Influence of seed mass and shape on light plasticity of germination of alpine plants on the Tibetan Plateau: The role of photoblastic taxa, dispersal ability, and life history

Abstract

Responses of post-disposal germination to light play a crucial role in shaping germination niches and determining the success of seedling establishment, ultimately impacting species distribution and community composition. Seed traits are pivotal factors that influence species' germination, dispersal, and life history strategies. However, it remains unclear whether the relationship between seed traits and the light plasticity of germination is regulated by factors such as life history, photoblastic taxa, and dispersal ability. We measured the seed shape and seed mass of 114 species on the grasslands of the Tibetan Plateau. Germination experiments were conducted under two light conditions: dark and light. We also classified species based on photoblastic taxa (photostimulation vs. photoinhibition), life history (annual vs. perennial), and dispersal ability (weak vs. strong). Phylogenetic structural equation models (SEM) were used to test the complex relationship between seed traits, life history, dispersal ability, and light plasticity. We found that neither seed mass nor shape differed between the two photoblastic taxa. Species with photostimulation taxa exhibited a greater light plasticity of germination compared with photoinhibition taxa. Non-spherical seeds (elongated or flat) possessed low light plasticity of germination. The relationship between seed mass and germination light plasticity varied in different photoblastic taxa. Specifically, in photostimulation species, increased seed mass was associated with higher light plasticity of germination, whereas in photoinhibition species, an opposite relationship was evident. Moreover, dispersal ability and life history indirectly influenced the light plasticity of germination via seed shape. Our results imply that different combinations of seed traits can shape germination strategies in response to light stimulation, which in turn may influence the germination niches differentiation and species persistence in soil. Furthermore, life history and dispersal ability can indirectly affect the light plasticity of germination, which implies that the reproductive strategy of species to adapt to the environment may be regulated by multi-faceted life history strategies.