Geochemical patterns and microbial contribution to iron plaque formation in the rice plant (Oryza sativa) rhizosphere
Final Report Abstract
The rice plant rhizosphere shows a high spatially and temporally variable geochemistry. Sharp redox gradients are formed by the oxygen release of the roots into the anoxic soil. Along these gradients a special pattern of iron geochemistry has developed, which is characterized by the formation of low crystalline iron(III) minerals by oxidation of reduced iron with oxygen diffusing from the roots. The formation of these minerals has massive consequences for the sorption capacity of pollutants and nutrients in the rice plant rhizosphere. In our research we have established an experimental setup and measuring methods that allow to follow the propagation of the roots and the development of the geochemical gradients non-invasively. By coupling microsensor measurements, pixel analysis and optical O2 measurement methods, we have been able for the first time to realize a temporal and spatial quantitative correlation between oxygen release by plant roots and iron plaque formation. The collected data not only allowed us to determine the spread of potential habitats for microaerophilic iron(II) oxidizing bacteria, but also to quantify that oxygen release by rice roots can influence about 5% of iron mineral formation in rice paddy soils. By isolating typical representatives of Fe(II)-oxidizing and Fe(III)-reducing bacteria in rice paddy soils, the characterization of which allows the quantification of Fe turnover rates, important insights into the otherwise extremely complex iron cycle of rice paddy soils could be gained in additional experiments. For example, we were able to demonstrate for the first time that Fe(II)-oxidizing bacteria can only temporarily or at geochemical hotspots increase the formation of iron minerals at roots with sufficient but not excessive amounts of O2. On the other hand, we could observe how Fe(III)-reducing bacteria can massively influence the mineral transformation at the root by Fe(III)-reduction, which in turn has far-reaching consequences for the Fe(II) availability in the rhizosphere, the mineralogy of iron plaque, and last but not least the pollutant (im)mobility in rice-field soils.
Publications
- (2018) Quantitative analysis of O2 and Fe2+ profiles in gradient tubes for cultivation of microaerophilic iron(II)-oxidizing bacteria, FEMS Microbiology Ecology, 94(2)
Lueder, U., Druschel, G., Emerson, D., Kappler, A., Schmidt, C.
(See online at https://doi.org/10.1093/femsec/fix177) - (2019) Iron Lung – How rice roots induce iron redox changes in the rhizosphere and create niches for microaerophilic Fe(II)-oxidizing bacteria. Environmental Science and Technology Letters
Maisch, M., Lueder, U., Kappler, A., Schmidt, C.
(See online at https://doi.org/10.1021/acs.estlett.9b00403) - (2019) Quantification of microaerophilic iron(II) oxidation rates in the presence of ferric (bio)minerals. Environmental Science & Technology
Maisch, M., Lueder, U., Laufer, K., Scholze, C., Kappler, A., Schmidt, C.
(See online at https://doi.org/10.1021/acs.est.9b01531) - (2020) From Plant to Paddy — How Rice Root Iron Plaque Can Affect the Paddy Field Iron Cycling. Soil Systems 4(2) 28
Maisch, M., Lueder, U., Kappler, A., Schmidt, C.
(See online at https://doi.org/10.3390/soilsystems4020028)
