Abstract
Nodule CO2 fixation via PEPC provides malate for bacteroids and oxaloacetate for N assimilation. The process is therefore of central importance for efficient nitrogen fixation. Nodule CO2 fixation is known to depend on external CO2 concentration. The hypothesis of the present paper was that nitrogen fixation in alfalfa plants is enhanced when the nodules are exposed to elevated CO2 concentrations. Therefore nodulated plants of alfalfa were grown in a hydroponic system that allowed separate aeration of the root/nodule compartment that avoided any gas leakage to the shoots. The root/nodule compartments were aerated either with a 2500 microl l(-1) (+CO2) or zero microl l(-1) (-CO2) CO2-containing N2/O2 gas flow (80/20, v/v). Nodule CO2 fixation, nitrogen fixation, and growth were strongly increased in the +CO2 treatment in a 3-week experimental period. More intensive CO2 and nitrogen fixation coincided with higher per plant amounts of amino acids and organic acids in the nodules. Moreover, the concentration of asparagine was increased in both the nodules and the xylem sap. Plants in the +CO2 treatment tended to develop nodules with higher %N concentration and individual activity. In a parallel experiment on plants with inefficient nodules (fix-) the +CO2 treatment remained without effect. Our data support the thesis that nodule CO2 fixation is pivotal for efficient nitrogen fixation. It is concluded that strategies which enhance nodule CO2 fixation will improve nitrogen fixation and nodule formation. Moreover, sufficient CO2 application to roots and nodules is necessary for growth and efficient nitrogen fixation in hydroponic and aeroponic growth systems.
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Claims 10
Claim · model-written summary
Elevated root-zone CO2 strongly increased nodule CO2 fixation.
- Taxon
- alfalfa
Medicago sativae1 - Treatment
- +CO2 treatmente0
- Outcome
- Nodule CO2 fixatione0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Nodule CO2 fixation, nitrogen fixation, and growth were strongly increased in the +CO2 treatment in a 3-week experimental period.”
e1“nodulated plants of alfalfa”
Claim · model-written summary
Elevated root-zone CO2 strongly increased nitrogen fixation.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- +CO2 treatmente0
- Outcome
- nitrogen fixatione0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Nodule CO2 fixation, nitrogen fixation, and growth were strongly increased in the +CO2 treatment in a 3-week experimental period.”
e1“nodulated plants of alfalfa”
Claim · model-written summary
Elevated root-zone CO2 strongly increased alfalfa growth.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- +CO2 treatmente0
- Outcome
- growthe0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Nodule CO2 fixation, nitrogen fixation, and growth were strongly increased in the +CO2 treatment in a 3-week experimental period.”
e1“nodulated plants of alfalfa”
Claim · model-written summary
Greater CO2 and nitrogen fixation coincided with higher amino and organic acid amounts in nodules.
- Taxon
- alfalfaMedicago sativae1
- Organ / stage
- nodulese0
- Outcome
- per plant amounts of amino acids and organic acids in the nodulese0
- Direction
- highere0
Not reportedTreatment
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“More intensive CO2 and nitrogen fixation coincided with higher per plant amounts of amino acids and organic acids in the nodules.”
e1“nodulated plants of alfalfa”
Claim · model-written summary
Elevated CO2 increased asparagine concentration in nodules and xylem sap.
- Taxon
- alfalfaMedicago sativae1
- Organ / stage
- nodules and the xylem sape0
- Treatment
- +CO2 treatmente2
- Outcome
- concentration of asparaginee0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the concentration of asparagine was increased in both the nodules and the xylem sap”
e1“nodulated plants of alfalfa”
e2“Plants in the +CO2 treatment tended”
Claim · model-written summary
Plants under elevated CO2 tended to have nodules with higher nitrogen concentration and individual activity.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- +CO2 treatmente0
- Outcome
- %N concentration and individual activitye0
- Direction
- highere0
- Qualifier
- tended toe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Plants in the +CO2 treatment tended to develop nodules with higher %N concentration and individual activity.”
e1“nodulated plants of alfalfa”
Claim · model-written summary
Elevated CO2 had no reported effect on plants with inefficient nodules.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- +CO2 treatmente0
- Outcome
- plants with inefficient nodulese0
- Direction
- without effecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In a parallel experiment on plants with inefficient nodules (fix-) the +CO2 treatment remained without effect.”
e1“nodulated plants of alfalfa”
Claim · model-written summary
The authors infer that nodule CO2 fixation is pivotal for efficient nitrogen fixation.
- Taxon
- alfalfaMedicago sativae1
- Outcome
- efficient nitrogen fixatione0
- Qualifier
- nodule CO2 fixatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“nodule CO2 fixation is pivotal for efficient nitrogen fixation”
e1“nodulated plants of alfalfa”
Claim · model-written summary
The authors conclude that increasing nodule CO2 fixation would improve nitrogen fixation and nodule formation.
- Taxon
- alfalfaMedicago sativae1
- Outcome
- strategies which enhance nodule CO2 fixatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“strategies which enhance nodule CO2 fixation will improve nitrogen fixation and nodule formation”
e1“nodulated plants of alfalfa”
Claim · model-written summary
The authors recommend sufficient CO2 application to roots and nodules for growth and nitrogen fixation in hydroponic and aeroponic systems.
- Taxon
- alfalfaMedicago sativae1
- Outcome
- sufficient CO2 application to roots and nodulese0
- Setting
- hydroponic and aeroponic growth systemse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“sufficient CO2 application to roots and nodules is necessary for growth and efficient nitrogen fixation in hydroponic and aeroponic growth systems”
e1“nodulated plants of alfalfa”
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