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Chlorophyll Concentrations and Photosynthesis in Three Forest Understory Mosses in Northeastern Kansas

1991; American Bryological and Lichenological Society; Volume: 94; Issue: 1 Linguagem: Inglês

10.2307/3243713

1938-4378

Kimberly K. McCall, Craig E. Martin,

Peatlands and Wetlands Ecology

Chlorophyll concentrations and rates of photosynthetic 02, evolution were measured in Dicranum scoparium, Leucobryum glaucum, and Thuidium delicatulum collected from a forest understory in northeastern Kansas. In all species photosynthesis saturated around 200 j.mol m-2 sec.-', reflecting the intermediate nature of sun-shade adaptation in these species. The highest concentration of chlorophyll was found in L. glaucum and correlated with higher rates of photosynthesis at low light levels. These findings lend support to the expectation that higher chlorophyll concentrations in mosses will enhance light capture at low light levels. Numerous studies have shown that plants growing in low light have higher chlorophyll concentrations than those growing in high light (Baker & Long 1986; Bjoirkman 1981; Boardman 1977). Similar results have been obtained with mosses (Aro & Valanne 1979; Glime 1984; Kershaw & Webber 1986; Martin & Churchill 1982; Valanne 1977). Such differences in chlorophyll concentration often correlate with photosynthetic rates such that plants with high chlorophyll concentrations exhibit higher rates of photosynthesis under low light, relative to plants with less pigment (Bj6rkman 1981; Boardman 1977). In addition to higher pigment concentrations, shade plants often exhibit lower chlorophyll a/b ratios than do sun plants (Bj6rkman 1981; Martin & Churchill 1982). In the past, this has been attributed to differences in the functions of chlorophyll a and chlorophyll b. Chlorophyll b is involved only with light harvesting, whereas chlorophyll a is also involved in energy transduction within the chloroplast membranes (Thornber et al. 1976). Changes in environmental conditions may result in altered chlorophyll a/b ratios (Alberte et al. 1976; Bj6rkman 1981), presumably because the light-harvesting complexes are variable in size while the energy transducing complexes are less variable (Leong & Anderson 1983). Furthermore, proportional increases in the concentration of chlorophyll b might allow greater efficiency of photon capture in the shaded understory of a forest, as the upper canopy absorbs proportionally more light in the absorption band of chlorophyll a (Boardman 1977). Nevertheless, shade plants do not always exhibit lower a/b ratios than sun plants (Martin et al. 1985; Vapaavuori & Nurmi 1982). Reasons for this are presently