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30 March 2016 Mechanisms for altering phosphorus sorption characteristics induced by low-molecular-weight organic acids
Yongzhuang Wang, Joann K. Whalen, Xin Chen, Yanhong Cao, Bin Huang, Caiyan Lu, Yi Shi
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Abstract

Exudation of low-molecular-weight organic acids (LMWOAs) from plant roots enhances phosphorus (P) acquisition from soil, either by dissolving P fixed in secondary minerals or by reducing P sorption to organo-minerals. How LMWOAs may modify P sorption in soils with contrasting pH is not well understood, much less the mechanisms involved. The effects of three common LMWOAs (oxalic, citric, and malic acids) on P sorption in calcareous, neutral, and acidic soils were studied in batch experiments, followed by sequential P fractionation to elucidate the mechanisms whereby LMWOAs alter P sorption. The sorption data of the three soils fitted better to the Freundlich equation (r2 = 0.325-0.994, P < 0.05) than the Langmuir and linear equations. Oxalic, citric, and malic acids at 10 mmol kg-1 soil decreased the Freundlich P sorption parameters Kf and n, which represent P sorption capacity and energy, due to the fact that LMWOAs reduced P sorption in NaHCO3-Pi (soil soluble and exchangeable Pi, 23.8-30.9%) and NaOH-Pi (Fe-Pi and Al-Pi, 21.6-54.2%) fractions of the three soils. Comparing acidified P-LMWOAs solutions with the pH-adjusted P-LMWOAs solutions (pH = 7) had a minor effect on P sorption. Our results indicated that the reduction in soil P sorption was due to ligand exchange and chelation of LMWOAs with Fe and Al minerals, and the acid strength of LMWOAs had a minor effect on P sorption in calcareous, neutral, and acid soils.

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Yongzhuang Wang, Joann K. Whalen, Xin Chen, Yanhong Cao, Bin Huang, Caiyan Lu, and Yi Shi "Mechanisms for altering phosphorus sorption characteristics induced by low-molecular-weight organic acids," Canadian Journal of Soil Science 96(3), 289-298, (30 March 2016). https://doi.org/10.1139/cjss-2015-0068
Received: 25 July 2015; Accepted: 1 March 2016; Published: 30 March 2016
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KEYWORDS
batch experiments
expérience en lots
extraction séquentielle
fraction du P inorganique
fraction du P organique
inorganic P fraction
ligands des acides organiques
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