation and DNA extraction samples digested to 3'-deoxynucleoside 5'-monophosphates (dNMP). A MS/MS attached to a HPLC analyzed each P-species through collision-induced dissociation. The resin-extractable and bicarbonate 18O- Pi and 16O- Pi fractions displayed similar precipitation and adsorption-desorption trends. Biotic activity measured in the NaOH and dNMP fractions rapidly delabelled 18O- Pi; however, the MS/MS measured some 18O that remained between the P backbone and deoxyribose sugars. After 6 weeks, the 18O- Pi had not reached the HCl soil pool, highlighting the long-term nature of P movement. Our methodology improves on previous isotopic tracking methods as endogenous P does not dilute the system, unlike 32P techniques, and measured total P is not a ratio, dissimilar from natural abundance techniques. Measuring 18O- Pi using MS/MS provides information to enhance land sustainability and stewardship practices regardless of soil type by understanding both the inorganic movement of P fertilizers and the dynamic P pool in microbial DNA.
磷（P）肥料对于在农业系统中达到生产力峰值至关重要。然而，通过微生物掺入和土壤库之间的交换过程，P 肥料的命运尚未得到很好的理解。18 氧标记的磷酸盐（18O-Pi）可以在其循环通过土壤系统时进行追踪。我们的研究使用串联质谱（MS/MS）方法描述了生物和地球化学 P 动态，该方法用于 18O-Pi 的绝对定量。土壤微宇宙经历了三种处理：（i）18O-Pi，（ii）未标记的磷酸盐（16O-Pi）或（iii）溶解在生物刺激溶液中的 Milli-Q 对照。在 6 周的系列中，对微宇宙进行采样，通过 Hedley 顺序分级法测量 P，并提取 DNA 样品进行消化以得到 3'-脱氧核苷 5'-单磷酸（dNMP）。连接到 HPLC 的 MS/MS 通过碰撞诱导解离分析每个 P 物种。树脂可提取和碳酸氢盐 18O-Pi 和 16O-Pi 分数显示出相似的沉淀和吸附-解吸趋势。NaOH 和 dNMP 分数中测量的生物活性迅速使 18O-Pi 去标记；然而，MS/MS 测量了一些仍然存在于 P 主链和脱氧核糖糖之间的 18O。6 周后，18O-Pi 尚未到达 HCl 土壤库，这突出了 P 迁移的长期性。我们的方法优于以前的同位素追踪方法，因为与 32P 技术不同，内源性 P 不会稀释系统，并且与自然丰度技术不同，所测量的总 P 不是比率。使用 MS/MS 测量 18O-Pi 可以提供信息，通过了解 P 肥料的无机运动和微生物 DNA 中的动态 P 库，增强土地可持续性和管理实践，而与土壤类型无关。
