Abstract
Climatic tolerance, especially drought tolerance, is one of the major factors shaping the geographic distributions of plant species. Thus, the general decline in rainfall from the Himalaya-Hengduan Mountains (HHM) to the inner Qinghai-Tibet Plateau (QTP) might account for the significant differences in species distributions and richness between the two regions. To test this hypothesis, we conducted a water stress experiment using four Anisodus species (A. tanguticus, A. luridus, A. carniolicoides and A. acutangulus), which were treated with different levels of water stress in a glasshouse, and examined their differences in physiological responses. The results suggest that A. tanguticus, which inhabits the inner QTP, generally has higher fitness under severe water stress than the other species based on its high root:shoot ratio, long-term water use efficiency and photosynthetic rate, indicating that it possesses a genetically based drought tolerance mechanism. Our results suggest that plant species inhabiting the inner QTP may be more drought tolerant than those inhabiting the HHM regions. This provides a new example supporting the hypothesis that climatic tolerance plays a major role in shaping plant distributions on the QTP and its adjacent highlands and presents new insights into the patterns of geographic distribution and diversity of the plants inhabiting these areas.
Highlights
One of the fundamental goals for ecologists and evolutionary biologists is to explain the patterns and mechanisms involved in species geographic distributions and abundance[1]
Water deficits can limit plant growth, reproduction and distribution, and various mechanisms have evolved in plants inhabiting water-limited regions to enhance drought tolerance by adjusting their physiological and morphological traits[28,29]
Anisodus tanguticus occupies the inner Qinghai-Tibet Plateau (QTP), while the other three Anisodus species are restricted to the Himalaya-Hengduan Mountains (HHM) regions, and rainfall in the growing season (May-September) on the inner QTP is significantly lower than in the HHM regions (Fig. 1A)
Summary
One of the fundamental goals for ecologists and evolutionary biologists is to explain the patterns and mechanisms involved in species geographic distributions and abundance[1] This could aid in the understanding of numerous phenomena, including the formation of biodiversity in a given region[2]. The QTP and its adjacent highlands, including the HHM, provide a natural system to test the effects of drought gradients on the geographic distribution of plant species. We examined the responses of A. tanguticus and its congeneric species to changes in soil water content to test the hypothesis that only plants with higher drought tolerance could colonize and survive on the inner QTP as a contribution to broaden efforts to enhance the understanding of the current geographic distribution of plant species and the formation of biodiversity on the inner QTP and its adjacent highlands
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