Abstract
BACKGROUND AND AIMS: Plants use diffuse light more efficiently than direct light. However, experimental comparisons between diffuse and direct light have been obscured by co-occurring differences in environmental conditions (e.g. light intensity). This study aims to analyse the factors that contribute to an increase in crop photosynthesis in diffuse light and to quantify their relative contribution under different levels of diffuseness at similar light intensities. The hypothesis is that the enhancement of crop photosynthesis in diffuse light results not only from the direct effects of more uniform vertical and horizontal light distribution in the crop canopy, but also from crop physiological and morphological acclimation. METHODS: Tomato (Solanum lycopersicum) crops were grown in three greenhouse compartments that were covered by glass with different degrees of light diffuseness (0, 45 and 71 % of the direct light being converted into diffuse light) while maintaining similar light transmission. Measurements of horizontal and vertical photosynthetic photon flux density (PPFD) distribution in the crop, leaf photosynthesis light response curves and leaf area index (LAI) were used to quantify each factor's contribution to an increase in crop photosynthesis in diffuse light. In addition, leaf temperature, photoinhibition, and leaf biochemical and anatomical properties were studied. KEY RESULTS: The highest degree of light diffuseness (71 %) increased the calculated crop photosynthesis by 7·2 %. This effect was mainly attributed to a more uniform horizontal (33 % of the total effect) and vertical PPFD distribution (21 %) in the crop. In addition, plants acclimated to the high level of diffuseness by gaining a higher photosynthetic capacity of leaves in the middle of the crop and a higher LAI, which contributed 23 and 13 %, respectively, to the total increase in crop photosynthesis in diffuse light. Moreover, diffuse light resulted in lower leaf temperatures and less photoinhibition at the top of the canopy when global irradiance was high. CONCLUSIONS: Diffuse light enhanced crop photosynthesis. A more uniform horizontal PPFD distribution played the most important role in this enhancement, and a more uniform vertical PPFD distribution and higher leaf photosynthetic capacity contributed more to the enhancement of crop photosynthesis than did higher values of LAI.
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Claims 6
Claim · model-written summary
The highest light diffuseness increased calculated crop photosynthesis by 7·2 %.
- Taxon
- Tomato
Solanum lycopersicume0 - Treatment
- highest degree of light diffuseness (71 %)e1
- Outcome
- calculated crop photosynthesise1
- Direction
- increasede1
- Value
- 7·2 %e1
- Comparator
- 0e0
- Setting
- greenhouse compartmentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Tomato (Solanum lycopersicum) crops were grown in three greenhouse compartments that were covered by glass with different degrees of light diffuseness (0, 45 and 71 % of the direct light being converted into diffuse light)”
e1“The highest degree of light diffuseness (71 %) increased the calculated crop photosynthesis by 7·2 %.”
Claim · model-written summary
More uniform horizontal light distribution accounted for 33 % of the photosynthesis effect.
- Taxon
- TomatoSolanum lycopersicume0
- Outcome
- horizontale1
- Value
- 33 % of the total effecte1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Tomato (Solanum lycopersicum) crops”
e1“more uniform horizontal (33 % of the total effect) and vertical PPFD distribution (21 %) in the crop.”
Claim · model-written summary
More uniform vertical PPFD distribution accounted for 21 % of the effect.
- Taxon
- TomatoSolanum lycopersicume0
- Outcome
- vertical PPFD distributione1
- Value
- 21 %e1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Tomato (Solanum lycopersicum) crops”
e1“more uniform horizontal (33 % of the total effect) and vertical PPFD distribution (21 %) in the crop.”
Claim · model-written summary
Higher leaf photosynthetic capacity in the crop middle contributed 23 % of the photosynthesis gain.
- Taxon
- TomatoSolanum lycopersicume0
- Outcome
- photosynthetic capacity of leaves in the middle of the crope1
- Direction
- highere1
- Value
- 23e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Tomato (Solanum lycopersicum) crops”
e1“higher photosynthetic capacity of leaves in the middle of the crop and a higher LAI, which contributed 23 and 13 %, respectively, to the total increase in crop photosynthesis in diffuse light.”
Claim · model-written summary
Higher LAI contributed 13 % of the photosynthesis gain.
- Taxon
- TomatoSolanum lycopersicume0
- Outcome
- LAIe1
- Direction
- highere1
- Value
- 13 %e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Tomato (Solanum lycopersicum) crops”
e1“a higher LAI, which contributed 23 and 13 %, respectively, to the total increase in crop photosynthesis in diffuse light.”
Claim · model-written summary
Diffuse light lowered leaf temperature and photoinhibition at the canopy top under high irradiance.
- Taxon
- TomatoSolanum lycopersicume0
- Treatment
- diffuse lighte1
- Outcome
- leaf temperaturese1
- Direction
- lowere1
- Qualifier
- when global irradiance was highe1
- Comparator
- direct lighte2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Tomato (Solanum lycopersicum) crops”
e1“diffuse light resulted in lower leaf temperatures and less photoinhibition at the top of the canopy when global irradiance was high.”
e2“diffuse and direct light”
The same questions in other papers
light · physiology: photosynthesis · Solanum lycopersicum (tomato)Positive and negative results
64 papers in the same direction as this paper · 43 in the opposite direction · 5 reporting no difference from an alternative
- no effect
- positive
- positive
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