Leaf and root traits, but not relationships among traits, vary with ontogeny in seedlings

Although leaf and root traits may change considerably throughout plant development, ontogenetic variation is rarely considered in trait-based ecology. Studies focused on how morphological root traits change throughout ontogeny are especially rare. Our objectives were to determine how ontogeny influences seedling traits to inform trait selection for future studies and to advance understanding of how traits at early developmental stages influence seedling growth. We measured traits from eleven herbaceous species at several developmental stages. We used Bayesian random effects models to assess the effects and variation resulting from species identity and ontogeny for each trait. We used principal component analysis and multiple regression to identify which dominant axes of variation were correlated with future growth rates. Variation in traits resulting from ontogeny was greatest for growth rates and root elongation rates. Relationships among traits were similar at all ontogenetic stages, but which principal component axes were correlated with future growth depended on stage; at the earliest harvest, the axis related to tissue construction was linked to future growth rate, whereas, at the last harvest, three independent axes were related to future growth rate. In our study, traits including leaf dry matter content, root tissue density, and root diameter varied little throughout seedling development and thus may be promising candidates for future trait-based studies. Linking suites of traits to growth strategies may be particularly fruitful for understanding plant strategies throughout early development, as multivariate relationships among traits appear to be more ontogenetically stable than individual traits.