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

Yongbin Li,Sanfeng Chen,Qin Li,Guohua Guan

doi:10.7717/peerj.9062

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.

Highlights

Biological nitrogen (N) fixation (BNF) is the main N input in many ecosystems (Berthrong et al, 2014)
We investigated the effects of experimental treatments on (1) host plant biomass, (2) rhizosphere soil total N, available P and nitrogenase activity, (3) plant tissue total N, total P and relative expression of nifH and (4) the Pearson’s correlation coefficient between the nitrogenase activity/nifH expression and P nutrition of the soil/plant tissues
Plant growth parameters Compared to CK treatment, B1, BJ-18, Mix and BJ-18+P treatments significantly increased wheat root length (Fig. 1A; 8%, 7%, 22% and 23%) and shoot length (Fig. 1B; 14%, 18%, 30% and 27%)

Summary

Introduction

Biological nitrogen (N) fixation (BNF) is the main N input in many ecosystems (Berthrong et al, 2014). In this process, diazotrophic bacteria convert atmospheric N2 into ammonia (Vitousek et al, 2002), and fix 50–70 Tg microbial N in agricultural systems annually (Herridge, Peoples & Boddey, 2008). In low phosphorus (P)-content soil, How to cite this article Li Y, Li Q, Guan G, Chen S. Phosphate solubilizing bacteria stimulate wheat rhizosphere and endosphere biological nitrogen fixation by improving phosphorus content. P controls the rates of heterotrophic BNF (Reed, Cleveland & Townsend, 2007, 2011) and often limits BNF in the rhizobial symbiosis (Kleinert et al, 2014)

Methods

Results

Conclusion