Abstract
The effects of an increase in ultraviolet-B radiation (UV-B, 280–320 nm) on growth, photosynthesis and photoinhibition of a UV-B sensitive variety of cucumber ( Cucumis sativus L. cv. Poinsett) were investigated at four levels of applied nitrogen (N, 0.5, 2.0, 5.0 and 10.0 mol m-3). Plants were grown for 33 days in a UV-B transparent greenhouse at ambient and ambient +25% biologically effective UV-B radiation (UV-BBE). A modulated lamp system controlled supplemental UV-B levels; average doses of UV-BBE were 2.5 ± 0.8 (ambient) and 3.1 ± 1.0 (ambient +25%) kJ m-2 d-1. The doses are comparable to the expected change in UV-BBE between 1979 and 1999 under similar weather conditions at this latitude. Plant biomass, height, and leaf N, chlorophyll and leaf carbon content increased with increasing amounts of applied N. At the highest level of N application, supplemental levels of UV-B caused a near identical decrease in leaf area (20%), height (28%) and total biomass (20%) compared with plants grown under ambient UV-B conditions. There was no such effect when N stress was imposed. Apparent quantum yield (&phis;app), dark respiration and photosynthetic rate were unaffected by the supplemental UV-B and photodestruction of reaction centres was not evident. However, there was a significant increase in photoinhibition at midday in the N-replete plants. In leaves with N content <3%, supplemental levels of UV-B caused the concentration of UV-B absorbing compounds to increase significantly (72% at the lowest level of applied N). The epidermis was thicker at all levels of N under supplemental UV-B. The stress response to low N may confer secondary protection against UV-B damage and changes in N status due to fertilisers or pollution may lead to changes in UV-B sensitivity.
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Claims 13
Claim · model-written summary
Plant biomass and height of cucumber increased with increasing amounts of applied nitrogen.
- Taxon
- cucumber
Cucumis sativust0 - Treatment
- increasing amounts of applied Ne1
- Outcome
- Plant biomass, heighte1
- Direction
- increasede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Plant biomass, height, and leaf N, chlorophyll and leaf carbon content increased with increasing amounts of applied N”
t0“cucumber”
Claim · model-written summary
Leaf nitrogen, chlorophyll and leaf carbon content of cucumber increased with increasing amounts of applied nitrogen.
- Taxon
- cucumberCucumis sativust0
- Treatment
- increasing amounts of applied Ne1
- Outcome
- leaf N, chlorophyll and leaf carbon contente1
- Direction
- increasede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Plant biomass, height, and leaf N, chlorophyll and leaf carbon content increased with increasing amounts of applied N”
t0“cucumber”
Claim · model-written summary
At the highest nitrogen level, supplemental UV-B decreased cucumber leaf area by 20% relative to ambient UV-B.
- Taxon
- cucumberCucumis sativust0
- Treatment
- supplemental levels of UV-Be1
- Outcome
- leaf areae1
- Direction
- decreaseinferrede1
- Value
- 20%e1
- Qualifier
- At the highest level of N applicatione1
- Comparator
- plants grown under ambient UV-B conditionse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“At the highest level of N application, supplemental levels of UV-B caused a near identical decrease in leaf area (20%), height (28%) and total biomass (20%) compared with plants grown under ambient UV-B conditions”
t0“cucumber”
Claim · model-written summary
At the highest nitrogen level, supplemental UV-B decreased cucumber height by 28% relative to ambient UV-B.
- Taxon
- cucumberCucumis sativust0
- Treatment
- supplemental levels of UV-Be1
- Outcome
- heighte1
- Direction
- decreaseinferrede1
- Value
- 28%e1
- Qualifier
- At the highest level of N applicatione1
- Comparator
- plants grown under ambient UV-B conditionse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“At the highest level of N application, supplemental levels of UV-B caused a near identical decrease in leaf area (20%), height (28%) and total biomass (20%) compared with plants grown under ambient UV-B conditions”
t0“cucumber”
Claim · model-written summary
At the highest nitrogen level, supplemental UV-B decreased cucumber total biomass by 20% relative to ambient UV-B.
- Taxon
- cucumberCucumis sativust0
- Treatment
- supplemental levels of UV-Be1
- Outcome
- total biomasse1
- Direction
- decreaseinferrede1
- Value
- 20%e1
- Qualifier
- At the highest level of N applicatione1
- Comparator
- plants grown under ambient UV-B conditionse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“At the highest level of N application, supplemental levels of UV-B caused a near identical decrease in leaf area (20%), height (28%) and total biomass (20%) compared with plants grown under ambient UV-B conditions”
t0“cucumber”
Claim · model-written summary
Supplemental UV-B had no such growth-reducing effect on cucumber when nitrogen stress was imposed.
- Taxon
- cucumberCucumis sativust0
- Outcome
- no such effecte1
- Qualifier
- when N stress was imposede1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“There was no such effect when N stress was imposed”
t0“cucumber”
Claim · model-written summary
Apparent quantum yield, dark respiration and photosynthetic rate of cucumber were unaffected by supplemental UV-B.
- Taxon
- cucumberCucumis sativust0
- Treatment
- supplemental UV-Be1
- Outcome
- Apparent quantum yield (&phis;app), dark respiration and photosynthetic ratee1
- Direction
- unaffectede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Apparent quantum yield (&phis;app), dark respiration and photosynthetic rate were unaffected by the supplemental UV-B”
t0“cucumber”
Claim · model-written summary
Photodestruction of reaction centres was not evident in cucumber under supplemental UV-B.
- Taxon
- cucumberCucumis sativust0
- Outcome
- photodestruction of reaction centres was not evidente1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“photodestruction of reaction centres was not evident”
t0“cucumber”
Claim · model-written summary
There was a significant increase in photoinhibition at midday in nitrogen-replete cucumber plants.
- Taxon
- cucumberCucumis sativust0
- Outcome
- photoinhibition at middaye1
- Direction
- increasee1
- Qualifier
- N-replete plantse1
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“there was a significant increase in photoinhibition at midday in the N-replete plants”
t0“cucumber”
Claim · model-written summary
In cucumber leaves with N content below 3%, supplemental UV-B significantly increased the concentration of UV-B absorbing compounds, by 72% at the lowest level of applied N.
- Taxon
- cucumberCucumis sativust0
- Organ / stage
- leavese1
- Treatment
- supplemental levels of UV-Be1
- Outcome
- concentration of UV-B absorbing compoundse1
- Direction
- increaseinferrede1
- Value
- 72%e1
- Qualifier
- N content <3%e1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“In leaves with N content <3%, supplemental levels of UV-B caused the concentration of UV-B absorbing compounds to increase significantly (72% at the lowest level of applied N)”
t0“cucumber”
Claim · model-written summary
The epidermis of cucumber was thicker at all nitrogen levels under supplemental UV-B.
- Taxon
- cucumberCucumis sativust0
- Organ / stage
- epidermise1
- Treatment
- supplemental UV-Be1
- Outcome
- epidermise1
- Direction
- thickere1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“The epidermis was thicker at all levels of N under supplemental UV-B”
t0“cucumber”
Claim · model-written summary
The authors suggest that the stress response to low nitrogen may confer secondary protection against UV-B damage.
- Taxon
- cucumberCucumis sativust0
- Outcome
- secondary protection against UV-B damagee1
- Qualifier
- stress response to low Ne1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“The stress response to low N may confer secondary protection against UV-B damage”
t0“cucumber”
Claim · model-written summary
The authors suggest that changes in nitrogen status due to fertilisers or pollution may lead to changes in UV-B sensitivity.
- Taxon
- cucumberCucumis sativust0
- Treatment
- changes in N status due to fertilisers or pollutione1
- Outcome
- UV-B sensitivitye1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“changes in N status due to fertilisers or pollution may lead to changes in UV-B sensitivity”
t0“cucumber”
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