Data from: First-year Acacia seedlings are anisohydric ‘water-spenders’ but differ in their rates of water use
Cory, Scott (2022), Data from: First-year Acacia seedlings are anisohydric ‘water-spenders’ but differ in their rates of water use, Dryad, Dataset, https://doi.org/10.5061/dryad.7h44j0zwx
Premise of the study: The first-year tree seedling (FYS) life stage may be a critical demographic bottleneck in semi-arid, seasonally dry ecosystems such as savannas. Given the highly variable water availability and potentially strong FYS-grass competition for water here, FYS water-use strategies may play a crucial role in FYS establishment and, ultimately, tree-grass competition and coexistence.
Methods: We examined drought responses in FYS of two tree species that are dominant on opposite ends of an aridity gradient in Serengeti, Acacia (=Vachellia) tortilis and A. robusta. Within a glasshouse experiment, gas exchange and whole-plant hydraulic conductance (Kplant) were measured while soil water potential (Ψsoil) declined. Trajectory of the Ψleaf/Ψsoil relationship during drought elucidated the degree of iso/anisohydry.
Key results: Both species were strongly anisohydric “water-spenders,” allowing rapid wet-season C gain after pulses of moisture availability. Despite being equally vulnerable to declines in Kplant under severe drought, they differed in their rates of water use. A. tortilis, which occurs in the more arid regions, initially had greater Kmax, transpiration (E), and photosynthesis (Anet) than A. robusta.
Conclusions: This work demonstrates an important mechanism of FYS establishment in savannas: rather than investing in drought tolerance, savanna FYS maximize gas exchange during wet periods at the expense of desiccation during dry seasons. FYS establishment appears dependent upon high C uptake during the pulses of water availability that characterize habitats dominated by these species. This study increases our understanding of species-scale plant ecophysiology and ecosystem-scale patterns of tree-grass coexistence.
National Science Foundation, Award: BCS – 1461728
Vecellio Fund at Wake Forest University