Behind the plant-bacteria system: The role of zucchini and its secondary metabolite in shaping functional microbial diversity in MCPA-contaminated soil.

MCPA (2-methyl-4-chlorophenoxyacetic acid) contamination is an emerging problem, especially in water reservoirs. The early removal of MCPA residues from soil can prevent its spread to untreated areas. It has been found that the growth of cucurbits and the addition of selected plant secondary metabolites (PSMs) can stimulate MCPA removal from soil. However, the effect of these treatments on soil microbial activity remains poorly studied. Hence, the aim of this research was to evaluate the influence of zucchini (C. pepo cv Atena Polka) and its characteristic PSM: syringic acid (SA) on the functional diversity of soil microorganisms in MCPA-contaminated soil using Biolog® EcoPlates™. It also examines soil physicochemical properties and the growth parameters of zucchini. Microbial activity was enhanced by both zucchini cultivation and SA. All unplanted variants showed significantly lower microbial activity (average well color development, AWCD, ranging from 0.35 to 0.51) than the planted ones (AWCD ranging from 0.77 to 1.16). SA also stimulated microbial activity in the soil: a positive effect was observed from the beginning of the experiment in the unplanted variants, but over a longer time span in the planted variants. SA ameliorated the toxic effect of MCPA on the studied plants, especially in terms of photosynthetic pigment production: the MCPA+SA group demonstrated significantly increased chlorophyll content (401 ± 4.83 µg/g), compared to the MCPA group without SA (338 ± 50.1 µg/g). Our findings demonstrated that zucchini and the amendment of soils with SA, the characteristic PSM of cucurbits, can shape functional diversity in MCPA-contaminated soil. The changes of soil properties caused by the application of both compounds can trigger changes in functional diversity. Hence, both SA and MCPA exert indirect and direct effects on soil microbial activity.

The effects of syringic acid on the properties of MCPA-contaminated soil and the growth of two cucurbit species.

The aim of this study was to determine the influence of syringic acid (SA), a plant secondary metabolite (PSM), on the properties of soil contaminated with 2-methyl-4-chlorophenoxyacetic acid (MCPA) and the condition of two cucurbit species zucchini (C. pepo L. 'Atena Polka') and cucumber (C. sativus 'Cezar') grown on that soil. It was found that amendment with MCPA and MCPA + SA modified the soil physico-chemical properties. Content of N and K was significantly higher for variants amended with SA and/or MCPA, while P content was lower in variant amended with SA. The cucurbits demonstrated varied efficiencies in mitigating the phytotoxicity of the MCPA-treated soil. For soil amended with MCPA + SA, samples remediated with cucumber were characterized as slightly toxic or toxic (45.2%-81.5%), while those planted with zucchini were nontoxic or slightly toxic (-40.6%-47.8%). Development of cucumber seedlings was fully inhibited by MCPA, regardless of SA application, zucchini demonstrated enhanced growth in soil treated with MCPA + SA and no statistically significant differences between morphological parameters of MCPA + SA-treated zucchini in comparison to control plants were observed. The obtained findings suggest that the application of SA is a promising way to mitigate the toxic influence of MCPA in the soil, depending on the cultivated plant species. Novelty statement: The study meets the criteria of novelty and innovativeness. Most importantly, the study is focused on: phytotoxicity studies to inform about the limitations of phytotechnology based on PSMs. Additionally, this manuscript provides an interdisciplinary description of the effects of MCPA and naturally occurring PSM- SA on cucurbits and soil parameters. Such studies, which combine the interactions between cucurbits, their secondary metabolite (SA) and their role in mitigation of phytotoxicity in MCPA-contaminated soil, has not been performed before.

The effect of sewage sludge application on soil properties and willow (Salix sp.) cultivation.

The aim of the study was to determine the impact of sewage sludge from three wastewater treatment plants of different sizes (small, medium and large) applied in two doses (3 and 9 tons per hectare) on soil properties, determined as the content of organic carbon and humus fractions, bacterial abundance, phytotoxicity and PCDD/PCDF TEQ concentrations. The study also evaluated the impact of this sewage sludge on the biometric and physiological parameters and detoxification reaction of willow (Salix sp.) as a typical crop used for the remediation of soil following sludge application. The cultivation of willow on soil treated with sludge was found to result in a gradual increase of humus fractions, total organic carbon content and bacterial abundance as well as soil properties measured using Lepidium sativum. However, it also produced an initial increase of soil phytotoxicity, indicated by Sinapis alba and Sorghum sacharatum, and PCDD/PCDF Toxic Equivalent (TEQ) concentrations, which then fell during the course of the experiment, particularly in areas planted by willow. Although the soil phytotoxicity and PCDD/PCDF TEQ content of the sewage sludge-amended soil initially increased, sludge application was found to have a positive influence on willow, probably due to its high nutrient and carbon content. The obtained results reveal increases in willow biomass, average leaf surface area and leaf length as well as chlorophyll a+b content. Moreover, a strong decline was found in the activity of the detoxifying enzyme glutathione S-transferase (GSTs), a multifunctional enzyme involved in the metabolism of xenobiotics in plants, again demonstrating the used sludge had a positive influence on willow performance.