AOBPreview originally published online on August 19, 2004
Annals of Botany 2004 94(4):593-603; doi:10.1093/aob/mch178
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Annals of Botany 94/4, © Annals of Botany Company 2004; all rights reserved
Are Bryophytes Shade Plants? Photosynthetic Light Responses and Proportions of Chlorophyll a, Chlorophyll b and Total Carotenoids
1 Department of Plant Physiology, Eszterházy Károly College, H-3301 Eger, Leányka út 6–8, Hungary, and 2 Department of Biological Sciences, University of Exeter, Washington Singer Laboratories, Perry Road, Exeter EX4 4QG, UK
* For correspondence. E-mail M.C.F.Proctor{at}exeter.ac.uk
Received: 10 March 2004 Returned for revision: 21 June 2004 Accepted: 29 June 2004 Published electronically: 19 August 2004
• Background and Aims Data are presented from 39 species of mosses and 16 liverworts for ratios of chlorophylls and total carotenoids, and light saturation of photosynthetic electron flow or photosynthetic CO2 uptake, in relation to the postulate that bryophyte cells in general show shade-plant characteristics.
• Methods Pigment concentrations were measured by spectrophotometer in 80 % acetone extracts. Light-saturation curves were constructed by (modulated) chlorophyll florescence and for some species by infra-red gas analysis.
• Key Results The pigment measurements were widely variable but broadly in line with the findings of previous authors. Median values (mosses/liverworts) were: total chlorophyll, 1·64/3·76 mg g–1; chlorophyll a : b, 2·29/1·99; chlorophylls : carotenoids, 4·74/6·75). The PPFD values at 95 % saturation (estimated from fitted curves) also ranged widely, but were almost all <1000 µmol m–2 s–1; the median for mosses was 583 and for liverworts 214 µmol m–2 s–1. The two highest PPFD95% values were from Polytrichum species with lamella systems forming a ventilated photosynthetic tissue. Total chlorophyll, chlorophyll a : b and chlorophylls : carotenoids all correlated significantly with PPFD95%.
• Conclusions Bryophytes include but are not inherently shade plants. Light-saturation levels for species of open sun-exposed habitats are lower than for vascular sun plants and are probably limited by CO2 diffusion into unistratose leaves; this limit can only be exceeded by bryophytes with ventilated photosynthetic tissues which provide increased area for CO2 uptake.
Key words: Bryophytes, chlorophyll a : b ratio, chlorophyll : carotenoid ratio, chlorophyll fluorescence, liverworts, light responses, light saturation, mosses, NPQ, photoprotection, PPFD responses
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