Small-scale interaction of iron and phosphorus in flooded soils with rice growth

• Published in: The Science of the total environment Vol. 669; pp. 911 - 919
• Main Authors: Wang, Yu, Yuan, Jia-Hui, Chen, Hao, Zhao, Xu, Wang, Dengjun, Wang, Shen-Qiang, Ding, Shi-Ming
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.06.2019
• Subjects: DGT; Environmental Monitoring; Fe/P ratio; Fertilizers - analysis; Floods; HR-peeper; Iron - metabolism; Oryza - growth & development; Oryza - metabolism; Paddy soils; Phosphorus; Phosphorus - metabolism; Rice rhizosphere; Soil - chemistry; DGT; Phosphorus; Rice rhizosphere; HR-peeper; Fe/P ratio; Paddy soils
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.03.054

In the rhizosphere of flooded paddy soils, the solubilization, efflux, and uptake of phosphorus (P) are highly intertwined with iron (Fe) redox cycling. However, the direct observation of Fe-P coupling in the rhizosphere is challenging. This study combined high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) techniques to capture the one-dimensional distributions of soluble reactive P (SRP), soluble Fe(II), and labile P and Fe in the root zone of rice (Oryza sativa L.), respectively. The results show a depletion of soluble/labile P and Fe concentrations around the rice root zone, compared to anaerobic bulk soils that have two different soil Olsen-P levels. Two-dimensional (2D) measurements of DGT-labile P concentrations exhibited similar but stronger trends of P depletion due to uptake of P from soil solids. In low-P soil treatment, 97.8% soluble Fe(II) was depleted in the rice root zone relative to bulk soil, and a 540% enrichment of total Fe in Fe plaques appeared in comparison to that in high-P soil. This demonstrated that the rice plant showed an adaptive metabolic reaction to combat P deficiency in low-P soil by increasing Fe plaque formation. This reaction directly resulted in stronger depletion of P in low-P soil, as indicated by the results of 2D measurements of DGT-labile P concentrations. Moreover, the significant (P < 0.001, R2 = 0.175–0.951) positive corrections between SRP vs. soluble Fe(II), and DGT-labile P vs. Fe were observed in combination with pronounced peaks at the same position in the rice root zone, thus verifying that the cycling of Fe dictated P depletion. A notably lower value of the DGT-labile Fe/P ratio was found in high-P soil, which indicates a relatively higher risk of P release compared to that in low-P soil. [Display omitted] •P and Fe in rice rhizosphere were measured at mm and submm resolutions.•The depletion of P and Fe(II) in porewaters was observed around the rice root zone.•Notable depletion of Fe(II) and enrichment of total Fe content in iron plaque was found in P-low soil.•The significant positive correction between P and Fe in porewaters and soil solid was observed.•Notable lower value for the DGT-labile Fe/P ratio was indicated in high-P soils.