Abstract
Environmental tolerance of a species has been shown to correlate positively with its geographical range. On the Ordos Plateau, three Caragana species are distributed sequentially along the precipitation gradient. We hypothesized that this geographical distribution pattern is related to environmental tolerances of the three Caragana species during seed germination and seedling emergence stages. To test this hypothesis, we examined seed germination under different temperature, light and water potentials, and monitored seedling emergence for seeds buried at eight sand depths and given different amounts of water. Seeds of C. korshinskii germinated to high percentages at 5 : 15 to 25 : 35 °C in both light and darkness, while those of C. intermedia and C. microphylla did so only at 15 : 25 and 25 : 35 °C, respectively. Nearly 30 % of the C. korshinskii seeds germinated at -1.4 MPa at 20 and 25 °C, while no seeds of the other two species did so. Under the same treatments, seedling emergence percentages of C. korshinskii were higher than those of the other two species. The rank order of tolerance to drought and sand burial of the three species is C. korshinskii > C. intermedia > C. microphylla. The amount of precipitation and sand burial depth appear to be the main selective forces responsible for the geographical distribution of these species.
Highlights
The growth and distribution of a plant is limited if any environmental factor exceeds its tolerance (Gates et al 1956)
Seed germination of all three Caragana species was strongly inhibited by water potentials (WPs) lower than 21.0 MPa, which is similar to the inhibition found for some other desert species (Tobe et al 2005; Zheng et al 2005b)
The seed/seedling stage of C. microphylla is least tolerant to aridity and burial, which we suggest plays a role in restricting its distribution primarily to the eastern part of the Ordos Plateau
Summary
The growth and distribution of a plant is limited if any environmental factor exceeds its tolerance (Gates et al 1956). Environmental tolerance has been shown to correlate positively with the geographical range of a species (Brown 1984; Slatyer et al 2013). Species with broad environmental tolerances can occupy a wide variety of habitats and achieve an extensive geographical. Studies of the environmental tolerances of plants, especially during life history stages of germination and seedling establishment, can contribute to our understanding of the relationship between their distribution and environmental factors (Gaston and Spicer 2001; Brandle et al 2003; Slatyer et al 2013; Wasof et al 2013)
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