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

Purpose

The turnover of organic phosphorus (P_o) 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 P_o change pattern and how abiotic and biotic factors influence P_o transformation in tropical region. Thus, this study was aimed to the characteristics and controls of P_o transformation towards the advanced stage of tropical soil evolution.

Methods

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 P_o compounds in all soils determined by solution ³¹P nuclear magnetic resonance spectroscopy.

Results

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 P_o (including phosphate diester and its degradation products) increased continuously across the chronosequence, suggesting that long-term tropical soil evolution promoted labile P_o accumulation that was vital to maintain P supply in highly weathered and P-deficient soil. Redundancy analysis revealed that P_o transformation was jointly affected by soil total nitrogen, total organic carbon, phytase, and amorphous iron, accounting for 37.5% (p < 0.01), 29.5% (p < 0.01), 20.7% (p < 0.05), and 14.8% (p < 0.05) of explanation in the variations of P_o compounds, respectively.

Conclusion

Our study has supplemented the blank of P_o transformation during tropical soil evolution over a 2.30-million-year time scale and emphasizes the important role of soil C, N in regulating P_o changes.