Abstract
Seed size and number are two important components of plant reproductive traits. Previous theoretical studies suggested that resource limitation led to a strong trade-off between seed size and seed number. However, empirical evidence from natural communities remains scarce. In this study, the relationships between seed size and seed number were tested in community level and in three functional groups- graminoids, forbs and legumes in a natural alpine steppe community in Tianshan Mountains. And the role of limiting resources in determining trade-off patterns was also examined by treating reproductive biomass of each species as a resource pool for producing seeds. Our results showed a significant trade-off between seed size and seed number at the community level. This trade-off was primarily determined by the graminoid group, while no negative relationships were observed in the forb and legume groups. Moreover, the graminoid group had lower reproductive biomass than the forb and legume groups, which indicates that the species in the graminoid group were more strictly limited by reproductive resources. In the future, more comprehensive studies are needed to test this trade-off pattern in other ecosystems and explore the underlying mechanisms in natural communities.