Arbuscular mycorrhizal fungi associated with the rhizosphere of an endemic terrestrial bromeliad and a grass in the Brazilian neotropical dry forest.

Arbuscular mycorrhizal fungi form symbiotic associations with 80-90% of all known plants, allowing the fungi to acquire plant-synthesized carbon, and confer an increased capacity for nutrient uptake by plants, improving tolerance to abiotic and biotic stresses. We aimed at characterizing the mycorrhizal community in the rhizosphere of Neoglaziovia variegata (so-called `caroa`) and Tripogonella spicata (so-called resurrection plant), using high-throughput sequencing of the partial 18S rRNA gene. Both plants are currently undergoing a bioprospecting program to find microbes with the potential of helping plants tolerate water stress. Sampling was carried out in the Caatinga biome, a neotropical dry forest, located in northeastern Brazil. Illumina MiSeq sequencing of 37 rhizosphere samples (19 for N. variegata and 18 for T. spicata) revealed a distinct mycorrhizal community between the studied plants. According to alpha diversity analyses, T. spicata showed the highest richness and diversity based on the Observed ASVs and the Shannon index, respectively. On the other hand, N. variegata showed higher modularity of the mycorrhizal network compared to T. spicata. The four most abundant genera found (higher than 10%) were Glomus, Gigaspora, Acaulospora, and Scutellospora, with Glomus being the most abundant in both plants. Nonetheless, Gigaspora, Diversispora, and Ambispora were found only in the rhizosphere of N. variegata, whilst Scutellospora, Paraglomus, and Archaeospora were exclusive to the rhizosphere of T. spicata. Therefore, the community of arbuscular mycorrhizal fungi of the rhizosphere of each plant encompasses a unique composition, structure and modularity, which can differentially assist them in the hostile environment.

Impact of Water Shortage on Soil and Plant Attributes in the Presence of Arbuscular Mycorrhizal Fungi from a Harsh Environment.

Arbuscular mycorrhizal fungi (AMF) play a crucial role in plant health due to their ability to improve tolerance to biotic and abiotic stresses. Our aim was to evaluate the effectiveness of a pool of native AMF from a harsh environment on plant performance and changes in soil attributes under different levels of drought. An experiment using maize was established, varying the soil water content to simulate severe drought (30% of the water-holding capacity [WHC]), moderate (50% of the WHC) and no drought (80% of the WHC, control treatment). Soil and plant attributes were measured (enzyme activity, microbial biomass, AMF root colonisation and plant biomass and nutrient uptake). There was a two-fold increase in plant biomass under moderate drought when compared to no drought treatment, but there was no difference in nutrient uptake. Under severe drought, there were the highest enzyme activities related to phosphorus (P) cycling and P microbial biomass, indicating higher P microbial immobilization. The increase in AMF root colonisation was observed in plants under moderate and no drought. Our findings demonstrated that the better use of the AMF inoculum varied according to drought levels, with better performance under moderate drought due to the increase in plant biomass.

Potential of growth-promoting bacteria in maize (Zea mays L.) varies according to soil moisture.

Climate change has caused irregularities in water distribution, which affect the soil drying-wetting cycle and the development of economically important agricultural crops. Therefore, the use of plant growth-promoting bacteria (PGPB) emerges as an efficient strategy to mitigate negative impacts on crop yield. We hypothesized that the use of PGPB (in consortium or not) had potential to promote maize (Zea mays L.) growth under a soil moisture gradient in both non-sterile and sterile soils. Thirty PGPB strains were characterized for direct plant growth-promotion and drought tolerance induction mechanisms and were used in two independent experiments. Four soil water contents were used to simulate a severe drought (30% of field capacity [FC]), moderate drought (50% of FC), no drought (80% of FC) and, finally, a water gradient comprising the three mentioned soil water contents (80%, 50%, and 30% of FC). Two bacteria strains (BS28-7 Arthrobacter sp. and BS43 Streptomyces alboflavus), in addition to three consortia (BC2, BC4 and BCV) stood out in maize growth performance in experiment 1 and were used in experiment 2. Overall, under moderate drought, inoculation with BS43 surpassed the control treatment in root dry mass and nutrient uptake. Considering the water gradient treatment (80-50-30% of FC), the greatest total biomass was found in the uninoculated treatment when compared to BS28-7, BC2, and BCV. The greatest development of Z. mays L. was only observed under constant water stress conditions in the presence of PGPB. This is the first report that demonstrated the negative effect of individual inoculation of Arthrobacter sp. and the consortium of this strain with Streptomyces alboflavus on the growth of Z. mays L. based on a soil moisture gradient; however, future studies are needed for further validation.

Does Organomineral Fertilizer Combined with Phosphate-Solubilizing Bacteria in Sugarcane Modulate Soil Microbial Community and Functions?

Soil bacterial and fungal communities are suitable soil ecosystem health indicators due to their sensitivity to management practices and their role in soil ecosystem processes. Here, information on composition and functions of bacterial and fungal communities were evaluated at two phenological stages of sugarcane (six and twelve months, equivalent to the most intensive vegetative stage and to final maturation, respectively) when organomineral fertilizer, combined with phosphate-solubilizing bacteria (PSB), was added into the soil. Organic compost enriched with apatite (C + A) or phosphorite (C + P) and compost without phosphate enrichment (C) were used in the presence or absence of PSB. In addition, we used a control fertilized with soluble triple superphosphate. The differences were more related to the sampling period than to the type of organomineral fertilizer, being observed higher available phosphorus at six months than at twelve months. Only in the C treatment we observed the presence of Bacillaceae and Planococcaceae, while Pseudomonadaceae were only prevalent in inoculated C + A. As for fungi, the genera Chaetomium and Achroiostachys were only present in inoculated C + P, while the genus Naganishia was most evident in inoculated C + A and in uninoculated C + P. Soliccocozyma represented 75% of the total fungal abundance in uninoculated C while in inoculated C, it represented 45%. The bacterial community was more related to the degradation of easily decomposable organic compounds, while the fungal community was more related to degradation of complex organic compounds. Although the microbial community showed a resilient trait, subtle changes were detected in microbial community composition and function, and this may be related to the increase in yield observed.

Arbuscular Mycorrhizal Fungi and Soil Quality Indicators in Eucalyptus genotypes With Different Drought Tolerance Levels.

Silviculture has great importance worldwide, and the use of Eucalyptus species, which account for 75% of the local planted forest in Brazil, is one of the factors that contributes to the success of this activity in the country. Despite its adaptability, the yield of Eucalyptus is often affected by climate change, particularly water deficiency. Plants have developed strategies to mitigate water stress, for example, through their association with mycorrhizal fungi. The genus Eucalyptus, particularly in the plant domain, establishes symbioses with arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (ECMF). The influence of Eucalyptus species on AMF and soil quality indicators is not well understood. Our aim was to conduct a preliminary evaluation of the various responses of soil AMF communities and soil nutrient dynamics in the presence of Eucalyptus species with different degrees of drought tolerance. A field experiment was established containing six Eucalyptus species, E. brassiana, E. camaldulensis, E. citriodora, E. cloeziana, E. grandis, and E. urophylla, all of which were planted in large plots. Soil and root samples were taken when the plants were 1.7 and 2.2 years old. We found that Eucalyptus species with low (E. grandis and E. urophylla) and intermediate drought tolerance (E. citriodora and E. cloeziana) showed stronger correlations with the AMF community than Eucalyptus species with high drought tolerance (E. brassiana and E. camaldulensis). Differences were also found between Eucalyptus species for AMF spore numbers and root colonization percentages, which was most evident for E. urophylla. The microbiological attributes found to be most responsive to Eucalyptus species were soil enzyme activities, AMF spore numbers, root colonization percentages, and fungal abundance. Soil organic carbon, phosphorus, potassium, zinc, copper, and iron were the main chemical drivers related to the soil AMF community structure in the presence of E. brassiana.