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Changes in UV‐B radiation screening effectiveness with leaf age in Rhododendron maximum
Author(s) -
Ruhland C. T.,
Day T. A.
Publication year - 1996
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1996.tb00409.x
Subject(s) - penetration (warfare) , transmittance , ultraviolet , ultraviolet radiation , understory , botany , age groups , horticulture , penetration depth , absorbance , radiation , chemistry , materials science , biology , canopy , optics , mathematics , chromatography , radiochemistry , physics , optoelectronics , operations research , sociology , demography
We examined how ultraviolet‐B radiation (UV‐B; 300 nm) screening effectiveness changes with leaf age in Rhododendron maximum growing in a shaded understory by measuring depth of penetration and epidermal transmittance with a fibre‐optic microprobe. Depth of penetration (and epidermal transmittance) of UV‐B decreased with leaf age in 1‐ to 4‐year‐old leaves, averaging 62 (32), 52 (22), 45 (16) and 48 μm (13%), respectively. Epidermal thickness increased with age in 1‐ to 4‐year‐old leaves due to a thickening of the cuticle from an average of 20 to 29μm. Ultraviolet‐B‐absorbing compound concentrations increased with age from 1–3 to 1–5 A 300 cm −2 leaf area. Concentrations of UV‐B‐absorbing compounds (area basis) were a strong predictor of depth of penetration (r 2 = 0.82) and epidermal transmittance (r 2 = 0.95) of UV‐B in mature (1–4 year‐old) foliage. Chlorophyll concentrations (area basis) increased in leaves up to 3 years of age. Current‐year leaves (30 d old) were exceptional in that while they were particularly effective at screening UV‐B (depth of penetration and epidermal transmittance averaged 39μm and 5%, respectively) they had relatively low concentrations of UV‐B‐absorbing compounds (1.3 A 300 cm −2 ). Our findings show that UV‐B‐screening effectiveness is not necessarily related to absorbing compound concentrations on a whole‐leaf basis, possibly due to anatomical changes within the epidermis that occur with leaf age.