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.
Table 1 Genera and species statistics for the dominant families of karst epilithic mosses
Family
|
Number of Genera
|
Percentage of total genera (%)
|
Number of Species
|
Percentage of total species (%)
|
|
|
|
Pottiaceae
|
16
|
17.20
|
35
|
16.91
|
|
Brachytheciaceae
|
4
|
4.30
|
21
|
10.14
|
|
Thuidiaceae
|
7
|
7.53
|
16
|
7.73
|
|
Bryaceae
|
3
|
3.23
|
15
|
7.25
|
|
Hypnaceae
|
7
|
7.53
|
12
|
5.80
|
|
Mniaceae
|
4
|
4.30
|
13
|
6.28
|
|
Entodontaceae
|
2
|
2.15
|
10
|
4.83
|
|
Meteoriaceae
|
6
|
6.45
|
10
|
4.83
|
|
Neckeraceae
|
5
|
5.38
|
7
|
3.38
|
|
Anomodontaceae
|
2
|
2.15
|
7
|
3.38
|
|
Total
|
57
|
60.22
|
146
|
70.53
|
|
Diversity of moss life forms
The life form is the external growth form used by plants to adapt to the environment. Life forms determine the most basic functional traits of plants and are an important parameter for describing the appearance characteristics of communities (Ordoñez et al., 2010). Bryophytes of the same life form generally have similar ecological habits and competitive strategies, so species with similar environmental requirements are classified as having the same life form. In this paper, according to the definition and division of bryophyte life forms by Magdefrau (1982) and other scholars, combined with field observations, karst epilithic moss lifeforms are divided into five life forms: turf, weft, cushion, slanting and pendant (Table 2). The cluster and weft life forms were observed in 82.52% of the total bryophytes and are the main life forms of karst epilithic mosses. (1) the Clustered mosses were mainly Pottiaceae and Bryaceae, with 79 species, accounting for 38.16% of the total species. Plants of this type of life form grow tightly together in a cluster, which has a great effect on water conservation and soil retention. In the stony karst environment, the light is strong, and the moss plants are more distributed in habitats with low air humidity. (2) Weft mosses are mainly Thuidiaceae, Hypnaceae, Brachytheciaceae, Anomodontaceae, Mniaceae, Entodontaceae, Plagiotheciaceae, Racopilaceae, and Leskeaceae, with 92 species, accounting for 44.44% of the total species identified in this study. This type of bryophyte interweaves and grows on the surface of the rock, which greatly enhances the water storage capacity of the cluster type and increases the water content of the rock surface. This life form is typically distributed in the wet karst habitat. (3) Cushion mosses are mainly found in Porellaceae, Aytoniaceae, Frullaniaceae, Pelliaceae, and Makinoaceae; 15 species were found in this study, accounting for 7.25% of the total species. Bryophytes of this life form often grow in pieces, making it difficult to distinguish the plants, and are mainly distributed in moist habitats. (4) Pendant mosses are mainly members of the Meteoriaceae family, and 11 species were identified in this study, accounting for 5.31% of the total species. These mosses are mainly distributed on rocky surfaces with high humidity. (5) Slanting mosses are typically in the Hypopterygiaceae and Neckeraceae families. A total of 10 species were found in this study, accounting for 4.83% of the total species. This bryophyte life form is mainly distributed on the surface of wet rock walls that are not exposed to direct sunlight and have water dripping down their surfaces.
Table 2 Statistics on the life forms of karst epilithic mosses
Life form
|
Number of Species
|
Percentage of total species (%)
|
Ecological characteristics
|
|
|
|
Turf
|
79
|
38.16
|
The main branches are erect and parallel, loosely or tightly arranged, with few branches and many bases with false roots.
|
|
Weft
|
92
|
44.44
|
The plants are intertwined with each other, forming loosely stacked clusters, usually branched, with few false roots attached to the substrate.
|
|
Cushion
|
15
|
7.25
|
The dome-shaped community grows from the initial center point, the branches and main branches have the same growth direction, and it is difficult 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 flat 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).
Table (3) Comparison of dominant species of karst epilithic mosses in different habitats
The dominant species of epilithic mosses in karst are mainly mosses, including plants in the dominant families such as Pottiaceae, Thuidiaceae, Racopilaceae, Brachytheciaceae, and Anomodontaceae. The dominant species of bryophytes at the Maolan National Nature Reserve are Thuidium kanedae, Pseudosymblepharis angustata, Trichostomum involutum, Racopilum cuspidigerum, Brachythecium helminthocladum, Thuidium cymbifolium, Herpetineuron toccoae and Racopilum orthocarpum. Among them, Thuidiaceae accounted for 37.5%, Pottiaceae accounted for 25%, Racopilaceae accounted for 25%, and Brachytheciaceae accounted for 12.5% of the total species. The dominant species of epilithic mosses at the Puding Karst Ecological Research Station are Eurohypnum leptothallum, Hyophila involuta, Racopilum cuspidigerum, Anomodon rugelii, Taxiphyllum taxirameum, Bryohaplocladium angustifolium, Prototheca acuminata, Didymodon constrictus.var.constrictus and Eurynchium longirameum; among them, Hypnaceae accounted for 37.5%, Pottiacea accounted for 25%, Thuidiaceae, Racopilaceae, and Anomodontaceae each accounted for 12.5% of the total species.
There are differences in the dominant species between the two research areas. The Maolan Nature Reserve is dominated by moist epilithic mosses of the family Bryaceae and Lichenaceae, while the drought-tolerant types of Hypnacea and Pottiacea dominated at the Puding Research Station. In short, habitat has an important influence on the population distribution of epilithic mosses in karst ecosystems.
The relationship between the distribution of bryophyte communities and the environment
Comparison of bryophyte richness between the different habitat types
The richness of karst epilithic mosses varied greatly between the different regions (Fig.1). The genera and species richness of bryophytes at the Maolan National Nature Reserve are greater than those at the Puding Karst Rocky Desertification Ecological Observation and Research Station. There are 37 families of bryophytes (27 families of mosses and 10 families of liverworts), 89 genera (76 genera of mosses and 13 genera of liverworts), and 200 species (180 species of mosses and 20 species of liverworts) at the Maolan Nature Reserve. At Puding Station, there are 14 families of bryophytes (11 families of mosses, 3 families of liverworts), 28 genera (25 genera of mosses, 3 genera of liverworts), and 63 species (59 species of mosses, 4 species of liverworts). The difference in species richness between mosses and liverworts is consistent with the difference in total species number. In short, the richness of bryophytes in karst forests in the Maolan National Nature Reserve is higher than that in karst rocky desertification areas, indicating that the health of the ecosystem is directly proportional to the biodiversity of bryophytes. The better the ecological environment, the greater the biodiversity of bryophytes.
Comparison of the similarity of bryophytes between different habitat types
There are 55 species in common between the two research areas, including 53 species of mosses and 2 species of liverworts. The species composition similarity coefficient is 41.83%. The species in common are mainly dominant species of the dominant genera in the Brachytheciaceae, Bryaceae, Mniaceae, and Anomodontaceae families, including Hygrophilus 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. The common species of liverworts are Porella japonica var. Japonica and Plagiochasma rupestre, which belong to Porellaceae and Aytoniaceae, respectively. These bryophytes have strong environmental adaptability, a wide distribution range, and a wide niche and are among the widespread species of karst epilithic mosses.
Analysis of differences in bryophytes between different habitat types
The difference coefficient for the epilithic moss species in the two study areas is 0.58, which is between 0.50 and 0.75, indicating that the epilithic moss communities of the Maolan Reserve and Puding Ecological Station are moderately dissimilar. There are large differences in richness (Figure 2). There are 200 species of bryophytes in 37 families and 89 genera at Maolan Nature Reserve, 63 species in 28 genera in 14 families of bryophytes at Puding Station. A total of 87.30% of the bryophyte species in the Puding Ecological Research Station are also distributed in the Maolan Nature Reserve, and the species in the Bryaceae family at Puding Ecological Station re exactly the same as the species of the Bryophyta family in the Maolan Nature Reserve. The diversity of the bryophytes, genera and species at the Maolan Nature Reserve is much higher than that at the Puding Ecological Station. For example, there are 15 genera and 34 species, 7 genera and 16 species, and 7 genera and 12 species of Pottiaceae, Thuidiaceae, and Hypnaceae at the Maolan Nature Reserve, respectively, while there are only 5 genera and 9 species, 2 genera and 4 species, and 3 genera and 4 species of these families at the Puding Ecological Station. Hypopterygiaceae, Bartramiaceae, Amblystegiaceae, Cryphaeaceae, Grimmiaceae, Calliergonaceae, Habrodontaceae, Metzgeriaceae, Pallaviciniaceae, Plagiochilaceae, Pelliaceae, and Makinoaceae only live in moist habitats and were only found in the Maolan Reserve in this study.
Distribution characteristics of karst epilithic mosses
Among the bryophytes in the Puding Ecological Station area, 58 species are found in dry habitats, and only 5 species are found in humid habitats. The 52 common species between the two areas are distributed in dry habitats (Figure 3A). This shows that the epilithic mosses in the Puding Ecological Station are mainly dry stony plants. These bryophytes have strong drought tolerance and are able to survive in arid and water-deficient environments. The species of stony bryophytes distributed in the moist habitats in the Maolan Nature Reserve are much larger than those distributed in dry habitats. Among them, the 35 common species between the two areas are distributed in both dry and moist habitats (Figure 3B). This shows that such plants have a wide niche, low requirements for environmental conditions, and strong adaptability and can be considered broad-spectrum species. The epilithic moss species that are unique to the Maolan Nature Reserve are mainly distributed in humid habitats, and the types distributed in dry habitats are different from those in the dry Puding area. This result shows that environmental factors such as rainfall, air humidity, light intensity, and forest canopy density in the region have a decisive effect on the species diversity and distribution of karst bryophytes.