Shifts in the Rhizosphere and Endosphere Colonizing Bacterial Communities Under Drought and Salinity Stress as Affected by a Biofertilizer Consortium

Abstract

The present research asks how plant growth-promoting bacterial (PGPB) inoculants and chemical fertilizers change rhizosphere and root endophytic bacterial communities in durum wheat, and its dependence on environmental stress. A greenhouse experiment was carried out under drought (at 40% field capacity), or salinity (150 mM NaCl) conditions to investigate the effects of a chemical fertilizer (containing nitrogen, phosphorus, potassium and zinc) or a biofertilizer (a bacterial consortium of four PGPBs). High-throughput amplicon sequencing of the 16S rRNA of the rhizosphere, non-sterilized, or surfacesterilized roots, showed shifts in bacterial communities in response to stress treatments, which were greater for salinity than for drought and tended to show increased oligotrophs relative abundances compared to non-stress controls. The results also showed that Proteobacteria, Acidobacteria, Bacteroidetes, Gemmatimonadetes, Thaumarchaeota, Firmicutes, and Verrucomicrobia had a higher relative abundance in the rhizosphere, while Actinobacteria were more abundant on roots, while Candidatus_Saccharibacteria and Planctomycetes inside roots. The results indicated that the root endophytic bacterial communities were more affected by (bio-) fertilization treatments than those in the rhizosphere, particularly as affected by PGPB inoculation. This greater susceptibility of endophytes to (bio-) fertilizers was associated with increased abundance of the 16S rRNA and acdS genes in plant roots, especially under stress conditions. These changes in root endophytes, which coincided with an improvement in grain yield and photosynthetic capacity of plants, may be considered as one of the mechanisms by which PGPB affect plants.

Earthworm-Driven Changes in Soil Chemico-Physical Properties, Soil Bacterial Microbiota, Tree/Tea Litter Decomposition, and Plant Growth in a Mesocosm Experiment with Two Plant Species

“…The outcome of the analyses of Bacteria α - and β -diversity for each plant species showed that bacterial community structure shifts were more pronounced for broccoli than for faba bean, especially in the presence of earthworms ( Figure 3 and Figure 4 ). Yaghoubi Khanghahi et al [ 34 ] found that a different plant phenotypic response provides an altered habitat, probably via adjusted root architecture. In our study, these effects were more pronounced in soils with broccoli, with a thin, deep, and dense taproot, compared to faba bean, which has shallow, diffuse, and longer roots [ 4 ].…”

Biofertilisation with a consortium of growth‐promoting bacterial strains improves the nutritional status of wheat grain under control, drought, and salinity stress conditions

“…It has been previously reported that plants growing in alkaline soils secrete organic acids, particularly citrate, from their roots to absorb nutrients such as phosphorus and iron by lowering the pH of the rhizosphere (Tahjib‐Ul‐Arif et al, 2021). This can explain the higher citrate levels in no fertilisation and chemical fertiliser treatments since the soils of southern Italy are slightly alkaline (pH > 8) (Yaghoubi Khanghahi et al, 2021b). The observed decrease in citrate content in treatments containing biofertilisers (BC and BC + ½CF), could be attributed to the nativeness of our beneficial bacteria and their adaptation to the conditions of high pH calcareous soils, which, by providing the necessary nutrients, eliminates the need for the plant to produce more of these organic acids.…”

“…Our earlier study showed that under non‐stress conditions, PGPB inoculation enhanced grain yield to a smaller degree than treatment with chemical fertilisers, while under stress conditions, they tended to be at least as effective. These results suggested that, in contrast to chemical fertilisation, the microbial consortium is able to activate stress tolerance mechanisms (Yaghoubi Khanghahi et al, 2021b).…”

“…These bacterial strains showed a promising ability, not only in transforming the insoluble complexes of phosphate, potassium, and zinc to soluble forms and biological fixing of nitrogen in vitro conditions, respectively (Yaghoubi Khanghahi et al, 2021c), but also in improving some agronomic and physiological parameters of durum wheat plants in a greenhouse experiment (Yaghoubi Khanghahi et al, 2021a). Also, it was determined how the application of these beneficial bacterial strains, as bio‐inoculant, shaped the rhizosphere and root‐associated bacterial communities under stress (Yaghoubi Khanghahi et al, 2021b). Apart from the previous investigation on the physiological and molecular changes in the roots and leaves in stressed plants in response to the bio‐inoculation, the debate about plant grains, as an important source of dietary nutrients, has also gained fresh prominence, especially since their metabolic compounds in response to biofertiliser have not been addressed in a comprehensive study, so far.…”

The Effect of Date Palm Genotypes on Rhizobacterial Community Structures under Saline Environments

“…Consistently, a study carried out by Canfora, et al [ 37 ] showed a decreasing abundance of Acidobacteria as soil salinity increased. The high abundance of Planctomycetes in saline treatment could be explained by their aquatic nature, consistent with them being mainly found in brackish, marine, and freshwater [ 38 , 39 ]. The results also showed trace amounts of Chlamydae in the “Umsila” control libraries and in one “Zabad” treated library.…”