Impacts of Environmental Heterogeneity on Moss Diversity and Distribution of Didymodon (Pottiaceae) in Tibet, China

Abstract

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. This study aimed to characterize the diversity and distribution of Didymodon (Pottiaceae) in Tibet, and model the potential distribution of its species. A total of 221 sample plots, each with a size of 10 × 10 m and located at different altitudes, were investigated across all vegetation types. Of these, the 181 plots in which Didymodon species were found were used to conduct analyses and modeling. Three noteworthy results were obtained. First, a total of 22 species of Didymodon were identified. Among these, Didymodon rigidulus var. subulatus had not previously been recorded in China, and Didymodon constrictus var. constrictus was the dominant species. Second, analysis of the relationships between species distributions and environmental factors using canonical correspondence analysis revealed that vegetation cover and altitude were the main factors affecting the distribution of Didymodon in Tibet. Third, based on the environmental factors of bioclimate, topography and vegetation, the distribution of Didymodon was predicted throughout Tibet at a spatial resolution of 1 km, using the presence-only MaxEnt model. Climatic variables were the key factors in the model. We conclude that the environment plays a significant role in moss diversity and distribution. Based on our research findings, we recommend that future studies should focus on the impacts of climate change on the distribution and conservation of Didymodon.

Fig 1. The study area containing 221 sampling plots, which was investigated in 2007, 2011, and 2012.

Pale green represents arid areas that receive an annual precipitation of less than 200 mm; medium green indicates semiarid regions, where the annual precipitation is between 200 and 500 mm; and dark green indicates humid areas, where the annual precipitation is greater than 500 mm.

Fig 2. CCA ordination of 22 Didymodon species, environmental factors, and sampling plots in the study area.

A: CCA ordination of 22 Didymodon species and environmental factors; B: CCA ordination of 22 Didymodon species and the 181 sampling plots where they were found to grow. The black triangles represent 22 species of Didymodon; the blue circles represent the 181 sampling plots where Didymodon was found. The red arrows depict environmental factors: Temp represents temperature, Veg-cove represents vegetation cover, Veg-type represents vegetation type, and TDR 3.8 represents soil moisture soil depth of 3.8 cm. S1–S22 refers to Didymodon species listed in Table 3.

Fig 3. The presence probability of Didymodon spatial distributions in Tibet.

The red circles represent the Didymodon species in the plots that were investigated.

Fig 4. The importance of 22 environmental variables in modeling the distribution of Didymodon in Tibet.

The training gain describes how much better the MaxEnt distribution fits the presence data compared to a uniform distribution. The names and descriptions of environmental variables are listed in Table 2. The white squares represent the effect of removing a single variable from the full model. The gray squares represent the training gains when using only one environmental variable in MaxEnt. The black square represents the training gains when all variables were run in MaxEnt (1.61).

Fig 5. Response curves for the relationship between the probability distributions of Didymodon and environmental variables.

The curves show the change in the response of Didymodon distribution to specific environmental variables.