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Department of Biological Sciences, The University of Alabama, Tuscaloosa, Alabama 35487
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Uniflagellate zoosporic "fungi" (=Chytridiomycota and the zoosporic protista Hyphochytriomycota) are common inhabitants of soil. However, at what scale differences in their spatial distribution can be detected is poorly known. The first objective of this study was to assess the association of organismal distribution and frequency with two microhabitats: moss-covered and exposed forest soils, at four macroscopically similar but spatially separate sites in the Blue Ridge and Allegheny Mountains of Virginia. The second objective was to provide statistically either acceptance or denial of inferences derived from sampling regimes involving a more limited number of samples. To evaluate the scale where distributional differences may occur within a site, protocols involved four collection regimes and random point and linear transect sampling. Chytrid frequency on thalli of two moss genera was greatest in the soil surrounding and under the moss rhizoids. Random point sampling methods suggested differences in zoosporic fungal frequency between moss-covered soil and the exposed soil adjacent to mosses, as well as between two moss taxa. Linear transect sampling methods also suggested differences in zoosporic fungal frequencies between moss-covered soil and soil proximal to mosses. However, statistical analysis of random point samples using a goodness-of-fit test demonstrated that there was no significant difference in frequency of zoosporic fungi from moss-covered soil and exposed soil proximal to mosses. More importantly, there was a significant difference in the frequency of ubiquitous and common zoosporic fungal species between different moss/soil complexes. This study demonstrates that differences in chytrid distribution can be detected at a microscale while at a larger scale, similarity in frequency and distribution was found.
Key words: Chytridiomycota, diversity, ecology, Hyphochytriomycota, microhabitat
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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, States 1981, Bisby 1995, Persiani et al 1998, Davel and Rouxel 2000, Ellanskaya et al 2000, Gusmao et al 2001). Their role, prevalence, and distribution in soils are poorly known. Although extensive inventories of these microfungi have been produced (Coker 1927, Sparrow 1952, 1957, Scott 1960, Willoughby 1961, 1965, Scott et al 1963, Miller 1965b, Hasija and Miller 1970, Booth 1971a, b, e, Booth and Barrett 1971, Roane 1973, Sparrow and Lange 1977, Karling 1981, Willoughby and Rigg 1983, Lee 2000, Letcher and Powell 2001), a clear concept of the scale of distributional differences has not yet been established. A study of soil at 4 macroscopically similar but spatially separate collection sites in forests of the Blue Ridge and Appalachian Mountains of Virginia over a 6 mo period produced an inventory of 15 saprophytic and parasitic zoosporic fungi (Letcher and Powell 2001). Five species were either ubiquitous or common among the sites, while the remaining species were scarce to rare. The four sites were similar on a macro scale in frequency of ubiquitous or common species although there were distributional differences among the sites, as well as within an individual site. Additionally, enrichment culture of a large number of samples acquired by random point sampling of soils at a single collection site over a period of one year failed to detect seasonal succession of ubiquitous or common zoosporic fungal species.
That study (Letcher and Powell 2001) also indicated that distribution of zoosporic fungi in a given habitat parallels that of other microbial life forms (Atlas and Bartha 1993). A few species were ubiquitous or common and prevalent within the habitat, while the majority of species were scarce to rare. It was the ubiquitous and common species that characterized community structure, while the scarce to rare species to a great extent determined the species diversity of the community. Filamentous microfungi appear to exhibit habitat specificity (Apinis 1972, Christensen 1981), and research (Letcher and Powell 2001) reaffirmed previous studies of chytridiaceous microfungi in soil, which indicated that individual species and guilds of species exhibit habitat specificity (Willoughby 1961, 1962, 1964, 1965, Booth 1969, 1971a, b, c, d, e, Booth and Barrett 1971, 1975, Karling 1981, Willoughby and Rigg 1983). A study of chytrid distribution in different but contiguous habitats (Willoughby 1961) of meadow, pond, and the terrestrial/aquatic interface between the two indicated that certain chytridiaceous fungi exhibited habitat specificity. Studies have not addressed chytrid distributional patterns within a single habitat using linear transects to determine scale of distribution.
Although recognizable assemblages of soil microfungi correlate positively with recognizable vegetation types (Apinis 1972, Christiansen 1981), specific plant-chytrid associations have not been explored. Non-vascular plants, such as mosses, are known to have associations with all major groups of fungi (Smith 1949, Gerdemann 1968, Redhead 1981, Mago et al 1992), although affinities of mosses with zoosporic fungi has only limited and peripheral documentation (Sparrow and Barr 1955, Sparrow 1960, 1965, Scott et al 1963, Willoughby 1964, Miller 1965a, b, Booth and Barrett 1975, Sparrow and Lange 1977, Lange 1978, Dewel and Dewel 1987). These reports suggest, however, the need for more specific investigations of potential correlations between chytrids and moss distribution.
It is commonly accepted that Chytridiomycota are associated with mosses, and hence, a good place to collect zoosporic fungi is near mosses, because mosses retain soil moisture. In an attempt to establish whether specific patterns of zoosporic fungi exist in the soil encompassing a single moss taxon (genus) or with mosses in general, a sampling protocol involving four sample collection regimes was employed. First, four different thallus regions associated with two moss taxa from a single collection site were cultured and examined to see if there were differences in species present, and moss thallus regions required to adequately sample chytrids were determined. Second, four similar collection sites (Letcher and Powell 2001) with the same two moss taxa present in each site were identified. From all four sites, both soil under mosses and exposed soil adjacent to mosses were sampled for diversity of zoosporic fungal species, as well as indications of frequency and distributional patterns. Third, at a single collection site, a sampling procedure involving linear transects was employed to attempt to define inferences relating to spatial distribution of zoosporic fungi in moss-covered soil and exposed soil proximal to mosses. Fourth, at a single collection site, results of random point sampling of moss-covered soil and exposed soil proximal to mosses were subjected to statistical analysis to determine zoosporic fungal distribution patterns. This study attempts for the first time to resolve the spatial scale of sampling required to reveal zoosporic fungal distributional patterns in the soil, if patterns do indeed exist. Such research complements the longstanding interest among ecologists in detecting scales and pattern in ecological data (O'Neill 1989).
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). From these sites, soil samples were collected from both moss-covered soil and exposed soils. Mosses in the four sites were inventoried in an attempt to locate two morphological forms present in all four sites. Collections of mosses were identified to species using Crum and Anderson (1981). Two moss genera were selected on the basis of gross morphology and abundance. Polytrichum Hedw. is a moss with a generally robust gametophyte (6–45 cm) with extensive rhizoids; several of its species occur in loose tufts. Dicranum Hedw. is a moss with short, dense, tomentose tufts of gametophytes 2.5–5 cm tall with short, abrupt rhizoids. Individual moss patches, extensive enough for sampling, were selected. Samples from mosses and moss-covered soil consisted of ca 5–10 g of the moss plant material or the soil in which the moss was growing. Exposed soil samples adjacent to or proximal to mosses consisted of ca 5 g of soil, and were obtained from soils which were devoid of moss or other vegetational cover, from which the litter layer was removed prior to sampling. Samples from both mosses and exposed soils were placed in individual quart ziplock bags and stored in a chilled insulated cooler and were immediately refrigerated at 4 C upon return from the field. Enrichment culturing procedure – To identify a rational strategy for portraying potential zoosporic fungal distribution patterns with mosses and exposed soils, four collection regimes were employed (Table I).
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, Stevens 1974). Cultures dishes were placed at room temperature (21 C), and baits were examined microscopically at days 7, 14, 21, and 42. Individual zoosporic fungal species presence was scored if the species was observed at any of the examination intervals. ii. Random point sampling: moss-covered soil and exposed soil adjacent to mosses. To assess the zoosporic fungal inventory, and frequency and distribution of zoosporic fungi associated with two mosses and adjacent exposed soils at four sampling sites, samples from two mosses and two adjacent exposed soils were collected at four collection sites on three dates. Hereafter, the term "adjacent" refers to sampling on a scale of meters, as moss-covered soil samples and adjacent exposed soil samples were no less than 4 m apart (Table I, collection regime ii). For each moss-covered soil sample or adjacent exposed soil sample, 3–5 g of moss rhizoids and soil (morphological region 3), soil below the moss rhizoids (morphological region 4), or adjacent exposed soil were cultured using sweet gum pollen as bait. Samples were incubated and examined as described above. For individual moss-covered soil samples and adjacent exposed soil samples, soil moisture level was recorded at the time the sample was collected.
Frequencies for individual zoosporic fungal species were determined from observations recording presence or absence with moss morphological regions, individual mosses, and adjacent exposed soils. Frequency for individual species was the number of samples in which an individual species was present out of the total number of samples examined (Willoughby 1961, Letcher and Powell 2001). Quantification of zoosporic fungal species frequency in broad categories in this study is derived from frequency of individual species with mosses and/or exposed soils. Frequency for individual zoosporic fungi follows the Braun-Blanquet scale (Braun-Blanquet 1928, Kershaw 1973, Letcher and Powell 2001): ubiquitous = 80.1–100%; common = 60.1–80%; often present = 40.1–60%; scarce = 20.1–40%; rare = 0.1–20%. Mycographs (Peyronel 1955, States 1981, Letcher and Powell 2001) were constructed to illustrate the proportional frequencies of ubiquitous and common species of zoosporic fungi with mosses and adjacent exposed soils, and with different mosses (Figs. 1, 2).
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iii. Linear transect sampling: moss-covered soil and exposed soil proximal to mosses. To determine if scale was a factor in inferred differences in zoosporic fungal frequency from moss-covered and adjacent exposed soils (Table I, collection regime ii), sampling along linear transects crossing through moss patches was performed (Table I, collection regime iii). For each of two mosses, six moss patches large enough for repeated sampling (patches ca 30–40 cm in diameter) were located. Six samples, each 15 cm apart, were taken along a linear transect through each moss patch: two proximal soil samples from either side of the moss patch, and two moss-covered soil samples from within the moss patch. Hereafter, the term "proximal" refers to sampling on a scale of centimeters, as moss-covered and proximal soils were no more than 30 cm apart (Table I, collection regimes iii and iv). Samples were cultured, incubated, and examined as previously enumerated, using sweet gum pollen as bait. Sample collections were made on two occasions. Mycographs were constructed to analyze data pertinent to frequency of zoosporic fungi with the two mosses and proximal soil (Figs. 3–5). Data were analyzed as frequency of zoosporic fungal species with either of the mosses P. ohioense or D. polysetum and with proximal soils.
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For both the linear transect sampling with moss-covered soils and adjacent soils (Table I, collection regime iii) and random point sampling with moss-covered soils and proximal soils (Table I, collection regime iv), samples were taken with a #12, 20-mm diameter plug borer to a depth of ca 5 cm. Individual soil cores were discharged from the plug borer into sterile whirl-pack bags with a 19 mm dowel rod. After each sample was discharged from the plug borer, the inside of the borer was swabbed with a cotton patch soaked with 95% EtOH which was pushed through the borer with the dowel rod. Bagged samples were placed in a chilled ice chest and refrigerated at 4 C prior to enrichment culturing. Culturing was initiated within 48 h of sample collection. Cultures from each sample were prepared as previously enumerated and baited with sweet gum pollen, and examined at days 10–12 and 20–24 for occurrence of zoosporic fungi. The data set was subsampled, using only the six most frequent zoosporic fungal species (Gill 1978, Healey 1999). Data were analyzed using a G-log likelihood goodness-of-fit test applied to contingency tables (Table IV) and executed using SAS/STAT (1990).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Within the four collection sites, an inventory of mosses determined that two moss species (Polytrichum ohioense Ren. & Card. and Dicranum polysetum Sw.) were common to all sites. Enrichment culturing procedure – i. Enrichment cultures to determine moss thallus area for culture. None to few zoosporic fungi occurred in the cultures of moss regions 1 and 2 (aerial parts); as well, none to few species appeared on the chitin and hemp seed baits of region 3 (stem base and rhizoids) and region 4 (soil beneath the rhizoids), in contrast to prolific species frequency on the pollen bait of regions 3 and 4.
ii. Random point sampling: moss-covered soil and exposed soil adjacent to mosses.
Observations of enrichment cultures from random point sampling revealed 15 zoosporic fungal species (Letcher and Powell 2001, Figs. 1–17). Data pertinent to frequency of individual species indicated that among the four sites one to three species were ubiquitous, none to three species were common, two to four species were often present, one to five species were scarce, three to five species were rare, and none to three species were absent. Eighty percent of all species occurred at all four collection sites; 93% of all species occurred at three collection sites. Data from these collections were used to obtain frequencies of individual species with two mosses and adjacent exposed soils (Table II).
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The frequency of zoosporic fungi from random point sampling of moss-covered soils indicated there were no particularly noticeable differences in species frequency between regions 3 and 4 with either moss. When a particular zoosporic fungal species was present in one region, then it tended to be present in the other region. This trend was apparent for the ubiquitous, common, and often present species (Rhizophydium sphaerotheca, Rhizophydium subangulosum, Rhizophydium stipitatum, Septosperma rhizophydii, Phlyctochytrium aureliae, and Chytriomyces poculatus) but less apparent with the majority of zoosporic fungi which were scarce or rare, such as Phlyctochytrium mucronatum, Phlyctochytrium reinboldtae, Rhizophydium obpyriformis, Phlyctochytrium sp. #1, Phlyctochytrium sp. #2, Phlyctochytrium sp. #3, Chytriomyces annulatus, Chytriomyces hyalinus, and Rhizidiomyces bullatus. Because no noticeable differences existed in frequencies of the more commonly occurring zoosporic fungi in the two regions of the moss thallus, sample data from these two regions were pooled for analysis (Gill 1978).
Mycographs (Figs. 1, 2) reflecting frequency of the eight most commonly occurring zoosporic fungal species at the four collection sites infer differences between species profiles from moss-covered soils and adjacent exposed soils (Fig. 1) and between the two mosses (Fig. 2). R. sphaerotheca, R. stipitatum, and R. subangulosum were the most frequently found zoosporic fungi. When comparing frequencies of zoosporic fungi from moss-covered soils and adjacent exposed soils, R. stipitatum, S. rhizophydii, and R. obpyriformis were more frequent with moss-covered soils. Phlyctochytrium sp. #1 was less common with mosses than in adjacent exposed soils (Fig. 1). Zoosporic fungi were generally more frequent with the moss P. ohioense than with D. polysetum (Fig. 2).
iii. Linear transect sampling. Thirteen of the 15 zoosporic fungal species were recovered in linear transect sampling cultures of moss-covered soil and exposed soil proximal to mosses. In all linear transects, four species (R. sphaerotheca, R. stipitatum, R. subangulosum, and C. poculatus) were the most frequent (Table III), being present in at least 52% of the samples, followed by S. rhizophydii, present in at least 45% of the samples. Phlyctochytrium aureliae was three times more prevalent with the P. ohioense/exposed proximal soil sampling than with the D. polysetum/exposed proximal soil sampling. Seven other species occurred sporadically with frequencies between 0 and 38% in all linear transects.
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iv. Random point sampling: moss-covered soils and exposed soils proximal to mosses. In the random point sampling of moss-covered and exposed proximal exposed soils, 13 zoosporic fungal species occurred among the 100 samples. Frequencies for individual species ranged from 2 to 84 percent.
Statistical analysis of frequency of zoosporic fungal species with moss-covered soils and exposed proximal soils.
For statistical analysis, six species were selected on the basis of high frequency in the 25 cultures each of the two mosses and proximal soil samples: R. sphaerotheca, R. stipitatum, R. subangulosum, S. rhizophydii, P. aureliae, and C. poculatus. Other species had frequencies less than 20 percent and were excluded from analysis (Gill 1978, Healey 1999).
Polytrichum ohioense and proximal soil. The null hypothesis stated that zoosporic fungi were equally likely to occur in soil under P. ohioense as they were from exposed soil proximal to P. ohioense. There was no significant difference in the frequency of six species between P. ohioense and proximal soil (G = 0.459, df = 5, p = 0.994).
Dicranum polysetum and proximal soil. The null hypothesis stated that zoosporic fungi were equally likely to occur in soil under D. polysetum as they were from exposed soil proximal to D. polysetum. There was no significant difference in the frequency of six species between D. polysetum and proximal soil (G = 1.757, df = 5, p = 0.882).
Statistical analysis of frequency of zoosporic fungal species with different moss/soil complexes. Because no significant difference existed in profiles of six commonly occurring zoosporic fungal species between P. ohioense and exposed proximal soil, or between D. polysetum and exposed proximal soil, the P. ohioense data and its proximal soil data were combined, as were the D. polysetum data and its proximal soil data, to increase the sample size of a moss/soil complex. The null hypothesis stated that zoosporic fungi were equally likely to occur under the P. ohioense/soil complex as they were under the D. polysetum/soil complex. There was a significant difference in the frequency of six species between the moss/soil complexes. Zoosporic fungi were more likely to occur with the P. ohioense/soil complex than with the D. polysetum/soil complex (G = 11.805, df = 5, p = 0.038).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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In approaching the first objective, two collection regimes were employed. The first collection regime was based on water being the medium of zoosporic fungal motility, and the possibility of species occurring from soil to aerial moss parts. Analysis of culture data indicated that species occurrence was almost entirely limited to the two moss regions associated with the soil, which is where soil microfungi reside to a large extent (Griffin 1972). Zoosporic fungi also occurred abundantly on the pollen substrate rather than on chitin or hemp seeds. These results suggested a second collection regime restricting sampling to moss regions 3 and 4, as previously defined, using only pollen as bait.
The second collection regime consisted of 48 moss-covered soil samples and 24 adjacent exposed soil samples from 4 collection sites collected over a three month period to determine frequencies of individual zoosporic fungi. Although the number of samples for both moss-covered and exposed soils was not large enough for statistical analysis of results, graphic analysis provided inferences about species frequency and distribution, and scale of sampling. Frequencies derived from observations in the second collection regime indicated that no remarkable differences in species frequency existed between moss regions 3 and 4. However, differences in numbers did exist, demonstrating the problem with appropriate scale for sampling to determine zoosporic microfungal community structure. Combined data from the two moss regions compared to data derived from cultures of adjacent exposed soil samples indicated that differences may exist in species frequency from soil under mosses and exposed soil adjacent to mosses. A higher, more equivalent number of soil samples would logically provide a more accurate comparison.
The zoosporic fungal composition for the collection sites was revealed in the first part of this study through extensive observations of a limited number of samples from the four sites. Many of the zoosporic fungi observed with mosses in this study also occurred in previous studies of bogs or moss-covered soil. It can be readily demonstrated that pollen is invaded by chytridiaceous fungi after it has fallen into wet moss or water (Sparrow and Lange 1977); those researchers found R. sphaerotheca, R. stipitatum, S. rhizophydii, C. poculatus, P. aureliae, P. mucronatum, P. reinboldtae, and possibly R. subangulosum with baited sphagnum samples and bog water. Willoughby (1964) found R. stipitatum, S. rhizophydii, C. poculatus and C. hyalinus with mossy soil in England; Miller (1965a, b) collected R. sphaerotheca, S. rhizophydii, R. obpyriformis, R. subangulosum, R. bullatus, and possibly Phlyctochytrium sp.#2 from bogs in Virginia; Lange (1978) listed S. rhizophydii, R. stipitatum, P. mucronatum, and P. aureliae as commonly found bog chytrids. Sparrow (1965) found a Phlyctochytrium species with sphagnum samples; Booth and Barrett (1975) identified a Rhizophydium species as occurring frequently in snow bed moss areas.
If there were a specific association of zoosporic fungi with mosses, then one might expect to find differences in frequency of species found in soil under mosses and soil not covered with vegetation. This is what was observed. Frequency of zoosporic fungal species from the moss samples and adjacent exposed soil samples exhibited some noticeable differences. When frequencies of eight zoosporic fungal species exhibiting high frequencies were plotted as mycographs, the resulting octagons demonstrated the differences from soil under mosses and exposed soil adjacent to mosses (Fig. 1). The inference was that chytrids occurred more frequently with mosses than in adjacent exposed soil. Additionally, if there were a specific association of zoosporic fungi with a specific moss taxon, then one might expect to find different chytrid profiles with different mosses. This is what was found, and comparison of octagons illustrated the considerable differences (Fig. 2) which suggest that chytrids occur with greater frequency with P. ohioense than with D. polysetum.
The findings here show that in the specific habitat represented by the four collection sites, those zoosporic fungi which exhibited high frequencies also exhibited high constancy of occurrence over time (Letcher and Powell 2001), as well as abundance. These frequently found fungi can be considered as the chytridiaceous indicators of the habitat (Warcup 1951, Sewell 1959). Because of their constant presence over a time period of years (Christensen 1969, States 1981), as indicated by repeated annual sampling, prevalent fungi are good indicators of community structure. Those zoosporic fungi which are scarce to rare, less constant over time, and less abundant are complementary to a chytrid profile, but cannot serve reliably as community indicators, at least on a macroscale. However, if a scarce or rare chytrid exhibits a high frequency in a specific sample or site, then discontinuous distribution or site specificity may be indicated (Willoughby 1962). Extensive microscopic examinations of cultures in this study indicated such might be the case. For example, P. mucronatum and R. bullatus were more frequent with the moss D. polysetum than with P. ohioense or adjacent exposed soils; P. reinboldtae was more frequent with D. polysetum and adjacent exposed soils than with P. ohioense.
The second objective of the study was to evaluate inferences derived from the point sampling statistically. Analysis of zoosporic fungal community composition from the statistically valid sampling regime showed that no significant difference existed between zoosporic fungal profiles of individual mosses and exposed proximal soils. However, a significant difference did exist between profiles of different moss species/soil complexes from a single collection site. This zoosporic fungal affinity for one moss/soil complex over another may be due to an edaphic factor such as soil type associated with a moss, to an environmental factor such as specific moss habitat, to a vegetational factor such as moss rhizoidal biomass or degree of rhizoidal penetration of soil, or to variation in soil moisture levels. Our data revealed higher moisture levels with moss-covered soils than with exposed soils in both spring and autumn recordings, indicating moisture retention capacity of mosses.
Spatial scale is a factor worth strong consideration when attempting to discover if there are associations of zoosporic fungi with moss-covered or exposed soil. Zoosporic fungi have limited rhizoidal systems which penetrate only immediate substrates (i.e., pollen grains, insect exuviae) and as such do not exhibit extensive thalli, and thus distribution may be more discontinuous on a microscale. Production of a small number of motile zoospores which depend on water for dispersion tends to restrict species distribution. Consideration of these physiological aspects is necessary when evaluating their distribution.
The frequency of chytrids in moss-covered soils was not statistically significantly different from that in exposed soils proximal to moss patches. However, there were statistically significant differences in chytrid frequency between moss/soil complexes. The ability of mosses to retain moisture in underlying soils and to release dead organic material might influence chytrid frequency in soils under mosses as well as in the proximal soils. The more constant reservoir of moisture and organic nutrients could allow populations of chytrids to build up in soils under mosses more readily than in exposed forest soils. Spatially, the distance chytrid zoospores can radiate outward from a point source in soil is dependent on the moisture conditions of soils because, in the majority of chytrids, dispersal is by unwalled zoospores. One exception is the rocket-shaped walled resting spore of Septosperma rhizophydii which disarticulates from a basal cell and is highly amenable to distribution in runoff water (Powell and Blackwell 1991). During periods of heavy rains and soil saturation, zoospores percolate into adjacent soils by water runoff, if soils remain saturated long enough for sporangial discharge of zoospores. However, other than in times of soil saturation, dispersal of zoospores is limited to the extent and continuity of the network of capillary water in soils. Most of the time zoosporic dispersal would radiate from soils under mosses as a point source into the most nearby soils. Consequently it is not surprising that chytrid frequencies in soils under mosses and in proximal soils are most similar.
The microscopic examination of cultures is a labor intensive and time consuming aspect of investigation of these microfungi in the soil. To maximize the efficiency of a sampling strategy, as a protocol for sampling for zoosporic fungal distribution and frequency in soils, an initial sampling procedure involving extensive observations of a limited number of samples in order to identify and inventory the zoosporic fungal community is an essential first step. Once the species have been identified and can be recognized in mixed culture, less time has to be spent on individual culture observations. Hence, a higher number of cultures can be examined in a reasonable amount of time, allowing for accumulation of enough data for statistical analysis, a second necessary step for community assessment. Statistical analyses, although not offering proof of any condition, add substantial weight to inferences and conclusions.
The fact that statistical analysis of sampling data pertinent to zoosporic fungal species frequency and distribution with moss-covered and proximal exposed soils has led to the conclusion that species in a specific habitat are more likely to occur with one moss/soil complex than another raises many questions. Is there a difference in soil composition under different mosses? If so, is that difference due to moss microhabitat specificity, biochemical processes and resultant metabolic products produced by the moss, or physiological or physical properties of the moss relative to the soil? Are zoosporic fungi engaged in functional roles beyond saprophyte and parasite, such as mycorrhizal associations? A sampling protocol, such as presented here, which can statistically verify aspects of frequency and distribution of motile soil microfungi may contribute to resolving such tantalizing aspects of microfungal ecology.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Accepted for publication March 1, 2002.
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LITERATURE CITED |
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