Characterization of Phosphorus in Subtropical Coastal Sand Dune Forest Soils

• Main Authors: Chiao-Wen Lin, Guanglong Tian, Chung-Wen Pai, Chih-Yu Chiu
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: Forests
• Subjects: sequential chemical extraction; ³¹P-nuclear magnetic resonance spectroscopy (³¹P-NMR); phosphorus; coastal sand dune; <i>Casuarina</i> forests
• Online Access: https://www.mdpi.com/1999-4907/9/11/710

Continuous research into the availability of phosphorus (P) in forest soil is critical for the sustainable management of forest ecosystems. In this study, we used sequential chemical extraction and ³¹P-nuclear magnetic resonance spectroscopy (³¹P-NMR) to evaluate the form and distribution of inorganic P (P_i) and organic P (P_o) in <i>Casuarina</i> forest soils of a subtropical coastal sand dune in Houlong, Taiwan. The soil samples were collected from humic (+2&#8315;0 cm) and mineral layers (mineral-I: 0&#8315;10, mineral-II: 10&#8315;20 cm) at two topographic locations (upland and lowland) with different elevations. Sequential chemical extraction revealed that the NaOH-P_o fraction, as moderately recalcitrant P, was the dominant form in humic and mineral-I layers in both upland and lowland soils, whereas the cHCl-P_i fraction was the dominant form in the mineral-II layer. The resistant P content, including NaOH-P_i, HCl-P_i, cHCl-P_i, and cHCl-P_o fractions, was higher in the upland than in the lowland. However, the labile P content, NaHCO₃-P_o, showed the opposite pattern. The content of resistant P_i (NaOH-P_i, HCl-P_i, and cHCl-P_i) increased significantly with depth, but that of labile P_i (resin-P_i and NaHCO₃-P_i) and recalcitrant P_o (NaHCO₃-P_o, NaOH-P_o, and cHCl-P_o) decreased significantly with depth at both locations. ³¹P-NMR spectroscopy revealed inorganic orthophosphate and monoesters-P as the major forms in this area. The proportions of P_i and P_o evaluated by sequential chemical extraction and ³¹P-NMR spectroscopy were basically consistent. The results indicate that the soils were in weathered conditions. Furthermore, the P distribution and forms in this coastal sand dune landscape significantly differed between the upland and lowland because of the variation in elevation and eolian aggradation effects.