The impact of cardinal temperature variation on the germination of Haloxylon aphyllum L. seeds

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Seed germination is a biological process that is affected by a variety of genetic and environmental factors. The cardinal temperature and thermal time are required for germination. The principal objective of this study was to identify and characterize variations in the base, optimum, and maximum germination temperatures of Haloxylon aphyllum L. from two seed sources, in order to establish models for use in predicting seeding dates. Mature H. aphyllum seeds were germinated at temperatures between 5 and <TEX>$35^{\circ}C$</TEX>. The germination behavior of H. aphyllum seeds to different temperature regimens in light was evaluated over a temperature range of <TEX>$5-35^{\circ}C$</TEX> at intervals of <TEX>$5^{\circ}C$</TEX>. The rate of germination increased between base and optimum thermal conditions, and decreased between optimum and maximum thermal conditions; the germination rate varied in a linear fashion at both sub-optimal and supra-optimal temperatures. The linear regression fit the range of germination rates at <TEX>$5^{\circ}C$</TEX> to <TEX>$25^{\circ}C$</TEX> and <TEX>$25^{\circ}C$</TEX> to <TEX>$30^{\circ}C$</TEX>, and thus the base temperature, optimum temperature, and maximum temperature for the germination of H. aphyllum were measured to be <TEX>$0.6^{\circ}C$</TEX>, <TEX>$25.69^{\circ}C$</TEX>, <TEX>$37.90^{\circ}C$</TEX>, and <TEX>$1.76^{\circ}C$</TEX>, <TEX>$21.56^{\circ}C$</TEX>, <TEX>$37.90^{\circ}C$</TEX> for Qom and the Fars dune desert respectively.