The germination of mucilaginous seeds of Plantago coronopus, Reboudia pinnata, and Carrichtera annua on cyanobacterial soil crust from the Negev Desert

We studied the effect of intact, crushed or sterile cyanobacterial soil crust from the Negev Desert highlands of Israel as substrates for the germination of seeds of three annual plant species from local populations that produce mucilaginous seeds Plantago coronopus, Reboudia pinnata and Carrichtera annua. Mucilaginous seeds of these species were wetted on local intact cyanobacterial soil crust which inhibited their germination in comparison with their germination on filter paper. However, the percentage of germination of each species differed on sterile and crushed soil crust after 72 h of wetting. Germination of Plantago coronopus seeds was inhibited mechanically and biologically on intact soil crust, since it was significantly higher on both crushed and sterile soil crust. Germination of Reboudia pinnata seeds was slightly mechanically and biologically inhibited on intact soil crust, but germination on live crushed crust was higher than on sterile crushed crust. By contrast, germination of Carrichtera annua seeds was not mechanically inhibited by live soil crust but there was significant biological acceleration of germination on intact soil crust relative to crushed soil crust. Each of the three species exhibited different requirements for germination. Germination of P. coronopus is promoted by disturbances and removing the crust components (including its biological and structural effects). R. pinnata and C. annua germination is less affected by crust disturbance but is generally inhibited after removing the live components of the cyanobacterial crust. These species differences suggest different functions of the mucilage of the seed coat for the three species.