Abstract
Abstract Water deficiency brings about a marked limitation in soybean ( Glycine max. L. Merr.) yield by impairing photosynthesis and symbiotic N 2 fixation. The objective of this study was to determine the photosynthetic and N 2 ‐fixation response to short‐ and long‐duration water status variations in leaves and nodules. Plants were grown in pots in a greenhouse. Carbon dioxide exchange rate was measured by gas analysis and N 2 fixation by the acetylene reduction method. Leaf water status was determined with a pressure bomb and nodule water potential with a psychrometer. Dinitrogen fixation decreased steadily throughout the water deficiency period whereas photosynthesis first decreased only slightly, and then dropped dramatically. After a severe water stress, partial recovery was slower for N 2 fixation than for photosynthesis. The N 2 ‐fixation response appeared to be directly related to a reduction in nodule mass, which affected nodule structural constituents after a severe stress. During the water deficiency period, the water status of the nodules responded only partially to water status variations within the plant during the day. Dinitrogen fixation depended more on the water status of the nodules than on the changes in nodule mass. There was a higher dependence of N 2 fixation on nodule water content than on nodule water potential, particularly for values <‐1.2 MPa. The N 2 ‐fixation activity maintained during the severe phase of water stress, when photosynthesis was zero, resulted from the relative independence of the nodules on the daily water variations within the plant and from the strong binding of the nodule water.
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Claims 8
Claim · model-written summary
Dinitrogen fixation declined steadily during water deficiency.
- Taxon
- Soybean
Glycine maxt0 - Treatment
- water deficiencye0
- Outcome
- Dinitrogen fixatione0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Dinitrogen fixation decreased steadily throughout the water deficiency period”
t0“Soybean”
Claim · model-written summary
Photosynthesis initially declined slightly then dramatically during water deficiency.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- water deficiency periode1
- Outcome
- photosynthesise0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“photosynthesis first decreased only slightly, and then dropped dramatically”
e1“throughout the water deficiency period”
t0“Soybean”
Claim · model-written summary
N2 fixation recovered more slowly than photosynthesis after severe water stress.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- severe water stresse0
- Outcome
- recoverye0
- Direction
- slowere0
- Comparator
- photosynthesise0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“After a severe water stress, partial recovery was slower for N 2 fixation than for photosynthesis”
t0“Soybean”
Claim · model-written summary
N2 fixation response appeared linked to reduced nodule mass after severe stress.
- Taxon
- SoybeanGlycine maxt0
- Organ / stage
- nodulee0
- Outcome
- N 2 ‐fixation responsee0
- Direction
- reductione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N 2 ‐fixation response appeared to be directly related to a reduction in nodule mass, which affected nodule structural constituents after a severe stress”
t0“Soybean”
Claim · model-written summary
Nodule water status only partly tracked within-plant daily water status changes.
- Taxon
- SoybeanGlycine maxt0
- Organ / stage
- nodulese0
- Outcome
- water status of the nodulese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“water status of the nodules responded only partially to water status variations within the plant during the day”
t0“Soybean”
Claim · model-written summary
N2 fixation depended more on nodule water status than nodule mass changes.
- Taxon
- SoybeanGlycine maxt0
- Organ / stage
- nodulese0
- Outcome
- Dinitrogen fixatione0
- Direction
- moree0
- Comparator
- changes in nodule masse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Dinitrogen fixation depended more on the water status of the nodules than on the changes in nodule mass”
t0“Soybean”
Claim · model-written summary
N2 fixation depended more on nodule water content than potential below -1.2 MPa.
- Taxon
- SoybeanGlycine maxt0
- Organ / stage
- nodulee0
- Outcome
- N 2 fixatione0
- Direction
- highere0
- Value
- <‐1.2 MPae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“higher dependence of N 2 fixation on nodule water content than on nodule water potential, particularly for values <‐1.2 MPa”
t0“Soybean”
Claim · model-written summary
Fixation persisted during severe stress when photosynthesis reached zero, attributed to nodule water buffering.
- Taxon
- SoybeanGlycine maxt0
- Outcome
- N 2 ‐fixation activity maintainede0
- Qualifier
- strong binding of the nodule watere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N 2 ‐fixation activity maintained during the severe phase of water stress, when photosynthesis was zero, resulted from the relative independence of the nodules on the daily water variations within the plant and from the strong binding of the nodule water”
t0“Soybean”
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