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An Ecological Study of the Bryophytes of a Natural Prairie in Northwestern Iowa

1983; American Bryological and Lichenological Society; Volume: 86; Issue: 1 Linguagem: Inglês

10.2307/3242695

1938-4378

Judith O'Keefe van der Linden, Donald R. Farrar,

Lichen and fungal ecology

The Freda Haffner Kettlehole Preserve, a natural prairie remnant in Dickinson County, Iowa, supports 34 species of bryophytes. Most of the taxa are common and widespread elsewhere and many are typical weedy pioneers of poor soils or recently disturbed sites. The greater number of species and all pleurocarpous species occurred on slopes with a northern aspect. Acrocarpous species occurred on all slopes but were more abundant on slopes with a southern aspect. These distribution patterns may be attributed to a relation between growth form and measured differences in maximum surface temperature and evaporation on the two slope aspects. Total bryophyte abundance strongly correlated with slope steepness and ground-level light intensity, the latter determined primarily by vascular plant density and height. Prairie species Bryum creberrimum and Weissia controversa reached light compensation points at higher light intensities and approached maximum photosynthesis more slowly with increasing light intensity than did two forest species Atrichum undulatum and Mnium cuspidatum. Maximum photosynthesis was reached by Weissia controversa at 400C, and by the other three species at 300C. Weissia controversa occurred on both slope aspects whereas Bryum creberrimum was restricted to slopes of northern aspect. Some bryophytes appear to be specifically adapted to the high light intensities and high temperatures of the prairie habitat. Insufficient light may limit bryophyte growth under dense prairie vascular communities although bare soil and sufficient moisture are present. Study of bryophytes in prairie habitats has been largely neglected by bryologists. The few published studies are primarily lists of taxa (Shimek 1915; Sorenson 1962; Zales 1971), although the two latter authors included brief descriptions of typical micro-habitats of species they found. Bird (1962) pointed out that most species he identified were not restricted to prairies but also occurred commonly in other habitats. The growth of bryophytes in prairies is generally considered much restricted by high light intensities, temperature extremes, and widely-fluctuating air and soil moisture (Shimek 1911). However, some bryophytes possess characteristics that allow them to grow in habitats of such extremes. Zales (1971) observed that some prairie bryophytes are ephemerals that complete their short life cycles in spring or fall and thus avoid the temperature 007-2745/83/1-13$1.55/0 This content downloaded from 157.55.39.215 on Tue, 30 Aug 2016 06:30:44 UTC All use subject to http://about.jstor.org/terms 2 THE BRYOLOGIST [Volume 86 and moisture extremes of summer and winter. However, most bryophytes that grow on prairies are tolerant of repeated desiccation and other environmental extremes. The physiological basis of this tolerance has been the subject of a number of recent studies. The photosynthetic response of prairie bryophytes to the high temperature and light intensities generally encountered in their habitat has not previously been investigated, but studies in other habitats indicate that the optimal ranges of temperature and light for photosynthesis in bryophytes may be correlated with the temperature and light conditions under which they naturally occur. Hosokawa and Odani (1957) found that bryophytes growing on the upper boughs of trees were adapted to photosynthesize optimally at consistently higher light levels than species occurring on lower boughs of the same trees. Rastorfer and Higinbotham (1968) determined that net photosynthesis in Bryum sandbergii (= Roellia roellia (Broth. ex Roell) Andr. ex Crum) occurred between 4?C and 390C, a range of temperatures similar to that which the moss encounters at different elevations. The response of this moss with respect to light intensity closely approximated that of other plants of shady habitats. Bazzaz et al. (1970), working with Polytrichum juniperinum Hedw., demonstrated that plants from a lowland forest and a cool, alpine habitat had similar temperature optima, but that the forest plants continued to photosynthesize at 300C, whereas the alpine plants did not. On the other hand, alpine plants appeared better adapted to high light intensities, reaching light saturation at approximately 600 AE m-2 sec-1, as compared to 200 AE m-2 sec-1 for forest plants. Rastorfer (1970) compared the photosynthetic responses of two Bryum species in Antarctica, B. argenteum Hedw., a cosmopolitan moss, and B. antarcticum Hook. f. and Wils., believed to be endemic to Antarctica. He found that B. argenteum photosynthesized at optimum and maximum temperatures that were 100C higher than those of B. antarcticum, and suggested that the differences were related to the difference in distribution and habitat tolerance of the two species. Similar photosynthetic adaptations should be expected in prairie bryophytes. The extremes of water stress to which prairie bryophytes are subject have been investigated by a number of workers in recent years. These studies have focused on the effects of desiccation on the ultrastructure and metabolism of certain bryophytes (Bewley & Pacey 1978; Dhindsa & Bewley 1977; Kellomdiki & Hari 1976; Krochko et al. 1978; Tucker et al. 1975; Tobiessen et al. 1979) and the general pattern of recovery of bryophytes after desiccation (Hinshiri & Proctor 1971; Proctor 1972; Dilks & Proctor 1974; Peterson & Mayo 1975; Gupta 1977; Tobiessen et al. 1978). Such studies have demonstrated remarkable tolerance to desiccation, as well as the ability to recover photosynthetic ability with sufficient rapidity to allow the plants to take advantage of brief summer rains. Tobiessen et al. (1979) further pointed out that bryophytes rapidly achieve respiratory dormancy with drying, assuring that they do not suffer a negative carbon balance while in that condition. Although not addressed as a group by these studies, prairie species probably possess these traits to a high degree. A few studies have attempted to correlate bryophyte cover and diversity to environmental variables. Most notable of these is Slack's (1977) comprehensive study in the Adirondack Mts. in which she compared bryophyte cover and diversity with differences in elevation, microclimate parameters and vascular plant cover. The following study identifies bryophytes typical of Iowa prairies and describes their general distribution and their specific microhabitats on the prairie. It also investigates the possible adaptations of prairie species to conditions of high light and temperature through comparisons of photosynthesis in typical prairie and woodland species. This content downloaded from 157.55.39.215 on Tue, 30 Aug 2016 06:30:44 UTC All use subject to http://about.jstor.org/terms 1983] O'KEEFE VAN DER LINDEN & FARRAR: PRAIRIE BRYOPHYTES 3