Spatial Distribution of Trophic Groups of Amoebae Around the Root Zone of Zea Mays Mycorrhizal With Rhizophagus Intraradices Grown in Microcosms

Fitness and productivity of most terrestrial plants depend on early associations with arbuscular mycorrhizal fungi and mutualistic bacteria. Plants select most of the microbial communities cohabiting their roots and mycorrhizosphere, attracting also all types of microbial predators. Naked amoebae are among the most voracious predators inflicting significant changes in soils bacterial and fungal populations. We evaluated how roots of Zea mays with or without Rhizophagus intraradices mycorrhizosphere (AMF) influence trophic groups of amoebae, along vertical (3, 6, and 9-cm) and horizontal soil distribution (roots and free-root compartments) grown in microcosms after, 20 days. Amoebae community in Non-AMF showed a high species richness in the root zone at 3 to 6-cm depth, and at the two free-root compartment away from plants. Conversely, AMF and mycelium zones modified the amoeba community at 6 to 9-cm depth, recording higher diversity of trophic groups than unplanted soil compartments. The highest bacterivorous diversity was found at the closer compartment to AMF roots, but fungivorous amoebae was not recorded. Amoebae feeding preferences were similar in both AMF and Non-AMF microcosms in where bacterivorous amoebae were dominant, while protozoa-eating amoebae were more frequent at the mycelium compartments. Rare amoebae species were found in AMF microcosms in comparison to those recorded from Non-AMF and unplanted microcosms.

Perfluorooctanoic Acid (PFOA) Transport in Soil and Absorption and Distribution in Alfalfa (Medicago sativa)

Perfluorooctanoic acid (PFOA), used as a surfactant in consumer and industrial products, is frequently found in biosolids from wastewater treatment plants. When present in biosolids applied to croplands, PFOA has potential to contaminate feed and fodder used by livestock, but the extent of PFOA transfer from soil to plants is not well characterized. A single dose of [ 14 C]-PFOA was applied to unplanted soil or soil containing growing alfalfa. PFOA transport through unplanted soil and uptake by alfalfa was monitored over a 10-week study period. Radiocarbon was initially measured in roots, stems, and leaves 7 days after PFOA application to soil. PFOA accumulation was greatest in leaves during the 10-week sampling. By week 10, PFOA migration through unplanted soil had reached a depth of 22.8 ± 2.5 cm. In contrast, PFOA migrated to 7.5 ± 2.5 cm in soil containing alfalfa plants. The greatest predictor of PFOA concentration in alfalfa leaves was PFOA concentration in the top 5 cm of soil; PFOA concentrations at lower depths were not correlated with alfalfa PFOA levels. PFOA transport through soil may be slowed by the presence of forage, however PFOA accumulation in edible portions of forage plants may increase food animal exposure to PFOA residues.

Role of Rhizospheric Microbiota as a Bioremediation Tool for the Protection of Soil-Plant Systems from Microcystins Phytotoxicity and Mitigating Toxin-Related Health Risk

Frequent toxic cyanoblooms in eutrophic freshwaters produce various cyanotoxins such as the monocyclic heptapeptides microcystins (MCs), known as deleterious compounds to plant growth and human health. Recently, MCs are a recurrent worldwide sanitary problem in irrigation waters and farmland soils due to their transfer and accumulation in the edible tissues of vegetable produce. In such cases, studies about the persistence and removal of MCs in soil are scarce and not fully investigated. In this study, we carried out a greenhouse trial on two crop species: faba bean (Vicia faba var. Alfia 321) and common wheat (Triticum aestivum var. Achtar) that were grown in sterile (microorganism-free soil) and non-sterile (microorganism-rich soil) soils and subjected to MC-induced stress at 100 µg equivalent MC-LR L−1. The experimentation aimed to assess the prominent role of native rhizospheric microbiota in mitigating the phytotoxic impact of MCs on plant growth and reducing their accumulation in both soils and plant tissues. Moreover, we attempted to evaluate the health risk related to the consumption of MC-polluted plants for humans and cattle by determining the estimated daily intake (EDI) and health risk quotient (RQ) of MCs in these plants. Biodegradation was liable to be the main removal pathway of the toxin in the soil; and therefore, bulk soil (unplanted soil), as well as rhizospheric soil (planted soil), were used in this experiment to evaluate the accumulation of MCs in the presence and absence of microorganisms (sterile and non-sterile soils). The data obtained in this study showed that MCs had no significant effects on growth indicators of faba bean and common wheat plants in non-sterile soil as compared to the control group. In contrast, plants grown in sterile soil showed a significant decrease in growth parameters as compared to the control. These results suggest that MCs were highly bioavailable to the plants, resulting in severe growth impairments in the absence of native rhizospheric microbiota. Likewise, MCs were more accumulated in sterile soil and more bioconcentrated in root and shoot tissues of plants grown within when compared to non-sterile soil. Thereby, the EDI of MCs in plants grown in sterile soil was more beyond the tolerable daily intake recommended for both humans and cattle. The risk level was more pronounced in plants from the sterile soil than those from the non-sterile one. These findings suggest that microbial activity, eventually MC-biodegradation, is a crucial bioremediation tool to remove and prevent MCs from entering the agricultural food chain.

Estimation of the pH of soybean rhizoplane, rhizosphere and bulk soil and its effect on availability and uptake of phosphorus in calcareous Vertisols

Vertisols are spread over central and western parts in Madhya Pradesh in India.As the Vertisolsare calcareous and/or alkaline in nature, mobility of P from soil to root surface is carried by diffusion process, and this diffusion rate is quite low i.e. 0.13mm day-1 (Jungk 1991). One of the major limitation is thatmany rhizosphere chemical interactions that can be involved in the changes ofP ion concentration in the soil solution and in the replenishment of the depleted soil solution (P buffering capacity)do not taken into account (Darrah, 1993).This prompted us to re-evaluate the P-fertility of Vertisols. In the study an attempt has been made to evaluate the most suitable method for P availability in calcareous Vertisols for crops considering the pH of rhizosphere. By agar plate technique, the pH of rhizoplane and rhizoplane soil was found acidic even though soil pH was7.6. The major portion of inorganic P in Vertisols is associated with Ca (Ca-P), which can be soluble more under acid condition than pH 8.5 of Olsen’s condition. The pH of bulk soil, that is unplanted soil which is treated in same way of applied nutrient and water as the planted pots, is 7.9. Soybean crop decreased the pH of rhizosphere and rhizoplane by 7.5and 6.0 respectively. Following the various crops the pH of rhizosphere decreased. Among various crops tested the lowest pH (5.8) of the rhizosphere and rhizoplane -attached soil was noticed in care of Chickpea. In case of pea, maize, sorghum and wheat the pH of rhizosphere and rhizoplane were 7.4 and 6.1, 7.6 and 6.4, 7.5 and 6.4, 7.5 and 6.3, respectively. Decreased pH due to rhizosphere can dissolve the phosphorus from the Calcium and increase the availability of P in Calcareous/ Alkaline soil.

The influence of maize on the rhizosphere eukaryotic community

The microbiota colonizing the rhizosphere contributes to plant growth, productivity, carbon sequestration, and phytoremediation. Several studies address plant-associated bacteria; however, few studies analyze the effect of plant genotype on the eukaryotic community. Here, we analyzed the eukaryotic composition of maize rhizosphere from three different plant landraces and one inbred line grown in the same soil (common garden approach). This experimental design, coupled with 18S rDNA gene amplicon sequencing, allowed us to test the influence of maize and its genotype on the rhizosphere's eukaryotic community. We found that plant growth modified the eukaryotic community in soil, as diversity comparisons between maize rhizosphere and unplanted soil revealed significantly different eukaryotic composition. Various genera of nematodes and fungi, predominantly bacterial feeding nematodes and mycorrhizal fungi among other taxa, were increased in the rhizosphere samples. We also observed that maize genotype differentially shaped the relative abundance of the following fungal families in the rhizosphere: Acaulosporaceae, Aspergillaceae, Chaetomiaceae, Claroideoglomeraceae, Corticiaceae, Mortierellaceae, Trichocomaceae and Trichomeriaceae. Thus, plant genotype has a selective influence on establishing fungal communities in the rhizosphere. This study emphasizes the importance of an integrated consideration of plant genetics for future agricultural applications of microbes to crops.

Impacts of Wetland Plants on Microbial Community and Methane Metabolisms

Aims Microbial activity in the soil of wetlands is responsible for the emission of more methane to the atmosphere than all other natural sources combined. This microbial activity is heavily impacted by plant roots, which influence the microbial community by exuding organic compounds and by leaking oxygen into an otherwise anoxic environment. This study compared the microbial communities of planted and unplanted wetland soil from an Alaskan bog to elucidate how plant growth influences populations and metabolisms of methanogens and methanotrophs. Methods A common boreal wetland sedge, Carex aquatilis, was grown in the laboratory and DNA samples were sequenced from the rhizosphere, unplanted bulk soil, and a simulated rhizosphere with oxygen input but no organic carbon. Results The abundance of both methanogens and methanotrophs were positively correlated with methane emissions. Among the methanotrophs, both aerobic and anaerobic methane oxidizing microbes were more common in the rhizosphere of mature plants than in unplanted soil, while facultative methanotrophs capable of utilizing either methane or other molecules became relatively less common. Conclusions These trends indicate that roots create an environment which favors highly specialized microbial metabolisms over generalist approaches. One aspect of this specialized microbiome is the presence of both aerobic and anaerobic metabolisms, which indicates that oxygen is present but is a limiting resource controlling competition.

Can management improve the lawn’s functioning in the conditions of multiple anthropogenic stressors?

<p>Release of heavy metals, salts and other toxic agents in the environment is of increasing concern in urban areas. Contaminants not solely decline the quality of the local environment and affect the health of human population and urban ecosystems but are also spread through runoff and leaching into non-contaminated areas. Urban lawns are the most distributed green infrastructure in the cities. Management of lawn system may either exacerbate the negative effects of contaminants on lawn functioning either help to withstand the toxic effects and maintain the lawn ecosystem health and the efficient release of ecosystem services.  </p><p>The aim of this study was to evaluate the interactions between the lawn management, the lawn functioning, and the release into the soil of typical urban contaminants. For this purpose, <em>Festuca arundinacea</em> grass was planted in a turf-sand mixture with and without amendment addition (zeolite + vermicompost). To reproduce the impact of traffic-related contaminants in proximity of the road, pots were treated with a solution containing de-icing salt (NaCl) and 6 heavy metals (Zn, Cd, Pb, Cr, Cu, Ni), imitating road runoff solution. After contamination, half of pots was maintained at optimum soil water content (Smart irrigation), another half was left to periodical drying in order to simulate conditions with discontinuous watering (Periodical irrigation). The same experimental scheme was reproduced for unplanted soil. CO<sub>2</sub> net ecosystem exchange (NEE), soil and ecosystem respiration as well as flux from unplanted soil (heterotrophic respiration) were measured shortly after the treatment (short-term) and up 3 months since the treatment start (long-term).</p><p>Soil amendment stimulated plant productivity and increased the efficiency of the system in C uptake (+56% NEE). A relevant reduction of NEE was observed from 14 to 40 days after the application of traffic-related contaminants in both amended and non amended pots. During this period the contaminants had the greatest impact on lawn NEE subjected to Periodic irrigation (-49% and -66% in amended and non amended pots, respectively), while lawn under Smart irrigation was less affected (-35% and -26% in amended and non amended pots, respectively). Different respiration sources (ecosystem respiration, soil respiration, heterotrophic respiration) were characterized by different sensitivity to management and contamination. Heterotrophic flux was not sensitive to soil amending but declined with contamination with enhanced negative effect under Smart irrigation. Response of ecosystem respiration to contamination was less pronounced in confront to soil respiration suggesting leaf-level buffering.    </p><p>Three months later,  the effect of contaminants on lawn gas exchange ceased for all treated pots. Instead, the irrigation effect persisted depending on whether pots were amended or not. In non amended pots NEE was reduced by 18% under Periodic irrigation, while this effect was not present in amended pots. We conclude, that performance of such green infrastructure as lawns in terms of C sequestration under multiple anthropogenic stressors could be efficiently improved through soil amending and irrigation control.</p><p>Current research was financially supported by RFBR No. 19-29-05187 and RSF No. 19-77-30012.</p>

Mechanisms of improving coastal saline-alkali soil by periphyton

Periphyton plays an indispensable role in coastal saline-alkali land, but its function is poorly understood. Soil physical and chemical properties (pH value, salinity, soil organic matter), enzyme activity and microbial diversity (based on 16s rDNA, ITS and functional genes) were measured in periphyton formed on rice-growing coastal saline-alkali soil modified by a new type of soil conditioner. The results showed that the content of organic matter and catalase activity in periphyton were significantly higher than in the unplanted control soil. Soil pH and salinity were decreased in periphyton compared to the unplanted control soil. Based on the relative abundance, bacterial genera Desulfomicrobium, Rhodobacter, cyanobacterium_scsio_T−2, Gemmatimonas, and Salinarimonas as well as fungal genus Fusarium were more abundant in periphyton than the unplanted control soil. In terms of functional genes, the cbbM and cbbL sequencing showed higher abundance of Hydrogenophaga, Rhodovulum, Magnetospira, Leptothrix, and Thiohalorhabdus, whereas the nifH sequencing indicated higher abundance of Cyanobacteria in the periphyton compared to the unplanted soil. The relative abundance and community structure of soil microorganisms were improved by periphyton, thus reducing soil salinity and pH, increasing soil organic matter and enzyme activity. This indicated that the periphyton can improve the conditions and offer a suitable environment for plant growth in coastal saline-alkali soil.

Potential of Salicylic Acid and Synthetic Surfactant on Anthracene and Fluoranthene Remediation by Impatiens Balsamina

Plant growth regulators and synthetic surfactants are choices for enhancing the efficiency of PAH phytoremediation. In this study, the use of salicylic acid alone, surfactant alone (Triton X-100 or Tween 80), or salicylic acid together with Triton X-100 or Tween 80 on anthracene and fluoranthene removal by Impatiens balsamina were investigated. On days 15 and 30 of the experiment, the spraying of salicylic acid as 0.01 mM and watering of 1X CMC of Triton X-100 or Tween 80 were performed. Then, the plant growth parameters and anthracene or fluoranthene remaining in the soil were analyzed on day 45 of the experiment. The results revealed that I. balsamina did not enhance anthracene (77.4 % remained) and fluoranthene (74.6 % remained) removal when compared with unplanted soil (63.8 % of anthracene and 70.0 % of fluoranthene remained). Salicylic acid spraying in combination with watering of Triton X-100 (47.1 % anthracene remained) or Tween 80 (59.7 % anthracene remained) enhanced anthracene removal in unplanted soil; however, enhanced fluoranthene removal was not observed. In planted soil, salicylic acid spraying alone, Tween 80 watering alone or salicylic acid spraying in combination with synthetic surfactant (Triton X-100 or Tween 80) watering slightly enhanced anthracene removal (54.9-58.0 % of anthracene remained) but not fluoranthene (67.9 - 81.9 % of fluoranthene remained). The results revealed that planting contaminated soil with I. balsamina was not suitable to stimulate anthracene and fluoranthene degradation in this study. Biostimulation of unplanted soil with synthetic surfactant and salicylic acid was suitable to stimulate the removal of anthracene from the soil.