Dual effects of FeNPs on maize growth and water use are actively mediated by arbuscular mycorrhizal fungus via rhizosphere interactions

Nanoscale zero-valent iron (FeNPs) can affect plant growth and water uptake positively or negatively. Yet, its mechanism is still unclear, particularly for differentiate functional roles of FeNPs in plant-soil interaction. To address this issue, we first confirmed 1.0 and 1.5 g·kg-1 FeNPs as growth-promotion concentrations and 1.5 g·kg-1 as optimal one, while 2.0 g·kg-1 turned to restrict growth in maize seedlings, comparing with CK. When AM fungus (Funneliformis mosseae) was inoculated and cultured with FeNPs, 1.0 and 1.5 g·kg-1 FeNPs further evidently enhanced water uptake and biomass accumulation (P<0.05). ), as affected by the activated AMF colonization carrier. Contrarily, FeNPs turned to promote AMF colonization and development, achieving greater iron translocation efficiency in mycorrhiza (P < 0.05). Yet, 2.0 g·kg-1 FeNPs restricted AMF infection in roots, a negative effect. To investigate the mycorrhizal-FeNPs symbiosis, scanning electron microscopy was used to scan the extraradical hyphae, showing that hyphae intercepted excessive iron nanoparticles, alleviating the blockage of root surface apertures and ultimately restoring root activity. Therefore, dual effects of FeNPs on maize physiology were actively mediated by AMF via rhizosphere interactions. The findings provided new insights into safe and efficient utilization of nanomaterials in agro-ecosystems.

Rhizosphere Microbial Communities and Heavy Metals

The rhizosphere is a microhabitat where there is an intense chemical dialogue between plants and microorganisms. The two coexist and develop synergistic actions, which can promote plants’ functions and productivity, but also their capacity to respond to stress conditions, including heavy metal (HM) contamination. If HMs are present in soils used for agriculture, there is a risk of metal uptake by edible plants with subsequent bioaccumulation in humans and animals and detrimental consequences for their health. Plant productivity can also be negatively affected. Many bacteria have defensive mechanisms for resisting heavy metals and, through various complex processes, can improve plant response to HM stress. Bacteria-plant synergic interactions in the rhizosphere, as a homeostatic ecosystem response to HM disturbance, are common in soil. However, this is hard to achieve in agroecosystems managed with traditional practices, because concentrating on maximizing crop yield does not make it possible to establish rhizosphere interactions. Improving knowledge of the complex interactions mediated by plant exudates and secondary metabolites can lead to nature-based solutions for plant health in HM contaminated soils. This paper reports the main ecotoxicological effects of HMs and the various compounds (including several secondary metabolites) produced by plant-microorganism holobionts for removing, immobilizing and containing toxic elements.

Specialized Plant Growth Chamber Designs to Study Complex Rhizosphere Interactions

The rhizosphere is a dynamic ecosystem shaped by complex interactions between plant roots, soil, microbial communities and other micro- and macro-fauna. Although studied for decades, critical gaps exist in the study of plant roots, the rhizosphere microbiome and the soil system surrounding roots, partly due to the challenges associated with measuring and parsing these spatiotemporal interactions in complex heterogeneous systems such as soil. To overcome the challenges associated with in situ study of rhizosphere interactions, specialized plant growth chamber systems have been developed that mimic the natural growth environment. This review discusses the currently available lab-based systems ranging from widely known rhizotrons to other emerging devices designed to allow continuous monitoring and non-destructive sampling of the rhizosphere ecosystems in real-time throughout the developmental stages of a plant. We categorize them based on the major rhizosphere processes it addresses and identify their unique challenges as well as advantages. We find that while some design elements are shared among different systems (e.g., size exclusion membranes), most of the systems are bespoke and speaks to the intricacies and specialization involved in unraveling the details of rhizosphere processes. We also discuss what we describe as the next generation of growth chamber employing the latest technology as well as the current barriers they face. We conclude with a perspective on the current knowledge gaps in the rhizosphere which can be filled by innovative chamber designs.

Phytoplankton consortia as a blueprint for mutually beneficial eukaryote-bacteria ecosystems based on the biocoenosis of Botryococcus consortia

Bacteria occupy all major ecosystems and maintain an intensive relationship to the eukaryotes, developing together into complex biomes (i.e., phycosphere and rhizosphere). Interactions between eukaryotes and bacteria range from cooperative to competitive, with the associated microorganisms affecting their host`s development, growth and health. Since the advent of non-culture dependent analytical techniques such as metagenome sequencing, consortia have been described at the phylogenetic level but rarely functionally. Multifaceted analysis of the microbial consortium of the ancient phytoplankton Botryococcus as an attractive model food web revealed that its all abundant bacterial members belong to a niche of biotin auxotrophs, essentially depending on the microalga. In addition, hydrocarbonoclastic bacteria without vitamin auxotrophies seem adversely to affect the algal cell morphology. Synthetic rearrangement of a minimal community consisting of an alga, a mutualistic and a parasitic bacteria underpins the model of a eukaryote that maintains its own mutualistic microbial community to control its surrounding biosphere. This model of coexistence, potentially useful for defense against invaders by a eukaryotic host could represent ecologically relevant interactions that cross species boundaries. Metabolic and system reconstruction is an opportunity to unravel the relationships within the consortia and provide a blueprint for the construction of mutually beneficial synthetic ecosystems.