Intensive Reclamation of Landfills and Polygons for Solid Waste Disposal

This research proposed the use of one of the most effective complexons – oxyethylidenediphosphonic acid, namely its derivative compound – phenyldiacetic acid,for the active sorption matrices of humus of mineral origin. The application of active components that stimulate plant growth and photosynthesis processes in hybrid preparations during reclamation were also proposed. Keywords: recultivation of landfill, plant growth stimulation, phytoremediation

A Low Level of NaCl Stimulates Plant Growth by Improving Carbon and Sulfur Assimilation in Arabidopsis thaliana

High-salinity stress represses plant growth by inhibiting various metabolic processes. In contrast to the well-studied mechanisms mediating tolerance to high levels of salt, the effects of low levels of salts have not been well studied. In this study, we examined the growth of Arabidopsis thaliana plants under different NaCl concentrations. Interestingly, both shoot and root biomass increased in the presence of 5 mM NaCl, whereas more than 10 mM NaCl decreased plant biomass. To clarify the biological mechanism by which a low level of NaCl stimulated plant growth, we analyzed element accumulation in plants grown under different NaCl concentrations. In addition to the Na and Cl contents, C, S, Zn, and Cu contents were increased under 5 mM NaCl in shoots; this was not observed at higher NaCl concentrations. Adverse effects of high salinity, such as decreased levels of nitrate, phosphate, sulfate, and some cations, did not occur in the presence of 5 mM NaCl. An increase in C was possibly attributed to increased photosynthesis supported by Cl, Zn, and Cu, which also increased in shoots after NaCl application. Salt stress-responsive gene expression was enhanced under 20 mM NaCl but not at lower doses. Among the S metabolites analyzed, cysteine (Cys) was increased by 5 mM NaCl, suggesting that S assimilation was promoted by this dose of NaCl. These results indicate the usefulness of NaCl for plant growth stimulation.

Bioactivity and Plant Growth Stimulation Studies using Mangifera indica L. Gum

The potential of plant gum as a bioactive agent and plant growth enhancer has not been exploited well and plant gums are suitable for such purposes as they are non-toxic and biodegradable. Therefore, the aim of this study was to verify the potential of Mangifera indica (MI) gum as a bioactive agent and plant growth enhancer. Plant gum was collected from the bark of MI and polysaccharides were extracted, purified and characterized with ultraviolet-visible (UV-Vis) spectroscopic, Fourier-transform infrared spectroscopy and gas chromatography (GC) analyses. Crude and purified polysaccharides were tested for their antibacterial and antioxidant activity. The crude gum was subjected to plant growth stimulation study like germination percentage, shoot length, root length and wet weight of chilli (Capsicum frutescens). The effect of MI gum on soil porosity and water holding capacity (WHC) was also tested. UV-Vis and GC analyses of gum polysaccharide showed the presence of several types of monosaccharides in MI gum. The plant gum did not show any antibacterial activity against Escherichia coli, Pseudomonas sp., Bacillus sp. and Staphylococcus aureus, but was found to exhibit low antioxidant activity. The gum was found to enhance the seed germination and seedling growth in-vitro and in-vivo.

Plant Growth Stimulation by Microbial Consortia

Plant-associated microorganisms play an important role in agricultural production. Although various studies have shown that single microorganisms can exert beneficial effects on plants, it is increasingly evident that when a microbial consortium—two or more interacting microorganisms—is involved, additive or synergistic results can be expected. This occurs, in part, due to the fact that multiple species can perform a variety of tasks in an ecosystem like the rhizosphere. Therefore, the beneficial mechanisms of plant growth stimulation (i.e., enhanced nutrient availability, phytohormone modulation, biocontrol, biotic and abiotic stress tolerance) exerted by different microbial players within the rhizosphere, such as plant-growth-promoting bacteria (PGPB) and fungi (such as Trichoderma and Mycorrhizae), are reviewed. In addition, their interaction and beneficial activity are highlighted when they act as part of a consortium, mainly as mixtures of different species of PGPB, PGPB–Mycorrhizae, and PGPB–Trichoderma, under normal and diverse stress conditions. Finally, we propose the expansion of the use of different microbial consortia, as well as an increase in research on different mixtures of microorganisms that facilitate the best and most consistent results in the field.

Nematicidal Amendments and Soil Remediation

The intensification of agriculture has created concerns about soil degradation and toxicity of agricultural chemicals to non-target organisms. As a result, there is great urgency for discovering new ecofriendly tools for pest management and plant nutrition. Botanical matrices and their extracts and purified secondary metabolites have received much research interest, but time-consuming registration issues have slowed their adoption. In contrast, cultural practices such as use of plant matrices as soil amendments could be immediately used as plant protectants or organic fertilizers. Herein, we focus on some types of soil amendments of botanical origin and their utilization for nematicidal activity and enhancement of plant nutrition. The mode of action is discussed in terms of parasite control as well as plant growth stimulation.

Agricultural and Other Biotechnological Applications Resulting from Trophic Plant-Endophyte Interactions

Endophytic microbiota plays a role not only in supplying plants with the basic nutrients indispensable for their growth, but also helps them in the mechanisms of adaptation to various environmental stresses (i.e., salinity, drought), which is important in the aspect of crop yields. From the agricultural and biotechnological points of view, the knowledge of endophytes and their roles in increasing crop yields, plant resistance to diseases, and helping to survive environmental stress is extremely desirable. This paper reviews some of the beneficial plant–microbe interactions that might be potentially used in both agriculture (plant growth stimulation effect, adaptation of host organisms in salinity and drought conditions, and support of defense mechanisms in plants), and in biotechnology (bioactive metabolites, application of endophytes for bioremediation and biotransformation processes, and production of biofertilizers and biopreparations). Importantly, relatively recent reports on endophytes from the last 10 years are summarized in this paper.