Inconsistent relationships detected between seed size, shape and persistence for different plant functional groups in...

Knowledge on seed persistence is vital from both theoretical and practical considerations but directly collecting persistence data for many species is unfeasible. Therefore, there is a need to identify traits associated with seed persistence, but studies about the effects of seed size and shape on persistence have yielded results varying across regions. We studied 392 species of the Pannonian flora (Central Europe) to assess (1) how seed mass and shape are related to seed persistence, (2) whether this relationship is consistent across plant functional groups, and (3) whether seed mass and shape are correlated in different functional groups.

We collected data on the seed mass and persistence of species and performed measurements to calculate their seed shape index, with higher values indicating greater deviation from sphericity. To account for phylogenetic non-independence, we analysed how seed mass and seed shape index affect persistence in all 392 herbaceous species and separately in four plant functional groups using phylogenetic logistic regressions. To test how seed mass and shape are related to each other in these groups, we applied phylogenetic generalized least squares regression.

Across all species, both seed mass and seed shape index were negatively related to persistence, with seed mass having a stronger association. The same relationship was observed in forbs and short-lived species, but only seed shape was related to persistence in graminoid species. The relationship between seed mass and seed shape also varied between functional groups.

Consistent with many studies in other floras, both seed mass and shape were negatively related to persistence in the Pannonian flora after accounting for phylogeny. However, only seed shape was associated with persistence in graminoid species, suggesting that different factors may be at play in forbs and graminoids. Therefore, future studies of this relationship may need to treat and analyse graminoids separately.