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Inoculation with five diazotrophs alters nitrogen metabolism during the initial growth of sugarcane varieties with contrasting responses to added nitrogen

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Abstract

Aims

We examined the influence of inoculation with five species/strains of diazotrophic bacteria on the modulation of two enzymes involved in the assimilation of N and on the soluble N fractions in the sugarcane varieties RB867515 (adapted for low fertility soils) and IACSP95-5000 (adapted for medium to high fertility soils) under high- (3 mM) and low (0.3 mM)-N conditions in hydroponic cultivation for 59 days.

Methods

The sugarcane plants were produced in three steps to obtain the hydroponic cultivation: the supply of 3 mM N for 30 days (first harvest), N depletion for 72 h (second harvest), and cultivation in high- and low-N conditions over 26 days (final harvest). Inoculation was performed by immersion of the minisetts in a diluted solution of five diazotrophic bacteria. After the final harvest, plants were divided into roots and shoots to assess their dry weight and N, P, and K accumulation.

Results

The variety played an important role in the interaction with diazotrophs, each showing distinct behavior in the activity of their N-assimilation enzymes. The nitrate reductase activity (NRa—EC 1.7.1.1) was increased in var. RB867515 by 26% in the shoots and by 48% in the roots after 72 h under N depletion, while var. IACSP95-5000 showed a reduced enzymatic activity in the roots (by 62%) but not in the shoots. Under high-N conditions, the inoculated IACSP95-5000 plants showed 31% higher glutamine synthetase activity (GSa—EC 6.31.2) compared with 19% in RB867515. Under low-N conditions, the GSas were 21% and 16% higher in the inoculated RB867515 and IACSP95-5000 plants, respectively, compared with that of the control. The content of nitrogen in the form of nitrate (N-nitrate) confirmed these varietal differences, but the soluble sugar content did not.

Conclusions

The varieties utilized N sources differently, and inoculation modified the activity of two N-assimilation enzymes as well as the biomass accumulation, with the highest improvement seen in the low fertility-adapted variety RB867515; it showed a greater response to inoculation compared with that of the high fertility-adapted variety IACSP95-5000, with an increase in biomass and nutrient accumulation (N, P, K), especially when cultivated under low-N conditions. This suggests that the best response to inoculation with diazotrophs will be achieved using low fertility-adapted sugarcane varieties under low-N conditions.

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Acknowledgments

The authors express their gratitude to the Coordination of Improvement of Higher Education Personnel - CAPES and the Foundation Carlos Chagas de Amparo à Pesquisa do Estado do Rio de Janeiro - FAPERJ for the fellowships and to the National Council of Scientific and Technological Development - CNPq [grant number INCT 456133/2014-2 and 470824/2013-1].

Funding

This work was supported by Newton Fund grant BB/N013476/1 “Understanding and Exploiting Biological Nitrogen Fixation for Improvement of Brazilian Agriculture”, co-funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the Brazilian National Council for State Funding Agencies (CONFAP).

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Correspondence to Veronica Massena Reis.

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Responsible Editor: Euan K. James.

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dos Santos, S.G., da Silva Ribeiro, F., Alves, G.C. et al. Inoculation with five diazotrophs alters nitrogen metabolism during the initial growth of sugarcane varieties with contrasting responses to added nitrogen. Plant Soil 451, 25–44 (2020). https://doi.org/10.1007/s11104-019-04101-1

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