Seed dormancy, climate changes, desertification and soil use transformation threaten the Mediterranean endemic monospecific plant Petagnaea gussonei

This study investigated the germination capacity (endogenous factor) of Petagnaea gussonei (Spreng.) Rauschert, an endemic monospecific plant considered as a relict species of the ancient Mediterranean Tertiary flora. This investigation focused also on the temporal trends of soil-use, climate and desertification (exogenous factors) across the natural range of P. gussonei. The final germination percentage showed low values between 14 and 32%, the latter obtained with GA(3) and agar at 10 degrees C. The rising temperatures in the study area will further increase the dormancy of P. gussonei, whose germination capacity was lower and slower at temperatures higher than 10 degrees C. A further limiting factor of P. gussonei is its dormancy, which seems to be morpho-physiological. Regarding climate trends, in the period 1931-2020, the average temperature increased by 0.5 degrees C, from 15.4 to 15.9 degrees C, in line with the projected climate changes throughout the twenty-first century across the Mediterranean region. The average annual rainfall showed a relatively constant value of c. 900 mm, but extreme events grew considerably in the period 1991-2020. Similarly, the land affected by desertification expanded in an alarming way, by increasing from 21.2% in 2000 to 47.3% in 2020. Soil-use changes created also a complex impacting mosaic where c. 40% are agricultural areas. The effective conservation of P. gussonei should be multilateral by relying on germplasm banks, improving landscape connectivity and vegetation cover, and promoting climate policies.