The high accumulation of phosphorus in high-yield paddy soils: A new insight from cutans.

Conceptual diagram of coupled interactions between iron and phosphorus across redox conditions in paddy soils. [PO 4 3-] x : Dissolved phosphate species include all variations. PSM: Phosphate-solubilizing microorganisms. [Display omitted] • The Fe-enriched cutans were composed of red spherical particles. • The amorphous Fe oxide in the cutans contributed substantially to sorption of P. • Both microbial diversity and P-solubilizing fungi were accumulated in the cutans. • The cutans are "Hot Spots" of P in paddy soil. Phosphorus (P) is a key limiting nutrient for crops. Oscillation of redox conditions usually induces formation of Fe-enriched cutans in the plow layer of paddy soils. This study investigated P biogeochemistry in the cutans, which were collected from high-yield paddy soils in Taihu Lake region, China. Mössbauer spectroscopy showed that the content of Fe3+ was eight times higher than Fe2+ in the cutans. Based on the evidences from XRD and wet chemical analysis, the enriched Fe in the cutans mostly existed as amorphous oxides, which owned high surface areas for P sorption. In addition, the cutans were composed of spherical particles with diameters of 20–130 μm under microscopy. Moreover , the particles showed evident "trench" structures on their top surface under SEM imaging. These features caused the cutans to retain three times higher P than that in the matrix soils. Furthermore, the cutans demonstrated both high microbial richness and community diversity, in contrast to the matrix soils. In particular, the abundance of phosphate-solubilizing fungi (with relatively highly competitive saprophytic ability) was also significantly promoted. Therefore, the cutans could be considered as hotspots of P accumulation in paddy soils. The subsequent enhancement of the available P would promote rice production. [ABSTRACT FROM AUTHOR]