TY - JOUR

T1 - Organic phosphorus in soil water under a European beech (Fagus sylvatica L.) stand in northeastern Bavaria, Germany: Seasonal variability and changes with soil depth

AU - Kaiser, Klaus

AU - Guggenberger, Georg

AU - Haumaier, Ludwig

N1 - Funding information: The study was funded by the Deutsche Forschungsgemeinschaft joint research program ROSIG and the University of Bayreuth. H. Ciglasch, J. Dilling, S. Peter, U. Roth, and A. Wetzel assisted during the field and laboratory work. A part of the analyses was carried out by the Central Analytical Department of the Bayreuth Institute of Terrestrial Ecosystem Research. We are grateful to the staff of the Bavarian Forest Administration at Bayreuth and Betzenstein for help during the selection of sites and support during sampling. The manuscript profited much from the suggestions of three anonymous referees.

PY - 2003/12

Y1 - 2003/12

N2 - Organically bound phosphorus (P) is a mobile form of phosphorus in many soils and thus its dynamics relevant for the leaching and cycling of this clement. Despite its importance, little is known about the chemical composition of dissolved organic P. We studied the concentrations, fluxes, and chemical composition of organic P in forest floor leachates and soil solutions in a Rendzic Leptosol under a 90-year-old European beech (Fagus sylvatica L.) forest over a 27-month period (1997-1999). The chemical composition of organic P was analysed using XAD-8 fractionation and 31P-nuclear magnetic resonance (NMR) spectroscopy. Organic P was the dominant P form in forest floor leachates as well as in porewaters of the mineral soil. The largest concentrations of organic P were observed during summer and peaked (330-400 μg dissolved organic P l-1) after rain storms following short dry periods, concurrently with the concentrations of organic carbon (OC). Because of high rainfall, fluxes of organic P (and C) were greatest in autumn although concentrations of organic C and P were lower than in summer. In forest floor leachates, the hydrophilic fraction of dissolved organic matter contained 83 ± 13% of the bulk organic P. In soil solutions from 90 cm depth, organic P was almost exclusively in the hydrophilic fraction. Because of the low retention of the hydrophilic fraction of dissolved organic matter in the mineral soils, concentrations of organic P in soil water remained almost constant with depth. Consequently, organic P contributed > 95% of the total P leached into deeper subsoils. The overall retention of organic P in the weakly developed mineral soils was little and so the average annual fluxes of organic P in subsoils at 90 cm depth (38 mg m-2) comprised 67% of those from the forest floors (57 mg m-2) during the study period. Hence, organic P proved to be mobile in the studied soil. 31P-NMR spectroscopy confirmed the dominance of organic P species in soil water. Signals due to inorganic P occurred only in spectra of samples collected in winter and spring months. Spectra of samples from summer and autumn revealed traces of condensed phosphates. Due to low P contents, identification of organic P species in samples from winter and spring was not always possible. In summer and autumn, monoester and diester phosphates were the dominant organic species and varied little in their relative distributions. The distribution of organic species changed little from forest floor leachates to ihe subsoil solutions indicating that the composition of P-containing compounds was not influenced by sorptive interactions or biological transformation.

AB - Organically bound phosphorus (P) is a mobile form of phosphorus in many soils and thus its dynamics relevant for the leaching and cycling of this clement. Despite its importance, little is known about the chemical composition of dissolved organic P. We studied the concentrations, fluxes, and chemical composition of organic P in forest floor leachates and soil solutions in a Rendzic Leptosol under a 90-year-old European beech (Fagus sylvatica L.) forest over a 27-month period (1997-1999). The chemical composition of organic P was analysed using XAD-8 fractionation and 31P-nuclear magnetic resonance (NMR) spectroscopy. Organic P was the dominant P form in forest floor leachates as well as in porewaters of the mineral soil. The largest concentrations of organic P were observed during summer and peaked (330-400 μg dissolved organic P l-1) after rain storms following short dry periods, concurrently with the concentrations of organic carbon (OC). Because of high rainfall, fluxes of organic P (and C) were greatest in autumn although concentrations of organic C and P were lower than in summer. In forest floor leachates, the hydrophilic fraction of dissolved organic matter contained 83 ± 13% of the bulk organic P. In soil solutions from 90 cm depth, organic P was almost exclusively in the hydrophilic fraction. Because of the low retention of the hydrophilic fraction of dissolved organic matter in the mineral soils, concentrations of organic P in soil water remained almost constant with depth. Consequently, organic P contributed > 95% of the total P leached into deeper subsoils. The overall retention of organic P in the weakly developed mineral soils was little and so the average annual fluxes of organic P in subsoils at 90 cm depth (38 mg m-2) comprised 67% of those from the forest floors (57 mg m-2) during the study period. Hence, organic P proved to be mobile in the studied soil. 31P-NMR spectroscopy confirmed the dominance of organic P species in soil water. Signals due to inorganic P occurred only in spectra of samples collected in winter and spring months. Spectra of samples from summer and autumn revealed traces of condensed phosphates. Due to low P contents, identification of organic P species in samples from winter and spring was not always possible. In summer and autumn, monoester and diester phosphates were the dominant organic species and varied little in their relative distributions. The distribution of organic species changed little from forest floor leachates to ihe subsoil solutions indicating that the composition of P-containing compounds was not influenced by sorptive interactions or biological transformation.

KW - Chemical composition

KW - Dissolved organic phosphorus

KW - Fluxes

KW - Liquid-state P NMR

KW - Seasonal variations

KW - XAD-8 fractionation

UR - http://www.scopus.com/inward/record.url?scp=0345791407&partnerID=8YFLogxK

U2 - 10.1023/B:BIOG.0000005325.86131.5f

DO - 10.1023/B:BIOG.0000005325.86131.5f

M3 - Article

AN - SCOPUS:0345791407

VL - 66

SP - 287

EP - 310

JO - BIOGEOCHEMISTRY

JF - BIOGEOCHEMISTRY

SN - 0168-2563

IS - 3

ER -