Abstract
Symbiotic nitrogen fixation may be adversely affected by saline environments. This dissertation describes experiments that assess the salt sensitivity of: 1) Rhizobium as free living organisms; 2) soybean nodule function; and 3) soybean nodule formation. In addition, a split-root plant growth system is described which can be used to separate the effects of salinity stress on host yield potential from the effects of salinity on nodule processes. The growth rate of Rhizobium in culture media is slowed by the addition of NaCl. Some strains were incapable of growth at the highest level of salt used (120 mM NaCl). However, all withstood substantial osmotic shock and most survived for extended periods in saline solutions equivalent to the concentration of sea water. The results show that the effects of increasing moisture tension and salinity on Rhizobium survival in soil are additive. By independently subjecting nodules and shoots to salinity stress it was possible to show that the soybean-Rhizobium japonicum nodule system was not greatly affected by exposure to 120 mM NaCl. The main reduction in nitrogen fixation was the indirect effect of salinity on leaf expansion, shoot yield potential and the sink for nitrogen. The early processes of nodule formation were extremely sensitive to NaCl in the rooting medium. When only 26.3 mM NaCl was added to the nutrient solution two hours prior to inoculation, nodule number and mass were reduced by 50% and 79.9 mM NaCl reduced nodule number, mass and nitrogen fixation to less than 10% of the controls. Rhlzobium japonicum, reisolated from nodules from the high salt treatment did not form more nodules under saline conditions than isolates from controls. By independently subjecting the various processes of the symbiosis to salinity stress it was determined that the early steps in nodule formation are the most sensitive to salinity. This sensitivity indicates that high quality irrigation water must be used during the establishment of symbiotic legumes.
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Claims 12
Claim · model-written summary
Added NaCl slowed Rhizobium growth in culture media.
- Taxon
- Soybean
Glycine maxt0 - Treatment
- addition of NaCle0
- Outcome
- growth rate of Rhizobium in culture mediae0
- Direction
- slowede0
RhizobiumNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e0“The growth rate of Rhizobium in culture media is slowed by the addition of NaCl”
Claim · model-written summary
Some strains could not grow at 120 mM NaCl.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- 120 mM NaCle1
- Outcome
- incapable of growthe1
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e1“Some strains were incapable of growth at the highest level of salt used (120 mM NaCl)”
Claim · model-written summary
All Rhizobium strains withstood substantial osmotic shock.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- substantial osmotic shocke2
- Outcome
- withstoode2
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e2“all withstood substantial osmotic shock and most survived for extended periods in saline solutions equivalent to the concentration of sea water”
Claim · model-written summary
Most Rhizobium strains survived extended exposure to saline solutions equal in concentration to sea water.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- saline solutions equivalent to the concentration of sea watere2
- Outcome
- survived for extended periodse2
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e2“all withstood substantial osmotic shock and most survived for extended periods in saline solutions equivalent to the concentration of sea water”
Claim · model-written summary
Increasing moisture tension and salinity had additive effects on Rhizobium survival in soil.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- increasing moisture tension and salinitye3
- Outcome
- Rhizobium survival in soile3
- Direction
- additivee3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e3“The results show that the effects of increasing moisture tension and salinity on Rhizobium survival in soil are additive”
Claim · model-written summary
The soybean-Rhizobium nodule system was not greatly affected by 120 mM NaCl.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- 120 mM NaCle4
- Outcome
- nodule systeme4
- Direction
- not greatly affectede4
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e4“the soybean-Rhizobium japonicum nodule system was not greatly affected by exposure to 120 mM NaCl”
Claim · model-written summary
The main reduction in nitrogen fixation is attributed to indirect effects of salinity on leaf expansion, shoot yield potential and the sink for nitrogen.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- salinitye5
- Outcome
- reduction in nitrogen fixatione5
- Qualifier
- indirect effect of salinity on leaf expansion, shoot yield potential and the sink for nitrogene5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e5“The main reduction in nitrogen fixation was the indirect effect of salinity on leaf expansion, shoot yield potential and the sink for nitrogen”
Claim · model-written summary
Early processes of nodule formation were extremely sensitive to NaCl in the rooting medium.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- NaCl in the rooting mediume6
- Outcome
- early processes of nodule formatione6
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e6“The early processes of nodule formation were extremely sensitive to NaCl in the rooting medium”
Claim · model-written summary
NaCl at 26.3 mM added before inoculation reduced nodule number and mass by 50%.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- 26.3 mM NaCle7
- Outcome
- nodule number and masse7
- Direction
- reducede7
- Value
- 50%e7
- Qualifier
- two hours prior to inoculatione7
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e7“When only 26.3 mM NaCl was added to the nutrient solution two hours prior to inoculation, nodule number and mass were reduced by 50%”
Claim · model-written summary
NaCl at 79.9 mM reduced nodule number, nodule mass and nitrogen fixation to less than 10% of the controls.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- 79.9 mM NaCle7
- Outcome
- nodule number, mass and nitrogen fixatione7
- Direction
- reducede7
- Value
- less than 10%e7
- Comparator
- the controlse7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e7“79.9 mM NaCl reduced nodule number, mass and nitrogen fixation to less than 10% of the controls”
Claim · model-written summary
Rhizobium reisolated from high-salt nodules did not form more nodules under saline conditions than isolates from controls.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- high salt treatmente6
- Interactor
- Rhlzobium japonicume6symbiont
- Outcome
- nodulese6
- Direction
- did not form moree6
- Comparator
- isolates from controlse6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e6“Rhlzobium japonicum, reisolated from nodules from the high salt treatment did not form more nodules under saline conditions than isolates from controls”
Claim · model-written summary
High-quality irrigation water must be used during establishment of symbiotic legumes.
Verbatim
t0“in the Soybean-Rhizobiurn Japonicum”
e7“This sensitivity indicates that high quality irrigation water must be used during the establishment of symbiotic legumes”
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