Germination of Sedum oxypetalum (Crassulaceae) in a primary lava-field shrubland

Sedum oxypetalum is one of the dominant species in the xerophilous shrublands in the lava fields of the Basin of Mexico. Germination of this species was evaluated to understand its ecological response. We tested the effects of different pre-germination treatments (cold, and dry and wet heat) and storage time, as well as those of natural priming in two microhabitats with different disturbance levels. Experiments were performed in laboratory conditions under constant (25 A degrees C) and fluctuating (20/30 A degrees C) temperatures. Seeds did not germinate during burial and proved to be positively photoblastic. Under pre-germination treatments, final germination percentage was higher at 20/30 A degrees C in seeds after four or more months of storage. None of the pre-germination treatments favored germination. Seeds can survive for more than 1 year and form a seed bank. Thus, seeds underwent natural priming that favored final germination percentage; however, germination rate and lag time were not affected by this process. In natural conditions, germination is delayed until the rainy season, improving the success of seedling establishment and growth. We discuss the role of fluctuating temperature in germination processes and the adaptations of seeds to their seasonal environment.