Soil Microbiome Metabolomics: A Way Forward to Sustainable Intensification

Introduction: Wheat (Triticum aestivum L.) is a strategic crop and one of the world's most essential cereals, providing most of the world's calories and protein needs. Drought stress is one of the main limitations for crop production such as wheat in arid and semi-arid regions. Plants can accumulate antioxidants, carbohydrates, and stress hormones that stimulate cell and molecular regeneration under stress conditions. Irrigation saves water, improves crop photosynthesis, and increases plant ability to absorb water and elements from soil. Therefore, irrigation at the right time or supplementary irrigation can help plant growth and crop yield under drought conditions. Appropriate nutrition with fertilizers increases plants' stress tolerance. Bio-fertilizers are restorative elements used in soil to improve tolerance to stresses such as drought stress. A well-known class of bio-fertilizers is plant growth promoting rhizobacteria (PGPR). These rhizosphere bacteria affect plant development and productivity by interacting with roots. Arbuscular mycorrhizal fungi (AMF) alleviate drought stress in plants by enhancing their ability to absorb water and nutrients from the soil. Seaweed extract bio-fertilizer is organic matter used to increase crop growth and soil fertility. This bio-fertilizer is utilized as growth stimulants and food supplements. Our research analyzed the effects of rhizobia and seaweed extracts on wheat's drought resistance mechanisms.

Materials and methods: This research was conducted in Iran in the crop years of 2017–2018 and 2018–2019 in the research farm of Kurdistan University Faculty of Agriculture located in Dehgolan with coordinates 47°18′ 55″ East and 35°19′ 10″ North with an altitude of 1866 meters above sea level, 45 kilometers east It was done on the wheat plant in Sanandaj city. The experiment was conducted in the form of a split-split plot in the form of a randomized complete block design with four replications. Irrigation treatments as the main factor (no irrigation or dry-land, one irrigation in the booting stage, two irrigations in the booting and spike stages), two wheat cultivars (Sardari and Sirvan) as secondary factors, and the application of biological fertilizers at eight levels including Mycorrhiza + Nitrozist and Phosphozist, Seaweed extract + Nitrozist and Phosphozist, Mycorrhiza + Seaweed extract, Mycorrhiza + Nitrozist and Phosphozist and no application of biological fertilizers (control) as Sub-sub-factors were considered.

Results and discussion: According to the study, when bio-fertilizer was applied with once and twice supplementary irrigation levels, leaf relative water content (RWC) and soluble protein content (SPC) increased, while lack of irrigation increased malondialdehyde (MDA). In both years, bio-fertilizers, especially their combinations, increased the amount and activity of enzymatic and non-enzymatic antioxidants, including peroxidase (POD), superoxide dismutase (SOD), phenol (Phe), flavonoid (Fla), and anthocyanin (Anth). Also, it enhanced the inhibition of free radicals by 2-2-Diphenyl picryl hydrazyl (DPPH) and cleared active oxygen species. It was found that malondialdehyde (MDA) levels were very low in wheat under two times irrigation with averages of 3.3909 and 3.3865 μmol g⁻¹ FW. The results indicated a significant positive relationship between non-enzymatic and enzymatic antioxidants such as Phe, Fla, Anth, DPPH, POD, and SOD enzymes and their role in improving stress under dry-land conditions, especially in the Sardari variety. Biological fertilizers (Mycorrhiza + Nitrozist and Phosphozist + Seaweed extract) increased wheat yield compared to the control. Furthermore, Mycorrhiza + Nitrozist and Phosphozist + Seaweed extract improved grain yield by 8.04% and 6.96% in the 1st and 2nd years, respectively. Therefore, appropriate combinations of microorganisms, beneficial biological compounds, and supplementary irrigation can reduce the adverse effects of drought stress in arid and semi-arid regions.

Phosphate solubilizing microbes (PSM) can improve soil P availability by P dissolution. These microbes can make substances that regulate plant growth, which promotes plant growth. The present study aimed to characterize PSM and determine how PSM application affected P solubilization, soil phosphatase activity, and upland rice yield. The greenhouse experiment used a factorial randomized block design (RBD) with two factors and three replications. The first factor was PSM isolates, which came in four different forms: without microbes, with microbes (Burkholderia sp.), with fungus (Penicillium sp.), and with a combination of microbes (Burkholderia sp. and Penicillium sp.). The PSM isolates were characterized to analyze the production of organic acids, phosphatase enzymes, and phytohormones. The second factor was the superphosphate fertilizer dose, which has four levels: 0, 50, 75, and 100 kg P ha⁻¹. According to the PSM characterization, it produced organic acids such as lactate acid, oxalate acid, citric acid, and acetate acid, as well as phytohormones (IAA) and the enzyme phosphatase. The pot experiment results show that the PSM inoculation raised the available P and soil phosphatase, P content of the plant, decreased soil organic P, and increased upland rice production. For improving available P, phosphatase activity, P content of the plant, and upland rice yields, mixed inoculants of phosphate-solubilizing bacteria and fungi performed better. The availability of soil P, the activity of the enzyme phosphatase, and the upland rice yields were all improved by applying P fertilizer at 75 kg P ha⁻¹. This study showed that PSM as a biofertilizer reduced the dosage of inorganic fertilizers by up to 25%.