Abstract
Biological N(2) fixation can fulfil the N demand of legumes but may cost as much as 14% of current photosynthate. This photosynthate (C) sink strength would result in loss of productivity if rates of photosynthesis did not increase to compensate for the costs. We measured rates of leaf photosynthesis, concentrations of N, ureides and protein in leaves of two soybean cultivars (Glycine max [L.] Merrill) differing in potential shoot biomass production, either associated with Bradyrhizobium japonicum strains, or amended with nitrate. Our results show that the C costs of biological N(2) fixation can be compensated by increased photosynthesis. Nodulated plants shifted N metabolism towards ureide accumulation at the start of the reproductive stage, at which time leaf N concentration of nodulated plants was greater than that of N-fertilized plants. The C sink strength of N(2) fixation increased photosynthetic N use efficiency at the beginning of plant development. At later stages, although average protein concentrations were similar between the groups of plants, maximum leaf protein of nodulated plants occurred a few days later than in N-fertilized plants. The chlorophyll content of nodulated plants remained high until the pod-filling stage, whereas the chlorophyll content of N-fertilized plants started to decrease as early as the flowering stage. These results suggest that, due to higher C sink strength and efficient N(2) fixation, nodulated plants achieve higher rates of photosynthesis and have delayed leaf senescence.
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Claims 8
Claim · model-written summary
Biological nitrogen fixation carbon costs were compensated by increased soybean photosynthesis.
- Taxon
- soybean
Glycine maxt0 - Treatment
- biological N(2) fixatione0
- Outcome
- photosynthesise0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Our results show that the C costs of biological N(2) fixation can be compensated by increased photosynthesis.”
t0“soybean”
Claim · model-written summary
Nodulated plants accumulated ureides at the start of the reproductive stage.
- Taxon
- plantsViridiplantaee0
- Organ / stage
- start of the reproductive stagee0
- Interactor
- Nodulatede0
- Outcome
- ureide accumulatione0
Verbatim
e0“Nodulated plants shifted N metabolism towards ureide accumulation at the start of the reproductive stage”
Claim · model-written summary
Nodulated plants had greater leaf nitrogen concentration than nitrogen-fertilized plants at the start of reproduction.
Verbatim
e0“leaf N concentration of nodulated plants was greater than that of N-fertilized plants.”
Claim · model-written summary
Nitrogen fixation increased photosynthetic nitrogen use efficiency early in development.
Verbatim
e0“The C sink strength of N(2) fixation increased photosynthetic N use efficiency at the beginning of plant development.”
Claim · model-written summary
Average leaf protein concentrations were similar between nodulated and nitrogen-fertilized plants at later stages.
- Taxon
- plantsViridiplantaee0
- Outcome
- average protein concentrationse0
- Direction
- similare0
- Qualifier
- At later stagese0
Verbatim
e0“At later stages, although average protein concentrations were similar between the groups of plants”
Claim · model-written summary
Maximum leaf protein occurred later in nodulated than nitrogen-fertilized plants.
Verbatim
e0“maximum leaf protein of nodulated plants occurred a few days later than in N-fertilized plants.”
Claim · model-written summary
Chlorophyll content remained high until pod filling in nodulated plants but declined from flowering in nitrogen-fertilized plants.
Verbatim
e0“The chlorophyll content of nodulated plants remained high until the pod-filling stage, whereas the chlorophyll content of N-fertilized plants started to decrease as early as the flowering stage.”
Claim · model-written summary
The authors attribute higher photosynthesis and delayed leaf senescence in nodulated plants to carbon sink strength and efficient fixation.
- Taxon
- plantsViridiplantaee0
- Outcome
- higher rates of photosynthesis and have delayed leaf senescencee0
- Qualifier
- higher C sink strength and efficient N(2) fixatione0
Verbatim
e0“due to higher C sink strength and efficient N(2) fixation, nodulated plants achieve higher rates of photosynthesis and have delayed leaf senescence.”