In arid and semi-arid ecosystems, shrubs may act as fertility islands but their effect may vary depending on their morphology and ecologic impacts. This research was aimed to study effect of three shrubs Scariola orientalis, Astragalus heratensis, and Rosa persica on soil physical (e.g. texture) and chemical (e.g. pH, EC, organic matter, and nitrogen) properties and on the microclimate conditions (temperature, luminance, and soil moisture) of their understory in the steppe rangelands of Kakhek Gonabad. Along 50-m transects, flexible plot sizes were selected to measure the microclimate factors of understory species and the open spaces next to the shrubs based on the canopy diameters of each intercepted shrubs. Soil samples were taken from understory of shrubs. The microclimatic factors of understory and open spaces were analyzed by using paired-t test. The soil factors were analyzed under 3 shrubs and open spaces by using ANOVA and these factors were analyzed separately only under shrubs. The results showed that temperature and luminance were significantly lower understory than the open spaces (p<0.05). Soil depth moistures (15-55 cm) were higher in understory than open space while soil surface moistures (0-10 cm) did not vary. Among the investigated shrubs, Astragalus heratensis had the greatest facilitation effect on microclimatic factors. The soil criteria of EC, organic matter, and nitrogen were significantly higher understory of Astragalus heratensis than the open space. These effects can be related to the wider canopy cover, greater stature, and possibly nitrogen fixation for Astragalus.

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