Effect of Pyroligneous Acid on the Microbial Community Composition and Plant Growth-Promoting Bacteria (PGPB) in Soils

Pyroligneous acid (PA) is often used in agriculture as a plant growth and yield enhancer. However, the influence of PA application on soil microorganisms is not often studied. Therefore, in this study, we investigated the effect of PA (0.01–5% w/w in soil) on the microbial diversity in two different soils. At the end of eight weeks of incubation, soil microbial community dynamics were determined by Illumina-MiSeq sequencing of 16S rRNA gene amplicons. The microbial composition differed between the lower (0.01% and 0.1%) and the higher (1% and 5%) concentration in both PA spiked soils. The lower concentration of PA resulted in higher microbial diversity and dehydrogenase activity (DHA) compared to the un-spiked control and the soil spiked with high PA concentrations. Interestingly, PA-induced plant growth-promoting bacterial (PGPB) genera include Bradyrhizobium, Azospirillum, Pseudomonas, Mesorhizobium, Rhizobium, Herbaspiriluum, Acetobacter, Beijerinckia, and Nitrosomonas at lower concentrations. Additionally, the PICRUSt functional analysis revealed the predominance of metabolism as the functional module’s primary component in both soils spiked with 0.01% and 0.1% PA. Overall, the results elucidated that PA application in soil at lower concentrations promoted soil DHA and microbial enrichment, particularly the PGPB genera, and thus have great implications for improving soil health.

Teamwork to Survive in Hostile Soils: Use of Plant Growth-Promoting Bacteria to Ameliorate Soil Salinity Stress in Crops

Plants and their microbiomes, including plant growth-promoting bacteria (PGPB), can work as a team to reduce the adverse effects of different types of stress, including drought, heat, cold, and heavy metals stresses, as well as salinity in soils. These abiotic stresses are reviewed here, with an emphasis on salinity and its negative consequences on crops, due to their wide presence in cultivable soils around the world. Likewise, the factors that stimulate the salinity of soils and their impact on microbial diversity and plant physiology were also analyzed. In addition, the saline soils that exist in Mexico were analyzed as a case study. We also made some proposals for a more extensive use of bacterial bioinoculants in agriculture, particularly in developing countries. Finally, PGPB are highly relevant and extremely helpful in counteracting the toxic effects of soil salinity and improving crop growth and production; therefore, their use should be intensively promoted.

İklim Değişikliğinin Bitki-Faydalı Mikroorganizma Etkileşimleri Üzerindeki Etkileri

Global climate is estimated to change drastically over the next century and the ecosystems will be affected in this changing environment. Plant-associated beneficial microorganisms can stimulate plant growth and increase resistance to biotic and abiotic stresses. Nowadays, the effects of climate change factors such as increased carbon dioxide (CO2), drought and warming on plant-beneficial microorganism interactions are increasingly being investigated in the scope of plant growth and health. Recent studies have shown that high CO2 level has a positive effect on the abundance of mycorrhizal fungi, whereas the effects on plant growth promoting bacteria and endophytic fungi are more variable. Elevated CO2 conditions lead to increased colonization of beneficial fungi. Additionally, the results of increasing CO2 levels, warming and drought, depend upon the plant and the microbial genotype. Also, plant growth promoting microorganisms, especially bacteria, positively affect plants exposed to drought stress. Altered communities of beneficial microorganisms depending on climate changes, might have to compete with different microbial communities and, therefore microbial activities may also get affected. This work presents that climate change is an important factor affecting microorganism and plant interactions, needs to take into consideration the adaptation processes in plants and microorganisms and might require the selection of adapted plant cultivars.

Plant Growth-Promoting Bacteria Associated with the Nests of the Seed-Harvester Ant, Trichomyrmex Scabriceps

Colonies of seed harvester ants are commonly found in semiarid and arid areas of the world and have been studied for their seed dispersal behaviour. The present study focused on the bacteria associated with the nests of the harvester ant, Trichomyrmex scabriceps, and reveals that ant colonies link the aboveground resources with the belowground microbial communities as they accumulate organic debris in the close vicinity of their nests via their ecosystem engineering activities. Soil samples were collected from the nest chambers and the external debris piles of T. scabriceps colonies, located in managed ecosystems. The nest soil-associated bacteria were examined for their plant growth-promoting abilities via biochemical assays including phosphate solubilization, Indole acetic acid production, siderophore production and physiological assays including biocontrol potential against the soil pathogen, Sclerotium rolfsii. More than 60% of bacteria isolated from the ant nest-associated soil displayed plant-growth promoting ability. Bacillus sp., Azotobacter sp., Klebsiella sp., Comamonas sp., Tsukamurella sp., and Pseudoxanthomonax sp., demonstrated significantly high levels of gnotobiotic growth of the treated chickpea plants. The activities of phenylalanine ammonia-lyase and peroxidase enzymes were higher in plant growth-promoting bacteria treated and pathogen inoculated plants as compared to the control plants lacking the bacteria. Since T. scabriceps colonies often make their nests in the compact soil of unpaved paths of agroecosystems and gardens, these bacteria can act as highly effective biofertilizers and promote growth of the cultivated plants by increasing soil fertility and disease resistance attributes of the plant.

Halotolerant Rhizobacteria for Salinity-Stress Mitigation: Diversity, Mechanisms and Molecular Approaches

Agriculture is the best foundation for human livelihoods, and, in this respect, crop production has been forced to adopt sustainable farming practices. However, soil salinity severely affects crop growth, the degradation of soil quality, and fertility in many countries of the world. This results in the loss of profitability, the growth of agricultural yields, and the step-by-step decline of the soil nutrient content. Thus, researchers have focused on searching for halotolerant and plant growth-promoting bacteria (PGPB) to increase soil fertility and productivity. The beneficial bacteria are frequently connected with the plant rhizosphere and can alleviate plant growth under salinity stress through direct or indirect mechanisms. In this context, PGPB have attained a unique position. The responses include an increased rate of photosynthesis, high production of antioxidants, osmolyte accumulation, decreased Na+ ions, maintenance of the water balance, a high germination rate, and well-developed root and shoot elongation under salt-stress conditions. Therefore, the use of PGPB as bioformulations under salinity stress has been an emerging research avenue for the last few years, and applications of biopesticides and biofertilizers are being considered as alternative tools for sustainable agriculture, as they are ecofriendly and minimize all kinds of stresses. Halotolerant PGPB possess greater potential for use in salinity-affected soil as sustainable bioinoculants and for the bioremediation of salt-affected soil.

Poly-γ-glutamic acid enhanced the drought resistance of maize by improving photosynthesis and affecting the rhizosphere microbial community

Background Compared with other abiotic stresses, drought stress causes serious crop yield reductions. Poly-γ-glutamic acid (γ-PGA), as an environmentally friendly biomacromolecule, plays an important role in plant growth and regulation. Results In this project, the effect of exogenous application of γ-PGA on drought tolerance of maize (Zea mays. L) and its mechanism were studied. Drought dramatically inhibited the growth and development of maize, but the exogenous application of γ-PGA significantly increased the dry weight of maize, the contents of ABA, soluble sugar, proline, and chlorophyll, and the photosynthetic rate under severe drought stress. RNA-seq data showed that γ-PGA may enhance drought resistance in maize by affecting the expression of ABA biosynthesis, signal transduction, and photosynthesis-related genes and other stress-responsive genes, which was also confirmed by RT–PCR and promoter motif analysis. In addition, diversity and structure analysis of the rhizosphere soil bacterial community demonstrated that γ-PGA enriched plant growth promoting bacteria such as Actinobacteria, Chloroflexi, Firmicutes, Alphaproteobacteria and Deltaproteobacteria. Moreover, γ-PGA significantly improved root development, urease activity and the ABA contents of maize rhizospheric soil under drought stress. This study emphasized the possibility of using γ-PGA to improve crop drought resistance and the soil environment under drought conditions and revealed its preliminary mechanism. Conclusions Exogenous application of poly-γ-glutamic acid could significantly enhance the drought resistance of maize by improving photosynthesis, and root development and affecting the rhizosphere microbial community.