Evolution and controls of organic phosphorus based on 31P nuclear magnetic resonance spectroscopy along a 2-million-year tropical soil chronosequence in northern Hainan Island, China

The turnover of organic phosphorus (Po) may be an important way to maintain P supply for plant growth under the phosphorus (P) deficiency in highly weathered tropical soils. However, there is limited information on Po change pattern and how abiotic and biotic factors influence Po transformation in tropical region. Thus, this study was aimed to the characteristics and controls of Po transformation towards the advanced stage of tropical soil evolution. A well-establish tropical soil chronosequence (0.09, 0.146, 0.64, 1.12, 1.81, and 2.30 million years) derived from basalt in northern Hainan Island, China, was selected and the Po compounds in all soils determined by solution 31P nuclear magnetic resonance spectroscopy. Phosphate monoester showed a rapid increase in the earlier stage of pedogenesis (< 0.15 million year), thereafter declined to the minimum in the 1.12-million-year site and fluctuated in older soils. Meanwhile, the proportion of labile Po (including phosphate diester and its degradation products) increased continuously across the chronosequence, suggesting that long-term tropical soil evolution promoted labile Po accumulation that was vital to maintain P supply in highly weathered and P-deficient soil. Redundancy analysis revealed that Po transformation was jointly affected by soil total nitrogen, total organic carbon, phytase, and amorphous iron, accounting for 37.5