Abstract
Photosynthetic rates and allocation of dry matter, nitrogen, and nonstructural carbohydrates were determined during onset of and recovery from a nitrogen stress for reproductive soybean (Glycine max [L.] Merrill cv Ransom) plants. Until the beginning of seed fill, non-nodulated plants were grown in flowing solution culture with 1.0 mM NO3- in a complete nutrient solution. One set of plants then was transferred to minus-nitrogen solution for 24 d of seed fill; a second set was transferred to a minus-nitrogen solution for 14 d followed by return to the complete solution with 1.0 mM NO3- for the remaining 10 d of seed fill; and a third set was continued on the complete solution. Net CO2 exchange rates of individual leaves, which remained nearly constant during seed fill for nonstressed plants, declined at an accelerated rate during onset of nitrogen stress as the specific content of reduced nitrogen in the leaves was decreased by remobilization of nitrogen to support pod growth. The rate of nitrogen remobilization out of leaves initially was relatively greater than the decrease in photosynthetic rate. While rate of pod growth declined in response to the developing nitrogen stress, photosynthetic assimilation of carbon exceeded reproductive demand and nonstructural carbohydrates accumulated within tissues. Following resupply of exogenous NO3-, specific rate of NO3- uptake by roots was enhanced relative to nonstressed plants. While there was little increase in content of reduced nitrogen in leaves, net remobilization of nitrogen out of leaves ceased, and the decline in photosynthetic rate stabilized at about 51% of that for nonstressed plants. This level of photosynthesis, combined with the availability of elevated pools of carbohydrates accumulated during stress, was sufficient to support the increases in both the specific rates of NO3- uptake and the rate of pod growth during recovery.
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Claims 11
Claim · model-written summary
Nitrogen stress accelerated the decline in leaf CO2 exchange.
- Treatment
- nitrogen stresse0
- Outcome
- Net CO2 exchange ratese0
- Direction
- declinede0
- Comparator
- nonstressed plantse0
Not reportedTaxon
Verbatim
e0“Net CO2 exchange rates of individual leaves, which remained nearly constant during seed fill for nonstressed plants, declined at an accelerated rate during onset of nitrogen stress as the specific content of reduced nitrogen in the leaves was decreased by remobilization of nitrogen to support pod growth.”
Claim · model-written summary
Leaf reduced nitrogen content declined during nitrogen remobilization to pods.
- Organ / stage
- leavese0
- Outcome
- specific content of reduced nitrogen in the leavese0
- Direction
- decreasede0
Not reportedTaxon
Verbatim
e0“the specific content of reduced nitrogen in the leaves was decreased by remobilization of nitrogen to support pod growth.”
Claim · model-written summary
Nitrogen remobilization from leaves initially exceeded the relative decline in photosynthesis.
- Outcome
- rate of nitrogen remobilization out of leavese0
- Direction
- relatively greatere0
- Comparator
- decrease in photosynthetic ratee0
Not reportedTaxon
Verbatim
e0“The rate of nitrogen remobilization out of leaves initially was relatively greater than the decrease in photosynthetic rate.”
Claim · model-written summary
Pod growth declined under developing nitrogen stress.
Not reportedTaxonComparator
Verbatim
e0“While rate of pod growth declined in response to the developing nitrogen stress, photosynthetic assimilation of carbon exceeded reproductive demand and nonstructural carbohydrates accumulated within tissues.”
Claim · model-written summary
Photosynthetic carbon assimilation exceeded reproductive demand during nitrogen stress.
Not reportedTaxon
Verbatim
e0“photosynthetic assimilation of carbon exceeded reproductive demand and nonstructural carbohydrates accumulated within tissues.”
Claim · model-written summary
Nonstructural carbohydrates accumulated in tissues during nitrogen stress.
Not reportedTaxon
Verbatim
e0“nonstructural carbohydrates accumulated within tissues.”
Claim · model-written summary
After nitrate resupply, specific root nitrate uptake exceeded that of nonstressed plants.
- Treatment
- resupply of exogenous NO3-e0
- Outcome
- specific rate of NO3- uptake by rootse0
- Direction
- enhancede0
- Comparator
- nonstressed plantse0
Not reportedTaxon
Verbatim
e0“Following resupply of exogenous NO3-, specific rate of NO3- uptake by roots was enhanced relative to nonstressed plants.”
Claim · model-written summary
After nitrate resupply, reduced nitrogen content in leaves increased little.
Not reportedTaxon
Verbatim
e0“While there was little increase in content of reduced nitrogen in leaves, net remobilization of nitrogen out of leaves ceased, and the decline in photosynthetic rate stabilized at about 51% of that for nonstressed plants.”
Claim · model-written summary
Net nitrogen remobilization from leaves ceased after nitrate resupply.
Not reportedTaxon
Verbatim
e0“net remobilization of nitrogen out of leaves ceased, and the decline in photosynthetic rate stabilized at about 51% of that for nonstressed plants.”
Claim · model-written summary
Photosynthesis stabilized at about 51% of the nonstressed rate.
Not reportedTaxon
Verbatim
e0“the decline in photosynthetic rate stabilized at about 51% of that for nonstressed plants.”
Claim · model-written summary
Available photosynthesis and accumulated carbohydrate pools supported increased nitrate uptake and pod growth during recovery.
- Outcome
- specific rates of NO3- uptake and the rate of pod growthe0
- Direction
- increasese0
- Qualifier
- elevated pools of carbohydrates accumulated during stresse0
Not reportedTaxon
Verbatim
e0“This level of photosynthesis, combined with the availability of elevated pools of carbohydrates accumulated during stress, was sufficient to support the increases in both the specific rates of NO3- uptake and the rate of pod growth during recovery.”