Elevated carbon dioxide level along with phosphorus application and cyanobacterial inoculation enhances nitrogen fixation and uptake in cowpea crop

ABSTRACT

Climate change, as a result of increase in the concentration of greenhouse gases, influences growth and productivity of leguminous crops. A study was carried out to analyse the impacts of elevated carbon dioxide (CO₂) and cyanobacterial inoculation on growth, N₂ fixation and N availability and uptake in cowpea crop, under different doses of phosphorus. Cowpea crop was grown under ambient (400 µmol mol⁻¹) and elevated (550 ± 20 µmol mol⁻¹) CO₂ levels using Free-Air Carbon dioxide Enrichment facility. Elevated CO₂ level increased chlorophyll content in leaves, improved nodulation and nitrogen fixation by the crop. Increase in P dose up to 16 mg kg⁻¹ soil enhanced nodule development and N₂ fixation under high CO₂ condition. Cyanobacterial inoculation increased nodule weight, leghaemoglobin content in nodules and total nitrogenase activity. Although nitrogen concentration in cowpea seeds decreased in high CO₂ treatment, higher N uptake was recorded. Under elevated CO₂ condition, cyanobacterial inoculation and higher P doses led to enhanced root growth and N₂ fixation and availability of soil nitrogen. The study illustrated the synergistic effect of high CO₂ and cyanobacterial inoculation in enhancing crop growth and availability of soil N, mediated by biological N₂ fixation in cowpea under different levels of P.

KEYWORDS:

• Chlorophyll
• legumes
• nodules
• N-P interactions
• phototroph
• plant growth

Acknowledgements

The authors thank the PG School and Director, ICAR-IARI, for providing the fellowship towards pursuing M.Sc. program to SKD. Facilities used for this research work were partially funded by National Innovations in Climate Resilient Agriculture, Indian Council of Agricultural Research.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Fellowship was provided by ICAR-IARI to SKD for pursuing M.Sc. Facilities used for this research work were partially funded by National Innovations in Climate Resilient Agriculture, Indian Council of Agricultural Research.