COS 78-4 - Combining seed, seedling and adult traits to understand species-environment relationships

Abstract: Plant functional traits can provide an eco-physiological basis to more deeply understand species-environment relationships, but most studies to date have focussed on the traits of adults despite the likely importance of early-life strategies for population persistence. Early-life strategies are particularly relevant for annual plants that rely solely on seeds to regenerate. Once germinated, annuals are at their most vulnerable, presenting only delicate tissues and underdeveloped organs for resource capture. As young seedlings typically experience the highest mortality rates, this life stage is thought to be the most adaptive, making it a crucial period to account for when considering trait-environment relationships. Here we integrate the functional traits of seed, seedling and adult annual wildflowers to explain species’ abundance trends along both regional- and local-scale environmental gradients. In 2011, plant surveys were conducted along gradients of growing season precipitation and mean minimum temperature in remnants of York gum-jam woodland (Western Australia, Australia), a community characterised by a Mediterranean climate with a hyper-diverse winter annual understory. In 7 woodland remnants, fifteen 30 x 30 cm quadrats were surveyed in each of three 15 x 15 m blocks. Quadrats that did not include at least one focal species were excluded, totalizing 308 quadrats. Quadrat-scale variables included soil nitrogen, canopy and leaf litter cover. Fifteen traits representing species’ differences in growth and allocation strategies were measured on 14 common winter annual species across their life cycle. Trait dimensionality was reduced to two principal components for analyses. To capture how traits modulate species’ responses to their environment, analyses were carried out using hierarchical generalised linear mixed models. We found a significant interaction between growing season precipitation and the economic strategy of seedlings and adults. Seedlings with acquisitive leaves that transition to tall adults with conservative leaves tended to be more abundant in wetter remnants. Traits did not explain species-environment relationships along local environmental gradients. Despite the remaining challenge of explaining local-scale patterns of distribution, our results highlight the importance of integrating early-life traits to understand species-environment relationships and offer valuable insight into how plant traits influence species’ responses at a regional scale.