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Phosphorus Release from Mineral Soil by Acid Hydrolysis: Method Development, Kinetics, and Plant Community Composition Effects
Author(s) -
Hacker Nina,
Gleixner Gerd,
Lange Markus,
Wilcke Wolfgang,
Oelmann Yvonne
Publication year - 2017
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2017.02.0064
Subject(s) - chemistry , dissolution , calcareous , phosphate , pedogenesis , soil ph , kinetics , soil water , carbonate , environmental chemistry , rhizosphere , inorganic chemistry , geology , soil science , biochemistry , paleontology , physics , organic chemistry , quantum mechanics , bacteria
Core Ideas A modified pH stat approach captures P release kinetics in soil relevant for plant nutrition. The fast‐reacting P pool comprises P from charged surfaces and easily soluble Ca‐phosphates. The slow‐reacting P pool is a mixture of Ca‐phosphates and P released by dissolution of pedogenic oxides. Legumes increase the exploitation of more stable P pools. The release kinetics of phosphate (inorganic P [P i ]) at constant proton pressure in a pH stat experiment may be used as a proxy for P mobilization by rhizosphere acidification. pH stat experiments are challenging for calcareous soils because of the strong carbonate buffering. Our objectives were (i) to modify an existing pH stat method for calcareous soils and (ii) to determine plant species richness, plant functional group richness, and identity effects on pool sizes and rate constants (i.e., the fast‐ and slow‐reacting Pools A and B, respectively, and the associated release constants k a and k b ). The study was conducted in “The Jena Experiment” comprising grassland mixtures with different functional group composition and species richness. In 27 samples with inorganic C concentrations <10 g kg –1 , a constant pH value of 3 after 2 h was reached by removing all released cations with ion‐exchange membranes until all carbonates were destroyed. Thereafter, P release kinetics followed a biphasic course: the fast‐reacting Pool A contained 86% of the bioavailable P i extractable with NaHCO 3 plus NaOH. The slow‐reacting P pool additionally comprised P from dissolution of pedogenic oxides and more stable Ca‐phosphates containing 17 to 40% of HCl‐extractable P i . Legumes decreased both pools (Pool A: 40.61 ± 3.83 with legumes vs. 65.24 ± 5.88 mg kg –1 P i without legumes; Pool B: 36.88 ± 1.89 vs. 48.85 ± 1.81 mg kg –1 P i ) because of their increased P demand and associated ability to access hardly available P fractions. In conclusion, pH stat experiments are suitable for studying P dynamics in soil and reveal an aboveground plant composition feedback on soil P dynamics.