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Ecology |
2Departamento de Biología, Área de Botánica Estructural y Sistemática Vegetal, Universidad Autónoma Metropolitana-Iztapalapa, Av. Michoacán y La Purísima s/n, Col. Vicentina, Iztapalapa, C. P. 09340, México, D.F., México; 3Instituto de Ecología, Universidad Nacional Autónoma de México, Departamento de Ecología Funcional y Aplicada AP. 70-275, Circuito Exterior, Ciudad Universitaria, 04510 Mexico, D.F., México
Received for publication April 1, 2003. Accepted for publication December 19, 2003.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: ferns • Mexico • soil propagule banks • spores • vegetation types
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Kornás, 1985
; Komarova, 1987
; Leck and Simpson, 1987
; Hamilton, 1988
; Schneller, 1988
; Milberg, 1991
; Dyer and Lindsay, 1992
, 1996
; Dyer, 1994
), but only recently have there been attempts to do a systematic study of spore banks (Bisang, 1996
; Rydgren and Hestmark, 1997
; Pires et al., 1998
). After dispersal, fern spores may remain viable for days, months, years, and even decades in the soil's spore bank; many spores need light to break out of their latent state and germinate (Dyer and Lindsay, 1992
).
There is a great amount of information about seed banks but little is known about banks of fern spores. While most studies have focused on the amount of viable spores found in soil samples, only a few have dealt with depth-related species composition, the relationship with the pteridoflora of the uppermost layer of soil (Rydgren and Hestmark, 1997
) and the soil's structure (Simabukuro et al., 1998
, 1999
). Knowledge about the species—number and ways in which they are represented in the soil banks—is an essential element in discovering their role in nature and the starting point to begin to understand the dynamics of the banks of pteridophyte diaspores in general and of the ferns in particular (Dyer and Lindsay, 1992
).
The objective of this research is to describe the vertical structure of the natural banks of fern spores in three types of vegetation in the central region of Mexico. We analyzed the size and specific composition of these banks from the first 30 cm of soil, as well as the changes in spore abundance and specific richness in relation to depth. We also compared the species composition of the spore banks to the aboveground vegetation.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Site 1
20°25'58'' N, 98°41'11'' W, 1710 m above sea level (asl). With basaltic outcrops from the upper Tertiary period where lithosols develop; the weather is mild and semi-dry, with a hot summer; the vegetation type corresponds to xerophilous shrubland of Lemaireocereus dumortieri and Myrtillocactus geometrizans.
Site 2
20°40'21'' N, 98°40'27'' W, 2100 m asl. With a predominance of acid tuff of the upper Tertiary period, which gave rise to ortic luvisols; the weather is mild-humid and wet throughout the year; the vegetation type corresponds to a mixed forest of Pinus patula and Quercus affinis.
Site 3
20°43'19'' N, 98°43'36'' W, 1380 m asl. The rocky outcrops correspond to limestone and lutites from the upper Jurassic period. The predominant soils are ortic luvisols and eutric cambisols. The weather is mild and humid, and rains occur throughout the year. The vegetation type is a montane rain forest of Liquidambar styraciflua and Quercus sp.
Sampling
Within each vegetation type, in an area 200 m in diameter, the soil samples were taken from three places chosen at random in April 1999. In a trench, the first soil layer (0–10 cm) was taken vertically with a cylinder (8 x 10 cm). The two other soil layers (10–20 and 20–30 cm) were taken by pushing the cylinder (8 x 25 cm) parallel to the soil surface. In the laboratory, the soil at the bottom and the top of these two cylinders was eliminated (Schneller, 1998
). In the trench, samples were collected from the bottom to the surface to avoid contamination.
Each sample from each depth was subdivided into three subsamples giving 27 subsamples for each vegetation type. The subsamples were kept separately in black plastic bags to be transported to the lab. Simultaneously, we registered the fern sporophytes found around each sampled site (200 m in diameter) to determine the main aboveground pteridoflora's contribution to the soil's spore bank. The collected sporophytes were identified using specialized taxonomic keys (Smith, 1981
; Mickel and Beitel, 1988
; Mickel, 1992
; Palacios- Ríos, 1992
). They were used then as a reference for the correct identification of the ferns found in the banks.
Sowing
Soil (50 g) from each subsample was sieved. Fifteen days after the collection, each sample was put in transparent plastic containers measuring 7 cm in diameter (area = 38.5 cm2); they were covered with a transparent plastic, kept damp, and placed under light conditions (solar lamps, 75 W/ F96T12/D daylight [photon flux density = 437 µmol · m–2 · s–1]): photoperiod of 12 h of light, at 18–25°C (day–night, respectively). For 2 yr, the soil was always kept damp to induce spore germination. After 60 d, when the number of emerged prothallia remained constant, a final counting was done (with a stereoscopic microscope). Control samples (50 g sterilized soil) were made of each soil sample to detect possible contamination from spores in the environment.
Results were expressed as the average number of spores that germinated in each subsample. The identification of the taxa to species took approximately 2 yr; some specimens were only identified to genus due to their slow development and absence of reproductive structures. The identification of the sporophytes was done based on their morphological characteristics (Smith, 1981
; Mickel and Beitel, 1988
). A table was made of the presence or absence of the fern species that emerged during the 2 yr of cultivation, taking into consideration the total number of sporophytes that developed in samples taken from the different soil depths.
Data analysis
Spore density
The differences in the average densities of the viable spores and in the number of sporophytes that developed in the subsamples of soil from the different depth categories and vegetation types were compared by analysis of variance (ANOVA) and a Tukey's method (Sokal and Rohlf, 1987
), using Statgraphics Plus 5.0 statistics program for Windows (Manugistics, 2000, Rockville, Maryland, USA).
Specific richness and similarity
The similarity between sites and depth categories, as well as their affinity to the local pteridoflora, was determined by means of the Sørensen similarity index (S = 2C/[a + b], where C = number of species shared by the sites being compared during the experiment, a = number of species that emerged in site A, and b = number of species that emerged in site B). The Czekanowski index, which calculates similarity according to the abundance of the species in the community, was also calculated and compared to the specific composition of the propagule banks and the aboveground vegetation (ISC = 2 mi/[ai + bi], where mi = minimum value for the number of individuals of the most abundant species in the two compared sites, ai = total number of individuals in site A, bi = total number of individuals in site B) (Magurran, 1988
).
Diversity and dominance
We calculated the Shanon-Wiener diversity indexes for the spore banks of the three types of vegetation and depth category (H' = –
Pi[log Pi] where Pi = proportion between the individuals of each species in the sample and total individuals in the sample [ni/N]). The Berger- Parker dominance index was also calculated (D = Nmax/N, where: Nmax = number of individuals of the most abundant species and N = total number of individuals at each site) (Magurran, 1988
).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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The size of the banks decreased significantly with depth in the three types of vegetation (Fig. 1). The first layer had a significantly higher number of spores compared with the other two layers, which did not statistically differ significantly (Tukey test; P < 0.001), except in the montane rain forest where there was a more homogenous vertical distribution pattern in the three layers of the spores. Thus, a statistical difference only appeared between the first and third layers. The highest mean number of prothallia was seen in the soil samples from the uppermost (10 cm) of the xerophilous shrubland (137).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). The same pattern of vertical distribution of diaspores was seen in all of the vegetation types studied, the size of the banks notoriously decreased with depth. The small number of spores in the soil samples of the deepest layers can be simply attributed to the restricted descending movement of the spores into deeper layers. Additionally, a proportion of spores found in the surface soil layer probably were produced during the last sporulation, which is seasonal in the xerophyllous shrubland and continuous in the montane rain and pine–oak forests. In the xerophyllous shrubland, soil was sampled before the rainy season and 6 mo after spore dispersal; therefore, germination and movements of these spores to deeper soil layers probably did not occur.
Changes during the year in the spore bank could be more conspicuous in this vegetation type than in the studied forests. On the other hand, most ferns are homosporic and have long- lived spores (Lloyd and Klekowski, 1970
); but viability decreases with age, and only the longest living spores could be found in the deepest layers of soil (Dyer, 1979
; Page, 1979
). Nevertheless, it is unlikely that the spores remain within the soil in the same sequence as they were deposited because the soil is not a static medium (During and ter Horst, 1983
; During et al., 1987
; Hamilton, 1988
; Schneller, 1988
; Van Tooren and During, 1988
; Simabukuro et al., 1998
, 1999
).
A large spore bank in the soil of the montane rain forest can be attributed to the high diversity of pteridophytes on the surface. In this forest, the most homogeneous distribution of the spores could be the result of the intense nematode activity in the montane rain forest (personal observations) which contributes to the soil mix and the resulting movement of spores in all directions (Van Tooren and During, 1988
). In spite of the low diversity of pteridophytes in the standing vegetation, the xerophilous shrubland had a spore bank similar in size to the montane rain forest. This could be due to the contribution of spores from allochthonous species that arrived by long-distance dispersal from other nearby vegetation types and to the contribution of other species growing in the xerophyllous shrubland in other years or out of the sampled area. Although most ferns deposit their spores in the immediate vicinity of the parent sporophytes, some are transported across long distances by the wind during dispersal (Tryon, 1972
, 1986
; Conant, 1978
). For example, During and ter Horst (1983)
found viable fern spores in soil samples collected at a distance of 3– 4 km from the nearest spore source. According to our results, fern spores could be transported by the wind even longer distances, because the source of the nearest allochthonous spores are between 20 and 30 km from the xerophilous shrubland.
The small number of recovered spores from the pine–oak forest could be explained by the soil's extremely acid pH, which probably affected the spores' viability (Page, 1979
; Raghavan, 1989
).
Specific composition and diversity
The diversity and size of the spore banks were significantly reduced with depth: the first 10 cm of soil had a significantly higher number of species and of individuals by species in the three habitats studied. Rydgren and Hestmark (1997)
did not find significant differences in the vertical distribution of the spores in a boreal forest. Nevertheless, very few studies deal with the specific composition of spore banks and their variations in relation to depth.
The spore bank in the xerophilous shrubland and montane rain forest had a similar specific composition. According to the Sørensen similarity index, these types of vegetation share 61.5% of the species in the spore bank. This high similarity percentage confirms the spore deposition of allochthonous taxa in the shrubland's soil. The role of hazard in the transportation of spores must not be ignored in any research on spore banks (Bisang, 1996
).
Dyer and Lindsay (1992)
indicate that fern spores can be present in the soil of any habitat, even when the populations of parental sporophytes are far away. In fact, fern gametophytes have been detected in soil samples from a great variety of habitats in several countries such as the Netherlands (During and ter Horst, 1983
), Sweden (Milberg, 1991
), Spain (During et al., 1987
), and England (Clymo and Duckett, 1986
). Therefore, the survival of spores during the long-distance dispersal process and the successful establishment of their gametophytes can lead to a specific parallel composition between localities (Longton and Schuster, 1983
).
Nevertheless, the presence of species from the montane rain forest in the xerophyllous shrubland spore bank has no ecological importance, because these taxa have different ecological requirements from those of the native species. The presence of the epiphytic Elaphoglossum vestitum in the spore bank of the montane rain forest is also irrelevant. Nevertheless, for colonization, regeneration, or succession, spores that have dispersed across long distances to different vegetation types or substrates (soil bank, tree, or shrubland branches) could be an important source of fern regeneration (Milberg, 1991
).
On the other hand, the presence of certain taxa at specific depths suggests a differential distribution of species in the soil banks. This distribution pattern could be attributed to intrinsic spore characteristics such as size and degree of surface ornamentation (Dyer and Lindsay, 1992
) or to certain physical properties of the soil (texture, dampness, organic matter content, etc.) (Bisang, 1996
).
Spore bank vs. surficial pteridoflora
When considering the presence or absence of taxa, our results showed strong differences between the floristic composition of the soil's surface and the soil's spore banks, particularly in the xerophilous shrubland and the pine–oak forest. In the first one, only Cheilanthes sinuata is common, while in the second one it is Osmunda regalis (Table 4). However, in the montane rain forest, 41.6% of the surface species of pteridoflora is represented in the soil.
Spores of 22 of the 23 fern species registered in the surface have no chlorophyll, which suggests that all of them are potentially capable of forming persistent spore banks. Nevertheless, results revealed that only 50% of the species are represented in the soil. Roberts (1981)
indicates that the soil samples obtained for this type of studies represent small areas of the surface, which could lead to an underestimation of the species present. The low representation of pteridophytes species in the soil banks can also be attributed to the spores' viability loss; some of them are more vulnerable because of their thin walls (Page, 1979
).
The propagule bank on the first layer of soil gives an indication of the most recent history of the aboveground (standing) vegetation. Thus, the presence or absence of spores of some taxa in this stratum can reflect historical changes in species abundance as a result of succession (Rydgren and Hestmark, 1997
). The presence of spores of N. sinuata, Pityrogramma sp., P. altissima, T. ovata, and Thelypteris sp. in the first 10 cm of soil of the xerophilous shrubland can be the result of propagule dispersal from a distant place or might represent the most recent event in the disturbance history of the habitat (Fig. 7).
The presence of a spore bank in the soil constitutes a potential source for in situ regeneration (Schneller, 1988
; Rydgren and Hestmark, 1997
). On the other hand, the persistence of certain species in the community depends to a great extent on the survival of its propagules in the diaspore reservoir. This reservoir constitutes a "time escape" for those species that were present in the soil but not on the surface. In this sense, the vegetation that inherits the available space will be the one that is better represented in the propagule bank.
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FOOTNOTES |
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4 E-mail: bpg{at}xanum.uam.mx
; Tel.: 58 04 64 58; Fax: 58 04 46 88
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Clymo R. S. J. G. Duckett 1986 Regeneration of Sphagnum. New Phytology 102: 589-614[CrossRef]
Conant D. S. 1978 A radioisotope technique to measure spore dispersal of the tree fern Cyathea arborea Sm. Pollen & Spores 20: 583-593
During H. J. M. Bruges R. M. Cros F. Lloret 1987 The diaspore bank of bryophytes and ferns in some contrasting habitats around Barcelona, Spain. Lindbergia 12: 137-149
During H. J. B. Ter Horst 1983 The diaspore bank of bryophytes and ferns in chalk grassland. Lindbergia 9: 57-64[ISI]
Dyer A. F. 1979 The culture of fern gametophytes for experimental investigation. In A. F. Dyer [ed.], The experimental biology of ferns, 253– 305. Academic Press, New York, New York, USA
Dyer A. F. 1994 Natural soil spore banks—can they be used to retrieve lost ferns?. Biodiversity and Conservation 3: 160-175[CrossRef][ISI]
Dyer A. F. S. Lindsay 1992 Soil spore banks of temperate ferns. American Fern Journal 82: 89-122[CrossRef]
Dyer A. F. S. Lindsay 1996 Soil spore banks—a new resource for conservation. In J. M. Camus, M. Gibby, and R. J. Johns [eds.], Pteridology in perspective, 153–160. Royal Botanic Gardens, Kew, UK
Hamilton R. G. 1988 The significance of spore banks in natural populations of Athyrium pycnocarpon and A. thelypterioides. American Fern Journal 61: 171-182[CrossRef]
Komarova T. A. 1987 The spore regeneration of ferns in fresh burns of the South Sikhote-Alin. Botanicnyj zurnal-moskva 72: 215-220
Kornás J. 1985 Adaptative strategies of African pteridophytes to extreme environments. In A. F. Dyer and C. N. Page [eds.], Biology of pteridophytes, 391–396. Proceedings of the Royal Society of Edinburgh. The Royal Society of Edinburg, Edinburgh
Leck M. A. R. L. Simpson 1987 Spore bank of Delaware River freshwater tidal wetland. Bulletin of the Torrey Botanical Club 144: 1-7
Lloyd R. M. E. J. Klekowski 1970 Pteridophyta: evolutionary significance of chlorophyllous spores. Biotropica 2: 129-137
Longton R. E. R. M. Schuster 1983 Reproductive biology. In R. M. Schuster [ed.], New manual of bryology, vol. 1, 386–462. Hattori Botanical Laboratory, Nichinan, Japan
Magurran A. E. 1988 Ecological diversity and its measurement. Cambridge University Press, Cambridge, UK
Mickel J. 1992 Pteridophytes. In R. McVaugh [ed.], Flora Novo-Galiciana: a descriptive account of the vascular plants of western México. The University of Michigan Herbarium, Ann Arbor, Michigan, USA
Mickel J. J. Beitel 1988 Pteridophyte flora of Oaxaca. The New York Botanical Garden, New York, New York, USA
Milberg P. 1991 Fern spores in a grassland soil. Canadian Journal of Botany 69: 831-834[ISI]
Page Ch. N. 1979 Experimental aspects of fern ecology. In A. F. Dyer [ed.], The experimental biology of ferns, 551–589. Academic Press, New York, New York, USA
Palacios-Ríos M. 1992 Las pteridofitas del estado de Veracruz, México. Ms.C. thesis, Universidad Nacional Autónoma de México, México
Pérez-García B. A. Orozco-Segovia R. Riba 1982 El banco de esporas de helechos en el suelo de Los Tuxtlas, Ver. Boletín de la Sociedad Botánica de México 43: 89-92
Pires I. S. de O. E. A. Simabukuro L. M. Esteves G. M. Felippe 1998 Method for the extraction of live fern spores from soil. Hoehnea 25: 187-194
Raghavan V. 1989 Development biology of fern gametophytes. Cambridge University Press, Cambridge, UK
Roberts H. A. 1981 Seed banks in soil. In T. H. Coaker [ed.], Advances in applied biology, 1–55. Academic Press, New York, New York, USA
Rydgren K. G. Hestmark 1997 The soil propagule bank in a boreal old-growth spruce forest: changes with depth and relationship to aboveground vegetation. Canadian Journal of Botany 75: 121-128[ISI]
Schneller J. J. 1988 Spore bank, dark germination and gender determination in Athyrium and Dryopteris. Results and implications for population biology of pteridophyta. Botanica Helvetica 98: 77-86[ISI]
Schneller J. J. 1998 How much genetic variation in fern population is stored in the spore banks? A study of Athyrium filix-femina (L.) Roth. Botanical Journal of the Linnean Society 127: 195-206[CrossRef]
Simabukuro E. A. A. Begovacz L. M. Esteves G. M. Felippe 1999 Fern spore bank at Pedregulho (Itirapina, Sao Paulo, Brazil). Revista Brasileira de Biologia 59: 131-139
Simabukuro E. A. L. M. Esteves G. M. Felippe 1998 Analysis of a fern spore bank in Southeast, Brazil. Hoehnea 25: 45-57
Smith A. R. 1981 Flora of Chiapas. Pteridophytes. The California Academy of Sciences, San Francisco, California, USA
Sokal R. R. F. J. Rohlf 1987 Introduction to biostatistics, 2nd ed. Freeman, New York, New York, USA
Tryon R. 1972 Endemic areas and geographical speciation in tropical American ferns. Biotropica 4: 121-131[CrossRef]
Tryon R. 1986 The biogeography of species, with special reference to ferns. Botanical Review (Lancaster) 52: 117-156
Van Tooren B. F. H. J. During 1988 Viable plant diaspores in the guts of earthworms. Acta Botanica Neerlandica 37: 181-185[ISI]
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