Composition and distribution characteristics of karst epilithic moss communities

Bryophytes have an important ecological function in maintaining ecological diversity, material transformation, and energy cycles in ecosystems. In this study, bryophytes in a typical karst area were the research objects. The coverage and abundance of rocky bryophytes in established plots were recorded. The composition and distribution characteristics of the karst epilithic mosses were analyzed by importance values, a dissimilarity index and ggplot2 in R. The karst epilithic moss communities included 207 species in 93 genera and 37 families, including 185 species in 27 families and 80 genera of mosses and 22 species in 10 families and 13 genera of liverworts. The dominant families were Pottiaceae, Brachytheciaceae, Thuidiaceae, Bryaceae, Hypnaceae, Mniaceae, Entodontaceae, and Lichenaceae. The dominant species were Thuidium kanedae, Pseudosymblepharis angustata, Trichostomum involutum, Racopilum cuspidigerum, Brachythecium helminthocladum, Eurohypnum leptothallum, Hyophila involuta, Anomodon rugelii, Taxiphyllum taxirameum, and Bryohaplocladium angustifolium. Epilithic mosses in karst habitats have ve life forms: turf, weft, cushion, slanting, and pendant. The main life forms we observed were turf and weft. diversity bryophytes areas with high forest coverage, desertication habitats. Hypopterygiaceae involuta, Hyophila javanica, Trichostomum involutum, Eurohypnum leptothallum, Brachythecium pulchellum, Brachythecium viridefactum, Anonydon abbrevia, Anomodon minor, Bryum argenteum, Bryum algovicum, Racopilum cuspidigerum, Racopilum orthocarpum, Thuidium plumulosum, Thuidium kanedae, etc. Amblystegiaceae, Cryphaeaceae, Grimmiaceae, Calliergonaceae, Habrodontaceae, Metzgeriaceae, Pallaviciniaceae, Plagiochilaceae, Pelliaceae, and Makinoaceae only in moist and only found this There were 207 species of epilithic mosses in 37 families and 93 genera, including 185 species in 27 families and 80 genera of mosses and 22 species in 13 genera and 10 families of liverworts, in this study. According to previous studies, there are 1643 species of 366 genera in 94 families of bryophytes in Guizhou (Xiong&Cao, 2017), and the families, genera and species of stony karst mosses account for 39.36% of the total families, 25.41% of the total genera, and 12.54% of the total species of bryophytes in Guizhou. Among the bryophytes in Guizhou, 1/3 of the families and 1/4 of the genera are distributed on rock surfaces. This shows that epilithic mosses form an important part of the total bryophytes in Guizhou. At the same time, plants of different genera in the same family of bryophytes have different habitat requirements. Therefore, although the total number of epilithic mosses accounted for 39.36% of Guizhou bryophytes, the total number of species only accounted for 12.66% of the total species. The investigation found 200 species of stony bryophytes in 37 families and 89 genera, among which 27 families, 76 genera and 180 species are mosses and 10 families, 13 genera and 20 species are liverworts. Compared with the ndings of Zhang (1993), who identied 186 species, 93 genera, and 28 families of mosses (including soil, tree, rotwood and other types), our study found more families and species, which may be due to the greater sampling scope in this survey; our survey results showed a higher number of moss families, genera and species. However, compared with the 144 species, 94 genera and 45 families surveyed by Lin (1989) (including 49 species, 27 genera, and 21 families of liverworts as well as 95 species, 67 genera, and 24 families of moss), the total number of families was lower, especially for the liverworts. The Blepharostomataceae found in the 1989 investigation was not included in the Bryophyte Flora of Guizhou, and it may be that the editor did not collect this family after 1989.


Species composition of karst epilithic mosses
A total of 1,400 specimens were collected in the 2 research areas belonging to 37 families, 93 genera, and 207 species, including 27 families, 80 genera, and 185 species of mosses and 10 families, 13 genera, and 22 species of liverworts (see appendix for details). Statistics about the genera and species in the dominant families are shown in Table 1. The number of genera in the 10 most dominant families accounts for 60.22% of all genera, and the number of species in the dominant families accounts for 70.53% of the total species. Among the mosses are Pottiaceae, Brachytheciaceae, Thuidiaceae, Bryaceae, Hypnaceae, Mniaceae, Entodontaceae, Meteoriaceae, Neckeraceae, and Anomodontaceae, which were the ten most abundant families of karst epilithic mosses in this study (Table 1). These 10 families of mosses are widely distributed on the rock surface, have strong adaptability and are most common on the surface of karst rocks. The number of species of liverworts was much smaller than that of mosses. Among them, Plagiochilaceae and Porellaceae had 6 and 4 species, accounting for 2.90% and 1.93% of the total species, respectively, and are more common in humid karst rock environments.  The dome-shaped community grows from the initial center point, the branches and main branches have the same growth direction, and it is di cult to distinguish the plants from the outside.

Pendant 11 5.31
The plant grows into a creeping shape, and its main branches hang on the trunk, branches and other objects like hairs.
Slanting 10 4.83 The plant grows creeping or "inverted" and is slanted, but the plant is short and not overhanging, the stem is single or branched; the leaves are at and often bilaterally symmetrical.

Analysis of dominant karst epilithic moss species
The importance values of epilithic mosses at the Maolan Nature Reserve and the Puding Karst Ecological Research Station were calculated separately. The dominant species of epilithic mosses in karst obtained by sorting are shown in Table (3).  typical mixed karst evergreen broad-leaved forest and evergreen broad-leaved deciduous forest. The forest has high canopy density, low solar radiation received by the rock surface, low altitude, a warm and humid climate, and high habitat heterogeneity. However, the Puding Karst Ecosystem Observation and Research Station has low vegetation coverage, exposed rock, strong solar radiation received on the rock surface, severe rocky deserti cation, and low habitat heterogeneity. There are large differences in environmental factors such as air temperature, humidity, and light intensity between the two study areas, leading to large differences in the composition, distribution, and diversity of families, genera, and species of bryophytes in the two study areas.

Conclusion
Karst epilithic mosses are rich in biodiversity, with a total of 37 families, 93 genera and 207 species, including 27 families, 80 genera and 185 species of mosses and 10 families, 13  and weft. The species richness of karst bryophytes in moist habitats is signi cantly higher than that in dry habitats. This shows that the distribution of karst epilithic moss communities is closely related to their habitats. The richness of epilithic mosses in areas with high forest coverage, high humidity and abundant water and heat conditions is higher than that in stony deserti cation habitats. This shows that the biodiversity of bryophytes can be used as an evaluation index for the regional ecological environment. At the same time, droughttolerant plants such as Eurohypnum leptothallum, Hyophila involuta, and Anomodon rugelii, the dominant species in rocky deserti cation areas, can provide new ideas for the future comprehensive management of rocky deserti cation areas.

Study area
We selected typical karst areas at the Libo Maolan National Nature Reserve and the Puding Karst Ecosystem Observation and Research Station of the Chinese Academy of Sciences as the research areas (Fig.4). The Maolan National Nature Reserve is located in southeastern Guizhou, E107°52′10″~108°45′40″, N25°09′20″~25°20′50″ (Zhu, 1997), and is in the subtropical monsoon humid climate zone. The annual precipitation is 1752.5 mm, the average annual relative humidity is 83%, the average annual temperature is 15.3 °C, the average temperature of the coldest month (January) is 5.2°C, the average temperature of the hottest month (July) is 23.5°C, and the total annual solar radiation is 63289.80 Kw/m 2 . The karst peak forests and peak-cluster depressions in the area are composed of pure limestone and dolomite, forming a typical karst landform. The forest coverage rate is 87.4%, and the main vegetation type is a karst native mixed evergreen-deciduous broad-leaved forest. Rich in biodiversity and with a healthy ecosystem, it is unique for being the most stable karst where a is the number of common species between two communities, b and c are the numbers of unique species in the two communities, the β value is between 0 and 1. A β value between 0 and 0.25 indicates that the two communities are very similar; between 0.25 and 0.50 indicates that the two communities are moderately similar; between 0.50 and 0.75 indicates that the two communities are moderately dissimilar; and between 0.75 and 1.00 indicates that the two communities are extremely dissimilar.
Microsoft Excel 2010, Arc GIS10.2 and R language and ggplot2 were used for statistical data analysis and gure drawing.  Distribution characteristics of karst bryophytes and their relationship with the environment