Soil Inoculation With Beneficial Microbes Buffers Negative Drought Effects on Biomass, Nutrients, and Water Relations of Common Myrtle

Soil microbiome transplantation to enhance the drought response of Salvia officinalis L

Introduction

Soil microbiome transplantation is a promising technique for enhancing plant holobiont response to abiotic and biotic stresses. However, the rapid assessment of microbiome-plant functional integration in short-term experiments remains a challenge.

Methods

This study investigates the potential of three evergreen sclerophyll species, Pistacia lentiscus (PL), Rosmarinus officinalis (RO), and Juniperus phoenicea (JP), to serve as a reservoir for microbial communities able to confer enhanced tolerance to drought in Salvia officinalis cultivated under water shortage, by analyzing biomass production, plant phenotype, plant ecophysiological responses, and leaf metabolome.

Results

Our results showed that the inoculation with the three rhizomicrobiomes did not enhance total plant biomass, while it significantly influenced plant architecture, ecophysiology, and metabolic responses. The inoculation with the JP rhizomicrobiome led to a significant increase in root biomass, resulting in smaller leaves and a higher leaf number. These morphological changes suggest improved water acquisition and thermoregulation strategies. Furthermore, distinct stomatal conductance patterns were observed in plants inoculated with microbiomes from PJ and PL, indicating altered responses to drought stress. The metabolome analysis demonstrated that rhizomicrobiome transplantation significantly influenced the leaf metabolome of S. officinalis. All three rhizomicrobiomes promoted the accumulation of phenolic compounds, terpenoids, and alkaloids, known to play crucial roles in plant defense and stress response. Five molecules (genkwanin, beta-ionone, sumatrol, beta-peltatin-A-methyl ester, and cinnamoyl-beta-D-glucoside) were commonly accumulated in leaves of inoculated sage, independently of the microbiome. Furthermore, unique metabolic alterations were observed depending on the specific inoculated rhizomicrobiome, highlighting the specialized nature of plant-microbe interactions and the possible use of these specific molecules as biomarkers to monitor the recruitment of beneficial microorganisms.

Discussion

This study provides compelling evidence that microbiome transplantation can induce phenotypic and metabolic changes in recipient plants, potentially enhancing their resilience to water scarcity. Our findings emphasize the importance of considering multiple factors, including biomass, physiology, and metabolomics, when evaluating the effectiveness of microbiome engineering for improving plant stress tolerance.

Enterobacter-inoculation altered the C, N contents and regulated biomass allocation in Reaumuria soongorica to promote plant growth and improve salt stress tolerance

Soil salinization poses a significant ecological and environmental challenge both in China and across the globe. Plant growth-promoting rhizobacteria (PGPR) enhance plants' resilience against biotic and abiotic stresses, thereby playing a vital role in soil improvement and vegetation restoration efforts. PGPR assist plants in thriving under salt stress by modifying plant physiology, enhancing nutrient absorption, and synthesizing plant hormones. However, the mechanisms through which PGPR regulate the contents of carbon (C) and nitrogen (N), and biomass allocation of desert plant in response to salt stress is still unclear. This study explores the impact of PGPR on biomass allocation, C, and N contents of R. soongorica seedlings through a pot experiment. Strains P6, N20, and N21, identified as Enterobacter, were isolated from the rhizosphere of R. soongorica, and they exhibited various beneficial traits such as indole-3-acetic acid (IAA) production, phosphate solubilization, nitrogen fixation, and tolerance to up to 8% NaCl stress. We found that under NaCl stress, R. soongorica seedlings exhibit significant reductions in plant height, basal diameter, and root surface area (P<0.05). However, inoculation with strains P6, N20, and N21 reverses these trends. Compared to NaCl treatment alone, co-treatment with these strains significantly increases the biomass of roots, stems, and leaves, particularly root biomass, which increases by 99.88%, 85.55%, and 141.76%, respectively (P<0.05). Moreover, N contents decrease significantly in the roots, stems and leaves, C contents increase significantly in the roots and leaves compared to NaCl treatment (P<0.05). Specifically, N contents in roots decrease by 14.50%, 12.47%, and 8.60%, while C contents in leaves increase by 4.96%, 4.45%, and 4.94%, respectively (P<0.05). Additionally, stem and leaf biomasses exhibit a significant positive correlation with C contents and a significant negative correlation with N contents in these tissues. In conclusion, inoculation of Enterobacter strains enhanced the biomass of R. soongorica seedlings, regulated the biomass distribution, and modifies C and N contents to promote plant growth and improve salt stress tolerance. This study provides a novel adaptive strategy for the integrated use of PGPR and halophytes in saline-alkali soil improvement and vegetation restoration efforts.

Chasmophyte associated stress tolerant bacteria confer drought resilience to chickpea through efficient nutrient mining and modulation of stress response

In the present study, ten (10) selected bacteria isolated from chasmophytic wild Chenopodium were evaluated for alleviation of drought stress in chickpea. All the bacterial cultures were potential P, K and Zn solubilizer. About 50% of the bacteria could produce Indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. The bacteria showed wide range of tolerance towards pH, salinity, temperature and osmotic stress. Bacillus paralicheniformis L38, Pseudomonas sp. LN75, Enterobacter hormachei subsp. xiangfengensis LJ89, B. paramycoides L17 and Micrococcus luteus LA9 significantly improved growth and nutrient (N, P, K, Fe and Zn) content in chickpea under water stress during a green house experiment conducted following a completely randomized design (CRD). Application of Microbacterium imperiale LJ10, B. stercoris LN74, Pseudomonas sp. LN75, B. paralicheniformis L38 and E. hormachei subsp. xiangfengensis LJ89 reduced the antioxidant enzymes under water stress. During field experiments conducted following randomized block design (RBD), all the bacterial inoculations improved chickpea yield under water stress. Highest yield (1363 kg ha-1) was obtained in plants inoculated with Pseudomonas sp. LN75. Pseudomonas sp. LN75, B. paralicheniformis L38 and E. hormachei subsp. xiangfengensis LJ89 have potential as microbial stimulants to alleviate the water stress in chickpea. To the best of our knowledge this is the first report of using chasmophyte associated bacteria for alleviation of water stress in a crop plant.

Phytostimulants in sustainable agriculture

The consistent use of synthetic fertilizers and chemicals in traditional agriculture has not only compromised the fragile agroecosystems but has also adversely affected human, aquatic, and terrestrial life. The use of phytostimulants is an alternative eco-friendly approach that eliminates ecosystem disruption while maintaining agricultural productivity. Phytostimulants include living entities and materials, such as microorganisms and nanomaterials, which when applied to plants or to the rhizosphere, stimulate plant growth and induce tolerance to plants against biotic and abiotic stresses. In this review, we focus on plant growth-promoting rhizobacteria (PGPR), beneficial fungi, such as arbuscular mycorrhizal fungi (AMF) and plant growth-promoting fungi (PGPF), actinomycetes, cyanobacteria, azolla, and lichens, and their potential benefits in the crop improvement, and mitigation of abiotic and biotic stresses either alone or in combination. PGPR, AMF, and PGPF are plant beneficial microbes that can release phytohormones, such as indole acetic acid (IAA), gibberellic acid (GA), and cytokinins, promoting plant growth and improving soil health, and in addition, they also produce many secondary metabolites, antibiotics, and antioxidant compounds and help to combat biotic and abiotic stresses. Their ability to act as phytostimulator and a supplement of inorganic fertilizers is considered promising in practicing sustainable agriculture and organic farming. Glomalin is a proteinaceous product, produced by AMF, involved in soil aggregation and elevation of soil water holding capacity under stressed and unstressed conditions. The negative effects of continuous cropping can be mitigated by AMF biofertilization. The synergistic effects of PGPR and PGPF may be more effective. The mechanisms of control exercised by PGPF either direct or indirect to suppress plant diseases viz. by competing for space and nutrients, mycoparasitism, antibiosis, mycovirus-mediated cross-protection, and induced systemic resistance (ISR) have been discussed. The emerging role of cyanobacterial metabolites and the implication of nanofertilizers have been highlighted in sustainable agriculture.