ObjectiveDesert ecosystem is characterized by extremely restricted water and nutrient availability, high precipitation and temperature variability. Alxa Plateau of northern China covers large-area typical temperate desert ecosystems, with a total area of more than 200,000 km². These ecosystems are highly vulnerable to global environmental and land-use changes, whereas the relative influence of water, energy and habitat heterogeneity on plant regional species richness, and the associated difference among different functional groups, are still unclear.

MethodWith the distributions of 811 native plants, plant regional species richness of three groups, climatic and habitat variables, we tried to explore the biogeographic patterns and the underlying dominant factors of overall, woody and herb plant regional species richness of Alxa Plateau.

Result(1) Both the overall, woody and herb plant regional species richness in Alxa Plateau showed obvious longitudinal and latitudinal gradients, which increased from northwest to southeast. (2) We found that both plant regional species richness of three groups were positively correlated with water variables, but were negatively correlated with energy variables. Water and energy factors together explained 60.7%, 62.5% and 42.6% of the variation in overall, herb and woody species richness, respectively; and both water and energy factors could individually explained 15.2%−19.6% and 2.8%−5.3% of the variation in plant regional species richness of three groups. Habitat heterogeneity significantly explained 12.3%−29.3% of the variation in overall, herb and woody species richness, and also could individually explain 3.1%, 1.0% and 11.8% of variation in species diversity of three groups. The relative role of climate and habitat factors differed between herb and woody species richness. Herb plant regional species richness was predominantly determined by water and energy factors, whereas the woody plant regional species biodiversity was controlled by water, energy and habitat heterogeneity, together. (3) Water, energy and habitat heterogeneity together explained 54.4%−63.8% of the variance overall, herb and woody plant regional species richness, while with 36.2%−45.6% of the variance explained by other unknown factors.

ConclusionOur results propose that the plant regional species richness patterns are predominantly shaped by water and energy factors together; and water availability is the most key limited factors in shaping these plant regional species richness patterns. Habitat heterogeneity also play a non-negligible role in regulating these regional species richness in Alxa Plateau. We highlight that the dominant factors of species diversity may differ markedly depending on the plant functional group, and other unknown factors such as soil, neutral factors and human disturbances may also greatly influence plant species richness in Alxa Plateau.