A (sub)micro-scale investigation of Fe plaque distribution in a selected wetland plant root epidermis

This study focuses on investigation of the distribution of Fe plaque in the root epidermis of selected wetland plant species (Phragmites australis, Typha latifolia and Spartina alterniflora) using synchrotron X-ray microfluoresces, X-ray absorption near edge structure and transmission Xray microscope techniques with (sub)micro-scale resolution. The wetland plants were collected in Liberty State Park, New Jersey, USA, and Yangtze River intertidal zone, Shanghai, China, during different time period. Although a number of early studies have reported that Fe-oxides can precipitate on surface of aquatic plants in rhizosphere to form iron plaque, the role of Fe plaque in regulating metal biogeochemical cycle has been in discussion for decades. The results from this study show that Fe is mainly distributed in the epidermis non-uniformly, and the major Fe species is ferric Fe (Fe3+). This information is needed to make broad inferences about the relevant plant metal uptake mechanisms because Fe accumulation and distribution in the root system is important to understanding metal transport processes that control the mobility of metals in plants. This study improves our current knowledge of Fe plaque distributions and speciation in the wetland plant root system, and helps us to understand the function of Fe plaque in metal transport and accumulation through the root system.