Abstract

The carbon cost of nitrogenase activity was investigated to determine symbiotic efficiency of the actinorhizal root nodule symbiosis between the woody perennial Alnus incana and the soil bacterium Frankia. Respiration (CO, production) and nitrogenase activity (H, production) by intact nodulated root systems were continuously recorded in short-term assays in an open-flow gas exchange system. The assays were conducted in N-2:2,, thus under N-2-fixing conditions, in all experiments except for one. This avoided the declines in nitrogenase activity and respiration due to N-2 deprivation that occur in acetylene reduction assays and during extended Ar:O-2 exposures in H-2 assays. Two approaches were used: (i) direct estimation of root and nodule respiration by removing nodules, and (ii) decreasing the partial pressure of O-2 from 21 to 15% to use the strong relationship between respiration and nitrogenase activity to calculate CO2/H-2. The electron allocation of nitrogenase was determined to be 0.6 and used to convert the results into moles of CO, produced per 2e(-) transferred by nitrogenase to reduction of N2. The results ranged from 2.6 to 3.4 mol CO2 produced per 2e(-). Carbon cost expressed as g C produced per g N reduced ranged from 4.5 to 5.8. The result for this actinorhizal tree symbiosis is in the low range of estimates for N-2-fixing actinorhizal symbioses and crop legumes. Methodology and comparisons of root nodule physiology among actinorhizal and legume plants are discussed

Keywords

actinorhiza; Alnus incana; Frankia; N2 fixation; respiration; symbiosis

Published in

Plant and Soil
2005, Volume: 273, number: 1-2, pages: 235-244
Publisher: SPRINGER

SLU Authors

• Lundquist, Per-Olof

  • Department of Plant Biology, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Renewable Bioenergy Research


Publication identifier

DOI: https://doi.org/10.1007/s11104-004-7766-4

Permanent link to this page (URI)

https://res.slu.se/id/publ/8510