The role of floral traits in community assembly process at high elevations in Himalaya

1. There is a common agreement that, to maximise our understanding of trait-based community assembly, traits related to different organs should be considered as they relate to different ecological niche axes. Floral traits, in particular, have been suggested to play an important role in the plant community assembly along environmental gradients as they determine the reproductive success, one of the key functions in plants. However, the role of floral traits in community assembly research remains largely unverified empirically.

2. Using a large and novel dataset on plant traits and plant communities, we analysed the variability of six floral traits of 139 herbaceous species in 21 sites located along an elevation gradient (2,000–4,000 m) in the western Himalaya. The variability of floral traits along the gradient was analysed using community-weighted mean (CWM) trait values and functional diversities (FD) calculated for each study community.

3. The CWMs showed that with increasing elevation, flowering began later, and flowers tended to be larger with decreasing specific flower area (SFA). Along with the convergence in the onset of flowering and SFA (i.e., lower FD at high elevation sites), these patterns suggest that abiotic filtering and plant-pollinator interactions could affect the floral trait composition of the communities. Most likely, increasing low-temperature stress towards high-elevation sites selected for late-flowering species that produce flowers with larger display areas. The low abundance and activity of pollinators at high elevation could also explain why these traits were selected in the communities studied. Delayed flowering with increasing elevation might facilitate the phenological overlap of plants and their pollinators, as pollinator activity at higher elevation peaks in the second half of the vegetation period. The dominance of a species with low SFA and larger display area in high-altitude communities could be attributable to increased flower longevity and attraction of pollinators, respectively, to maximise pollination success under pollinator scarcity.

4. Synthesis. Our study provides empirical support for the recent argument that floral traits contribute considerably to the assembly of plant communities along environmental gradients. Thus, such traits should be included in community assembly research as they represent key ecological functions for reproduction.