Combining Multiple High-Resolution In Situ Techniques to Understand Phosphorous Availability Around Rice Roots

• Published in: Environmental science & technology Vol. 55; no. 19; pp. 13082 - 13092
• Main Authors: Fang, Wen, Williams, Paul N, Zhang, Hao, Yang, Yi, Yin, Daixia, Liu, Zhaodong, Sun, Haitao, Luo, Jun
• Format: Journal Article
• Language: English
• Published: Easton American Chemical Society 05.10.2021
• Subjects: Contaminants in Aquatic and Terrestrial Environments; Depletion; Heterogeneity; High resolution; Image resolution; Laser ablation; Life cycles; Mineralization; Nutrition; Phosphatase; Rhizosphere; Rice; Roots; Soils; Thin films; phosphatase activity; rice root; in situ sampling; iron lability; high-resolution visualization; phosphorus lability; soil imaging systems
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.1c05358

Resolving chemical/biological drivers of P behavior around lowland/flooded rice roots remains a challenge because of the heterogeneity of the plant–soil interactions, compounded by sampling and analytical constraints. High-spatial-resolution (sub-mm) visualization enables these processes to be isolated, characterized, and deciphered. Here, three advanced soil imaging systems, diffusive gradients in thin-film technique coupled with laser ablation-ICPMS (DGT-LA-ICPMS), O2 planar optode, and soil zymography, were integrated. This trio of approaches was then applied to a rice life cycle study to quantify solute-P supply, through two dimensions, in situ, and low-disturbance high-resolution (HR) chemical imaging. This allowed mechanisms of P release to be delineated by O2, Fe, and phosphatase activity mapping at the same scale. HR-DGT revealed P depletion around both living and dead rice roots but with highly spatially variable Fe/P ratios (∼0.2–12.0) which aligned with changing redox conditions and root activities. Partnering of HR-DGT and soil zymography revealed concurrent P depletion and phosphatase hotspots in the rhizosphere and detritusphere zones (Mantel: 0.610–0.810, p < 0.01). This close affinity between these responses (Pearson correlation: −0.265 to −0.660, p < 0.01) cross-validates the measurements and reaffirms that P depletion stimulates phosphatase activity and Porg mineralization. The μ-scale biogeochemical landscape of rice rhizospheres and detritusphere, as documented here, needs greater consideration when implementing interventions to improve sustainable P nutrition.