Plantview Support Rhizosphere ROS Dynamics Research: Novel insights into the factors influencing rhizosphere reactive oxygen species production and their role in polycyclic aromatic hydrocarbons tra

New progress has been made in understanding the production of reactive oxygen species (ROS) in localized soil microenvironments.

Professor Hanzhong Jia's research team from the College of Natural Resources and Environment, Northwest A&F University, has made new advances in the study of reactive oxygen species production in localized soil microenvironments. Their findings have been published in “Soil Biology & Biochemistry” (IF = 9.8, CAS Q1 Top journal), a leading journal in the field of soil science.

This study provides new insights into the spatial distribution and regulatory mechanisms of rhizosphere ROS, revealing how root development and environmental factors regulate ROS production and how ROS contribute to the transformation of organic pollutants. The findings offer new strategies for targeted enhancement of phytoremediation technologies.

Reactive oxygen species (ROS), a collective term for oxidatively active molecules such as superoxide radicals (O₂⁻), hydrogen peroxide (H₂O₂), and hydroxyl radicals (•OH), are widely present in various environmental media. They are not only key biogeochemical factors driving the carbon cycle, elemental transformation, and pollutant degradation, but also participate in regulating biological physiological processes, such as microbial respiration and mineral oxidation. Traditional views hold that ROS are primarily generated through photochemical reactions. However, recent studies have revealed that significant dark-reaction ROS production still occurs under light-free conditions, such as in the deep sea and groundwater aquifers. Notably, the rhizosphere microdomain—the dynamic interface where plant roots interact with soil—has emerged as a newly recognized hotspot for ROS due to its unique physicochemical properties, including organic matter enrichment, high microbial activity, and pronounced redox gradients. The complex interactions between root exudates released by plants, microorganisms, and minerals can induce non-photochemical ROS generation mechanisms, such as electron transfer, iron cycling, and phenolic compound oxidation, suggesting that the ecological functions of rhizosphere ROS in terrestrial ecosystems remain largely unexplored.

Although the rhizosphere has been identified as a potential "hotspot" for ROS, significant knowledge gaps remain regarding its spatiotemporal dynamics and regulatory mechanisms. First, the effects of root developmental heterogeneity on ROS production have not yet been fully elucidated. Differences in the composition and release rates of root exudates among different root orders (primary roots/lateral roots) may differentially regulate ROS generation pathways and intensities by altering microbial community structures, enzyme activities, and redox components (such as water-soluble phenolic compounds and dissolved organic carbon). However, the spatiotemporal evolutionary patterns underlying these processes lack in situ empirical evidence. Second, the synergistic mechanisms of environmental factors remain unclear. Temperature (by affecting root exudate release), moisture (by regulating microbial activity and diffusion), and oxygen (as a direct substrate) may collectively shape ROS production patterns. Nevertheless, no systematic studies have investigated how these three factors indirectly or directly influence ROS generation through alterations in the rhizosphere microenvironment. Furthermore, the potential of ROS in transforming organic pollutants has been severely underestimated, particularly with regard to their contribution to the degradation of highly toxic substances such as polycyclic aromatic hydrocarbons (PAHs), which has hindered the application of rhizosphere processes in pollution remediation.

As typical persistent organic pollutants, PAHs have traditionally been addressed through phytoremediation mechanisms primarily focused on microbial degradation and plant uptake, while ROS-mediated abiotic oxidation pathways have long been overlooked. Previous studies have shown that PAHs can indirectly stimulate ROS generation by inducing plant stress responses, thereby establishing a "pollutant–plant" positive feedback loop. However, the specific contribution, molecular mechanisms, and environmental regulatory factors of this process within rhizosphere microdomains have yet to be quantified. Using maize, an efficient crop for PAH remediation, as a model, this study decoupled environmental variables associated with root developmental stages, including temperature, moisture, and oxygen, to reveal the spatial migration patterns of ROS (from primary roots to lateral roots) and the optimal production thresholds (25°C + 45% moisture). Meanwhile, the study quantified for the first time the contribution of ROS to PAH degradation (31.4–43.3%), filling a critical knowledge gap between elucidating the generation mechanisms of rhizosphere ROS and their application in pollution remediation, and providing new strategies for the targeted enhancement of phytoremediation technologies.

Experiments using Plantview

In situ fluorescence imaging was employed to dynamically track the spatial distribution of ROS in the maize rhizosphere. Maize seedlings were planted in root boxes inclined at 45° to force the roots to grow along the inner walls. At different cultivation time points (1, 5, 9, 13, 17, and 35 days), the fluorescent probe DCFH-DA, which reacts with ROS to generate the fluorescent substance DCF, was sprayed onto the root–soil interface. Fluorescence signals were captured under dark conditions using the PlantView Plant In Vivo Imaging System from Guangzhou Biolight Biotechnology Co., Ltd. (excitation/emission wavelengths: 480/520 nm). The results showed that ROS were significantly enriched at the root–soil interface (Figure 1), and the proportion of hotspots initially increased and subsequently decreased with root development, reaching a peak of 17.3% on day 17. A key finding was that ROS hotspots migrated from primary roots to lateral roots: during the early stage (days 1–9), they were predominantly concentrated around primary roots, whereas during the later stage (days 13–35), they shifted to newly developed lateral roots, indicating that lateral roots are the major contributors to ROS generation. This spatial evolutionary pattern reveals that root development drives the microdomain heterogeneity of rhizosphere ROS.

DOI: 10.1016/j.soilbio.2024.109562