Self-fertilization in mosses: a comparison of heterozygote deficiency between species with combined versus separate sexes

Self-fertilization is a key difference of adaptive significance between species with combined versus separate sexes. In haploid-dominant species such as mosses and ferns, species with either combined or separate sexes (monoicous and dioicous, respectively) have the potential to self-fertilize (intergametophytic selfing), but being monoicous allows an additional mode of selfing (intragametophytic selfing). We used allozyme electrophoresis to estimate deviations from expected levels of heterozygosity under Hardy-Weinberg equilibrium to infer selfing rates in 10 moss species from 36 New Zealand populations. We found that while there were deficiencies of heterozygotes compared to expectation in both monoicous and dioicous mosses, monoicous species had significantly higher levels of heterozygote deficiency than dioicous species (F(IS)=0.89+/-0.12 and 0.41+/-0.11, respectively). Estimated selfing rates suggest that selfing occurs frequently in monoicous populations, and rarely in dioicous populations. However, in two dioicous species (Polytrichadelphus magellanicus and Breutelia pendula), we found significant indications of mixed mating or biparental inbreeding in a handful of populations. These data provide the first analysis of heterozygote deficiency and selfing among haploid-dominant species with breeding system variation, and we discuss our results with respect to the consequences of inbreeding depression and the evolution of breeding systems.     

Environmental drivers of the bryophyte propagule bank and its comparison with forest-floor assemblage in Central European temperate mixed forests

Species richness, composition and abundance of the bryophyte diaspore bank of Central European temperate mixed forests were compared with the forest-floor bryophyte assemblage. The impact of environmental variables and anthropogenic disturbances, including tree species composition, stand structure, microclimate, light conditions, soil and litter properties, management history, and landscape properties, potentially influencing bryophyte diaspore bank assemblages were explored. Thirty-four, 70–100 years old mixed stands with differing tree species composition were examined in the ?rség National Park, Western Hungary. The diaspore bank was studied by soil collection and cultivation, and data were analysed by multivariate methods. Contrary to the forest-floor bryophyte assemblage, where substrate availability, tree species composition and stand structure were the most influential environmental variables, the composition and abundance of the diaspore bank was mainly affected by site conditions (microclimate, litter and soil properties). Species richness of the bryophyte diaspore bank was lower than that of the forest-floor bryophyte assemblage. Short-lived mosses (colonists, short-lived shuttles) were dominant in the diaspore bank, as opposed to the forest-floor bryophyte community, where perennial mosses dominated. In the studied forests, the importance of the bryophyte diaspore bank was relatively low in the regeneration and maintenance of the forest-floor bryophyte vegetation.     

Recolonization potential of bryophyte diaspore banks in harvested boreal mixed-wood forest

Bryophyte diaspore banks are a potential source of reproductive propagules that may be able to colonize newly available habitat after forest harvesting. However, their role and the factors influencing the successful establishment of species remain poorly understood. To investigate these aspects of diaspore banks, we obtained mineral soil samples from mixed and coniferous stands of boreal mixed-wood forest in northern Alberta, Canada, which had recently experienced a range of harvesting intensities. Samples were germinated in growth cabinets under two light regimes. The composition of germinated bryophyte species was compared among forest types, harvesting intensities, and light levels, and also related to edaphic conditions and geographic location of the sample site. Germinated species composition was not related to forest type or harvesting intensity, but was associated with measured edaphic variables and geographic space, indicating that similarity in species composition reflected similarity in edaphic conditions and spatial proximity. This was partly because of spatial dependence of edaphic variables. Light intensity had a significant influence on the development of species assemblages and individual species responses. Richness and cover of acrocarpous mosses (fugitive, colonist, and shuttle life-history strategies) were significantly reduced under low light conditions, but pleurocarpous mosses (perennial strategy) were not affected. Shannon diversity and the frequency of reproduction were significantly greater with high light. Pleurocarpous mosses that are characteristic of intact forests germinated frequently, suggesting that diaspore banks may influence their recovery after disturbance. Diaspore banks are a repository of species at sites affected by forest harvesting; however, diaspore germination and establishment will be constrained by the local environment, including edaphic conditions and light intensity.     

Climate and microhabitat shape the prevalence of endozoochory in the seed rain of tropical montane forests

Endozoochory, the dispersal of seeds by animal ingestion, is the most dominant mode of seed dispersal in tropical forests and is a key process shaping current and future forest dynamics. However, it remains largely unknown how endozoochory is associated with environmental conditions at regional and local scales. Here, we investigated the effects of elevation, climate, and microhabitat conditions on the proportion of endozoochorous plant species in the seed rain of the tropical Andes of southern Ecuador. Over 1 year, we measured seed rain in 162 seed traps on nine 1-ha forest plots located at 1000, 2000, and 3000 m a.s.l. We recorded climatic conditions (mean annual temperature and rainfall) in each plot and microhabitat conditions (leaf area index and soil moisture) adjacent to each seed trap. In total, we recorded 331,838 seeds belonging to 323 morphospecies. Overall, the proportion of endozoochorous species in the seed rain decreased with elevation. The relative biomass of endozoochorous species decreased with increasing rainfall, whereas the relative seed richness of endozoochorous species increased with increasing temperature and leaf area index. These findings suggest an interplay between climate factors and microhabitat conditions in shaping the importance of endozoochorous plant species in the seed rain of tropical montane forests. We conclude that changing climatic and microhabitat conditions are likely to cause changes in the dominant dispersal modes of plant communities which may trigger changes in the current and future dynamics of tropical forests.     

Chromosomal distribution of rRNA genes in the karyotypes of two dioicous liverwort species from the genus Pellia Raddi

Over one hundred years have passed since the first cytogenetic studies were made on the liverwort genus Pellia Raddi. The karyotype of Pellia is characterised by large chromosomes, a varying heterochromatin content and the presence of sex chromosomes in the dioicous species. Most of the Pellia species are diploids with n?=?9, but one of them, Pellia borealis Lorb., has been described as an example of allopolyploidy in liverworts. Although the localisation of rRNA genes, which are essential components of the nuclear genome, remains a challenge in bryophytes, data on the number and chromosomal localisation of 35S and 5S rDNA in all of the Pellia species are now available. Previously, fluorescence in situ hybridisation using rDNA probes was performed on the mitotic chromosomes of 2 monoicous species. The aim of this study was to establish the number and chromosomal distribution of rRNA genes in 2 dioicous diploid species—Pellia endiviifolia (Dicks.) Dumort. and Pellia neesiana (Gottsche) Limpr. The relationships between the species within the genus Pellia can now be discussed in the context of the localisation of the rDNA sites and the range in the number of rDNA loci among bryophytes can also be verified.     

Association between bryophytes and seedlings in Nothofagus sub-Antarctic forests

Bryophytes, which include mosses, liverworts and hornworts, indeed play a significant role in the natural dynamics of native forests. They contribute to fundamental ecological processes such as tree regeneration. In this context, the objective was to analyse the association of bryophytes with Nothofagus seedlings, as well as whether the substrates where bryophytes grew influenced bryophyte-tree seedling association, in sub-Antarctic forests at two contrasting landscapes (coastal and mountain) of Tierra del Fuego (Argentina), to better understand their impacts on the natural regeneration processes. We hypothesized that bryophytes act as a substrate for seed germination and initial regeneration growth in pure and mixed forests of N. pumilio and N. betuloides, resulting in widespread tree seedlings–bryophyte associations in all landscapes. In each forest and landscape location, 60 transects were established (10 m in length) to evaluate bryophyte cover (by point intercept method) and substrate type (bare soil, decaying wood and litter cover) where they were growing. An adaptation of the relative interaction index (RII) based on tree seedling cover associated with bryophyte species (%) and tree seedling cover in the absence of bryophytes (%) was calculated and analysed to assess competition or facilitation between bryophytes and tree seedlings. Nothofagus pumilio seedlings were less abundant in bryophytes compared to other substrates, suggesting an inhibitory effect on the germination and/or survival of N. pumilio. In contrast, the seedlings of N. betuloides, in both pure and mixed forests, exhibited higher abundance on bryophyte substrates, particularly in mosses at mountain landscape (RII = 0.83 ± 0.08 in litter and 0.62 ± 0.11 in decaying wood). These findings suggest that bryophytes play a facilitating role for N. betuloides seedlings during germination and initial phases of growth, mainly in the mountain. Therefore, their conservation promotes N. betuloides forest continuity, both in pure and mixed structures.     

Functional diversity of epiphytes in two tropical lowland rainforests, French Guiana: using bryophyte life-forms to detect areas of high biodiversity

Recent studies have described a new tropical lowland forest type in the Guianas, the tropical lowland cloud forest. It is characterized by an enriched epiphytic species diversity particularly for bryophytes compared to common lowland rainforest, and is facilitated by frequent early morning fog events in valley locations. While the increase in epiphytic species diversity in lowland cloud forests has been documented, uncertainties remain as to (1) how this small scale variation in water supply is shaping the functional diversity of epiphytic components in lowland forests, and (2) whether information on functional group composition of epiphytes might aid in discerning these cloud forests from the common lowland rainforest. We compare the distribution of functional groups of epiphytes across height zones in lowland cloud forest and lowland rain forest of French Guiana in terms of biomass, cover as well as the composition of bryophyte life-forms. Both forests differed in functional composition of epiphytes in the canopy, in particular in the mid and outer canopy, with the cloud forest having a higher biomass and cover of bryophytes and vascular epiphytes as well as a richer bryophyte life-form composition. Bryophyte life-forms characteristic for cloud forests such as tail, weft and pendants were almost lacking in the canopies of common rain forest whereas they were frequent in lowland cloud forests. We suggest that ground-based evaluation of bryophyte life-form composition is a straightforward approach for identifying lowland cloud forest areas for conservation, which represent biodiversity hotspots in tropical lowland forests.     

西双版纳热带森林土壤种子库的季节变化

通过萌发实验法对西双版纳地区的一类热带季节雨林 (番龙眼、千果榄仁 )和 2类次生林(白背桐林、中平树林 )的土壤种子库的季节变化进行了探讨。结果表明 :该地区的土壤种子库动态具有明显的季节性。季节雨林的土壤种子库储量相对稳定 ,土壤上层 ( 0～ 2 cm )的种子储量在雨季末期较大。2类次生林土壤种子库的变化则相反 ,土壤种子库中的种子种类在旱季末期较雨季末期多 ,土壤上层的种子储量在旱季末期较大。各样地均有一些种类只出现在旱季末期或雨季末期。种子在土壤种子库的动态与植物的繁殖物候和所处的环境紧密相关 ,不同种类植物的土壤种子库由于植物本身的生物学特性、传播方式和所处环境的影响而表现出不同的动态模式     

中国藓类植物无性繁殖体的初步观察

无性生殖在苔藓植物的生活史中起着重要的作用,并且常通过各种无性繁殖体来完成。无性繁殖体的形态常被用来辅助鉴定一些不育的藓类植物。本文通过对38种藓类植物的无性繁殖体进行显微观察,结果显示：无性繁殖体在不同的藓类植物之间已经过多次演化;无性繁殖体的形态在种内是相对稳定的,且与其着生位置、配子体的分枝方式密切相关,而与植物的系统位置以及生境并无直接的关系;无性繁殖体的颜色与其胞壁的厚度以及表面纹饰密切相关。此外,无性繁殖体的产生常常与假根、原丝体有共存关系。在研究中发现,藓类植物的无性繁殖体主要包括原丝体芽胞、无性芽胞（叶生芽胞、中肋芽胞、枝生芽胞）、芽体、假根芽胞和假根状块茎;其中原丝体芽胞和无性芽胞最为常见。     

Effects of restoration treatments on the diaspore bank under dense Pteridium stands in the UK

Abstract. The diaspore bank (seeds of higher plants and spores of ferns and bryophytes) was assessed between 3 and 5 yr after experiments to control Pteridium aquilinum (bracken) and restore appropriate vegetation were initiated at two contrasting locations in the UK. We tested the response of the diaspore bank using univariate and multivariate analysis of variance. The two approaches were complementary and together improved the interpretation of these results. There were considerable differences in the diaspore banks of the two sites and among the experimental locations within sites. Within each experiment there were differences in species composition, with species that were (1) common to both diaspore bank and vegetation, (2) restricted to the diaspore bank and (3) restricted to the vegetation. There is a possibility of increasing the biodiversity of the developing vegetation if some of the species present in the diaspore bank can be germinated. This was especially true for ferns where four species were found in the spore bank which were not present in the vegetation. There were few significant effects of management treatment on the diaspore bank as the experiments had been in progress for only 3 to 5 yr, but a few species had different densities in the different treatments (Betula pubescens, Juncus effusus and some bryophytes). The greatest correlation between vegetation and diaspore bank was found at the top hierarchical level (entire dataset) and this progressively reduced with scale. We interpret this as a landscape/species pool effect: as the scale of the study reduces the correlation between diaspore bank and vegetation also reduces, at least over the time scale of our study. The relevance of these results for restoration ecology is discussed briefly.     

Molecular analysis of fungal diversity associated with three bryophyte species in the Fildes Region, King George Island, maritime Antarctica

The fungal communities associated with three bryophytes species (the liverwort Barbilophozia hatcheri, the mosses Chorisodontium aciphyllum and Sanionia uncinata) in the Fildes Region, King George Island, maritime Antarctica, were studied using clone library analysis. Fungal communities showed low diversity; the 680 clones belonged to 93 OTUs. Of these, 78 belonged to the phylum Ascomycota, 13 to the phylum Basidiomycota, 1 to the phylum Zygomycota, and 1 to an unknown phylum. Among the OTUs, the most common orders in the Ascomycota were Helotiales (42 OTUs) and Chaetothyriales (14 OTUs) and the most common orders in the Basidiomycota were Sebacinales (3 OTUs) and Platygloeales (3 OTUs). Most OTUs clustered within clades that contained phylotypes identified from samples in Antarctic or Arctic ecosystems or from bryophytes in other ecosystems. In addition, we found that host-related factor may shape the fungal communities associated with bryophytes in this region. This is the first systematic study of the fungal community in Antarctic bryophytes to be performed using culture-independent method and the results may improve understanding of the endophytic fungal evolution and ecology in the Antarctic ecosystem.     

Microhabitat determines how grazing affects bryophytes in wood-pastures

Wood-pastures are biodiverse biotopes where livestock graze among trees. The diversity of several species groups is related to the structural diversity created by herbivores and by trees, decaying wood and rocks. One of the greatest threats to wood-pastures is abandonment that results in decreased heterogeneity of soil microhabitats as well as encroachment by young trees. We studied the diversity of bryophytes on different microhabitat types (soil, rocks, trees and decaying wood) in grazed and abandoned boreal wood-pastures (48 sites). Most species grew on soil, rocks or both. For both soil and rocks currently grazed sites had higher bryophyte species richness and several individual species also preferred grazed sites over abandoned sites. The grazers increase biodiversity by creating patches of bare soil and exposed rock surfaces. Currently grazed and abandoned sites did not differ significantly in bryophyte species richness on decaying wood or trees, and the overall bryophyte richness on these substrates was quite low due to the scarcity of dead wood and large living deciduous trees with suitable bark conditions. Rare species were observed on all microhabitats, most abundantly on soil and decaying wood. Especially our result on higher richness on rock surfaces shows the complexity of grazing effects on biodiversity. Grazers may affect the biodiversity of a species group that is not consumed by them, on a surface which is not attractive to them. These unobvious interactions should be recalled when planning wood-pasture management and conservation.     

镜泊湖世界地质公园火山口地下森林苔藓植物区系

镜泊湖世界地质公园火山口孕育了罕见的原始地下森林，本研究为完善中国火山生态系统苔藓植物区系地理起源提供重要资料。基于前期野外调查、标本采集和物种鉴定数据，已知苔藓植物53科126属292种，采用分层聚类分析和主成分分析方法探讨区系地理特点。结果表明：(1)镜泊湖火山口地下森林苔藓植物单种属和寡种属占绝对优势，共106属(占总属数84.13%)152种(占总种数52.05%)。(2)区系地理成分共11种，北温带分布占主体(49.12%)，东亚分布次之(21.55%)，中国特有分布第三(8.48%)。(3)地下森林中国特有苔藓植物可能沿“北线”以山脉为通道进行传播。(4)镜泊湖火山口地下森林与镜泊湖火山熔岩台地苔藓植物区系相似性最高。此外，发现受威胁苔藓植物7种。总之，镜泊湖火山口地下森林苔藓植物区系的主要特点为起源古老，组成复杂，北温带性质明显，与东亚苔藓植物区系具有深厚的历史渊源，凭火山锥内部优越的微生境成为中国特有和珍稀濒危苔藓植物的避难所。     

Ploidy level,genetic diversity,and differentiation in two closely related mosses,Scorpidium cossonii and S. revolvens (Calliergonaceae)

As ploidy level and mating system can affect genetic diversity and differentiation, we conducted population genetic analyses of two closely related mosses, Scorpidium cossonii (Schimp.) Hedenäs, and S. revolvens (Sw. ex Anonymo) Rubers which differ in ploidy level and sexual system. We collected 315 specimens in total from five populations of S. cossonii and four populations of S. revolvens in the Swiss Alps. Ploidy level, genetic diversity within populations, and genetic differentiation between populations and species were estimated using nine microsatellite markers. In each S. cossonii sample, each locus bore only one allele, while in S. revolvens, seven out of the nine loci were fixed or nearly fixed for two alleles per locus per individual. These findings are consistent with a gametophytic haploid S. cossonii and allodiploid S. revolvens. The haploid and dioicous S. cossonii was genetically more diverse than the (allo)diploid and monoicous S. revolvens. Differences in genetic diversity between the two species may be explained by different mating systems, different population sizes, and different population histories. Genetic differentiation among populations of S. cossonii was higher than among those of S. revolvens. The low genetic differentiation among populations of the monoicous species was not unexpected, since monoicous species frequently produce sporophytes, long-distance spore dispersal is more likely and leads to low differentiation.     

Diversity of saproxylic bryophytes in old‐growth and managed beech forests in the central Balkans

Abstract

The diversity of saproxylic bryophyte species in beech forest stands from the wide region of the central Balkans (i.e. Serbia and Montenegro) was studied, and this study is the first of such a type in SE Europe. Comparison of preserved old‐growth and managed forests were made. Bryophyte species diversity is higher in primeval forest stands where the spectra of dead wood in various decaying stages of its dynamics are present. The ecological group of epixylic specialists is predominant among the bryophytes recorded. Threatened bryophyte species occur in old‐growth beech stands. The dead wood as habitat together with some other factors are extremely important for the surviving of epixylic bryophyte; so these species can be used as bioindicator bryophyte species of old‐growth or managed and structured forest ecosystems.     

Bole epiphytic bryophytes on <Emphasis Type="Italic">Lithocarpus xylocarpus</Emphasis> (Kurz) Markgr. in the Ailao Mountains,SW China

Epiphytic bryophytes growing on Lithocarpus xylocarpus (Kurz) Markgr. trunks of different diameter classes in primary (132 plots) and secondary (84 plots) Lithocarpus forests in the Ailao Mountains, SW China, were surveyed and analyzed to determine species composition and richness, and to identify environmental variables that may affect it. Among the 65 species (belonging to 32 genera, 19 families) found, 28 occurred in both forests, with Syrrhopodon gardneri (Hook.) Schwaegr. predominanting. Species richness and total coverage in primary forest were significantly higher than in secondary forest. We suggest that a period of perhaps much more than 110 years is necessary for the recovery of epiphytic bryoflora in montane forest of SW China. Fan, turf, and smooth mat are the most important life forms, with high occurrences in both forests. The life form composition of epiphytic bryophytes is determined mainly by microhabitat and host age. Tree age, the presence of primary forest, bark pH, and plot exposure are the environmental variables that have significantly influenced the composition of epiphytic bryophytes. Tree age explained most variations in epiphytic bryoflora. Bark pH is another important parameter that significantly influenced the epiphytic bryophyte community, but seemed indirectly correlated with tree age. Primary forest is a favorable habitat for epiphytes, due mainly to its diversified canopy structure and the presence of large diameter hosts. Moisture-laden southwest trade winds and forest structure could differentiate microclimate and impel a distinct composition of epiphytes in windward and leeward exposures.     

Old trees contribute bio-available nitrogen through canopy bryophytes

Symbiotic cyanobacteria??bryophyte associations on the forest floor are shown to contribute significantly to stand-level nitrogen budgets through the process of biological nitrogen fixation (BNF), but few studies have considered the role of canopy bryophytes. Given the high biomass of epiphytic bryophytes in many tree species of the North American temperate rain forest, we suggest that canopy bryophytes may contribute substantially to stand-level N dynamics. We confirm the presence of cyanobacteria and measure rates of BNF at three heights (0, 15 and 30 m) in Sitka spruce trees across three watershed estuaries of Clayoquot Sound, British Columbia, Canada. This study is the first to report BNF by cyanobacteria associated with epiphytic and forest floor bryophytes in the coastal temperate rain forest of North America. Cyanobacteria density was significantly greater in epiphytic bryophytes compared to mosses on the forest floor, and rates of BNF were highest at 30 m in the canopy. The majority of total stand-level BNF (0.76 kg N · ha^-1 · yr^-1) occurs in the canopy, rather than on the forest floor (0.26 kg N · ha^-1 · yr^-1). We suggest that BNF by cyanobacterial-bryophyte associations in the canopy of coastal temperate rain forests is a unique source of ecosystem N, which is dependent on large, old trees with high epiphytic bryophyte biomass.     

WOOD SPECIFIC GRAVITY GRADIENTS IN TROPICAL DRY AND MONTANE RAIN FOREST TREES

Pith to bark specific gravity (SG) trends were investigated in 18 tropical dry forest and six montane rain forest tree species of Costa Rica. Eleven dry forest species showed statistically significant increases in SG with distance from pith. The increases ranged from 20–80%; the greatest changes were exhibited by species which are known to occur in tropical wet as well as tropical dry forests. The other seven species showed no change in SG with distance from pith. Of the montane forest species, one showed a significant decrease of 20%, and three showed significant increases ranging from 20–40%. Two species exhibited no change in SG. Comparison of these changes with trends found in tropical wet forest and temperate forest suggests that the increase in SG with size is most common in tropical wet forest, least common in temperate forest, and intermediate in tropical dry and montane forests.     

Habitat type and primary colonisation of annual shoots of conifer saplings by epiphytic lichens

The ability of single lichen species to colonise annual shoots of Scots pine ( Pinus sylvestris ) and Norway spruce ( Picea abies ) under a variety of microclimatic conditions was assessed. Lichens were found to colonise the annual shoots of conifer saplings relatively slowly. Hypogymnia physodes is almost invariably the first sorediate species to attach to the bark whereas the other sorediate species appear only exceptionally on shoots in their first couple of years. The age of the substrate seems to be less important to pendulous species, however, probably due to their ability to reproduce also by thallus fragmentation and not only by soredia or spores as most other species do. The majority of the species colonise the annual shoots of spruce faster than those of pine, which suggests that bark exfoliation can effectively hinder colonisation. The colonisation rate of most of the species is clearly reduced under open canopy emphasising the importance of diaspore supply from lichens growing on mature trees.     

Regeneration of monsoon rain forest in northern Australia: the sapling bank

Abstract. As part of a wider study examining regeneration pathways in monsoon rain forest vegetation in northern Australia, a one-off, dry season census of saplings was undertaken along transects sampled at each of 33 relatively undisturbed sites broadly representative of the range of regional monsoon rain forest vegetation. Four floristic quadrat groups were derived through TWINSPAN classification. Subsequent analyses involved: (1) comparison of mean dry season stockings of juveniles occurring in different rain forest types, and their structural and environmental correlates; (2) comparison of the contributions of different life forms, and the influence of clonal reproduction in the sapling regeneration banks of different forest types; and (3) exploration of relationships between the distributions of saplings of common tree species with respect to seed bank, floristic, structural, and environmental variables. While data presented here require cautious interpretation given that processes of seedling/sapling recruitment and mortality are highly dynamic, sapling banks were found to be most dense on coarse-textured, moist soils, and least dense on coarse-textured, seasonally dry soils. Canopy cover and fire impact were shown to be highly influential on sapling distribution, especially for saplings of tree species and those growing on seasonally dry sites. Sapling densities were little influenced by proximity to rain forest margins, except for shrubs. The potential for clonal reproduction was significantly greater on dry sites, especially for trees. The majority of saplings sampled were derived from relatively few common, non-clonal, canopy tree species. Sapling distributions of 20 out of 23 common tree species were clumped in the vicinity of conspecific adults; for most species the strength of this relationship was greater than that for any other variable. These data support observations in the literature concerning the distribution of sapling banks in moist and dry tropical forests.