Abstract
ABSTRACT The evergreen shrub Buxus microphylla (Buxaceae; Japanese boxwood) forms distinctive ultramafic vegetation in Japan, with populations on Sugashima Island exhibiting unusually vivid crimson leaves in winter. To clarify the physiological and nutritional mechanisms underlying this coloration, we combined field monitoring with laboratory experiments to reproduce leaf reddening under controlled conditions. Field observations revealed that leaves of B. microphylla growing on ultramafic soils turned bright red each winter, whereas those from non‐ultramafic sites remained mostly green, except for slight reddening at the Mie University site. The crimson coloration coincided with a seasonal decline in leaf nitrogen (N) and chlorophyll content, suggesting that nutrient limitation enhances pigment imbalance. In laboratory assays, light exposure and sucrose addition strongly promoted chlorophyll degradation, increasing the carotenoid‐to‐chlorophyll ratio (Car/Chl) by more than 20%. Under dark conditions, both sucrose and N enhanced pigment retention. The Car/Chl ratio consistently ranked as water‐only > N‐only > multi‐nutrient media, indicating that nutrient sufficiency counteracts sugar‐induced photoinhibition and chlorophyll breakdown. These results demonstrate that leaf reddening in boxwood is not due to anthocyanin synthesis but rather to a relative enrichment of carotenoids following chlorophyll loss under photoinhibitory conditions. The combination of high irradiance, low temperature, and N deficiency on ultramafic soils promotes this imbalance, producing the intense “crimson boxwood” phenotype. Our findings highlight how nutrient limitation and photoprotection interact to shape adaptive pigmentation in plants growing on ultramafic soils.
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Claims 10
Claim · model-written summary
B. microphylla leaves on ultramafic soils turned bright red each winter, whereas leaves from non-ultramafic sites remained mostly green.
- Taxon
- B. microphylla
.jpg?width=60)
Buxus microphyllae0 - Outcome
- turned bright red each wintere0
- Comparator
- non‐ultramafic sitese0
- Setting
- ultramafic soilse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
e0“leaves of B. microphylla growing on ultramafic soils turned bright red each winter, whereas those from non‐ultramafic sites remained mostly green”
t0“Boxwood”
Claim · model-written summary
Crimson coloration coincided with a seasonal decline in leaf nitrogen.
Verbatim
e0“The crimson coloration coincided with a seasonal decline in leaf nitrogen (N) and chlorophyll content”
t0“Boxwood”
Claim · model-written summary
Crimson coloration coincided with a seasonal decline in chlorophyll content.
Verbatim
e0“The crimson coloration coincided with a seasonal decline in leaf nitrogen (N) and chlorophyll content”
t0“Boxwood”
Claim · model-written summary
Light exposure and sucrose addition promoted chlorophyll degradation.
- Taxon
- Boxwoodt0
- Treatment
- light exposure and sucrose additione0
- Outcome
- chlorophyll degradatione0
- Direction
- promotede0
Not reportedComparator
Verbatim
e0“light exposure and sucrose addition strongly promoted chlorophyll degradation, increasing the carotenoid‐to‐chlorophyll ratio (Car/Chl) by more than 20%”
t0“Boxwood”
Claim · model-written summary
Light exposure and sucrose addition increased the Car/Chl ratio by more than 20%.
- Taxon
- Boxwoodt0
- Treatment
- light exposure and sucrose additione0
- Outcome
- carotenoid‐to‐chlorophyll ratio (Car/Chl)e0
- Direction
- increasinge0
- Value
- more than 20%e0
Not reportedComparator
Verbatim
e0“light exposure and sucrose addition strongly promoted chlorophyll degradation, increasing the carotenoid‐to‐chlorophyll ratio (Car/Chl) by more than 20%”
t0“Boxwood”
Claim · model-written summary
Under darkness, sucrose enhanced pigment retention.
- Taxon
- Boxwoodt0
- Treatment
- sucrosee0
- Outcome
- pigment retentione0
- Direction
- enhancede0
- Qualifier
- dark conditionse0
Not reportedComparator
Verbatim
e0“Under dark conditions, both sucrose and N enhanced pigment retention”
t0“Boxwood”
Claim · model-written summary
Under darkness, nitrogen enhanced pigment retention.
Not reportedComparator
Verbatim
e0“Under dark conditions, both sucrose and N enhanced pigment retention”
t0“Boxwood”
Claim · model-written summary
The Car/Chl ratio ranked highest in water-only medium, followed by N-only medium, then multi-nutrient medium.
Verbatim
e0“The Car/Chl ratio consistently ranked as water‐only > N‐only > multi‐nutrient media”
t0“Boxwood”
Claim · model-written summary
The authors attribute red boxwood leaves to relative carotenoid enrichment after chlorophyll loss rather than anthocyanin synthesis.
Verbatim
e0“leaf reddening in boxwood is not due to anthocyanin synthesis but rather to a relative enrichment of carotenoids following chlorophyll loss under photoinhibitory conditions”
Claim · model-written summary
The authors infer that high irradiance, low temperature and nitrogen deficiency on ultramafic soils promote the crimson phenotype.
Verbatim
e0“The combination of high irradiance, low temperature, and N deficiency on ultramafic soils promotes this imbalance, producing the intense “crimson boxwood” phenotype”