Seed and seedling traits suggest ontogenetic coordination in the functional recruitment niche across semi-arid restoration species

Authors: Larson, Julie Elizab; NEUHAUS, DYLAN - University Of Central Arkansas; Copeland, Stella

Submitted to: Journal of Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/24/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: • Plant species differ in their environmental requirements for seed germination and seedling establishment, both of which influence the success of seed-based restoration. However, we understand little about the breadth of strategies across species, or how coordinated seed and seedling strategies may reveal different pathways for establishment success within a single system. • To address this, we explored seed and seedling traits related to size, speed, temperature and light response across 49 species common in semi-arid rangelands of the Western US. • We found that large-seeded species with larger seedlings and thicker roots/leaves tended to germinate in colder temperatures, while smaller species may avoid early-season risks by germinating in warmer temperatures. We also observed a separate tradeoff in how species may avoid environmental risk (by delaying germination via dormancy) or tolerate risk (by investing biomass in seedling roots). In contrast, seed light response or germination rate, may represent independent aspects of strategy among these species. • Together, these results suggests that co-occurring species can have diverse strategies of germinating and establishing in semi-arid ecosystems.

Technical Abstract: • Plant recruitment is shaped by functioning and performance across seed and seedling stages. Because seed morphology and germination directly influence seedling exposure to resources and environment, these two stages may be linked through trait synergies and tradeoffs that coordinate functioning through early ontogeny. However, the wide range of traits impacting environmental response at each stage are rarely explored in tandem to understand the potential dimensionality of the functional recruitment niche. • We explored covariation among 13 seed and seedling traits linked to size, speed (i.e. germination or growth rate), light and temperature response, and other functions for 49 species found in semi-arid rangelands. Using phylogenetically informed ordination and cluster analysis, we asked how trait covariation across multiple ontogenetic stages and functions shapes the dimensionality of the functional recruitment niche. • The first two trait dimensions at each stage aligned, providing some basis for ontogenetic coordination during recruitment. Morphological traits related to size (i.e. seed and seedling mass, root diameter) formed the strongest basis for coordination across stages, and also shared ties with traits reflecting seedling light response (specific leaf area), seedling speed (root elongation rate), and seed temperature response. We also observed an unexpected tradeoff in how seeds and seedlings may avoid risk (through dormancy) or tolerate risk (through root investment), respectively. • In contrast, seed light, seed speed, and seedling temperature metrics were not tightly linked to their ontogenetic counterparts, representing independent aspects of physiology among these species. This could expand the dimensionality of the recruitment niche depending on the functional significance of these traits in the field. • Synthesis. Both seed and seedling stages are characterized by multiple, independent dimensions of functioning, but ontogenetic coordination may moderate increasing dimensionality of the functional recruitment niche as a wider breadth of traits are explored together. At the same time, physiological traits linked to environmental response appear less connected to other traits and could complexify spatiotemporal recruitment dynamics across species. Both the independent and coordinated aspects of functioning observed here deserve exploration across a broader range of species, traits, and environments to understand the full dimensionality of the functional recruitment niche.