Acetylene reduction (nitrogen fixation) associated with corn inoculated with Spirillum

Area of Science:

• Agricultural Science
• Microbiology
• Plant Science

Background:

• Nitrogen (N2) fixation by microorganisms is crucial for plant nutrition.
• Sorghum and corn are important cereal crops that often require nitrogen fertilization.
• The potential of associative N2-fixing bacteria, such as Spirillum, to enhance crop yields is of interest.

Purpose of the Study:

• To evaluate the N2 fixation rates associated with corn and sorghum inoculated with Brazilian Spirillum strains.
• To assess the effectiveness of Spirillum inoculation on plant growth and nitrogen content.
• To investigate the reliability of acetylene reduction assays for estimating N2 fixation in these systems.

Main Methods:

• Field and greenhouse experiments with corn and sorghum.
• Inoculation with N2-fixing Spirillum strains.
• Acetylene reduction assays on root segments and in situ cultures.
• Measurement of plant dry weight and nitrogen content.

Main Results:

• Estimated N2 fixation rates were generally low (<4 g N2/ha/day) in field conditions.
• Greenhouse experiments showed higher acetylene reduction rates in inoculated corn roots, but in situ measurements were very low (0.4-2.3 g N2/ha/day).
• Inoculated plants without added nitrogen showed deficiency symptoms and reduced dry weight compared to fertilized plants.

Conclusions:

• Spirillum inoculation did not provide appreciable N2 fixation benefits to the tested corn and sorghum varieties under the experimental conditions.
• Acetylene reduction assays on pre-incubated root samples may overestimate N2 fixation.
• Further research is needed to identify effective associative N2-fixing bacteria for major cereal crops.