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Weathering of primary mineral phosphate in the early stages of ecosystem development in the Hailuogou Glacier foreland chronosequence

Zhou, J., Bing, H., Wu, Y., Sun, H., Wang, J.
European journal of soil science 2018 v.69 no.3 pp. 450-461
apatite, chronosequences, ecosystems, glaciers, pH, phosphorus, soil, soil formation, soil sampling, subtropics, vegetation types, weathering, China
Phosphorus (P) is an essential nutrient for plants. Although the transformation of P speciation and the availability of P in soil have been extensively investigated, the weathering processes and rates of weathering of primary mineral phosphate during the initial stage of pedogenesis are not well understood. Soil samples were collected from six sites that had been exposed for different lengths of time in the foreland of the Hailuogou Glacier, SW China. Three classes of P in different minerals were operationally defined using a sequential extraction procedure. The results revealed that the weathering processes of apatite in the Hailuogou chronosequence were divided into two stages: the first was observed at the 30‐, 40‐ and 52‐year‐old sites, where the average rate of weathering of primary mineral phosphate (RLP) increased from 2.6 to 8.7 mmol m⁻² year⁻¹, and the second was observed at the 80‐ and 120‐year‐old sites, where the average RLP increased markedly to 26.0 mmol m⁻² year⁻¹. The RLP at the 120‐year‐old site was significantly larger than at sites with similar ages in temperate and subtropical zones, mainly because of differences in climate, vegetation type and initial P content of the parent material. The rapid increase in RLP with age in the Hailuogou chronosequence was fitted well by a power function (RLP = 0.012 × Age¹.⁶⁶) and was affected mainly by the rapid decrease in soil pH and rapid development of vegetation. By compiling the data in this study and from the literature, we propose that changes in the RLP with age (100–12 000 years) can be described by a decreasing power function and can be divided roughly into three stages. The average RLP (14.1 mmol m⁻² year⁻¹) in the Hailuogou chronosequence was ∼47 times larger than the global rate of P release, thus indicating the importance of glacier forelands in global P cycling. HIGHLIGHTS: The rate of weathering of apatite (RLP) increased as a function: RLP = 0.012 × Age¹.⁶⁶ (Age ≤ 120). Rapid decrease in pH and development of vegetation controlled the rapid increase in RLP over 0–120 years. Change in RLP over hundreds to thousands of years depended mainly on length of exposure. Young glacier forelands are ‘hot spot’ areas of phosphate weathering.