Abstract
Abstract. Phosphorus (P) is a major element required for biological activity in terrestrial ecosystems. Although the total P content in most soils can be large, only a small fraction is available or in an organic form for biological utilization because it is bound either in incompletely weathered mineral particles, adsorbed on mineral surfaces, or, over the time of soil formation, made unavailable by secondary mineral formation (occluded). In order to adequately represent phosphorus availability in global biogeochemistry–climate models, a representation of the amount and form of P in soils globally is required. We develop an approach that builds on existing knowledge of soil P processes and databases of parent material and soil P measurements to provide spatially explicit estimates of different forms of naturally occurring soil P on the global scale. We assembled data on the various forms of phosphorus in soils globally, chronosequence information, and several global spatial databases to develop a map of total soil P and the distribution among mineral bound, labile, organic, occluded, and secondary P forms in soils globally. The amount of P, to 50cm soil depth, in soil labile, organic, occluded, and secondary pools is 3.6 ± 3, 8.6 ± 6, 12.2 ± 8, and 3.2 ± 2 Pg P (Petagrams of P, 1 Pg = 1 × 1015g) respectively. The amount in soil mineral particles to the same depth is estimated at 13.0 ± 8 Pg P for a global soil total of 40.6 ± 18 Pg P. The large uncertainty in our estimates reflects our limited understanding of the processes controlling soil P transformations during pedogenesis and a deficiency in the number of soil P measurements. In spite of the large uncertainty, the estimated global spatial variation and distribution of different soil P forms presented in this study will be useful for global biogeochemistry models that include P as a limiting element in biological production by providing initial estimates of the available soil P for plant uptake and microbial utilization.
Highlights
Our method relies on combining several global datasets and our understanding of P transformations during pedogenesis
We derived the global distribution of different forms of P based on surface lithology maps of the Earth, distribution of soil development stages, fraction of parent material P remaining for different soil weathering stages using chronosequence studies, and the distribution of P in different forms for each soil order based on the analysis of Hedley P data from a global literature collection of profile data
The general agreement between our estimated total P and measured total P indicates that initial P concentration in parent material and geochemical processes such as weathering of parent material and the loss of P via leaching are dominant in regulating soil phosphorus cycles in the long term
Summary
Our method relies on combining several global datasets and our understanding of P transformations during pedogenesis. We provide some background information about the datasets and the conceptual model we used. Soil P is initially supplied by the weathering of parent material. P concentration of parent material varies considerably, from 140 ppm in carbonate rocks to more than 1000 ppm in volcanic materials (Gray and Murphy, 2002). It follows that the distribution of different parent material exerts a strong control over the soil P status of terrestrial ecosystems (Buol and Eswaran, 2000)
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