『Abstract
　Organic phosphorus (P) is an important component of boreal forest humus soils, and its concentration has been found to be closely related to the concentration of iron (Fe) and aluminium (Al). We used solution and solid state ³¹P NMR spectroscopy on humus soils to characterize organic P along two groundwater recharge and discharge gradients in Fennoscandian boreal forest, which are also P sorption gradients due to differences in aluminium (Al) and iron (Fe) concentration in the humus. The composition of organic P changed sharply along the gradients. Phosphate diesters and their degradation products, as well as polyphosphates, were proportionally more abundant in low Al and Fe sites, whereas phosphate monoesters such as myo-, scyllo- and unknown inositol phosphates dominated in high Al and Fe soils. The concentration of inositol phosphates, but not that of diesters, was positively related to Al and Fe concentration in the humus soil. Overall, in high Al and Fe sites the composition of organic P seemed to be closely associated with stabilization processes, whereas in low Al and Fe sites it more closely reflected inputs of organic P, given the dominance of diesters which are generally assumed to constitute the bulk of organic P inputs to the soil. These gradients encompass the broad variation in soil properties detected in the wider Fennoscandian boreal forest landscape, as such our findings provide insight into the factors controlling P biogeochemistry in the region but should be of relevance to boreal forests elsewhere.

Keywords: Solution ³¹P NMR spectroscopy; Solid state ³¹P NMR; Sorption; Groundwater discharge; Groundwater recharge; Betsele』

Introduction
Methods
　Study site
　Soil sampling
　Solution ³¹P NMR
　　NaOH-EDTA extraction
　　Spectra acquisition
　Solid state ³¹P MAS NMR
　Soil chemical analyses
　Statistical analyses
Results
　Characterization of P composition by solution ³¹P NMR
　　Deconvolution analysis of the monoester region and T1ρ relaxation
　Change in P composition along the gradients
　Solid state ³¹P NMR
Discussion
　Organic P composition in highly sorbing soils
　Organic P composition in low sorbing soils
　Methodological considerations
Conclusions
Acknowledgments
References