Phytolith solubility in paddy soil

• Applicant: Professor Dr. Robert Mikutta, since 5/2021
• Subject Area: Soil Sciences
• Term: from 2017 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391495240

Major crop species such as rice and wheat actively adsorb large quantites of dissolved silicon (Si) from soil solution, which precipitates in the plants forming amorphous silicon dioxide bodies, the `phytoliths`. Silicon nutrition plays a crucial role in stress resistance of plants. The impact of straw recycling on Si cycling and bioavailability in rice soils depends on solubility of phytoliths in soil. Laboratory studies showed high dissolution rates for fresh phytoliths extracted from plant litter. These data, however, seem to contradict the sometimes large storage of phytoliths in topsoil and in archaeological sites. The proposed project plans to systematically study factors determing solubility of phytoliths during ageing in soil. It is hypothesized that phytolith solubility decreases over time due to (i) decreases in active surface area and (ii) formation of inorganic and organic coatings on the phytoliths surfaces (surface `passivation`). We furthermore assume that formation of iron-rich coatings is intensified by periodic changes in redox conditions in rice soils; the redox cycles should thus accelerate the passivation of phytolith surfaces. Mineral bags containing phytoliths extracted from rice straw will be buried in soil under different conditions, and the chemical and morphological changes at phytolith surfaces during phytolith ageing will be followed using a variety of analytical methods, including scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The solubility of the phytoliths retrieved from the mineral bags will be studied in laboratory experiments, and relations between parameters on chemical composition of the surfaces (e.g., Fe- and Al-concentrations) and phytolith solubility will be tested. The project will demonstrate whether/how an improved understanding of Si fluxes in soils can be gained by precise nanometer-scale characterization of chemical alterations at surfaces of reactive silicate minerals using modern techniques such as XPS. It will also enhance understanding on human impact on Si availability in soil by removing or recycling of harvest residues.

• DFG Programme: Research Grants
• Co-Investigators: Dr. Klaus Kaiser; Professorin Dr. Doris Vetterlein
• Ehemaliger Antragsteller: Dr. Thimo Klotzbücher, until 5/2021