Cracking the case: Seed traits and phylogeny predict time to germination in prairie restoration species

Abstract

Traits are important for understanding how plant communities assemble and function, providing a common currency for studying ecological processes across species, locations, and habitat types. However, the majority of studies relating species traits to community assembly rely upon vegetative traits of mature plants. Seed traits, which are understudied relative to whole‐plant traits, are key to understanding assembly of plant communities. This is particularly true for restored communities, which are typically started de novo from seed, making seed germination a critical first step in community assembly and an early filter for plant establishment. We experimentally tested the effects of seed traits (mass, shape, and embryo to seed size ratio) and phylogeny on germination response in 32 species commonly used in prairie grassland restoration in the Midwestern USA, analyzing data using time‐to‐event (survival) analysis. As germination is also influenced by seed dormancy, and dormancy break treatments are commonly employed in restoration, we also tested the effects of two pretreatments (cold stratification and gibberellic acid application) on time to germination. Seed traits, phylogeny, and seed pretreatments all affected time to germination. Of all traits tested, variables related to seed shape (height and shape variance) best predicted germination response, with high‐variance (i.e., pointier and narrower) seeds germinating faster. Phylogenetic position (the location of species on the phylogenetic tree relative to other tested species) was also an important predictor of germination response, that is, closely related species showed similar patterns in time to germination. This was true despite the fact that all measured seed traits showed phylogenetic signal, therefore phylogeny provided residual information that was not already captured by measured seed traits. Seed traits, phylogenetic position, and germination pretreatments were important predictors of germination response for a suite of species commonly used in grassland restoration. Shape traits were especially important, while mass, often the only seed trait used in studies of community assembly, was not a strong predictor of germination timing. These findings illustrate the ecological importance of seed traits that are rarely incorporated into functional studies of plant communities. This information can also be used to advance restoration practice by guiding restoration planning and seed mix design.

Plant Origin, but Not Phylogeny, Drive Species Ecophysiological Response to Projected Climate

“…Finally, the absence of phylogenetic signal in our study may also be because the traits we studied are easier to modify than traits showing high phylogenetic conservatism in previous studies. For example, many previous studies showed strong phylogenetic conservatism in seed size (e.g., Zhang et al, 2004;Moles et al, 2005;Barak et al, 2018) and seed size was in fact shown to be highly phylogenetically conserved in another study in the same system of the genus Impatiens (Veselá et al, 2019). Further studies on phylogenetic patterns of eco-physiological traits within a single genus are thus needed to assess the generality of our findings.…”

Phylogenetic relatedness mediates persistence and density of soil seed banks

“…An improved understanding of the factors affecting the ability of species to form persistent (and dense) seed banks is critical to predicting how seed plants might respond to global environmental changes (Cabin & Marshall, 2000;Harper, 1977;Ooi, 2012;Ooi et al, 2009;Walck, Hidayati, Dixon, Thompson, & Poschlod, 2011). Predicting which species may form persistent seed banks based on phylogenetic relationships is also important for conservation or restoration purposes (Barak, Lichtenberger, Wellman-Houde, Kramer, & Larkin, 2018;Faist, Ferrenberg, & Collinge, 2013;Phartyal et al, 2019). This is also important to develop measures aimed at preventing the introduction and control potentially invasive alien plant species, whose ability to become naturalized and invasive has been recently shown to be associated with the ability to form persistent seed banks (Gioria et al, 2019;Pyšek et al, 2015).…”

Using seedling phenotypic traits to select local seed sources for large-scale restoration: methods and outcomes in a Great Basin case study

“…Further, recent evidence suggests that more fine-scaled measures of seed characteristics, such as embryo size, could be more predictive of seed performance than simply size alone (Barak et al 2018). Even with this uncertainty, we highlighted the larger-seeded sources of both species as the ones that likely have the most beneficial traits.…”