Abstract
Abstract In major soybean‐producing regions such as the United States, farm yield has increased in recent years. This gain is accompanied by genetic improvements in net photosynthetic rate (P N ). However, farm yields in Japan remain low and unchanged, suggesting a lack of progress in improving yield and the underlying P N through recent breeding. It is unclear how much Japanese breeders have improved P N , or whether the P N of Japanese cultivars is inferior to cultivars from the United States and, if so, which physiological traits should be improved to increase P N in Japanese cultivars. To answer these questions, we compared P N and related physiological traits of cultivars released during the past 60 yr in the Tohoku region of northern Japan (JP group) with those of cultivars from the Midwestern United States (U.S. group). In the U.S. group, P N increased with year of release at both flowering and the beginning of seed filling (respectively, R2 and R5) stages, and was accompanied by an increase in leaf N content by area (N area ). This demonstrates improved P N resulting from recent breeding. In contrast, there was no difference in P N between old and new cultivars in the JP group, indicating that P N was not improved by breeding. P N at R5 in the JP group was lower than in the U.S. group and was associated with lower stomatal conductance in the JP group. N area at R5 was higher in the JP group than in the U.S. group and was associated with lower photosynthetic N use efficiency in the JP group.
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Claims 7
Claim · model-written summary
US cultivars increased net photosynthetic rate with release year at flowering and seed filling.
- Taxon
- soybean
Glycine maxt0 - Material
- U.S. groupe0
- Organ / stage
- flowering and the beginning of seed fillinge0
- Outcome
- P Ne0
- Direction
- increasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In the U.S. group, P N increased with year of release at both flowering and the beginning of seed filling (respectively, R2 and R5) stages”
t0“soybean”
Claim · model-written summary
US improvement in photosynthetic rate accompanied an increase in leaf nitrogen per area.
- Taxon
- soybeanGlycine maxt0
- Material
- U.S. groupe1
- Outcome
- leaf N content by areae0
- Direction
- increasee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“was accompanied by an increase in leaf N content by area (N area )”
t0“soybean”
e1“In the U.S. group”
Claim · model-written summary
Photosynthetic rate did not differ between old and new Japanese cultivars.
- Taxon
- soybeanGlycine maxt0
- Material
- JP groupe0
- Outcome
- P Ne0
- Direction
- no differencee0
- Comparator
- old and new cultivarse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“there was no difference in P N between old and new cultivars in the JP group”
t0“soybean”
Claim · model-written summary
At R5, Japanese cultivars had lower photosynthetic rate than US cultivars.
- Taxon
- soybeanGlycine maxt0
- Material
- JP groupe0
- Organ / stage
- R5e0
- Outcome
- P Ne0
- Direction
- lowere0
- Comparator
- U.S. groupe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“P N at R5 in the JP group was lower than in the U.S. group”
t0“soybean”
Claim · model-written summary
Lower Japanese photosynthetic rate was associated with lower stomatal conductance.
- Taxon
- soybeanGlycine maxt0
- Material
- JP groupe0
- Outcome
- stomatal conductancee0
- Direction
- lowere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“was associated with lower stomatal conductance in the JP group”
t0“soybean”
Claim · model-written summary
At R5, Japanese cultivars had higher leaf nitrogen per area than US cultivars.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N area at R5 was higher in the JP group than in the U.S. group”
t0“soybean”
Claim · model-written summary
Higher Japanese leaf nitrogen was associated with lower photosynthetic nitrogen use efficiency.
- Taxon
- soybeanGlycine maxt0
- Material
- JP groupe0
- Outcome
- photosynthetic N use efficiencye0
- Direction
- lowere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“was associated with lower photosynthetic N use efficiency in the JP group.”
t0“soybean”