Phosphate solubilizing bacteria stimulate wheat rhizosphere and endosphere biological nitrogen fixation by improving phosphorus content

Abstract

Phosphate (P) availability often limits biological nitrogen fixation (BNF) by diazotrophic bacteria. In soil, only 0.1% of the total P is available for plant uptake. P solubilizing bacteria can convert insoluble P to plant-available soluble P (ionic P and low molecular-weight organic P). However, limited information is available about the effects of synergistic application of diazotrophic bacteria and P solubilizing bacteria on the nitrogenase activity of rhizosphere and nifH expression of endosphere. In this study, we investigated the effects of co-inoculation with a diazotrophic bacterium (Paenibacillus beijingensis BJ-18) and a P-solubilizing bacterium (Paenibacillus sp. B1) on wheat growth, plant and soil total N, plant total P, soil available P, soil nitrogenase activity and the relative expression of nifH in plant tissues. Co-inoculation significantly increased plant biomass (length, fresh and dry weight) and plant N content (root: 27%, shoot: 30%) and P content (root: 63%, shoot: 30%). Co-inoculation also significantly increased soil total N (12%), available P (9%) and nitrogenase activity (69%) compared to P. beijingensis BJ-18 inoculation alone. Quantitative real-time PCR analysis showed co-inoculation doubled expression of nifH genes in shoots and roots. Soil nitrogenase activity and nifH expression within plant tissues correlated with P content of soil and plant tissues, which suggests solubilization of P by Paenibacillus sp. B1 increased N fixation in soils and the endosphere. In conclusion, P solubilizing bacteria generally improved soil available P and plant P uptake, and considerably stimulated BNF in the rhizosphere and endosphere of wheat seedlings.

Will Phosphate Bio-Solubilization Stimulate Biological Nitrogen Fixation in Grain Legumes?

“…This is because several metabolic processes that occur in plant cells notably, ammonium assimilation into amino acids and ureides were also found to be critically affected by P concentration (Batterman et al, 2013;Singh et al, 2013;Mitran et al, 2018). Li et al (2020) found that increasing P content in soil and wheat (Triticum aestivum) plant tissues also enhanced total N and nitrogenase activity in plant shoots and roots along with nifH gene expression, supporting our understanding of the role of P in the enhancement of BNF (Wani et al, 2007).…”

“…In fact, BNF as one of the main rhizosphere biological processes, is correlated with P availability wherein P deficiency strongly limits the activity of diazotrophic (i.e., N 2 -fixing bacteria), reduces the symbiotic partnership between plant host and rhizobia, as well as the N 2 -fixation process itself (Aziz et al, 2016;Martins et al, 2017;Sanz-Saez et al, 2017;Li et al, 2020;Tewari et al, 2020). Tewari et al (2020) further highlighted the role of P as a structural element in controlling the BNF process.…”

“…This finding was further confirmed by Ahmad et al (2019) who showed that increased growth and nutritional status of mung bean (Vigna radiata) plants following their inoculation with PSB strains (Bacillus aryabhattai S10 and Bacillus subtilis ZM63) were concomitant with enhanced nodulation, measured in terms of nodules number and weight. A recent study by Li et al (2020) showed that wheat co-inoculation with a diazotrophic bacterium (Paenibacillus beijingensis BJ-18) and a PSB (Paenibacillus sp. B1) significantly increased plant growth as well as P and N content of both the plant (roots and shoots) and the soil.…”

“…Traditionally, the application of organic and inorganic fertilizers to farm fields has been used to correct nutrient deficiencies and maintain nutrient balances (Li et al, 2020;Tewari et al, 2020), but negative environmental impacts could occur as a result of excessive and irrational nutrients application in agro-ecosystems that has received justified attention from stakeholders along the entire food value chain (Choudhury and Kennedy, 2005). There is increasing attention paid to the ability of purposefully selected soil microorganisms to enhance soil fertility through biological methods.…”

Multiple Potential Plant Growth Promotion Activities of Endemic Streptomyces spp. from Moroccan Sugar Beet Fields with Their Inhibitory Activities against Fusarium spp.

“…In contrast to the well-documented action of phosphate-solubilizing and nitrogen-fixing microorganisms in plant P and N nutrition [ 13 , 14 ], the importance of microbial activity on plant K nutrition is less well understood. It has been shown that bacteria and mycorrhizal fungi do solubilize mineral K by various mechanisms such as production of alkaline substances including ammonia and other metabolites upon death of microbial cells and subsequent proteolysis [ 15 , 16 ].…”