Preliminary Study On Diversity And Distribution Of Pottiaceae In Arid And Semiarid Area Of Tibet, China

Tibet makes up the majority of the Qinghai- Tibet Plateau, often referred to as the roof of the world. Its complex landforms, physiognomy, and climate create a special heterogeneous environment for mosses. Each moss species inhabits its own habitat and ecological niche. This, in combination with its sensitivity to environmental change, makes moss species distribution a useful indicator of vegetation alteration and climate change. Given its resistance to cold and drought, Pottiaceae is the dominant moss in Tibet. Pottiaceae exhibits apparent morphological, physiological, and genealogical adaptations to its particular environments. The Tibetan Plateau is an important area for the study of climate change and its effect on vegetation at large scales. Thus, understanding the diversity of Pottiaceae species, as well as their spatial distribution patterns and related environmental factors, is helpful for protecting Tibetan ecosystems, monitoring changes in vegetation and climate, and guiding future field surveys of unexplored areas in Tibet. In this paper, we studied diversity and distribution of Pottiaceae in arid and semiarid regions of Tibet, the objectives of this research were as follows:(1) to survey the species richness and diversity of Pottiaceae in arid and semiarid regions of Tibet, (2) to analyze the relationship between species distribution and micro-habitat environments, (3) to predict the spatial distribution of Pottiaceae and identify the macro-habitat factors affecting it on a broad spatial scale.Fieldwork was carried out from July to September in 2007,2011, and 2012. A total of 221 sample plots, each with a size of 10 x 10 m and located at different altitudes, were investigated across all vegetation types including alpine meadow, mountain steppe, pine forest, shrubbery, alpine tundra, deciduous broadleaved forest, desert steppe, swamp meadow, saline land, artificial woodland and alpine vegetation. In each sample plot, three to seven quadrats (1 m2 area) were used; in total,995 quadrats were used to investigate all ground-moss species. Moss coverage was measured using a metallic quadrat divided into 100 grid cells, detailed information about habitat characteristics were also recorded during the collection of species data in the sampling plots.A total of 24 genera and 112 species of Pottiaceae were identified, Didymodon was its dominant genus, Didymodon constricuts var. constricuts as the dominant species. Using a and β diversity index of species, the results showed that at different altitudes Pottiaceae species richness had obvious differences, but evenness was the similar, had no significant difference; Didymodon had little difference in species diversity at different elevations, their individual uniformity were similar in different vegetation types in the study area.Analysis of the relationships between Pottiaceae species and environmental factors using canonical correspondence analysis (CCA) revealed that the main environmental factors which affecting the the species diversity and growing coverage of Pottiaceae were altitude, vegetation type and tempreture in the study area. CCA analysis between Didymodon species and environmental factors showed that the vegetation cover, soil moisture, altitude and human disturbance were environmental factors which had main effects on species diversity and coverage of Didymodon, vegetation type almost had no effect on morphological characteristics variation of the species.Based on the environmental variables of bioclimate, topography, vegetation and human disturbance, the distribution of Pottiaceae and Didymodon were predicted throughout the study area at a spatial resolution of 1 km, using the presence-only MAXENT model and GIS software. Climatic variables were the key factors in the model. MAXENT models predicted a high precision, though the models we concluded that the potential distribution area of Pottiaceae was much larger than that of Didymodon, both mainly grew in semiarid region such as southern Nagqu, southeastern Xigaze and Lhasa city. The results showed the main environmental variables which influenced Pottiaceae and Didymodon spatial distribution was human disturbance, followed by bioclimate, vegetation and topography. Temperature, precipitation vegetation coverage increased can promote the growth of dominant specie.This study made substantial contributions to replenish information of Pottiaceae species in Tibet, human disturbance as a kind of environment variable was the first time for using in MAXENT species distribution models combinated with remote sensing technology to predict the spatial distribution of bryophytes in the study area. Based on the research findings, we explored the mechanism how Pottiaceae response to environmental change, discussed the same species how to adapt to different environment from the relations of morphological differentiation and environmental. The results help to reveal the bryophytes distribution characteristics in the arid and semiarid area of Tibet, and provide a scientific basis for the protection of bryophytes diversity and ecosystem.