Bryophytes, generally referring to mosses (Bryophyta), liverworts (Marchantiophyta) and hornworts (Anthocertophyta), represent the oldest extant lineages of land plants, with liverworts likely representing the earliest divergent group. The relationship between bryophytes and embryophytes (plants in which the embryo is enclosed, as in a seed) is interesting in the context of interpreting the evolution of several fundamental plant characteristics, including stomata and chloroplast morphology. Stomates, for example, are present in mosses and hornworts, but are absent in liverworts.
Despite occupying a diverse range of habitats with widely varying light regimes, from deep in the forest understory to open pocosins and desert sites, many bryophytes have chlorophyll a:b ratios similar to shade plants irrespective of the typical light regime of their habitat. The exceptions to this are generally species of brightly lit and perennially wet sites. The low chlorophyll a:b ratios in many of these plants likely relates to their poikilohydric nature: their physiology is tightly linked to the water status of the plant and under conditions of limited water availability they enter a desiccated dormant state. When water again becomes available, the plants rehydrate and physiological processes resume. For bryophytes in dry sites, the availability of water may be linked to cloud cover and thus it may be an advantage to have a shade adapted physiology.
The 6400-24 Bryophyte Chamber operates in conjunction with the LI-6400XT Portable Photosynthesis System to allow exploration of physiological processes in these diverse and interesting organisms. Loose material can be held in a shallow well in the bottom of the chamber for measurement, as was done with several capitula of a laboratory grown Sphagnum sp. to generate the data set shown in the figure. Alternately, material from foliose species can be placed on a raised screen, which allows measurement of gas exchange from both surfaces of a large thallus. By using the 6400-18A RGB Light Source with the chamber, measurements can be made that explore both response to light intensity and quality (see Application Note 5 for more details).
Photosynthetic response to light intensity for two laboratory grown cultures of Sphagnum sp. Measurements were made on capitula placed in the bryophyte chamber, from lowest to highest and back to lowest light intensity. Assimilation rates are expressed on a dry weight basis (µmol/gdwt/s).
Dilks, T.J.K., and M.C.F. Proctor. 1979. Photosynthesis, respiration and water content in bryophytes. New Phytol. 82:97-114
Marschall, M., and M.C.F. Proctor. 2004. Are bryophytes shade plants? Photosynthetic light responses and proportions of chlorophyll a, chlorophyll b and total carotenoids. Annals of Botany 94:593-603
LI-COR Instruments for Measuring Photosynthetic Rates of Bryophytes:
- Compact, rugged, field portable instrument
- Accurate and precise
- Measures fluorescence and gas exchange simultaneously
- Connects directly to the LI‑6400XT Portable Photosynthesis System
- Allows for loose material to be held in a shallow well for gas exchange measurements
- Can be used with the 6400-18A RGB Light Source to explore response to both light intensity and quality
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