Contrasting seed germination response to moss and lichen crusts in Stipa caucasica, a key species of the Irano-Turanian steppe

Biological soil crusts (BSC) play a crucial role in arid ecosystem functioning, yet the effect of their properties (e.g. whether they are dominated by mosses and lichens) on the germination has rarely been investigated. Here, we analysed the effects of intact, dead and removed moss or lichen BSC on seed germination of Stipa caucasica, a key species in the Iranian Artemisia steppes. Our results revealed that both dead and intact moss BSC significantly and strongly reduced and delayed germination putatively due to the physical properties of the crust limiting water supply to the large seeds of the focal species. Further, we found out that intact lichen BSC had no significant effect on the germination traits studied whereas lichen BSC removal and heat treatment (‘dead’ BSC) reduced germination percentage. The reduction is most likely due to the allelopathy effects and surface properties of the lichen crust. The detected patterns suggest that moss and lichen BSC play different roles in S. caucasica seed regeneration in the steppe; however, the effect on the species population dynamics deserve further study including also later stages of seedling establishment.