Background and aims
We aimed to investigate the effects of root carboxylate exudation in the interaction between Azospirillum brasilense and Zea mays. We hypothesized that root carboxylate exudation is a mechanism that increases colonization of the maize rhizosphere by A. brasilense and that carboxylate exudation would increase at a low soil phosphorus (P) availability.
We conducted a greenhouse experiment, using maize seeds inoculated and uninoculated with A. brasiliense. Seeds were planted in pots, supplied with nutrient solution, varying in P concentration. After 45 days we measured total plant biomass, root length and area, plant nutrient status, and the root carboxylate-exudation rate.
Inoculation increased the root length and area, and this effect increased with increasing P supply. Inoculated plants also showed an increased root carboxylate-exudation rate. For inoculated treatments, the exudation rate was positively correlated with root architecture parameters; however, it was negatively correlated with leaf manganese concentration, a proxy for the amount of carboxylates in the rhizosphere.
Inoculation of A. brasilense stimulated root carboxylate exudation, which was positively correlated with root length and area. These positive correlations are probably mediated by the effect of carboxylates on the rhizosphere microbial community. This indicates a positive feedback in which A. brasilense inoculation stimulates root carboxylate exudation, influencing the rhizosphere microbial community. It results in positive effects on maize root architecture. The root length of inoculated plants was positively correlated with P supply, indicating that P supply positively affects the microbial community, modulating the interaction between A. brasilense and Z. mays.
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The study was financially supported by the Programa Institucional de Bolsa de Iniciação Científica (PIBIC), of the National Council of Technological and Scientific Development (CNPq), by São Paulo Research Foundation (FAPESP Grant no. 2010/17204-0, FAPESP/Microsoft Grant no. 2011/52072-0), and by the Universidade Estadual de Campinas (UNICAMP). RSO received research productivity scholarship from CNPq. The fellowship between UNICAMP and University of Western Australia (UWA) was granted by the Ciências sem Fronteiras (CsF) program (CAPES: 88887.108541/2015-00). We are thankful for four anonymous reviewers for their very insightful and constructive comments. We thank I. Marriel, of Embrapa- Milho e Sorgo (CNPMS), for the donation of maize seeds used in this experiment, and F.B. Sei, of Total Biotecnologia, for the donation of the inoculant of Azospirillum brasilense used in this experiment. We are also thankful to A. Abrahão for critical reading of this manuscript; and A.L. Mansur for the assistance with the installation of the experiment; and P. Mazzafera for the use of the equipment (FAPESP 2008/58035-6).
Responsible Editor: Stéphane Compant.
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D’Angioli, A.M., Viani, R.A.G., Lambers, H. et al. Inoculation with Azospirillum brasilense (Ab-V4, Ab-V5) increases Zea mays root carboxylate-exudation rates, dependent on soil phosphorus supply. Plant Soil 410, 499–507 (2017). https://doi.org/10.1007/s11104-016-3044-5
- Leaf manganese concentration
- Plant growth-promoting rhizobacteria