Iron (Fe) oxides can serve as an efficient "rusty sink" increasing organic carbon (OC) stability through organo-mineral complexes formation acting as an important mechanism of carbon sequestration. However, Fe-reducing bacteria (FeRB) can result in organic carbon (OC) released from Fe oxides via microbial Fe reduction, which plays a crucial role for OC mineralization.
Plant-microorganism-mineral interactions are expected to lead to the difference in Fe-C relationship between rhizosphere and bulk soils, but there are little insights into the wetland plant root microsites so far.
A recent study was conducted by Zou Yuanchun and his graduate student DUAN Xun from Northeast Institute of Geography and Agroecology found that wetland plant roots significantly enriched Fe(III) and organically complexed Fe oxides (Fep) in rhizosphere soil through radial oxygen loss and rhizodeposition. Fe(III) could protected OC through adsorption and co-precipitation.
The study explored coupled relationship among Fe, C and FeRB in the rhizospheres and bulk soils of two typical plants (Calamagrostis angustifolia, Carex lasiocarpa) in the freshwater wetlands of Northeast China using in situ rhizoboxes. Each rhizobox was divided into one root chamber and two side chambers. Each side chamber was divided into the inner, middle and outer bulk soil parts by two 2.5-mm thick plexiglass sheets. The wetland plant roots were restricted so as to only grow in the root chamber.
Considering the rhizosphere effect was most significant at their mature timing, the soil and microbial indexes were measured by soil geochemical analyses, 16s RNA high-throughput sequencing and fourier transform infrared spectrometer after 100 d of cultivation when each rhizobox was filled with roots.
The study found that wetland plant roots did influence the coupled Fe-C microbial transformations and Fe-bound organic carbon was 3–5 fold greater in rhizosphere soil than bulk soils. The research highlighted the role of plant roots in the coupled Fe-C microbial transformations and identified the conserving hotspot of iron-bound organic carbon in wetland rhizosphere.
"A compelling story about coupled Fe-C transformations in freshwater wetland soils", said the Chief Editor Prof. Joann Whalen of Soil Biology & Biochemistry.
This study has been published in an article entitled “Iron-bound organic carbon is conserved in the rhizosphere soil of freshwater wetlands” in Soil Biology & Biochemistry.
Northeast Institute of Geography and Agroecology, CAS