Phosphorus Speciation during Soil Genesis in a Semi-Arid Environment.

Phosphorus speciation during soil genesis in a semi-arid environment

Chunhao Gu¹, Larry C. Munn¹, Stephen C. Hart², Yongfeng Hu³, and Mengqiang Zhu^1*

¹Department of Ecosystem Science and Management, University of Wyoming, Laramie, Wyoming, 82071

²School of Natural Sciences and Sierra Nevada Research Institute, University of California, Merced, California, 95344

³Canadian Light Source, University of Saskatchewan, Saskatoon, Canada, S7N 0X4

 

      Phosphorus (P) is a crucial nutritional element for life on earth. Almost all the P in terrestrial ecosystems is derived from rock weathering during soil genesis. The developmental stages of soils control P concentration, most importantly, its speciation and bioavailability in soils. P speciation transformation with time during soil genesis in humid ecosystems is relatively well known, which can be described by the conceptual model proposed by Walker and Syers. However, limited information is available about P speciation change in semi-arid ecosystems. Sequential chemical extractions (SCE) have been widely used to assess and quantify soil P species with different binding types and bioavailability. But SCE provides only operationally-defined P pools, and does not directly determine P speciation. Synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy is an efficient and direct approach that can distinguish different P species, particularly solid inorganic P (P_i) species, in environmental samples, such as soils. ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy is another technique that is powerful for determining speciation of extractable organic P (P_o) in soils. In this study, we attempt to determine soil P speciation from two soil chronosequences in a semi-arid natural environment using P XANES and ³¹P NMR spectroscopic analyses in addition to SCE. Surface soils were collected from two chronosequence sites that are located in the Laramie Basin, Wyoming and the San Francisco Volcanic Field, Arizona, respectively. The ages of the investigated soils range from 0.14 million years (MY) to 1.8 MY for the basin, and from 0.01 MY to 3 MY for the volcanic field, respectively. Results show that total soil P concentrations decreased with the substrate age. The P XANES and ³¹P NMR results on these samples will be presented which are shown to be helpful to improve the understanding of terrestrial ecosystem evolution in a semi-arid environment.

Submitted to ASA, CSSA and SSSA International Annual Meetings,

Nov 2 – 5, 2014, Long Beach, California