Assistant Professor University Of Michigan, United States
Abstract: Water availability is a key environmental factor influencing plant performance that is anticipated to shift under climate change. Droughts in temperate forests are predicted to become increasingly common leading to reductions in tree growth. However, studying responses to low water availability in forests is difficult because in addition to water, resources like light also influence plant performance. The seedling stage – a demographic bottleneck during which most tree mortality occurs – is strongly limited by light, but it is unclear which ecological strategies will be favored under variable conditions of water. Furthermore, we lack an understanding of the ability of seedlings to alter their ecological strategies to adapt to novel water and light conditions to maximize their performance. Seedlings ecological strategies can be defined by their functional traits – quantifiable characteristics that influence how organisms interact with their biotic and abiotic environment. In this study we examined how the functional traits of four species of commonly occurring temperate tree seedlings changed under different water and light availabilities, and the effects that these functional changes had on seedling growth and performance. To do so we implemented a fully factorial greenhouse experiment with three water and three light levels. We measured leaf, root, hydraulic, and photosynthetic traits in addition to growth. Our goal was to understand which ecological strategies are most beneficial for growth under different water and light conditions, and the capacity of different species to alter their traits to maximize their growth as conditions change. We found that different species of seedlings had differential growth responses to water and light availability, and that species with higher relative growth rates under ideal conditions (i.e., high water, high light) saw larger decreases in their growth rates under poor conditions (i.e., low water, low light) than did species with lower overall growth rates. Furthermore, we found that specific suites of traits were beneficial under different water and light treatments, and that certain species were able to shift their traits and adopt more advantageous strategies in response to different environments more readily than others. Our results suggest that under shifts in water availability due to climate change certain species will be better able to adapt to, and cope with, the altered environment, potentially driving the composition of future forests.
