Flooding is known to mobilise soil phosphorus (P). However, it is still not clear how climate change-driven extended periods of soil drying followed by flooding will affect soil-P dynamics. We tested the hypothesis under laboratory conditions that soil antecedent conditions (moist/dry) determine the amount of P mobilised upon flooding. A series of controlled laboratory experiments were carried out by flooding samples of two contrasting soils (a Dystric Cambisol [Crediton series] and a Stagni-Vertic Cambisol [Hallsworth series]), which had each been either dried (40°C for 10 days) or kept at field moisture conditions (25% moisture content). Flooding was simulated by maintaining a 10-cm water column depth in mesocosms. Periodically collected water samples were analysed for dissolved reactive P (DRP), total dissolved P (TDP) and dissolved unreactive P (DUP). The onset of flooding significantly (p < 0.001) increased dissolved concentrations of all forms of P. The release of TDP coincided with a reduction in redox potential, suggesting reductive dissolution of P bearing iron/manganese (Fe/Mn) minerals as indicated by a significant positive correlation between TDP and dissolved Fe (r = 0.430, p < 0.001) and TDP and dissolved Mn (r = 0.622, p < 0.001). Flooding of the dried soils caused a significantly greater increase in the dissolved P concentrations of all forms of P relative to their moist-flooded counterparts. This could be due to a combination of factors which are associated with soil drying and flooding. The Crediton dry-flooded soils released higher concentrations of DRP upon flooding (e.g. 0.14 mg P L⁻¹ on day 1 after flooding) perhaps due to its higher concentrations of water- and NaHCO₃-extractable P than the Hallsworth dry-flooded (HDF) soil (0.03 mg P L⁻¹ on day 1 after flooding). However, most of the P in the water column of the dry-flooded soils was unreactive, with the HDF soil releasing higher concentrations of DUP, likely due to its higher organic matter and microbial biomass P contents. The results suggest that flooding of dried soils has greater potential to enhance mobilisation of soil-P than flooding of moist soils and thus has potential implications for soil fertility and surface water quality.

中文翻译：

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干燥和模拟洪水对两种对比英国草原土壤的土壤磷动态的影响

众所周知，洪水会调动土壤磷 (P)。然而，尚不清楚气候变化驱动的土壤干燥时间延长和洪水将如何影响土壤-P动态。我们在实验室条件下检验了这一假设，即土壤先行条件（潮湿/干燥）决定了洪水时 P 的动员量。通过淹没两种对比土壤（Dystric Cambisol [Crediton 系列] 和 Stagni-Vertic Cambisol [Hallsworth 系列]）的样品进行了一系列受控实验室实验，每种土壤都已干燥（40°C 10 天）或保持在田间水分条件下（水分含量为 25%）。通过在中宇宙保持 10 厘米水柱深度来模拟洪水。分析定期收集的水样中溶解的活性 P (DRP)，总溶解 P (TDP) 和溶解的非反应性 P (DUP)。洪水开始显着（p  < 0.001) 增加了所有形式 P 的溶解浓度。TDP 的释放与氧化还原电位的降低同时发生，表明含 P 的铁/锰 (Fe/Mn) 矿物的还原溶解，如 TDP 和溶解的 Fe ( r  = 0.430, p  < 0.001) 和 TDP 和溶解的 Mn ( r  = 0.622, p  < 0.001)。相对于湿淹的对应物，干土的淹水导致所有形式的 P 的溶解 P 浓度显着增加。这可能是由于与土壤干燥和洪水有关的多种因素造成的。Crediton 干淹土壤在淹水时释放更高浓度的 DRP（例如 0.14 mg PL^-1（洪水后第 1 天）可能是由于其水和 NaHCO ₃可提取 P 的浓度高于 Hallsworth 干淹（HDF）土壤（洪水后第 1 天 0.03 mg PL ^-1）。然而，干淹土壤水柱中的大部分 P 没有反应，HDF 土壤释放更高浓度的 DUP，可能是由于其较高的有机质和微生物生物量 P 含量。结果表明，与潮湿土壤的洪水相比，干燥土壤的洪水具有更大的促进土壤-P 迁移的潜力，因此对土壤肥力和地表水质量具有潜在影响。