Abstract
Abstract Background In anaerobic lowland fields, ammonium (NH 4 + ) is the dominant form of nitrogen (N) taken up by rice plants, however, with the large expansion of water‐saving irrigation practices, nitrification is favored during drained periods, leading to an increased availability of nitrate (NO 3 − ). Aim Since the uptake and assimilation of the two N‐sources differ in their demand of photosynthates, leaf gas exchange may be subject to adjustments in response to N‐sources, particularly at high evaporative demand, when stomatal conductance (g s ) is very sensitive. Methods Three experiments were carried out to study leaf gas exchange of various lowland rice varieties in response to N‐source at low and high vapor pressure deficit (VPD). In the first experiment, seedlings of 12 rice varieties were grown at high VPD for 3 weeks. From this, four rice varieties differing in g s and CO 2 assimilation rate (A) were selected and grown for 2 weeks at low VPD, and after that, they were shifted to high VPD for 1 week, whereas in the third experiment, the same varieties were grown separately at low and high VPD conditions for 2 weeks. In all three experiments, plants were grown hydroponically in nutrient solution with N‐sources as sole NH 4 + or NO 3 − . Results At high VPD, NO 3 − nutrition led to a higher g s and A in four out of 12 varieties (IR64, BT7, NU838, and Nipponbare) relative to NH 4 + nutrition, while no effect was observed at low VPD or after a short‐term exposure to high VPD. Further, varieties with a high intrinsic water‐use efficiency (WUEi; IR64 and BT7) showed the strongest response to N‐source. Higher g s was partially supported by increased root/shoot ratio, but could not be fully explained by the measured parameters. However, higher A in NO 3 − ‐fed plants did not always result in increased plant dry matter, which is probably related to the higher energy demand for NO 3 − assimilation. Our results suggest that at high VPD, NO 3 − nutrition can improve leaf gas exchange in varieties having a high WUEi, provided a sufficient water supply. Conclusion Therefore, intensified nitrification under water‐saving irrigation measures may improve leaf gas exchange and the growth of rice plants under high transpirational demand. However, choice of variety seems crucial since large varietal differences were observed in response to N‐source. Further, breeding strategies for genotypes adapted to aerobic soil conditions should consider responses to NO 3 − , potentially using gas exchange measurements as a screening tool.
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Claims 7
Claim · model-written summary
At high VPD, nitrate raised stomatal conductance and assimilation in four of twelve rice varieties.
- Taxon
- rice
Oryza sativat0 - Material
- IR64, BT7, NU838, and Nipponbaree0
- Treatment
- NO 3 − nutritione0
- Outcome
- g s and Ae0
- Direction
- highere0
- Value
- four out of 12 varietiese0
- Qualifier
- At high VPDe0
- Comparator
- NH 4 + nutritione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At high VPD, NO 3 − nutrition led to a higher g s and A in four out of 12 varieties (IR64, BT7, NU838, and Nipponbare) relative to NH 4 + nutrition”
t0“Leaf gas exchange of lowland rice”
Claim · model-written summary
N source had no observed gas exchange effect at low VPD or after brief high VPD exposure.
- Taxon
- riceOryza sativat0
- Treatment
- nitrogen sourcet1
- Outcome
- leaf gas exchanget0
- Direction
- no effecte0
- Qualifier
- at low VPD or after a short‐term exposure to high VPDe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“no effect was observed at low VPD or after a short‐term exposure to high VPD”
t0“Leaf gas exchange of lowland rice”
t1“in response to nitrogen source and vapor pressure deficit”
Claim · model-written summary
High WUEi varieties responded most strongly to nitrogen source.
- Taxon
- riceOryza sativat0
- Material
- IR64 and BT7e0
- Outcome
- response to N‐sourcee0
- Direction
- strongeste0
- Qualifier
- high intrinsic water‐use efficiencye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“varieties with a high intrinsic water‐use efficiency (WUEi; IR64 and BT7) showed the strongest response to N‐source”
t0“Leaf gas exchange of lowland rice”
Claim · model-written summary
Higher stomatal conductance was partly supported by increased root-to-shoot ratio.
- Taxon
- riceOryza sativat0
- Outcome
- g se0
- Direction
- Highere0
- Qualifier
- increased root/shoot ratioe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Higher g s was partially supported by increased root/shoot ratio, but could not be fully explained by the measured parameters.”
t0“Leaf gas exchange of lowland rice”
Claim · model-written summary
Higher assimilation in nitrate-fed plants did not always increase dry matter.
- Taxon
- riceOryza sativat0
- Treatment
- NO 3 − ‐fede0
- Outcome
- plant dry mattere0
- Direction
- did not always result in increasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“higher A in NO 3 − ‐fed plants did not always result in increased plant dry matter”
t0“Leaf gas exchange of lowland rice”
Claim · model-written summary
Varieties differed substantially in response to nitrogen source.
- Taxon
- riceOryza sativat0
- Outcome
- varietal differencese0
- Qualifier
- in response to N‐sourcee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“large varietal differences were observed in response to N‐source”
t0“Leaf gas exchange of lowland rice”
Claim · model-written summary
Authors propose nitrate-response screening through gas exchange for aerobic-soil breeding.
- Taxon
- riceOryza sativat0
- Outcome
- breeding strategies for genotypes adapted to aerobic soil conditions should consider responses to NO 3 −e0
- Qualifier
- using gas exchange measurements as a screening toole0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“breeding strategies for genotypes adapted to aerobic soil conditions should consider responses to NO 3 − , potentially using gas exchange measurements as a screening tool”
t0“Leaf gas exchange of lowland rice”
The same questions in other papers
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