『Abstract
Phosphorus is widely considered to constrain primary productivity
in tropical rain forests, yet the chemistry of soil organic phosphorus
in such ecosystems remains poorly understood. We assessed contrasting
soils under lowland tropical forest in the Republic of Panama
using NaOH-EDTA extraction and solution 31P nuclear
magnetic resonance spectroscopy. The soils spanned a strong rainfall
gradient (1730-3404 mm y-1) and contained a wide range
of chemical properties (pH 3.3-7.0; total carbon 2.8-10.4％; total
phosphorus 74-1650 mg P kg-1). Soil organic phosphorus
concentrations ranged between 22 and 494 mg P kg-1
and were correlated positively with total soil phosphorus, pH,
and total carbon, but not with annual rainfall. Organic phosphorus
constituted 26±1％ (mean ±STD error, n=19) of the total phosphorus,
suggesting that this represents a broad emergent property of tropical
forest soils. Organic phosphorus occurred mainly as phosphate
monoesters (68-96％ of total organic phosphorus) with smaller concentrations
of phosphate diesters in the form of DNA (4-32％ of total organic
phosphorus). Phosphonates, which contain a direct carbon-phosphorus
bond, were detected in only two soils (3％ of the organic phosphorus),
while pyrophosphate, an inorganic polyphosphate with a chain length
of two, was detected in all soils at concentrations up to 13 mg
P kg-1 (3-13％ of extracted inorganic phosphorus). Phosphate
monoesters were a greater proportion of the total organic phosphorus
in neutral soils with high concentrations of phosphorus and organic
matter, whereas the proportion of phosphate diesters was greater
in very acidic soils low in phosphorus and organic matter. Most
soils did not contain detectable concentrations of either myo-
or scyllo-inositol hexa-kisphosphate, which is in marked contrast
to many temperate mineral soils that contain abundant inositol
phosphates. We conclude that soil properties exert a strong control
on the amounts and forms of soil organic phosphorus in tropical
rain forests, but that the proportion of the total phosphorus
in organic forms is relatively insensitive to variation in climate
and soil properties. Further work is now required to assess the
contribution of soil organic phosphorus to the nutrition and diversity
of plants in these species-rich ecosystems.
Keywords: DNA; Inositol phosphate; Lowland tropical forest; Panama;
Phosphate diesters; Phosphate monoesters; Soil organic phosphorus;
Solution31P NMR spectroscopy 』
Introduction
Methods
Sites and soils
Soil sampling and preparation
Determination of soil properties
NaOH-EDTA extraction and solution 31P NMR spectroscopy
Data analysis
Results
Soil properties
Phosphorus composition determined by NaOH-EDTA extraction and
solution 31P NMR spectroscopy
Carbon to organic phosphorus ratios
Relationships between phosphorus forms and soil properties
Discussion
Conclusions
Acknowledgements
References