Mixed growth of Salix species can promote phosphate-solubilizing bacteria in the roots and rhizosphere

Functional Characterization of Core and Unique Calcite-Dissolving Bacteria Communities from Peanut Fields

Calcium deficiency is a leading cause of reduced peanut (Arachis hypogaea) seed quality and has been linked to increased disease susceptibility, specifically to soilborne fungal pathogens. Sufficient calcium at flowering time is critical to ensure proper pod development. Calcite-dissolving bacteria (CDB) isolated from farming fields can dissolve calcite (CaCO3) on plates and increase soluble calcium levels in soil. However, the phylogenetic diversity and geographic distribution of CDB is unclear. Here, we surveyed soil samples from 15 peanut-producing fields in three regions in southern Georgia, representing distinct soil compositions. We isolated CDB through differentiating media and identified 52 CDB strains. CDB abundance was not associated with any of the soil characteristics we evaluated. Three core genera, represented by 43 strains, were found in all three regions. Paenibacillus was the most common CDB found in all regions, making up 30 of the 52 identified strains. Six genera, represented by eight strains, are unique to one region. Members of the core and unique communities showed comparable solubilization indexes on plates. We conclude that a diversified phylogenetic population of CDB is present in Georgia peanut fields. Despite the phylogenetic diversity, as a population, they exhibit comparable functions in solubilizing calcite on plates.

Endophytic microbiota and ectomycorrhizal structure of Alnus glutinosa Gaertn. at saline and nonsaline forest sites

The tolerance of European alder (Alnus glutinosa Gaertn.) to soil salinity can be attributed to symbiosis with microorganisms at the absorptive root level. However, it is uncertain how soil salinity impacts microbial recruitment in the following growing season. We describe the bacterial and fungal communities in the rhizosphere and endosphere of A. glutinosa absorptive roots at three tested sites with different salinity level. We determined the morphological diversity of ectomycorrhizal (ECM) fungi, the endophytic microbiota in the rhizosphere, and the colonization of new absorptive roots in the following growing season. While bacterial diversity in the rhizosphere was higher than that in the absorptive root endosphere, the opposite was true for fungi. Actinomycetota, Frankiales, Acidothermus sp. and Streptomyces sp. were more abundant in the endosphere than in the rhizosphere, while Actinomycetota and Acidothermus sp. dominated at saline sites compared to nonsaline sites. Basidiomycota, Thelephorales, Russulales, Helotiales, Cortinarius spp. and Lactarius spp. dominated the endosphere, while Ascomycota, Hypocreales and Giberella spp. dominated the rhizosphere. The ECM symbioses formed by Thelephorales (Thelephora, Tomentella spp.) constituted the core community with absorptive roots in the spring and further colonized new root tips during the growing season. With an increase in soil salinity, the overall fungal abundance decreased, and Russula spp. and Cortinarius spp. were not present at all. Similarly, salinity also negatively affected the average length of the absorptive root. In conclusion, the endophytic microbiota in the rhizosphere of A. glutinosa was driven by salinity and season, while the ECM morphotype community was determined by the soil fungal community present during the growing season and renewed in the spring.

Large effect of phosphate-solubilizing bacteria on the growth and gene expression of Salix spp. at low phosphorus levels

Phosphorus is one of the most important nutrients required for plant growth and development. However, owing to its low availability in the soil, phosphorus is also one of the most difficult elements for plants to acquire. Phosphorus released into the soil from bedrock quickly becomes unavailable to plants, forming poorly soluble complexes. Phosphate-solubilizing bacteria (PSB) can solubilize unavailable phosphorus-containing compounds into forms in which phosphorus is readily available, thus promoting plant growth. In this study, two willow species, Salix dasyclados cv. Loden and Salix schwerinii × Salix viminalis cv. Tora, were inoculated with two selected bacterial strains, Pantoea agglomerans and Paenibacillus spp., to evaluate the plant growth parameters and changes in gene expression in the presence of different concentrations of tricalcium phosphate: 0 mM (NP), 1 mM (LP), and 2 mM (HP). Inoculation with PSB increased root, shoot and leaf biomass, and for the HP treatment, significant changes in growth patterns were observed. However, the growth responses to plant treatments tested depended on the willow species. Analysis of the leaf transcriptomes of the phosphate-solubilizing bacterium-inoculated plants showed a large variation in gene expression between the two willow species. For the Tora willow species, upregulation of genes was observed, particularly for those involved in pathways related to photosynthesis, and this effect was strongly influenced by bacterial phosphate solubilization. The Loden willow species was characterized by a general downregulation of genes involved in pathway activity that included ion transport, transcription regulation and chromosomes. The results obtained in this study provide an improved understanding of the dynamics of Salix growth and gene expression under the influence of PSB, contributing to an increase in yield and phosphorus-use efficiency.