Ecological-anatomical comparative adaptability of two gypsophylic Astragalus species of gypsum soils

Astragalus semnanensis Bornm. & Rech. belongs to sect. Semnanensis, of thorny astragali and A. fridae, of non-thorny astragali, belongs to sect. Incani are the only endemic gypsophyllic species in western Semnan. The morphological and systematical studies available on these two species are scarce. Nor have the anatomical, distribution and adaptive capabilities in relation to soil and elevation of these species been investigated yet. Therefore, this study is aimed to comparatively investigate these features. The effect of soil and elevation on the anatomy, morphology and micro-morphology of the leaves of both species, as well as associated plant species, were analyzed using RDA and CCA analytical methods, Canoco 4.5 software. Comparison of RDA analysis of both species indicated that gypsum had the highest effect on the abundance of both species, while elevation had a strongly positive correlation with A. fridae and a negative correlation with A. semnanensis. Both species adsorb gypsum on their epidermis and part of the gypsum absorbed is accumulated in leaf parenchyma cells as calcium sulfate crystals. Adaptability of leaf surface is in the form of long and dense hairs which, in A. semnanensis, are longer and basifixed and, in A. fridae, thicker and medifixed. Increase in soil Ec and Na, K and Mg content and content of CaCO3 reduce both species abundances. Species such as Acantholimon cymosum and Prunus lycioides were found to be associated with A. semnanensis and species such as Moltkia gypsaceae and Euphorbia gypsicola with A. fridae.