Abstract
A comparative study has been made of the penetration of solar radiation through leaf canopies of contrasting structure. For this purpose experiments were undertaken on (a) Gladiolus with nearly vertical leaves, (b) Raphanus sativus with its rosette habit, (c) two varieties of Linum usitatissimum, one an unbranched flax type and the other a multi-stem linseed type, and (d) Agrostemma githago where the apical leaves are sharply inclined and the basal leaves disposed in a horizontal plane. Light gradients were evaluated at different densities and at varying stages of development by means of probes of silicon cells. Using a filter (cut off point 72-5 μ) simultaneous measurements were made of the infra-red and ‘visible’ radiation. The distributions of the leaf and stem area through the canopy were recorded so that light interception per unit surface could be assessed. The shape of the light gradient between the top and bottom of the canopy was sigmoidal for Gladiolus but much less so for the other species. Attenuation of the infra-red radiation with depth was markedly smaller. For valid estimates of the extinction coefficient (K) it is essential to include stem areas; that is on theoretical grounds half the total stem surface. The values of K were low for all species and in particular for Gladiolus. The relationship between light attenuation and leaf area was approximately exponential. For Gladiolus it was established that K can decrease with increasing density but no changes with depth in the canopy were evident. The implications of these observations in terms of canopy structure are discussed.
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Claims 6
Claim · model-written summary
The canopy light gradient was sigmoidal for Gladiolus and less so in other species.
GladiolusOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The shape of the light gradient between the top and bottom of the canopy was sigmoidal for Gladiolus but much less so for the other species.”
Claim · model-written summary
Infrared radiation attenuated less with depth.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Attenuation of the infra-red radiation with depth was markedly smaller.”
t0“Gladiolus with nearly vertical leaves”
Claim · model-written summary
Including stem area is essential to estimate the extinction coefficient.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“For valid estimates of the extinction coefficient (K) it is essential to include stem areas; that is on theoretical grounds half the total stem surface.”
t0“Gladiolus with nearly vertical leaves”
Claim · model-written summary
Extinction coefficients were low across species, especially Gladiolus.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The values of K were low for all species and in particular for Gladiolus.”
Claim · model-written summary
Light attenuation was approximately exponential with leaf area.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The relationship between light attenuation and leaf area was approximately exponential.”
t0“Gladiolus with nearly vertical leaves”
Claim · model-written summary
In Gladiolus, K can decrease as density rises, with no depth change evident.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“For Gladiolus it was established that K can decrease with increasing density but no changes with depth in the canopy were evident.”