Biodiversity Patterns And Environmental Interpretation Of Stipa Breviflora Grassland In Inner Mongolia

Biodiversity is a necessary prerequisite of ecosystem function and ecosystem services. It maintains both the sustainability of natural ecological systems and the well-being of human society. Besides providing material resources for the humanity directly, biodiversity has other important ecological, scientific, and aesthetic values. In recent years, unreasonable exploitation of natural resources by the society has accelerated habitat loss and species extinction. These adverse effects seriously damage ecosystem integrity and pose a threat to human survival and development. Therefore, biodiversity preservation and maintenance is the matter of urgent international concern.In this study we chose Stipa breviflora grassland as the research object and explored biodiversity patterns and their relationships with environmental factors at multiple scales. First, our research contributes to the understanding of ecosystem function and provides additional empirical evidence for theories developed in plant ecology and biodiversity. Second, our findings can provide the needed scientific basis and theoretical support for rational utilization of grasslands and restoration of damaged grassland ecosystems. Main results from the study are outlined below.1. Genetic diversity of S. breviflora grassland in Inner MongoliaGenetic diversity of S. breviflora populations and its relationship with climatic variables were studied using Geographic Information Systems (GIS) and the Random Amplified Polymorphism DNA analysis (RAPD). The RAPD produced a total of 308 bands with twenty-eight arbitrary decamer oligonucleotides. Among those,151 (or 49.03%) were polymorphic to the populations, and 45 (or 14.61%) were unique to specific populations. The genetic diversity of S. breviflora was high, but lower than that of the other two common species in the area-S. grandis and S. krylovii. Eight different geographical populations were analyzed by 3 different methods-the Hierarchical cluster analysis, the Principal Component Analysis (PCA), and the Unweighted Pair-Group Method with Arithmetic mean (UPGMA), which resulted in 2 groups of populations-warm-temperate and temperate. Mantel test showed a significantly positive correlation between genetic distance and geographical distance. Both detrended canonical correspondence analysis (DCCA) and Pearson correlation analysis showed that correlations between genetic differentiation and temperature were strong in the area. In particular, we found significant correlations of genetic differentiation with accumulated temperature≥10°, accumulated temperature≥0°, mean temperature of the coldest and the hottest months, annual mean temperature, and the number of frost-free days. We therefore conclude that temperature variations play an important role in the genetic differentiations of the investigated S. breviflora populations. Genetic flow was found to be and important process in genetic differentiation.2. Species diversity of S. breviflora grassland in Inner MongoliaThe studied populations of S. breviflora contained a total of 161 species belonging to 31 families and 96 genera of Spermatophytes. Species found belong to several families: Compositae (29), Leguminosae (25), Gramineae (23), Liliaceae (10). Hence, the floristic diversity is high. The ratio of genera to species of studied populations was 1/1.68, which is smaller than that of the entire Inner Mongolia (1/3.33) or China (1/8.73). This result suggests that the level of species differentiation is low. We found that vegetation composition is mainly characterized as being representative of the temperate zone, although certain elements of the tropical flora were also found, leading us to the conclusion about the transitional character of the local flora. Statistical analyses of life form occurrences showed that perennial herbs dominated the steppe communities. Besides, shrubs and semi-shrubs were also common life forms. They mainly occupied sandy soils that covered many areas in this region. While xerophytes generally dominated plant communities, non-xerophytes accounted for a larger proportion of species found. We found that different ecological types of water regime controlled the distribution of plant communities.Spatial distribution of S. breviflora grassland communities in Inner Mongolia clearly followed longitudinal and latitudinal gradients:species richness increased significantly with longitude increasing (west-east gradient) and latitude increasing (south-north gradient). We found that species richness increase along the latitudinal south-north gradient is mainly due to the collinearity between environmental factors that change along the latitudinal and longitudinal gradients in the study area. Average annual precipitation is the major climatic factor that controls species richness patterns followed by annual average temperature and potential evapotranspiration. Moreover, the average annual precipitation is the main predictor variable for primary productivity in arid and semi-arid regions. We hypothesized that primary productivity should be explained largely by modern climate patterns that, at the same time, may help us reveal distribution patterns of species richness in the area. Climate factors, however, explained only 23.7% of variation in spatial distribution of species richness suggesting that richness patterns are influenced by a variety of factors including historical legacies, modern climate, human disturbances, and other random factors. These groups of factors play different roles in different parts of our study area and at different analysis scales.We collected data on species diversity (richness) and productivity (peak above-ground biomass) of the S. breviflora association in Inner Mongolia grassland to examine spatial scale dependency and possible underlying mechanisms responsible for relationships found. One local and seven different landscape scales (the first level starts at a 100 x 100 km area, which is increased consecutively by 100 km at the next level resulting in the 700 x 700 km area at the highest level) were considered. Unimodal relationship dominated the local scale, but it varied depending on the position along successional gradients. Positive linear relationship was common at larger spatial scales. Biotic processes were the most likely primary factor underlying local scale unimodal relationships, but environmental heterogeneity, mainly precipitation patterns, was the main determinant of relationships found at larger spatial scales. While earlier research demonstrated positive linear species richness-productivity relationships across a number of ecological scales in the Inner Mongolia steppe, our study specifically tested a spectrum of geographical scales to confirm scale-dependency of this relationship.3. Community diversity of S. breviflora grassland in Inner MongoliaThe community level analysis of the S. breviflora grassland produced a classification with 16 distinct groups evident at the fourth level of division using the two-way indicator species analysis (TWINSPAN) algorithm. We also investigated the effects of environmental and spatial factors, as well as their interaction, on the structure of S. breviflora communities by using detrended canonical correspondence analysis (DCCA). Our results showed that the first two DCCA axes, which corresponded to gradients in temperature and precipitation, respectively, explained most of the variation in community structure (75.3%). Based on these results different S. breviflora communities were arranged into an ecological series.70.7% of the total variance in S. breviflora community structure was explained by all environmental factors and 55.6% by all spatial factors. When these factors were examined separately, only 29.5% and 11.4% of the total variance was explained by the two groups of factors, respectively.44.2% was simultaneously explained by the two groups, while 17.9% was explained by other undetermined factors. According to these, we concluded that environmental factors (precipitation and temperature) play an important role in community differentiations.We chose 3 typical S. breviflora grassland sites (Saihantala, Huade, and Zhunger) to analyze the influence of micro-landforms and soil on vegetation patterns. Local scale species distribution patterns, i.e. species composition and dominant species distribution, were affected by micro-landforms along the slope gradient. On the other hand, vegetation associations represented by community complexes were clearly differentiated between the upper slope and the lower slope due to different types of micro-landforms of the two localities. Climatic climax community grew in dominance toward the upper slope, while terrain community developed in the lower slope locations. Such patterns can be explained by differences in soil physical properties at the top soil horizons (especially the 0-5 cm layer). Community productivity is largely controlled by soil moisture. It is sufficiently higher in the more moisture-rich lower slope locations. We found that micro-landforms also determine species diversity by forming significant habitat heterogeneity within a very limited spatial area. It provides an important mechanism for the formation and maintenance of biological diversity at local scales.