Variations in seed characteristics among and within Stipa purpurea populations on the Qinghai-Tibet Plateau

Variation in seed size is common among plant species, populations, and individuals. On the Qinghai-Tibet Plateau, previous studies have mainly focused on interspecific variation in seed size, with little information available regarding intraspecific variation. The alpine steppe is among the most important vegetation types on the plateau, where it plays a vital role in preserving landscape heterogeneity and diversity. Stipa purpurea Griseb., endemic to the Qinghai-Tibet Plateau, is the predominant species of the alpine steppe. In the present study, we measured seed characteristics of nine S. purpurea populations and analyzed possible sources and consequences of variation in these characteristics. Seed characteristics varied greatly among and within populations. Our findings suggest that variation in seed size and awn length may affect germination and dispersal, respectively. Surprisingly, environmental factors, rather than genome size, were significantly correlated with seed size. For example, relative humidity and number of windy days were strongly correlated with seed size and awn length, respectively. We believe that variation in seed characteristics is a consequence of complex environmental conditions correlated with longitude and latitude. The results indicated that variation in seed characteristics of S. purpurea is an adaptation to environmental conditions.