Root‐induced soil deformation influences Fe, S and P: rhizosphere chemistry investigated using synchrotron XRF and XANES

Abstract

Rhizosphere soil has distinct physical and chemical properties from bulk soil. However, besides root-induced physical changes, chemical changes have not been extensively measured in situ on the pore scale.In this study, we couple structural information, previously obtained using synchrotron X-ray computed tomography (XCT), with synchrotron X-ray fluorescence microscopy (XRF) and X-ray absorption near-edge structure (XANES) to unravel chemical changes induced by plant roots.Our results suggest that iron (Fe) and sulfur (S) increase notably in the direct vicinity of the root via solubilization and microbial activity. XANES further shows that Fe is slightly reduced, S is increasingly transformed into sulfate (SO 4 2À ) and phosphorus (P) is increasingly adsorbed to humic substances in this enrichment zone. In addition, the ferrihydrite fraction decreases drastically, suggesting the preferential dissolution and the formation of more stable Fe oxides. Additionally, the increased transformation of organic S to sulfate indicates that the microbial activity in this zone is increased. These changes in soil chemistry correspond to the soil compaction zone as previously measured via XCT.The fact that these changes are colocated near the root and the compaction zone suggests that decreased permeability as a result of soil structural changes acts as a barrier creating a zone with increased rhizosphere chemical interactions via surface-mediated processes, microbial activity and acidification.

Co-fertilization of sulfur and struvite-phosphorus in a slow-release fertilizer improves soybean cultivation

“…30 Both PS and S8 require biological activity to be oxidized to sulfate, and roots may contribute to this by releasing organic compounds that stimulate soil microorganisms. 45 Therefore, even though P supply appeared to contribute more significantly to soybean root system distribution, the S sources probably played a role in root traits as well.…”

“…Sulfur uptake by control plants was probably obtained from mineralization of organic S, promoted by enhanced root growth. 45 S plays a central role in the synthesis of proteins in plants, and also in symbiotic N2 fixation, a process which soybean uses to assimilate nitrogen when this nutrient is deficient in soil. 46 However, nodule formation on roots was not observed, suggesting the unfertilized control plants did not fixate nitrogen.…”

Filling gaps in our understanding of belowground plant traits across the world: an introduction to a Virtual Issue

“…Furthermore, an advantage of horticultural and agricultural systems is the often detailed characterization of intraspecific variation (i.e. of varietals or lines) in root physiology, morphology and root system architecture, as well as the genetic underpinning of root traits (Wedger et al ., 2019), and explicit links between root traits and the function of individual roots (Martins et al ., 2020; van Veelen et al ., 2020; Pedersen et al ., 2021a) and root systems (Wen et al ., 2019; McKay Fletcher et al ., 2020).…”

“…For example, the amount, composition and diversity of living roots can affect microbial community richness and diversity (López‐Angulo et al ., 2020; Spitzer et al ., 2021; Sweeney et al ., 2021), as well as nitrogen cycling in the rhizosphere (Henneron et al ., 2020). Furthermore, root traits control growth patterns in response to deflecting soil particles (Martins et al ., 2020), and in turn root‐induced soil deformation affects soil properties ranging from compaction to chemical composition (van Veelen et al ., 2020). Even after roots die, the decomposition of roots by soil microbial communities is often mediated by root traits and root associations with mycorrhizal fungi, in addition to the surrounding environment (Lin et al ., 2020; Jiang et al ., 2021).…”

Perspectives from the Fritz‐Scheffer Awardee 2020—The mutual interactions between roots and soil structure and how these affect rhizosphere processes#

“…In a correlative analysis of synchrotron X‐ray fluorescence microscopy and X‐ray absorption near‐edge structure with X‐ray µCT, it was revealed by van Veelen et al. (2020) that the spatial variation in porosity strongly influences iron, sulfur and phosphate chemistry. In detail, dissolution processes were associated with the direct porous vicinity of the root due to optimal conditions for microbial activity, while the subsequent densification zone was defined by reduced permeability and increased binding and reactions on particle surfaces, for example, resulting in the formation of stable Fe oxides (van Veelen et al., 2020).…”